We thank M. Douglas Benson for initial conversations regarding secondary palate imaging. We also acknowledge David Castaneda-Castellanos (Leica) and Chris Rieken (Zeiss) for their help to adjust imaging conditions in confocal microscopy. We appreciate Lynsey Hamilton (Bitplane) for helpful suggestions for quantitative image analysis using Imaris software. This work was funded by NIH/NIDCR R01 DE025887.

All animal experiments were performed in accordance with the protocols of the University of California at San Francisco Institutional Animal Care and Use Committee.
1. Preparation of Live Imaging Media
<ol>
	<li>Preparation of liquid culture media
	<ol>
		<li>Add 20% fetal bovine serum (FBS), 2 mM L-glutamine, 100 U/mL penicillin, 100 &#181;g/mL streptomycin, 200 &#181;g/mL L-ascorbic acid, 15 mM HEPES to Dulbecco&#39;s Modified Eagle Medium (DMEM)/F12 media. 
		NOTE: L...

<ol>
	<li>Ray, H. J., Niswander, L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Mechanisms+of+tissue+fusion+during+development.">Mechanisms of tissue fusion during development.</a> Dev. Camb. Engl. 139, 1701-1711 (2012).</li><li>Dudas, M., Li, W. -. Y., Kim, J., Yang, A., Kaartinen, V. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Palatal+fusion+-+where+do+the+midline+cells+go?+A+review+on+cleft+palate,+a+major+human+birth+defect.">Palatal fusion - where do the midline cells go? A review on cleft palate, a major human birth defect.</a> Acta Histochem. 109, 1-14 (2007).</li><li>Bush, J. O., Jiang, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Palatogenesis:+morphogenetic+and+molecular+mechanisms+of+secondary+palate+development.">Palatogenesis: morphogenetic and molecular mechanisms of secondary palate development.</a> Development. 139, 231-243 (2012).</li><li>Lan, Y., Xu, J., Jiang, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Cellular+and+Molecular+Mechanisms+of+Palatogenesis.">Cellular and Molecular Mechanisms of Palatogenesis.</a> Curr Top Dev Biol. 115, 59-84 (2015).</li><li>Taya, Y., O'Kane, S., Ferguson, M. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Pathogenesis+of+cleft+palate+in+TGF-b3+knockout+mice.">Pathogenesis of cleft palate in TGF-b3 knockout mice.</a> Development. 126, 3869-3879 (1999).</li><li>Kim, S., 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=Convergence+and+Extrusion+Are+Required+for+Normal+Fusion+of+the+Mammalian+Secondary+Palate.">Convergence and Extrusion Are Required for Normal Fusion of the Mammalian Secondary Palate.</a> PLOS Biol. 13, 100122 (2015).</li><li>Yoshida, M., 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=Periderm+cells+covering+palatal+shelves+have+tight+junctions+and+their+desquamation+reduces+the+polarity+of+palatal+shelf+epithelial+cells+in+palatogenesis.">Periderm cells covering palatal shelves have tight junctions and their desquamation reduces the polarity of palatal shelf epithelial cells in palatogenesis.</a> Genes Cells. 17, 455-472 (2012).</li><li>Fitchett, J., Hay, E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Medial+edge+epithelium+transforms+to+mesenchyme+after+embryonic+palatal+shelves+fuse.">Medial edge epithelium transforms to mesenchyme after embryonic palatal shelves fuse.</a> Dev. Biol. 131, 455-474 (1989).</li><li>Akira, N., 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+expression+of+TGF-beta3+for+epithelial-mesenchyme+transdifferentiated+MEE+in+palatogenesis.">The expression of TGF-beta3 for epithelial-mesenchyme transdifferentiated MEE in palatogenesis.</a> J Mol Hist. 41, 343-355 (2010).</li><li>Sani, F. V., 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=Fate-mapping+of+the+epithelial+seam+during+palatal+fusion+rules+out+epithelial-mesenchymal+transformation.">Fate-mapping of the epithelial seam during palatal fusion rules out epithelial-mesenchymal transformation.</a> Dev. Biol. 285, 490-495 (2005).