Imaging was carried out on an upright Leica SP5 confocal microscope located within the FILM facility of Imperial College London, managed by Dr Martin Spitaler.
The specimen holder and headpiece was made in collaboration with the Chemical Engineering department of Imperial College London, with advice from Samuel Jones and Dr Simon Schultz.
Nicola Ruivo, Francisco Diaz and CBS staff at Imperial College were instrumental for their assistance and advice on mouse husbandry.&#160;Mark Scott is funded by HFSP and FILM, Olufolake Akinduro by CRUK and Cristina Lo Celso by CRUK, KKLF, BBSRC and HFSP.

All procedures involving the use of animals are carried according to the local legislation. Our work is approved by the UK Home Office as well as the Imperial College ethical review panel. The allowed procedures are described in the project license documentation and follow guidelines that ensure the welfare of the animal at all times. Ensure to adhere to the legislation on animal experimentation of the country where the work is performed.
1. Labeling and Injection of HSPCs:
<ol>
	<li>Harvest cells as described by Lo Celso14-15.</li>
	<li>Prepare the cells at a concentration of 106 cells/ml in PBS. NOTE: Use a hemocytometer or the information provided by the cell sorter to count the cells; the number of cells to be labeled and injected varies depending on the cell type (stain for example 10,000 - 20,000 HSCs, 100,000 - 300,000 HPCs); if working with less than 105 cells, resuspend in 100 &#181;l of PBS; it is important to have the cells in PBS without any serum, as serum inhibits the staining.</li>
	<li>Add DiD to the cell suspension at a final concentration of 5 &#181;M and vortex the suspension immediately to ensure the dye doesn&#39;t precipitate out of solution and fail to label the cells.</li>
	<li>Incubate for 10 min at 37 &#176;C then wash by spinning at 500 x g for 5 min, decanting the liquid and resuspending the pellet in an appropriate volume for IV injection (~100 - 150 &#181;l)</li>
	<li>Resuspend the cells in 200 &#181;l of PBS and collect into an insulin syringe. NOTE: an insulin syringe is recommended over a conventional syringe because it has no needle dead space and therefore allows administering the entire cell suspension to the mouse.</li>
	<li>Inject cells into a lethally irradiated mouse via tail vein injection. NOTE: Irradiation has known, considerable impact on the bone marrow microenvironment (both hematopoietic and stromal components), which develops over time. It is therefore very important to maintain consistent timing for irradiation, cell injection (4 to 24 hr from irradiation for best engraftment) and imaging. Here irradiation is performed 6 hr before injection and imaging is performed 20 hr after injection.
	<ol>
		<li>Place the mouse in a warm chamber (37 &#176;C) until the tail vein appears vasodilated.</li>
		<li>Move the mouse into the restrainer and carefully slide the needle into the tail vein.</li>
		<li>Inject the cells into the vein - no resistance to injection should be encountered.</li>
		<li>Leave the mouse O/N in order to allow the cells to migrate to the bone marrow spaces.</li>
	</ol>
	</li>
</ol>
2. Preparing the Mouse for Imaging
<ol>
	<li>Autoclave one pair of fine forceps and one pair of fine scissors as well as a headpiece prior to use and store in a sterile environment.</li>
	<li>Make up anesthetic as fresh as possible, (0.38 ml Ketamine + 0.25 ml Medetomidine + 4.47 ml Water). NOTE: other approved anesthetics, including isoflurane and other injectable, will be effective too. The cocktail described is to be administered intraperitoneally at 0.1 ml per 10 g of body weight, with top-ups of 30 - 50 &#181;l administered every 45 min to 1 hr.</li>
	<li>Switch on the two-photon laser if required then start the microscope and software, calibrating the stage when prompted. Switch on the lasers and allow them to warm up and stabilize while preparing the mouse for imaging.</li>
	<li>Anesthetize the mouse using the prepared anesthetic mixture (step 2.2) for the chosen anesthetic via intraperitoneal injection. Monitor the onset of deep anesthesia via pedal reflex now and at regular intervals throughout the protocol. NOTE: the mouse must be monitored carefully throughout the procedure and if anesthesia appears to be lightening (typically after 45 - 60 min) then administer a top-up dose (as detailed in 2.2). Expect some variation between mice of different ages and sex. It is important to discuss the anesthesia protocol with your local veterinary officer to ensure adequate precautions are taken to ensure the mouse&#39;s welfare.</li>
	<li>Swab the top of the scalp with 70% ethanol on a tissue, ensuring not to get any ethanol in the eyes of the mouse.</li>
	<li>Using sterile forceps and scissors, carefully remove the central portion of the scalp to expose the calvarium area to be imaged: make a small incision at the back of the head between the ears by lifting the skin up with the forceps. While holding the skin up, slide the scissors under the skin and gently cut along the outside of the desired imaging area.</li>
	<li>Wipe the exposed bone with sterile cotton bud moistened with sterile PBS to keep it moist.</li>
	<li>Attach the metal head piece to the skull of the mouse ready for imaging.
	<ol>
		<li>Mix an adequate amount of dental cement in a weigh boat until it becomes a paste and quickly apply to the bottom surface of the headpiece that will attach to the skull.</li>
		<li>Before the cement sets, place the headpiece onto the skull of the mouse, making sure not to get any dental cement on the imaging area, then wait for it to set.</li>
		<li>Apply a small amount of Intrasite Hydrogel which keeps the skull moist.</li>
	</ol>
	</li>
	<li>Attach the headpiece to the holder and secure in place using the screw, ensuring that the grooves fit within the holder notches.</li>
	<li>Remove the hydrogel from the skull with sterile cotton buds and clean with sterile PBS before transferring to the microscope.</li>
	<li>Insert the holder into the microscope stage, position the heating mat under the mouse, insert the rectal thermometer probe and secure everything in place on the stage with adhesive tape.</li>
	<li>Place a small drop of ophthalmic ointment on the eyes of the mouse to ensure they do not dry out while under anesthetic. NOTE: the mouse must not be left unattended at any time during the imaging process while under anesthesia.</li>
</ol>
3. In Vivo Imaging: High-resolution Stacks and Time-lapse Acquisition
<ol>
	<li>Focus on the skull via the eye pieces.
	<ol>
		<li>Fill the imaging window with purified, sterile water and using a water dipping lens, lower it so that it touches the water droplet.</li>
		<li>Focus on the top of the skull using the microscope eyepieces, using an external lamp as the light-source.</li>
		<li>Position the imaging area on the central suture and move towards the rear of the head to find the coronal suture as a starting position.</li>
	</ol>
	</li>
	<li>Set the microscope up to allow effective excitation and detection of the relevant fluorophores specified in the excitation and emission table. NOTE: while a Leica SP5 upright confocal with a conventional galvanometer scan head running the LAS-AF software platform is used here, the procedure can be easily replicated in other microscope/software platforms. The lens used here is the Leica HCX IRAPO L 25x W/0.95 N.A. but equivalent lenses of other manufacturers are available with suitable magnification and high N.A.