</li><li>Jin, J. -. Z., Ding, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Analysis+of+cell+migration,+transdifferentiation+and+apoptosis+during+mouse+secondary+palate+fusion.">Analysis of cell migration, transdifferentiation and apoptosis during mouse secondary palate fusion.</a> Development. 133, 3341-3347 (2006).</li><li>Xu, X., 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=Cell+autonomous+requirement+for+Tgfbr2+in+the+disappearance+of+medial+edge+epithelium+during+palatal+fusion.">Cell autonomous requirement for Tgfbr2 in the disappearance of medial edge epithelium during palatal fusion.</a> Dev. Biol. 297, 238-248 (2006).</li><li>Carette, M. J., Ferguson, M. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+fate+of+medial+edge+epithelial+cells+during+palatal+fusion+in+vitro:+an+analysis+by+Dil+labelling+and+confocal+microscopy.">The fate of medial edge epithelial cells during palatal fusion in vitro: an analysis by Dil labelling and confocal microscopy.</a> Development. 114, 379-388 (1992).</li><li>Muzumdar, M., Tasic, B., Miyamichi, K., Li, L., Luo, L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+global+double-fluorescent+Cre+reporter+mouse.">A global double-fluorescent Cre reporter mouse.</a> Genesis. 45, 593-605 (2007).</li><li>Dassule, H., Lewis, P., Bei, M., Mass, R., McMahon, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Sonic+hedgehog+regulates+growth+and+morphogenesis+of+the+tooth.">Sonic hedgehog regulates growth and morphogenesis of the tooth.</a> Development. 127, 4775-4785 (2000).</li><li>Eisenhoffer, G., 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=Crowding+induces+live+cell+extrusion+to+maintain+homeostatic+cell+numbers+in+epithelia.">Crowding induces live cell extrusion to maintain homeostatic cell numbers in epithelia.</a> Nature. 484, 501-546 (2012).</li><li>Riedl, J., 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=Lifeact:+a+versatile+marker+to+visualize+F-actin.">Lifeact: a versatile marker to visualize F-actin.</a> Nat Methods. 5, 605-607 (2008).</li><li>Riedl, J., 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=Lifeact+mice+for+studying+F-actin+dynamics.">Lifeact mice for studying F-actin dynamics.</a> Nat Methods. 7, 168-169 (2010).</li><li>Can, A., 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=Attenuation+correction+in+confocal+laser+microscopes:+a+novel+two-view+approach.">Attenuation correction in confocal laser microscopes: a novel two-view approach.</a> J Microsc. 211, (2003).</li><li>Veenman, C., Reinders, M., Backer, E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Resolving+motion+correspondence+for+densely+moving+points.">Resolving motion correspondence for densely moving points.</a> IEEE Trans Pattern Anal Mach Intell. 23, 54-72 (2001).</li><li>Udan, R., Piazza, V., Hsu, C., Hadjantonakis, A., Dickinson, M. <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+cell+dynamics+in+mouse+embryos+using+light-sheet+microscopy.">Quantitative imaging of cell dynamics in mouse embryos using light-sheet microscopy.</a> Development. 141, 4406-4414 (2014).</li><li>Stoller, J., 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=Cre+reporter+mouse+expressing+a+nuclear+localized+fusion+of+GFP+and+beta-galactosidase+reveals+new+derivatives+of+Pax3-expressing+precursors.">Cre reporter mouse expressing a nuclear localized fusion of GFP and beta-galactosidase reveals new derivatives of Pax3-expressing precursors.</a> Genesis. 46, 200-204 (2008).</li></ol>

Live imaging of tissue morphogenesis with 3D organ explant culture can provide detailed information regarding cellular processes that cannot be shown in conventional staining analysis of fixed tissue sections. Using in vitro explant culture of mouse embryonic secondary palate, we observed several interesting cellular behaviors leading us to propose a novel mechanism of palate fusion that involves epithelial convergence and cell extrusion.
One common challenge in studies of this type i...