	<ol>
		<li>Place the software into a mode to capture both XY images as well as a 3D Z-stack and set imaging speed to 400 Hz and resolution to 512 x 512 pixels. NOTE: the setup and hardware here result in a field of view of 620 &#181;m and this may differ on other platforms.</li>
		<li>Set the software so that multiple channels/tracks are able to be captured, as well as ensuring that the collection method is set to change settings between stacks if possible or between frames at the very least. Set up 3 independent capture settings, switching off the laser illumination at the end of the acquisition of each stack. NOTE: three channels will be required for this procedure to reduce crosstalk between channels.</li>
		<li>Setup the settings for the first sequential scan for the two photon SHG bone signal (840 nm excitation; 400 - 440 nm emission); open the shutter for the MP laser and ensure MP gain and offset are correctly setup, laser power is 12.5 - 25% and the laser is switched on.&#160; Select an appropriate PMT as the only detector and change the color to white.&#160; Note: NDD detectors with appropriate filters should be used for the bone detection when available to achieve a brighter, deeper signal.</li>
		<li>Repeat channel setup procedure used for the GFP channel for a combined autofluorescence (543 nm excitation; 560 - 600nm emission) and DiD (633 nm excitation; 650 - 720 nm emission) under the second settings scan, utilizing two appropriate PMTs.&#160; Change the channel color to green for the autofluorescence and red for the DiD.&#160; Note: using green as the auto-fluorescence channel allows easier detection of DiD positive cells when the two channels are overlayed - autofluorescent cells appear as yellow/orange due to being in both channels while DiD cells appear only as red since they only appear in the DiD channel.&#160;&#160; The auto-fluorescence channel is only used for this comparison and is not used in any final analysis, however if the user wishes to, this can be changed to a different color for display purposes to avoid confusion with the GFP channel.</li>
		<li>Finally, setup the third and final scan for GFP (488 nm excitation; 500 - 530 nm emission); make sure the shutter is open if required and then set the laser power of the 488 nm laser line to around 15% or an appropriate level for the laser being used, select an appropriate PMT as the only active detector and change its pseudocolor to green. </li>
		<li>Activate a &#39;Live&#39; imaging mode to begin a preview scan of the selected channel and adjust detector Gain and Offset for optimal exposure. Repeat this for each scan in the sequential window.</li>
		<li>Save the settings of these multi-channel scans for easy reuse. NOTE: this allows the user to reload the settings in subsequent sessions.</li>
	</ol>
	</li>
	<li>Activate multi-position capture, referred to as &#39;Mark and Find&#39; in the demonstrated software, and reset the coordinate points.</li>
	<li>Scan the bone imaging area, starting from the intersection between the central and coronal suture, scan the depth of bone marrow area using both autofluorescence (pseudo colored green) and DiD (pseudo-colored red) with a composite view. NOTE: autofluorescent cells will be present in both channels and appear orange/yellow in the composite image whereas DiD labeled cells will appear as red-only cells in the composite image.</li>
	<li>When a cell is detected, mark this as a new coordinate position (x, y and z) in the &#39;Mark and Find&#39; tool by clicking on the &#8220;Add New Position icon on the left hand side of the &#8220;Mark and Find&#8221; window.</li>
	<li>When the current field of view has been examined, move the stage the distance of one field of view either left/right/down/up. Repeat this process for each field of view, gradually working around the whole imaging window area to the left of the central suture, moving towards the nose of the mouse. Once the central suture bifurcation is in sight, move to the right side of the suture and repeat the procedure scanning the left side in the reverse direction (i.e., towards the coronal suture). Mark the coordinates of any new cells of interest using the &#39;Mark and Find&#39; tool.</li>
	<li>Once scanning of the imaging window is complete, use the &#39;Mark and Find&#39; tool to review the points (select the desired point and review each point individually). Set the top and bottom of a Z-stack around each cell for each position, (many software platforms will allow you to perform independent z-stacks for each position, which reduces capturing empty space). For each point, focus up and down and set top and bottom Z positions for 3D z-stack capture and update the individual point in the &#39;Mark and Find&#39;. Set Z-Stack interval to 5&#181;m and averaging for each sequential scan channel to an appropriate quality: Line or Frame average. NOTE: Increasing the number of scans to average increases the length of acquisition time.</li>
	<li>Acquire a high-quality reference stack for each point of interest by starting the entire scan procedure (often referred to as &#39;Start&#39; rather than &#8220;Capture&#8221;). NOTE: this scan can act as a reference for future high-speed imaging.</li>
	<li>Once finished with the high-quality scan, activate a time-lapse setting for the capture.</li>
	<li>In the time-lapse settings, set the time interval to 5 min and overall run time to the desired length (e.g., 5 hr). &#39;Apply&#39; these settings to the overall scan. NOTE: in order to reduce this scan time to allow a 5 min time lapse interval, one may need to reduce the number of scans used for averaging, limit the resolution to 512 x 512 pixels, convert the scanning to bidirectional (with required phase correction to align both scan directions), and/or increase the scan speed to 600 Hz or more (more than 600 Hz will cause zooming of the imaging area for the demonstrated software platform). It is also important to note that while a sequential imaging mode was used to acquire a high quality image stack initially, simultaneous acquisition is used to increase speed during the time-lapse imaging - this may result in some slight cross talk between channels which places extra importance on the initial capture of the accurately separated reference stacks.</li>
	<li>Commence imaging (as before by clicking the &#39;Start&#39; button in the demonstrated software). NOTE: be sure to maintain the appropriate level of anesthesia by administering further, smaller doses when needed, being careful not to overdose the mouse, regularly top up the water to ensure the objective does not dry out and monitor vital signs and heating-pad temperature throughout.</li>
	<li>When finished, raise the lens from the holder and then remove the holder from the microscope stage, ensuring the wires from the rectal probe and heating mat are not damaged.</li>
	<li>Unscrew the headpiece from the stage holder and carefully remove the mouse. Cull the mouse using cervical dislocation and remove the metal head-piece by snapping it off the skull. Save data to disk and transfer to server for later analysis. NOTE: The head piece is ideally cleaned by dipping in acetone for a few hours and finally rubbing the residual cement off.</li>
</ol>

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R., Kitamura, K., Post-Uiterweer, A., Krupic, J., H&#228;usser, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Spatial+Pattern+Coding+of+Sensory+Information+by+Climbing+Fibre-evoked+Calcium+Signals+in+Networks+of+Neighboring+Cerebellar+Purkinje+Cells.">Spatial Pattern Coding of Sensory Information by Climbing Fibre-evoked Calcium Signals in Networks of Neighboring Cerebellar Purkinje Cells.</a> J Neuroscience. 29 (25), 8005-8015 (2009).</li><li>Lo Celso, C., Lin, C. P., Scadden, D. T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=In+vivo+Imaging+of+Transplanted+Hematopoietic+Stem+and+Progenitor+Cells+in+Mouse+Calvarium+Bone+Marrow.">In vivo Imaging of Transplanted Hematopoietic Stem and Progenitor Cells in Mouse Calvarium Bone Marrow.</a> Nat Protoc. 6 (1), 1-14 (2011).</li><li>Lo Celso, C., Scadden, D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Isolation+and+Transplantation+of+Hematopoietic+Stem+Cells+(HSCs).">Isolation and Transplantation of Hematopoietic Stem Cells (HSCs).</a> Journal of Visualized Experiments. (2), e157 (2007).</li><li>Progatzky, F., Dallman, M. J., Lo Celso, ., C, <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=From+Seeing+to+Believing:+Labelling+Strategies+for+in+vivo+Cell-tracking+Experiments.">From Seeing to Believing: Labelling Strategies for in vivo Cell-tracking Experiments.</a> Interface Focus. 3 (3), 20130001 (2013).</li><li>Ellis, S. L., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+Relationship+Between+Bone,+Hemopoietic+Stem+Cells+and+Vasculature.">The Relationship Between Bone, Hemopoietic Stem Cells and Vasculature.</a> Blood. 118 (6), 1516-1524 (2011).</li><li>Nombela-Arrieta, C., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Quantitative+Imaging+of+Haematopoietic+Stem+and+Progenitor+Cell+Localization+and+Hypoxic+Status+in+the+Bone+Marrow+Microenvironment.">Quantitative Imaging of Haematopoietic Stem and Progenitor Cell Localization and Hypoxic Status in the Bone Marrow Microenvironment.</a> Nature Cell Biology. 15, 533-543 (2013).</li></ol>

There is nothing to disclose.

What was accomplished?
The protocol uses time-lapse multi-dimensional imaging to monitor the migration of FACS purified, ex vivo labeled, transplanted HSPCs in mouse calvarial bone marrow. Identification of single transplanted cells has been achieved and these have been monitored over prolonged periods of time (hr) with high accuracy. Breathing induced movement artifacts have been minimized and cells have been repeatedly reimaged over a prolonged time-course.
What are future directions?
Development of the technique could progress towards recovery experiments to allow for imaging on multiple days, over the course of a week or more and use of gas anesthetics such as isoflurane to shorten and simplify the recovery process for the mouse (Note: recovery experiments require strictly sterile surgery conditions and administration of appropriate analgesics). Development of a larger color-palette of in vivo dyes as well as efficient genetic labeling of hematopoietic cells will also facilitate multi-labeling experiments, provide more insight into cell-cell interactions within the bone marrow and allow for more complex experiments in the future. Additionally, simultaneous labeling of multiple bone marrow structures and stroma components will provide a more complete picture of the events taking place in HSPC niches. Image stability of the time-lapse movies could be improved preacquisition by stabilizing the microscope further as well as minimizing temperature gradients in the sample and postacquisition by using image registration algorithms.
Limitations:
The technique described presents some limitations. Survival of mice following administration of injectable anesthetics is unpredictable and it is very easy to experience complications depending on individual response to the anesthetic. Generally, the longer an imaging session, the harder is for the mouse to recover from anesthesia and it is therefore important to carefully plan if the mouse is to be recovered, ideally limiting the duration of time lapse imaging. The use of injectable anesthetics limits the time each imaging session can last for. While it is possible to prolong the anesthesia by readministering a smaller dose of anesthetic, it is difficult perform this accurately and overdosing the mouse is one of the most frequent causes of premature termination of in vivo imaging. Gas anesthesia is less toxic and allows for a longer initial imaging session, however rapid recovery of the mouse after &#62;2 hr long administration of isoflurane is rarely successful. Another limitation of the technique is the limited resolution of the images that can be obtained during multi-point time-lapse imaging, due to the necessity to acquire images rapidly. This, coupled with focal drift or field jumps (discussed above), can make tracking of cells difficult.
Comparison with alternative methods:
HSPCs are usually labeled with the lipophilic dye DiD, but DiR and DiI dyes are equivalent alternatives and other cell dyes can be used as long as sufficiently bright, as reviewed in[16]. Even though ex vivo labeling of cells with DiD has been shown to not affect the long-term function of HSCs, it has the limitation that DiD (or any other chemical dye) is diluted upon cell division. Since HSCs proliferate during the first days following transplantation, the signal to noise ratio for these cells rapidly deteriorates. Endogenous labeling of cells by means of genetic manipulation and expression of fluorescent proteins is a viable alternative method, as long as the fluorescent proteins are expressed at sufficiently high levels to generate signal detectable through the skull bone. There are a number of alternative techniques available to perform imaging of HSPCs within the bone marrow space, each with their own benefits and limitations. Insertion of fiber optic-based imaging devices allowed for imaging of bone marrow reconstitution in long bones[8], while confocal imaging following surgical exposure of the tibia and thinning of bone enamel with a surgical drill[12] produced detailed images of HSPCs residing in the peripheral areas of long bones. These methods however are far more invasive than the one described here and therefore do not permit to repeat imaging sessions focusing on the same bone marrow area within the same mouse. Moreover, it is possible that these techniques may affect the cells observed given the inevitable response to extensive damage in the surrounding tissue. HSPCs have been imaged for short periods of time through coverslips placed over excised, fractured femurs[11], however the impact of this harsh preparation of the tissue on HSPCs is not clear and the technique was used uniquely to obtain single time point observations. Fixed bones have been sectioned into serial sections, stained, and the obtained images reconstructed into a 3D model, providing excellent 3D resolution, especially when vascular casts are used[17], and recently Laser Scanning Cytometry (LaSC) has been used to obtain quantitative measures about HSPCs in situ, highlighted by immunostaining[18] but are unable to provide any temporal information about the cells behavior. The techniques described in this new technique provide a combination of good resolution in 3D, sufficient temporal sampling for monitoring cells in 4D and they are relatively non-invasive, therefore offering an ideal approach to achieve long-term monitoring of HSPCs interacting with the bone marrow microenvironment.