Tissue fusion is an important step in the development of multiple organs. Major human birth defects such as cleft lip and palate, spina bifida and malformations of the heart can result from defects in tissue fusion1. Mouse secondary palate fusion has been extensively studied to identify the cellular and molecular mechanisms controlling tissue fusion in development2,3,4. In the mouse, secondary palate development starts at around E11.5 with the outgrowth of a secondary palatal shelf from each of the bilateral maxillary processes. Initial growth of the palatal shelves occurs vertically along the tongue, until approximately E14.0, at which time, the palatal shelves become elevated horizontally above the tongue. Medially-directed growth results in physical contact between the apposing epithelia of the two palatal shelves, forming the midline epithelial seam (MES) at E14.5. The intervening MES must be removed from between the secondary palatal shelves to allow mesenchymal confluence and the development of an intact, completely fused secondary palate by E15.53.
How a shared epithelial MES cell layer is formed between two separate palatal shelves, and then removed to achieve mesenchymal confluency, has been a central question in palate development. Based on mouse histological and electron microscopy (EM) studies, explant culture studies, and functional mouse genetics experiments, several fundamental cell behaviors have been implicated in this process. Filopodia-like projections from the medial edge epithelium MEE of each palatal shelf facilitates initial contact5,6, followed by intercalation of these epithelial cells to a shared single MES6,7. Removal of the resulting shared MES has been proposed to proceed by three non-exclusive mechanisms. Early studies employing histological observation and ex vivo lineage tracing with vital dyes indicated that the MES might be removed by epithelial to mesenchymal transition (EMT) of MES cells8,9, though more recently, genetic lineage tracing of epithelial cells has raised uncertainty as to the long-term contribution of epithelial cells to the palatal shelf mesenchyme10,11,12. Significant numbers of apoptotic cells, and a reduction in their number in some mutants that fail to undergo proper palate fusion has led to the idea that apoptosis may be a major driver of MES dissolution2,3. Finally, based initially on studies involving epithelial labeling and static observation at progressive timepoints, MES cells were proposed to migrate in the oronasal and anteroposterior dimensions11,13, but such dynamic cell behaviors were initially unconfirmed due to an inability to observe them in live palatal tissue. Recently, we were able to directly observe these behaviors by developing a new live imaging methodology that combines mouse genetic methods of fluorescent labeling with confocal live imaging of explanted palatal shelves.
First, to visualize dynamic cellular behaviors in palate epithelial cells during palate fusion, we generated an epithelial-specific reporter mouse by crossing ROSA26-mTmGflox mice with Keratin14-cre mice14,15. Confocal live imaging of palate explant culture of the resulting embryos confirmed some previously proposed cellular behaviors and identified novel events in the fusion process6. Epithelial cell membrane protrusions preceded initial cell-cell contact followed by epithelial convergence by cell intercalation and oronasal cell displacement. Notably, we also discovered that cell extrusion, a process reported to play important roles in epithelial homeostasis, was a major mechanism driving mouse secondary palate fusion6,16. This imaging method can be used with other reporter lines; we utilized Lifeact-mRFPruby transgenic mice17,18 to examine actin cytoskeletal dynamics during the fusion process. Other reporters can also be employed to observe other specific aspects of palate fusion and this method can be adapted either to laser scanning confocal microscopy or spinning disk confocal microscopy, depending on imaging needs and microscope availability. Live imaging is increasingly becoming a keystone approach in developmental biology. Particularly, craniofacial morphogenesis is complex and human birth defects that affect the face are common. This confocal live imaging method will help to enable an improved understanding of underlying basic developmental mechanisms as well as origins of human craniofacial abnormalities.