Despite stem cell niches having been recognized for decades3 and well characterized in many tissues such as the olfactory bulb, muscle fiber, hair follicle bulge or CNS subventricular zone4-7, the interactions between hematopoietic stem cells (HSCs) and bone marrow microenvironment (BM) are still poorly understood due to the difficulty of directly observing single cells through the bone as well as the extremely fluid nature of the tissue itself. It has been shown, through a number of functional studies based on ablating or overexpressing specific genes in either HSCs or the stromal cells of the microenvironment itself, that an intricate network of different cell types and regulatory signals is responsible for regulating the delicate balance between quiescence, proliferation, expansion and differentiation of HSCs1-2. The crosstalk between HSCs and their niches can be understood in depth only through direct observation. This is achievable thanks to the development of advanced imaging protocols, combining the available technology not only in terms of microscopy, but also of specimen holder solutions and of acquisition software.
Single cell resolution live imaging of transplanted hematopoietic stem and progenitor cells (HSPCs) in the BM compartment of the mouse calvaria bones showed that engrafting HSPCs localize in proximity of SDF-1 and VCAM-1-positive vessels8-9 and that more immature cells are found within 15 - 20 microns from GFP-positive osteoblastic cells (Col2.3-GFP transgenic mouse line, in which the osteoblast-restricted collagen 1&#945; promoter drives GFP expression) while their progeny are more distal10. Similar observations were obtained from dissected and fractured femur bones11 and from thinned tibeal bones12. Imaging of calvarial bone marrow remains the least invasive approach to achieve direct visualization of HSPCs within their native microenvironment.
With any live specimen imaging there is an inherent need to keep the sample as still as possible to avoid any unnecessary artifacts due to sample movement. Breathing causes oscillatory movements of the mouse head, which need to be avoided when imaging calvarial bone marrow. Conventional stereotactic holders, used for example for brain imaging and electrophysiology, are not suitable for calvarium imaging because they obstruct the frontal bones. Starting from a mouse holder used to minimize distress during live imaging and electrophysiology studies13, a 2 component holder was developed, with a small piece fixed to the head of the mouse to create an imaging window connected to a larger arm ensuring steady hold with a heavy base plate which secures firmly into the microscope stage. Securing the head piece to the skull of the mouse allows free breathing while still immobilizing the head in place and adequately eliminating movements due to breathing. A &#39;lock-and-key&#39; mechanism linking the head-piece to the holder body allows the size of the window to be minimized as well as increased accuracy of positioning, therefore simplifying the surgery, and the fit of the base plate into the stage allows for accurate alignment on the microscope. To accurately monitor motile cells, a multi-point time lapse protocol was designed to allow tracking of cells over time with 5 min intervals between time points. Here, DiD labeled HSCs are injected into col2.3GFP osteoblasitc reporter mice10,14 and imaged approximately 20 hr later. The mouse holder that was designed and the imaging settings required to perform rapid multi-point time-lapse imaging of the same areas over a period of multiple hr are described in detail.

<table><tbody><tr><td>Ketamine (Narketan 100 mg/ml)</td><td>Vetoquinol</td><td>407575 0107 C</td><td>Other anesthetics may be used in place of this.</td></tr><tr><td>Medetomidine (Domitor 1 mg/ml)</td><td>Elanco</td><td>134800-2</td><td>Other analgesics may be used in place of this.</td></tr><tr><td>Vibrant DiD cell labeling solution</td><td>Roche Products Ltd.</td><td>V22887</td><td>Other colors are available and may be used if required.</td></tr><tr><td>Lacrilube ophtalmic ointment</td><td>Allergan</td><td>n/a</td><td>avaliable by prescription by the local vet</td></tr><tr><td>Kemdent &quot;Diamond Carve&quot; glass ionomer cement</td><td>Associated Dental Products Ltd. via Kemdent</td><td>SUN527</td><td>We use shade A3, but any shade of cement can be used.</td></tr><tr><td>PBS</td><td>multiple equivalent</td><td></td><td></td></tr><tr><td>Insulin syringes</td><td>Terumo Medical Corporation</td><td>SS10M3109</td><td>1 ml, 31 G</td></tr><tr><td>Mouse restrainer</td><td>Harvard Apparatus</td><td>340031</td><td>Cone type (small)</td></tr><tr><td>Autoclaved forceps and scissors</td><td>Agar Scientific</td><td>AGT577&lt;br/&gt; AGT5034</td><td>Iris scissors - 90 mm; Dumont HP tweezers (0.06 mm tip)</td></tr><tr><td>Weigh boat and cement stirrer</td><td>VWR</td><td>611-1996/231-0370</td><td>5 ml weigh-boat (black)/ Wooden tongue depressor</td></tr><tr><td>Leica SP5 upright confocal microscope with motorized stage and two-photon laser</td><td>Leica Microsystems</td><td></td><td>Call for quote</td></tr><tr><td>25x water dipping objective lens (N.A. = 0.95)</td><td>Leica Microsystems</td><td>11506323</td><td>HCX IRAPO L lens</td></tr><tr><td>Custom designed mouse holder</td><td>Imperial College Engineering Workshop</td><td></td><td>See Figure 1 for details</td></tr><tr><td>Heating pad with rectal thermometer probe</td><td>BASi Instrumentation</td><td>FHC-40902/ FHC-40908/ FHC-4090502</td><td>Heat mat/ Control box/ Thermometer probe</td></tr></tbody></table>

in vivo 4-dimensional tracking of hematopoietic stem and progenitor cells in adult mouse calvarial bone marrow

Through a delicate balance between quiescence and proliferation, self renewal and production of differentiated progeny, hematopoietic stem cells (HSCs) maintain the turnover of all mature blood cell lineages. The coordination of the complex signals leading to specific HSC fates relies upon the interaction between HSCs and the intricate bone marrow microenvironment, which is still poorly understood[1-2].
We describe how by combining a newly developed specimen holder for stable animal positioning with multi-step confocal and two-photon in vivo imaging techniques, it is possible to obtain high-resolution 3D stacks containing HSPCs and their surrounding niches and to monitor them over time through multi-point time-lapse imaging. High definition imaging allows detecting ex vivo labeled hematopoietic stem and progenitor cells (HSPCs) residing within the bone marrow. Moreover, multi-point time-lapse 3D imaging, obtained with faster acquisition settings, provides accurate information about HSPC movement and the reciprocal interactions between HSPCs and stroma cells.
Tracking of HSPCs in relation to GFP positive osteoblastic cells is shown as an exemplary application of this method. This technique can be utilized to track any appropriately labeled hematopoietic or stromal cell of interest within the mouse calvarium bone marrow space.

The custom made, high-precision mouse holder including a calvarium imaging window allows prolonged imaging of FACS purified, labeled HSPCs injected into lethally irradiated recipient mice (Figure 1A). Typically, after injection of between 15 - 20 thousand labeled cells, 8 to 15 cells are usually recognizable within the bone marrow imaging area of the skull the following day. Here it is shown how to acquire single cell resolution 3D stacks of HSPC-containing bone marrow areas of approximately 90 - 120 &#181;m thickness , (Figure 1B), followed by 4D time-lapse movies of the HSPCs identified (Figure 1C and movie).
Suboptimal results are obtained if the dental cement is not optimally prepared, for example the water could leak from non sealed areas, and even though it can be topped up from the top of the holder, any period of time in which the lens is not dipped into water leads to black frames. Some drift in the images is inevitable due to thermal expansion of the materials of the mouse holder, however it can be accentuated by suboptimal cement adhesion, leading to progressive detachment of the mouse, and by perturbations of the imaging set up, leading to sudden jumps of the focus during time-lapse imaging. Drift during multi-point time-lapse imaging can also be caused by inaccuracies in the stage movements when revisiting previously imaged positions. Drift and stutter artifacts in time-lapse movies can be corrected for by using image registration algorithms.
Table 1. Excitation and emission settings.
<table border="0" cellpadding="0" cellspacing="0">
	<tbody>
		<tr>
			<td style="width:204px;">Colour Channel</td>
			<td style="width:213px;">Excitation</td>
			<td style="width:208px;">Emission</td>
		</tr>
		<tr>
			<td style="width:204px;">GFP</td>
			<td style="width:213px;">488 nm</td>
			<td style="width:208px;">500 - 530 nm</td>
		</tr>
		<tr>
			<td style="width:204px;">Autofluorescence</td>
			<td style="width:213px;">543 nm</td>
			<td style="width:208px;">560 - 610 nm</td>
		</tr>
		<tr>
			<td style="width:204px;">DiD</td>
			<td style="width:213px;">633 nm</td>
			<td style="width:208px;">640 - 700 nm</td>
		</tr>
		<tr>
			<td style="width:204px;">SHG</td>
			<td style="width:213px;">840 nm (MP)</td>
			<td style="width:208px;">400 - 450 nm</td>
		</tr>
	</tbody>
</table>
<img alt="Figure 1" fo:content-width="6in" src="/files/ftp_upload/51683/51683fig1highres.jpg" width="600" /> 
Figure 1. In vivo 4D imaging of HSPCs in mouse calvarium. (A) Outline of the experiment. (B - C) examples of results obtained. (B) 2D slices from a 3D stack (total depth is 114 &#956;m), containing signal from collagen bone (white), DiD labeled cells (red), autofluorescent cells (yellow) and osteoblastic cells (green). Scale bars: 100 &#956;m. (C) 2D slices from a 4D time-lapse movie showing a DiD labeled HSC (red) migrating in the proximity of osteoblastic cells (green). The dotted line highlights the displacement of the cell. Scale bars: 50 &#956;m (B) and 100 &#956;m (C). NOTE: The movie obtained from the time-lapse acquisition in (C) is shown during the video article. <a href="https://www.jove.com/files/ftp_upload/51683/51683fig1large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>

Watch this Scientific Journal Video about In Vivo 4-Dimensional Tracking of Hematopoietic Stem and Progenitor Cells in Adult Mouse Calvarial Bone Marrow at JoVE.com

In Vivo 4-Dimensional Tracking of Hematopoietic Stem and Progenitor Cells in Adult Mouse Calvarial Bone Marrow

The nature of the interactions between hematopoietic stem and progenitor cells (HSPCs) and bone marrow niches is poorly understood. Custom hardware modifications and a multi-step acquisition protocol allow the use of two-photon and confocal microscopy to image ex vivo labeled HSPCs homed within bone marrow areas, tracking interactions and movement.

In Vivo 4-Dimensional Tracking of Hematopoietic Stem and Progenitor Cells in Adult Mouse Calvarial Bone Marrow

Through a delicate balance between quiescence and proliferation, self renewal and production of differentiated progeny, hematopoietic stem cells (HSCs) ...

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Research

JoVE Journal

Biology

13.8K Views.  Imperial College London.  De aard van de interactie tussen hematopoietische stamcellen en progenitorcellen (HSPCs) en beenmerg nissen wordt slecht begrepen. Aangepaste hardware wijzigingen en een meerstaps overname protocol maken het gebruik van twee-foton en confocale microscopie beeld ex vivo gemerkte HSPCs geadopteerd in beenmerg gebieden volgen interacties en beweging. 