<table border="0" cellpadding="0" cellspacing="0" width="1193">
	<colgroup>
		<col />
		<col />
		<col />
		<col />
	</colgroup>
	<tbody>
		<tr height="20">
			<td height="20" style="height:20px;width:348px;">Reagents</td>
			<td style="width:360px;"></td>
			<td style="width:225px;"></td>
			<td style="width:260px;"></td>
		</tr>
		<tr height="19">
			<td height="19" style="height:19px;">DMEM/F12</td>
			<td>Life technology</td>
			<td>11330-032</td>
			<td></td>
		</tr>
		<tr height="19">
			<td height="19" style="height:19px;">Fetal Bovine Serum</td>
			<td>Life technology</td>
			<td>16000-044</td>
			<td></td>
		</tr>
		<tr height="19">
			<td height="19" style="height:19px;">L-glutamine</td>
			<td>Life technology</td>
			<td>25030-081</td>
			<td></td>
		</tr>
		<tr height="19">
			<td height="19" style="height:19px;">L-Ascorbic acid</td>
			<td>Sigma</td>
			<td>A4544-100G</td>
			<td></td>
		</tr>
		<tr height="19">
			<td height="19" style="height:19px;">Pennicillin/Streptomycin</td>
			<td>Life technology</td>
			<td>15140-122</td>
			<td></td>
		</tr>
		<tr height="19">
			<td height="19" style="height:19px;">Low melting agarose</td>
			<td>BioExpress</td>
			<td>E-3111-125</td>
			<td></td>
		</tr>
		<tr height="19">
			<td height="19" style="height:19px;">35mm glass bottom dish</td>
			<td>MatTek</td>
			<td>P35G-1.5-10-C</td>
			<td></td>
		</tr>
		<tr height="19">
			<td height="19" style="height:19px;">Petrolieum Jelly (Vaseline)</td>
			<td>Sigma</td>
			<td>16415-1Kg</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Mice</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr height="19">
			<td height="19" style="height:19px;">Keratin14-cre</td>
			<td></td>
			<td>MGI: J:65294</td>
			<td>Allele = Tg(KRT14-cre)1Amc</td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;">ROSA26mTmG</td>
			<td></td>
			<td>MGI: J:124702</td>
			<td>Allele = Gt(ROSA)26Sortm4(ACTB-tdTomato,-EGFP)Luo</td>
		</tr>
		<tr height="19">
			<td height="19" style="height:19px;">Lifeact-mRFPruby</td>
			<td></td>
			<td>MGI: J:164274</td>
			<td>Allele = Tg(CAG-mRuby)#Rows</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Microscope</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr height="19">
			<td height="19" style="height:19px;">White Light SP5 confocal microscope</td>
			<td>Leica Microsystems</td>
			<td></td>
			<td></td>
		</tr>
		<tr height="19">
			<td height="19" style="height:19px;">Cell Observer spinning disk confocal microscope</td>
			<td>Zeiss Microscopy</td>
			<td></td>
			<td></td>
		</tr>
	</tbody>
</table>

live imaging of mouse secondary palate fusion

The fusion of the secondary palatal shelves to form the intact secondary palate is a key process in mammalian development and its disruption can lead to cleft secondary palate, a common congenital anomaly in humans. Secondary palate fusion has been extensively studied leading to several proposed cellular mechanisms that may mediate this process. However, these studies have been mostly performed on fixed embryonic tissues at progressive timepoints during development or in fixed explant cultures analyzed at static timepoints. Static analysis is limited for the analysis of dynamic morphogenetic processes such a palate fusion and what types of dynamic cellular behaviors mediate palatal fusion is incompletely understood. Here we describe a protocol for live imaging of ex vivo secondary palate fusion in mouse embryos. To examine cellular behaviors of palate fusion, epithelial-specific Keratin14-cre was used to label palate epithelial cells in ROSA26-mTmGflox reporter embryos. To visualize filamentous actin, Lifeact-mRFPruby reporter mice were used. Live imaging of secondary palate fusion was performed by dissecting recently-adhered secondary palatal shelves of embryonic day (E) 14.5 stage embryos and culturing in agarose-containing media on a glass bottom dish to enable imaging with an inverted confocal microscope. Using this method, we have detected a variety of novel cellular behaviors during secondary palate fusion. An appreciation of how distinct cell behaviors are coordinated in space and time greatly contributes to our understanding of this dynamic morphogenetic process. This protocol can be applied to mutant mouse lines, or cultures treated with pharmacological inhibitors to further advance understanding of how secondary palate fusion is controlled.

Live imaging of palate explant culture revealed multiple cellular processes mediating palate fusion6. Initial contacts between two epithelial cells are made by membrane protrusions (Figure 2B-2E). When two epithelial layers meet, they form a multi-cell layered MES followed by intercalation to make an integrated single cell-layer MES through epithelial convergence(Figure 2A-2E</stro...