Video: In Vivo 4-Dimensional Tracking of Hematopoietic Stem and Progenitor Cells in Adult Mouse Calvarial Bone Marrow

Automated Quantification of Hematopoietic Cell &#8211; Stromal Cell Interactions in Histological Images of Undecalcified Bone

Confocal microscopy is the method of choice for the analysis of localization of multiple cell types within complex tissues such as the bone marrow. However, the analysis and quantification of cellular localization is difficult, as in many cases it relies on manual counting, thus bearing the risk of introducing a rater-dependent bias and reducing interrater reliability. Moreover, it is often difficult to judge whether the co-localization between two cells results from random positioning, especially when cell types differ strongly in the frequency of their occurrence. Here, a method for unbiased quantification of cellular co-localization in the bone marrow is introduced. The protocol describes the sample preparation used to obtain histological sections of whole murine long bones including the bone marrow, as well as the staining protocol and the acquisition of high-resolution images. An analysis workflow spanning from the recognition of hematopoietic and non-hematopoietic cell types in 2-dimensional (2D) bone marrow images to the quantification of the direct contacts between those cells is presented. This also includes a neighborhood analysis, to obtain information about the cellular microenvironment surrounding a certain cell type. In order to evaluate whether co-localization of two cell types is the mere result of random cell positioning or reflects preferential associations between the cells, a simulation tool which is suitable for testing this hypothesis in the case of hematopoietic as well as stromal cells, is used. This approach is not limited to the bone marrow, and can be extended to other tissues to permit reproducible, quantitative analysis of histological data.

A strategy to quantitatively analyze histological data in the bone marrow is presented. Confocal microscopy of fluorescently labeled cells in tissue sections results in 2-dimensional images, which are automatically analyzed. Co-localization analyses of different cell types are compared to data from simulated images, giving quantitative information about cellular interactions.

Confocal microscopy is the method of choice for the analysis of localization of multiple cell types within complex tissues such as the bone marrow. ...

Developmental Biology

Combining Intravital Fluorescent Microscopy (IVFM) with Genetic Models to Study Engraftment Dynamics of Hematopoietic Cells to Bone Marrow Niches

Increasing evidence indicates that normal hematopoiesis is regulated by distinct microenvironmental cues in the BM, which include specialized cellular niches modulating critical hematopoietic stem cell (HSC) functions1,2. Indeed, a more detailed picture of the hematopoietic microenvironment is now emerging, in which the endosteal and the endothelial niches form functional units for the regulation of normal HSC and their progeny3,4,5. New studies have revealed the importance of perivascular cells, adipocytes and neuronal cells in maintaining and regulating HSC function6,7,8. Furthermore, there is evidence that cells from different lineages, i.e. myeloid and lymphoid cells, home and reside in specific niches within the BM microenvironment. However, a complete mapping of the BM microenvironment and its occupants is still in progress.
Transgenic mouse strains expressing lineage specific fluorescent markers or mice genetically engineered to lack selected molecules in specific cells of the BM niche are now available. Knock-out and lineage tracking models, in combination with transplantation approaches, provide the opportunity to refine the knowledge on the role of specific &#34;niche&#34; cells for defined hematopoietic populations, such as HSC, B-cells, T-cells, myeloid cells and erythroid cells. This strategy can be further potentiated by merging the use of two-photon microscopy of the calvarium. By providing in vivo high resolution imaging and 3-D rendering of the BM calvarium, we can now determine precisely the location where specific hematopoietic subsets home in the BM and evaluate the kinetics of their expansion over time. Here, Lys-GFP transgenic mice (marking myeloid cells)9 and RBPJ knock-out mice (lacking canonical Notch signaling)10 are used in combination with IVFM to determine the engraftment of myeloid cells to a Notch defective BM microenvironment.

Combining Intravital Fluorescent Microscopy IVFM with Genetic Models to Study Engraftment Dynamics of Hematopoietic Cells to Bone Marrow Niches

Intravital fluorescence microscopy (IVFM) of the calvarium is applied in combination with genetic animal models to study the homing and engraftment of hematopoietic cells into bone marrow (BM) niches.

Increasing evidence indicates that normal hematopoiesis is regulated by distinct microenvironmental cues in the BM, which include specialized cellular ...

Bioengineering of Humanized Bone Marrow Microenvironments in Mouse and Their Visualization by Live Imaging

Human hematopoietic stem cells (HSCs) reside in the bone marrow (BM) niche, an intricate, multifactorial network of components producing cytokines, growth factors, and extracellular matrix. The ability of HSCs to remain quiescent, self-renew or differentiate, and acquire mutations and become malignant depends upon the complex interactions they establish with different stromal components. To observe the crosstalk between human HSCs and the human BM niche in physiological and pathological conditions, we designed a protocol to ectopically model and image a humanized BM niche in immunodeficient mice. We show that the use of different cellular components allows for the formation of humanized structures and the opportunity to sustain long-term human hematopoietic engraftment. Using two-photon microscopy, we can live-image these structures in situ at the single-cell resolution, providing a powerful new tool for the functional characterization of the human BM microenvironment and its role in regulating normal and malignant hematopoiesis.

A method to create and live-image different humanized bone-marrow niches in mice is presented. Based on the supportive niche created by human mesenchymal cells, the addition of human endothelial cells induces the formation of human vessels, while the addition of rhBMP-2 induces the formation of human-mouse chimeric mature bone tissue.

Human hematopoietic stem cells (HSCs) reside in the bone marrow (BM) niche, an intricate, multifactorial network of components producing cytokines, growth ...

Tracking Mouse Bone Marrow Monocytes In Vivo

Real time multiphoton imaging provides a great opportunity to study cell trafficking and cell-to-cell interactions in their physiological 3-dimensionnal environment. Biological activities of immune cells mainly rely on their motility capacities. Blood monocytes have short half-life in the bloodstream; they originate in the bone marrow and are constitutively released from it. In inflammatory condition, this process is enhanced, leading to blood monocytosis and subsequent infiltration of the peripheral inflammatory tissues. Identifying the biomechanical events controlling monocyte trafficking from the bone marrow towards the vascular network is an important step to understand monocyte physiopathological relevance. We performed in vivo time-lapse imaging by two-photon microscopy of the skull bone marrow of the Csf1r-Gal4VP16/UAS-ECFP (MacBlue) mouse. The MacBlue mouse expresses the fluorescent reporters enhanced cyan fluorescent protein (ECFP) under the control of a myeloid specific promoter 1, in combination with vascular network labelling. We describe how this approach enables the tracking of individual medullar monocytes in real time to further quantify the migratory behaviour within the bone marrow parenchyma and the vasculature, as well as cell-to-cell interactions. This approach provides novel insights into the biology of the bone marrow monocyte subsets and allows to further address how these cells can be influenced in specific pathological conditions.