Watch this Scientific Journal Video about Live Imaging of Mouse Secondary Palate Fusion at JoVE.com

Live Imaging of Mouse Secondary Palate Fusion

Here, we present a protocol for live imaging of mouse secondary palate fusion using confocal microscopy. This protocol can be used in combination with a variety of fluorescent reporter mouse lines, and with pathway inhibitors for mechanistic insight. This protocol can be adapted for live imaging in other developmental systems.

The fusion of the secondary palatal shelves to form the intact secondary palate is a key process in mammalian development and its disruption can lead to ...

The overall goal of this confocal live imaging method is to directly observe the cellular processes, the drive's secondary palate fusion during cranial facial development. Begin by separating the head from the body of the embryo under a dissecting microscope in a petri dish containing fresh, room temperature PBS. Grasp the head with one pair of fine number five forceps and use a second pair of forceps to remove the upper brain, cutting away any extra tissue outside of the palatal shelves with a second pair of forceps.Remove the mandible carefully without damaging the palatal shelves. When the mandible has been detached, carefully remove the tongue and confirm the presence of a robust reporter signal in the midline epithelia seam. It's important not to damage it, palatal explained during dissection to keep the midline epithelia seam intact.Next, remove the hind brain, brain stem and both maxilli with the adhered palatal shelves. Cut the anterior upper jaw tissue, keeping both the primary and secondary palates intact. Remove the nasal septum on the nasal side of the explant to expose the midline epithelia seam and confirm that the epithelia layer between the tissue is intact.Now, add live imaging medium to a 35 millimeter glass bottom dish and place the dissected palatal shelves, oral side down in the dish as close to the glass bottom as possible. Then, place dry ice pellets on a conductive surface near the culture dish to expedite the solidification of the agarose within the imaging medium. When the agarose is semi-solid, mount the culture dish in an inverted confocal microscope equipped with a 37 degree celsius incubation chamber and use a syringe to apply petroleum jelly between the culture dish and the culture cover to prevent evaporation of the imaging medium.Select a low magnification objective to locate the region of interest. Then, select a high magnification objective and scan multiple z stacks with five micron steps for 16 to 24 hours, using the appropriate laser excitation. Live imaging of palate explant culture reveals multiple cellular processes that mediate palate fusion, with the initial contacts between the two epithelia cells being made by membrane protrusions.When the two epithelia layers meet, they form a multi cell layered midline epithelia seam, followed by intercalation to generate an integrated single cell layer, midline epithelia seam through epithelia convergence. The epithelia cells in deeper z levels are also progressively displaced to the oral side of the midline epithelia seam, contributing to the epithelia convergence process. Posterior directed cell migration is observed in middle palate midline epithelia seam.With epithelia cell extrusion events observed during palate fusion, suggesting that the epithelia cells in the midline epithelia seam can be removed by this active process. This integrated epithelia seam will ultimately break down to achieve confluency. Further, filamentis actin becomes enriched at the border between the epithelia and mazenkemo areas, forming a cable like structure along the anterior posterior axis.Software can be used to track specific cellular behaviors of interest, during palate fusion with the best method for cell tracking depending on the reporter signal used in the experiment.

live-imaging-of-mouse-secondary-palate-fusion

Research

JoVE Journal

Developmental Biology

7.4K ビュー.  University of California San Francisco. The overall goal of this confocal live imaging method is to directly observe the cellular processes, the drive's secondary palate fusion during cranial facial development. Begin by separating the head from the body of the embryo under a dissecting microscope in a petri dish containing fresh, room temperature PBS. Grasp the head with one pair of fine number five forceps and use a second pair of forceps to remove the upper brain, cutting away any extra tissue outside of the palatal shelves with...