Tracking Mouse Bone Marrow Monocytes In Vivo

Monocytes are key regulators of innate immunity and play a critical role in the renewal of the peripheral mononuclear phagocytic system and in case of inflammation. This manuscript describes the procedure of real time imaging of the mouse calvaria bone marrow to study the monocyte mobilisation mechanism.

Real time multiphoton imaging provides a great opportunity to study cell trafficking and cell-to-cell interactions in their physiological 3-dimensionnal ...

Immunology and Infection

Femur Window Chamber Model for In Vivo Cell Tracking in the Murine Bone Marrow

Bone marrow is a complex organ that contains various hematopoietic and non-hematopoietic cells. These cells are involved in many biological processes, including hematopoiesis, immune regulation and tumor regulation. Commonly used methods for understanding cellular actions in the bone marrow, such as histology and blood counts, provide static information rather than capturing the dynamic action of multiple cellular components in vivo. To complement the standard methods, a window chamber (WC)-based model was developed to enable serial in vivo imaging of cells and structures in the murine bone marrow. This protocol describes a surgical procedure for installing the WC in the femur, in order to facilitate long-term optical access to the femoral bone marrow. In particular, to demonstrate its experimental utility, this WC approach was used to image and track neutrophils within the vascular network of the femur, thereby providing a novel method to visualize and quantify immune cell trafficking and regulation in the bone marrow. This method can be applied to study various biological processes in the murine bone marrow, such as hematopoiesis, stem cell transplantation, and immune responses in pathological conditions, including cancer.

Femur Window Chamber Model for In Vivo Cell Tracking in the Murine Bone Marrow

The protocol describes a novel murine femur window chamber model that can be used to track movement of cells in the femoral bone marrow in vivo. Intravital multiphoton fluorescence microscopy is used to image three components of the femoral bone marrow (vasculature, collagen matrix, and neutrophils) over time.

Bone marrow is a complex organ that contains various hematopoietic and non-hematopoietic cells. These cells are involved in many biological processes, ...

Phenotypic Analysis and Isolation of Murine Hematopoietic Stem Cells and Lineage-committed Progenitors

The bone marrow is the principal site where HSCs and more mature blood cells lineage progenitors reside and differentiate in an adult organism. HSCs constitute a minute cell population of pluripotent cells capable of generating all blood cell lineages for a life-time1. The molecular dissection of HSCs homeostasis in the bone marrow has important implications in hematopoiesis, oncology and regenerative medicine. We describe the labeling protocol with fluorescent antibodies and the electronic gating procedure in flow cytometry to score hematopoietic progenitor subsets and HSCs distribution in individual mice (Fig. 1). In addition, we describe a method to extensively enrich hematopoietic progenitors as well as long-term (LT) and short term (ST) reconstituting HSCs from pooled bone marrow cell suspensions by magnetic enrichment of cells expressing c-Kit. The resulting cell preparation can be used to sort selected subsets for in vitro and in vivo functional studies (Fig. 2).
Both trabecular osteoblasts2,3 and sinusoidal endothelium4 constitute functional niches supporting HSCs in the bone marrow. Several mechanisms in the osteoblastic niche, including a subset of N-cadherin+ osteoblasts3 and interaction of the receptor tyrosine kinase Tie2 expressed in HSCs with its ligand angiopoietin-15 concur in determining HSCs quiescence. "Hibernation" in the bone marrow is crucial to protect HSCs from replication and eventual exhaustion upon excessive cycling activity6. Exogenous stimuli acting on cells of the innate immune system such as Toll-like receptor ligands7 and interferon-&alpha;6 can also induce proliferation and differentiation of HSCs into lineage committed progenitors. Recently, a population of dormant mouse HSCs within the lin- c-Kit+ Sca-1+ CD150+ CD48- CD34- population has been described8. Sorting of cells based on CD34 expression from the hematopoietic progenitors-enriched cell suspension as described here allows the isolation of both quiescent self-renewing LT-HSCs and ST-HSCs9. A similar procedure based on depletion of lineage positive cells and sorting of LT-HSC with CD48 and Flk2 antibodies has been previously described10. In the present report we provide a protocol for the phenotypic characterization and ex vivo cell cycle analysis of hematopoietic progenitors, which can be useful for monitoring hematopoiesis in different physiological and pathological conditions. Moreover, we describe a FACS sorting procedure for HSCs, which can be used to define factors and mechanisms regulating their self-renewal, expansion and differentiation in cell biology and signal transduction assays as well as for transplantation.

A method to analyse the distribution of bone marrow hematopoietic progenitors in flow cytometry as well as to efficiently isolate highly purified hematopoietic stem cells (HSCs) is described. The isolation procedure is essentially based on magnetic enrichment of c-Kit+ cells and cell sorting to purify HSCs for cellular and molecular studies.

The bone marrow is the principal site where HSCs and more mature blood cells lineage progenitors reside and differentiate in an adult organism. HSCs ...

In vivo Clonal Tracking of Hematopoietic Stem and Progenitor Cells Marked by Five Fluorescent Proteins using Confocal and Multiphoton Microscopy

We developed and validated a fluorescent marking methodology for clonal tracking of hematopoietic stem and progenitor cells (HSPCs) with high spatial and temporal resolution to study in vivo hematopoiesis using the murine bone marrow transplant experimental model. Genetic combinatorial marking using lentiviral vectors encoding fluorescent proteins (FPs) enabled cell fate mapping through advanced microscopy imaging. Vectors encoding five different FPs: Cerulean, EGFP, Venus, tdTomato, and mCherry were used to concurrently transduce HSPCs, creating a diverse palette of color marked cells. Imaging using confocal/two-photon hybrid microscopy enables simultaneous high resolution assessment of uniquely marked cells and their progeny in conjunction with structural components of the tissues. Volumetric analyses over large areas reveal that spectrally coded HSPC-derived cells can be detected non-invasively in various intact tissues, including the bone marrow (BM), for extensive periods of time following transplantation. Live studies combining video-rate multiphoton and confocal time-lapse imaging in 4D demonstrate the possibility of dynamic cellular and clonal tracking in a quantitative manner.