ビデオ: Live Imaging of Mouse Secondary Palate Fusion

Live-imaging of the Drosophila Pupal Eye

Inherent processes of Drosophila pupal development can shift and distort the eye epithelium in ways that make individual cell behavior difficult to track during live cell imaging. These processes include: retinal rotation, cell growth and organismal movement. Additionally, irregularities in the topology of the epithelium, including subtle bumps and folds often introduced as the pupa is prepared for imaging, make it challenging to acquire in-focus images of more than a few ommatidia in a single focal plane. The workflow outlined here remedies these issues, allowing easy analysis of cellular processes during Drosophila pupal eye development. Appropriately-staged pupae are arranged in an imaging rig that can be easily assembled in most laboratories. Ubiquitin-DE-Cadherin:GFP and GMR-GAL4&#8211;driven UAS-&#945;-catenin:GFP are used to visualize cell boundaries in the eye epithelium 1-3. After deconvolution is applied to fluorescent images captured at multiple focal planes, maximum projection images are generated for each time point and enhanced using image editing software. Alignment algorithms are used to quickly stabilize superfluous motion, making individual cell behavior easier to track.

Live-imaging of the Drosophila Pupal Eye

This protocol presents an efficient method for imaging the live Drosophila pupal eye neuroepithelium. This method compensates for tissue movement and uneven topology, enhances visualization of cell boundaries through the use of multiple GFP-tagged junction proteins, and uses an easily-assembled imaging rig.

Inherent processes of Drosophila pupal development can shift and distort the eye epithelium in ways that make individual cell behavior difficult to track ...

In Vitro Differentiation of Mature Myofibers for Live Imaging

Skeletal muscles are composed of myofibers, the biggest cells in the mammalian body and one of the few syncytia. How the complex and evolutionarily conserved structures that compose it are assembled remains under investigation. Their size and physiological features often constrain manipulation and imaging applications. The culture of immortalized cell lines is widely used, but it can only replicate the early steps of differentiation.
Here, we describe a protocol that enables easy genetic manipulation of myofibers originating from primary mouse myoblasts. After one week of differentiation, the myofibers display contractility, aligned sarcomeres and triads, as well as peripheral nuclei. The entire differentiation process can be followed by live imaging or immunofluorescence. This system combines the advantages of the existing ex vivo and in vitro protocols. The possibility of easy and efficient transfection as well as the ease of access to all differentiation stages broadens the potential applications. Myofibers can subsequently be used not only to address relevant developmental and cell biology questions, but also to reproduce muscle disease phenotypes for clinical applications.

In Vitro Differentiation of Mature Myofibers for Live Imaging

Muscle cells are among the most complex eukaryotic cells. We present a protocol for the in vitro differentiation of highly mature myofibers that allows for genetic manipulation and clear imaging during all developmental stages.

Skeletal muscles are composed of myofibers, the biggest cells in the mammalian body and one of the few syncytia. How the complex and evolutionarily ...

Live Confocal Imaging of Developing Arabidopsis Flowers

The study of plant growth and development has long relied on experimental techniques using dead, fixed tissues and lacking proper cellular resolution. Recent advances in confocal microscopy, combined with the development of numerous fluorophores, have overcome these issues and opened the possibility to study the expression of several genes simultaneously, with a good cellular resolution, in live samples. Live confocal imaging provides plant biologists with a powerful tool to study development, and has been extensively used to study root growth and the formation of lateral organs on the flanks of the shoot apical meristem. However, it has not been widely applied to the study of flower development, in part due to challenges that are specific to imaging flowers, such as the sepals that grow over the flower meristem, and filter out the fluorescence from underlying tissues. Here, we present a detailed protocol to perform live confocal imaging on live, developing Arabidopsis flower buds, using either an upright or an inverted microscope.

Live confocal imaging provides biologists with a powerful tool to study development. Here, we present a detailed protocol for the live confocal imaging of developing Arabidopsis flowers.

The study of plant growth and development has long relied on experimental techniques using dead, fixed tissues and lacking proper cellular resolution. ...

Long-term Live Imaging of Drosophila Eye Disc

Live imaging provides the ability to continuously track dynamic cellular and developmental processes in real time. Drosophila larval imaginal discs have been used to study many biological processes, such as cell proliferation, differentiation, growth, migration, apoptosis, competition, cell-cell signaling, and compartmental boundary formation. However, methods for the long-term ex vivo culture and live imaging of the imaginal discs have not been satisfactory, despite many efforts. Recently, we developed a method for the long-term ex vivo culture and live imaging of imaginal discs for up to 18 h. In addition to using a high insulin concentration in the culture medium, a low-melting agarose was also used to embed the disc to prevent it from drifting during the imaging period. This report uses the eye-antennal discs as an example. Photoreceptor R3/4-specific m&#948;0.5-Ga4 expression was followed to demonstrate that photoreceptor differentiation and ommatidial rotation can be observed during a 10 h live imaging period. This is a detailed protocol describing this simple method.

Long-term Live Imaging of Drosophila Eye Disc

This protocol describes a detailed method for the long-term ex vivo culture and live imaging of a Drosophila imaginal disc. It demonstrates photoreceptor differentiation and ommatidial rotation within the 10 h period of live imaging of the eye disc. The protocol is simple and does not require expensive setup.

Live imaging provides the ability to continuously track dynamic cellular and developmental processes in real time. Drosophila larval imaginal discs have ...

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 ...

In Vitro Ovule Cultivation for Live-cell Imaging of Zygote Polarization and Embryo Patterning in Arabidopsis thaliana

In most flowering plants, the zygote and embryo are hidden deep in the mother tissue, and thus it has long been a mystery of how they develop dynamically; for example, how the zygote polarizes to establish the body axis and how the embryo specifies various cell fates during organ formation. This manuscript describes an in vitro ovule culture method to perform live-cell imaging of developing zygotes and embryos of Arabidopsis thaliana. The optimized cultivation medium allows zygotes or early embryos to grow into fertile plants. By combining it with a poly(dimethylsiloxane) (PDMS) micropillar array device, the ovule is held in the liquid medium in the same position. This fixation is crucial to observe the same ovule under a microscope for several days from the zygotic division to the late embryo stage. The resulting live-cell imaging can be used to monitor the real-time dynamics of zygote polarization, such as nuclear migration and cytoskeleton rearrangement, and also the cell division timing and cell fate specification during embryo patterning. Furthermore, this ovule cultivation system can be combined with inhibitor treatments to analyze the effects of various factors on embryo development, and with optical manipulations such as laser disruption to examine the role of cell-cell communication.

In Vitro Ovule Cultivation for Live-cell Imaging of Zygote Polarization and Embryo Patterning in Arabidopsis thaliana

This manuscript describes an in vitro ovule cultivation method that enables live-cell imaging of Arabidopsis zygotes and embryos. This method is utilized to visualize the intracellular dynamics during zygote polarization and the cell fate specification in developing embryos.

In most flowering plants, the zygote and embryo are hidden deep in the mother tissue, and thus it has long been a mystery of how they develop dynamically; ...

Live Cell Imaging of Chromosome Segregation During Mitosis

Chromosomes must be reliably and uniformly segregated into daughter cells during mitotic cell division. Fidelity of chromosomal segregation is controlled by multiple mechanisms that include the Spindle Assembly Checkpoint (SAC). The SAC is part of a complex feedback system that is responsible for prevention of a cell progress through mitosis unless all chromosomal kinetochores have attached to spindle microtubules. Chromosomal lagging and abnormal chromosome segregation is an indicator of dysfunctional cell cycle control checkpoints and can be used to measure the genomic stability of dividing cells. Deregulation of the SAC can result in the transformation of a normal cell into a malignant cell through the accumulation of errors during chromosomal segregation. Implementation of the SAC and the formation of the kinetochore complex are tightly regulated by interactions between kinases and phosphatase such as Protein Phosphatase 2A (PP2A). This protocol describes live cell imaging of lagging chromosomes in mouse embryonic fibroblasts isolated from mice that had a knockout of the PP2A-B56&#947; regulatory subunit. This method overcomes the shortcomings of other cell cycle control imaging techniques such as flow cytometry or immunocytochemistry that only provide a snapshot of a cell cytokinesis status, instead of a dynamic spatiotemporal visualization of chromosomes during mitosis.

This protocol describes an easy and convenient method to label and visualize live chromosomes in mitotic cells using Histone2B-GFP BacMam 2.0 label and a spinning disc confocal microscopy system.

Chromosomes must be reliably and uniformly segregated into daughter cells during mitotic cell division. Fidelity of chromosomal segregation is controlled ...