In vivo Clonal Tracking of Hematopoietic Stem and Progenitor Cells Marked by Five Fluorescent Proteins using Confocal and Multiphoton Microscopy

Combinatorial 5 fluorescent proteins marking of hematopoietic stem and progenitor cells allows in vivo clonal tracking via confocal and two-photon microscopy, providing insights into bone marrow hematopoietic architecture during regeneration. This method allows non-invasive fate mapping of spectrally-coded HSPCs-derived cells in intact tissues for extensive periods of time following transplantation.

We developed and validated a fluorescent marking methodology for clonal tracking of hematopoietic stem and progenitor cells (HSPCs) with high spatial and ...

Intrafemoral Injection for Bone Marrow Study in Live Mice

Simplified Intrafemoral Injections Using Live Mice Allow for Continuous Bone Marrow Analysis

Despite the complexity of hematopoietic cell transplantation in humans, researchers commonly perform intravenous or intrafemoral (IF) injections in mice. In murine models, this technique has been adapted to enhance the seeding efficiency of transplanted hematopoietic stem and progenitor cells (HSPCs). This paper describes a detailed step-by-step technical procedure of IF injection and the following bone marrow (BM) aspiration in mice that allows for serial characterization of cells present in the BM. This method enables the transplantation of valuable samples with low cell numbers that are particularly difficult to engraft by intravenous injection. This procedure facilitates the creation of xenografts that are critical for pathological analysis. While it is easier to access peripheral blood (PB), the cellular composition of PB does not reflect the BM, which is the niche for HSPCs. Therefore, procedures providing access to the BM compartment are essential for studying hematopoiesis. IF injection and serial BM aspiration, as described here, allow for the prospective retrieval and characterization of cells enriched in the BM, such as HSPCs, without sacrificing the mice.

This protocol describes the intrafemoral injection of a few hematopoietic or leukemic stem cells, including gene-edited cells, in murine xenograft models, which will not only enable the quick and safe transplantation of cells but also serial analyses of the bone marrow.

Despite the complexity of hematopoietic cell transplantation in humans, researchers commonly perform intravenous or intrafemoral (IF) injections in mice. ...

Medicine

In Vivo Two-photon Imaging of Megakaryocytes and Proplatelets in the Mouse Skull Bone Marrow

Platelets are produced by megakaryocytes, specialized cells located in the bone marrow. The possibility to image megakaryocytes in real time and their native environment was described more than 10 years ago and sheds new light on the process of platelet formation. Megakaryocytes extend elongated protrusions, called proplatelets, through the endothelial lining of sinusoid vessels. This paper presents a protocol to simultaneously image in real time fluorescently labeled megakaryocytes in the skull bone marrow and sinusoid vessels. This technique relies on a minor surgery that keeps the skull intact to limit inflammatory reactions. The mouse head is immobilized with a ring glued to the skull to prevent movements from breathing.
Using two-photon microscopy, megakaryocytes can be visualized for up to a few hours, enabling the observation of cell protrusions and proplatelets in the process of elongation inside sinusoid vessels. This allows the quantification of several parameters related to the morphology of the protrusions (width, length, presence of constriction areas) and their elongation behavior (velocity, regularity, or presence of pauses or retraction phases). This technique also allows simultaneous recording of circulating platelets in sinusoid vessels to determine platelet velocity and blood flow direction. This method is particularly useful to study the role of genes of interest in platelet formation using genetically modified mice and is also amenable to pharmacological testing (study the mechanisms, evaluating drugs in the treatment of platelet production disorders). It has become an invaluable tool, especially to complement in vitro studies as it is now known that in vivo and in vitro proplatelet formation rely on different mechanisms. It has been shown, for example, that in vitro microtubules are required for proplatelet elongation per se. However, in vivo, they rather serve as a scaffold, elongation being mainly promoted by blood flow forces.

In Vivo Two-photon Imaging of Megakaryocytes and Proplatelets in the Mouse Skull Bone Marrow

We describe here the method for imaging megakaryocytes and proplatelets in the marrow of the skull bone of living mice using two-photon microscopy.

Platelets are produced by megakaryocytes, specialized cells located in the bone marrow. The possibility to image megakaryocytes in real time and their ...

Intravital Longitudinal Imaging of Vascular Dynamics in the Calvarial Bone Marrow

Intravital longitudinal fluorescence microscopy imaging has emerged as a crucial technique for studying dynamic biological processes, notably in the context of tissue regeneration, tumor development, and therapeutic responses. Particularly, the calvarial bone marrow is a highly dynamic tissue, where the hematopoietic fate is interconnected with the surrounding microenvironment, with specialized vessels responding to normal and pathologic hematopoiesis. Traditional imaging of fixed tissues offers static information, often limiting a comprehensive understanding of these processes. 
The integration of transgenic animals expressing cell-specific markers, live cell tracers, advancements in imaging equipment, and the use of specialized chambers has elevated intravital microscopy to a pivotal tool for gaining insights into dynamic biological phenomena. One application of intravital imaging is the investigation of tumor vessel behavior and therapeutic effects. A newly designed 3D-printed titanium head fixation implant can be stably connected to the mouse skull and is suitable for longitudinal imaging during multiple sessions. 
The proposed protocol allows for the spatial and temporal examination of vascular dynamics in the calvarial bone marrow, including visualization and quantification of vascular heterogeneity, interaction with stromal and hematopoietic cells, and measurement of vascular functional parameters. Additionally, the technique enables the visualization of established vascular beds and the monitoring of therapeutic effects, stem cell mobilization, and the localization of chemotherapeutic compounds over time using two-photon microscopy. Overall, this intravital longitudinal imaging protocol provides a comprehensive platform for investigating both tumor vessel behavior and hematopoietic cell dynamics, offering valuable insights into the intricate processes governing these biological phenomena.

Intravital microscopy allows the study of dynamic biological processes such as tissue regeneration and tumor development. The calvarial bone marrow, a highly dynamic tissue, offers insights into hematopoiesis and vascular function. Using a biocompatible 3D-printed head fixation implant allows for repetitive longitudinal imaging, enhancing our understanding of tissue dynamics and the tumor microenvironment.

Intravital longitudinal fluorescence microscopy imaging has emerged as a crucial technique for studying dynamic biological processes, notably in the ...

In Vivo 4-Dimensional Tracking of Hematopoietic Stem and Progenitor Cells in Adult Mouse Calvarial Bone Marrow

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