Live Imaging and Analysis of Muscle Contractions in Drosophila Embryo

Coordinated muscle contractions are a form of rhythmic behavior seen early during development in Drosophila embryos. Neuronal sensory feedback circuits are required to control this behavior. Failure to produce the rhythmic pattern of contractions can be indicative of neurological abnormalities. We previously found that defects in protein O-mannosylation, a posttranslational protein modification, affect the axon morphology of sensory neurons and result in abnormal coordinated muscle contractions in embryos. Here, we present a relatively simple method for recording and analyzing the pattern of peristaltic muscle contractions by live imaging of late stage embryos up to the point of hatching, which we used to characterize the muscle contraction phenotype of protein O-mannosyltransferase mutants. Data obtained from these recordings can be used to analyze muscle contraction waves, including frequency, direction of propagation and relative amplitude of muscle contractions at different body segments. We have also examined body posture and taken advantage of a fluorescent marker expressed specifically in muscles to accurately determine the position of the embryo midline. A similar approach can also be utilized to study various other behaviors during development, such as embryo rolling and hatching.

Live Imaging and Analysis of Muscle Contractions in Drosophila Embryo

Here, we present a method to record embryonic muscle contractions in Drosophila embryos in a non-invasive and detail-oriented manner.

Coordinated muscle contractions are a form of rhythmic behavior seen early during development in Drosophila embryos. Neuronal sensory feedback circuits ...

Vascular Casting of Adult and Early Postnatal Mouse Lungs for Micro-CT Imaging

Blood vessels form intricate networks in 3-dimensional space. Consequently, it is difficult to visually appreciate how vascular networks interact and behave by observing the surface of a tissue. This method provides a means to visualize the complex 3-dimensional vascular architecture of the lung.
To accomplish this, a catheter is inserted into the pulmonary artery and the vasculature is simultaneously flushed of blood and chemically dilated to limit resistance. Lungs are then inflated through the trachea at a standard pressure and the polymer compound is infused into the vascular bed at a standard flow rate. Once the entire arterial network is filled and allowed to cure, the lung vasculature may be visualized directly or imaged on a micro-CT (&#181;CT) scanner.
When performed successfully, one can appreciate the pulmonary arterial network in mice ranging from early postnatal ages to adults. Additionally, while demonstrated in the pulmonary arterial bed, this method can be applied to any vascular bed with optimized catheter placement and endpoints.

The aim of this technique is ex vivo visualization of pulmonary arterial networks of early postnatal and adult mice through lung inflation and injection of a radio-opaque polymer-based compound via the pulmonary artery. Potential applications for casted tissues are also discussed.

Blood vessels form intricate networks in 3-dimensional space. Consequently, it is difficult to visually appreciate how vascular networks interact and ...

Dissection and Live-Imaging of the Late Embryonic Drosophila Gonad

The Drosophila melanogaster male embryonic gonad is an advantageous model to study various aspects of developmental biology including, but not limited to, germ cell development, piRNA biology, and niche formation. Here, we present a dissection technique to live-image the gonad ex vivo during a period when in vivo live-imaging is highly ineffective. This protocol outlines how to transfer embryos to an imaging dish, choose appropriately-staged male embryos, and dissect the gonad from its surrounding tissue while still maintaining its structural integrity. Following dissection, gonads can be imaged using a confocal microscope to visualize dynamic cellular processes. The dissection procedure requires precise timing and dexterity, but we provide insight on how to prevent common mistakes and how to overcome these challenges. To our knowledge this is the first dissection protocol for the Drosophila embryonic gonad, and will permit live-imaging during an otherwise inaccessible window of time. This technique can be combined with pharmacological or cell-type specific transgenic manipulations to study any dynamic processes occurring within or between the&#160;cells in their natural gonadal environment.

Dissection and Live-Imaging of the Late Embryonic Drosophila Gonad

Here, we provide a dissection protocol required to live-image the late embryonic Drosophila male gonad. This protocol will permit observation of dynamic cellular processes under normal conditions or after transgenic or pharmacological manipulation.

The Drosophila melanogaster male embryonic gonad is an advantageous model to study various aspects of developmental biology including, but not limited to, ...