We would like to thank Alexandra Joyner for her support when this protocol was being established, Edwina McGlinn and Yi-cheng Chang for sharing retinoic acid. The Australian Regenerative Medicine Institute is supported by grants from the State Government of Victoria and the Australian Government.

All the experiments should be carried out following the local governmental and institutional guidelines of ethical handling of laboratory animals.
1. Preparations Prior to the Day of Bone Culture
<ol>
	<li>Set up timed mouse matings to obtain fetuses and pups from embryonic day 14.5 (E14.5) and onward. 
	NOTE: The culture of long bones can be successfully applied to different mouse strains; in the present protocol, outbred Swiss Webster wild-type mice are used.</li>
	<l...

<ol>
	<li>Long, F., Ornitz, D. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Development+of+the+endochondral+skeleton.">Development of the endochondral skeleton.</a> Cold Spring Harbor Perspectives in Biology. 5 (1), a008334 (2013).</li><li>Mackie, E. J., Ahmed, Y. A., Tatarczuch, L., Chen, K. S., Mirams, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Endochondral+ossification:+how+cartilage+is+converted+into+bone+in+the+developing+skeleton.">Endochondral ossification: how cartilage is converted into bone in the developing skeleton.</a> The International Journal of Biochemistry &amp; Cell Biology. 40 (1), 46-62 (2008).</li><li>Goldring, M. B., Tsuchimochi, K., Ijiri, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+control+of+chondrogenesis.">The control of chondrogenesis.</a> Journal of Cellular Biochemistry. 97 (1), 33-44 (2006).</li><li>Kronenberg, H. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Developmental+regulation+of+the+growth+plate.">Developmental regulation of the growth plate.</a> Nature. 423 (6937), 332-336 (2003).</li><li>Mackie, E. J., Tatarczuch, L., Mirams, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+skeleton:+a+multi-functional+complex+organ:+the+growth+plate+chondrocyte+and+endochondral+ossification.">The skeleton: a multi-functional complex organ: the growth plate chondrocyte and endochondral ossification.</a> The Journal of Endocrinology. 211 (2), 109-121 (2011).</li><li>Maes, 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=Osteoblast+precursors,+but+not+mature+osteoblasts,+move+into+developing+and+fractured+bones+along+with+invading+blood+vessels.">Osteoblast precursors, but not mature osteoblasts, move into developing and fractured bones along with invading blood vessels.</a> Developmental Cell. 19 (2), 329-344 (2010).</li><li>Park, 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=Dual+pathways+to+endochondral+osteoblasts:+a+novel+chondrocyte-derived+osteoprogenitor+cell+identified+in+hypertrophic+cartilage.">Dual pathways to endochondral osteoblasts: a novel chondrocyte-derived osteoprogenitor cell identified in hypertrophic cartilage.</a> Biology Open. 4 (5), 608-621 (2015).</li><li>Yang, L., Tsang, K. Y., Tang, H. C., Chan, D., Cheah, K. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Hypertrophic+chondrocytes+can+become+osteoblasts+and+osteocytes+in+endochondral+bone+formation.">Hypertrophic chondrocytes can become osteoblasts and osteocytes in endochondral bone formation.</a> Proceedings of the National Academy of Sciences of the United States of America. 111 (33), 12097-12102 (2014).</li><li>Zhou, 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=Chondrocytes+transdifferentiate+into+osteoblasts+in+endochondral+bone+during+development,+postnatal+growth+and+fracture+healing+in+mice.">Chondrocytes transdifferentiate into osteoblasts in endochondral bone during development, postnatal growth and fracture healing in mice.</a> PLoS Genetics. 10 (12), e1004820 (2014).</li><li>Wilsman, N. J., Bernardini, E. S., Leiferman, E., Noonan, K., Farnum, C. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Age+and+pattern+of+the+onset+of+differential+growth+among+growth+plates+in+rats.">Age and pattern of the onset of differential growth among growth plates in rats.</a> Journal of Orthopaedic Research: Official Publication of the Orthopaedic Research Society. 26 (11), 1457-1465 (2008).</li><li>Cooper, K. 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=Multiple+phases+of+chondrocyte+enlargement+underlie+differences+in+skeletal+proportions.">Multiple phases of chondrocyte enlargement underlie differences in skeletal proportions.</a> Nature. 495 (7441), 375-378 (2013).</li><li>Smith, E. L., Rashidi, H., Kanczler, J. M., Shakesheff, K. M., Oreffo, R. O. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+effects+of+1alpha,+25-dihydroxyvitamin+D3+and+transforming+growth+factor-beta3+on+bone+development+in+an+ex+vivo+organotypic+culture+system+of+embryonic+chick+femora.">The effects of 1alpha, 25-dihydroxyvitamin D3 and transforming growth factor-beta3 on bone development in an ex vivo organotypic culture system of embryonic chick femora.</a> PloS One. 10 (4), e0121653 (2015).</li><li>Li, Y., Li, A., Junge, J., Bronner, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Planar+cell+polarity+signaling+coordinates+oriented+cell+division+and+cell+rearrangement+in+clonally+expanding+growth+plate+cartilage.">Planar cell polarity signaling coordinates oriented cell division and cell rearrangement in clonally expanding growth plate cartilage.</a> eLife. 6, (2017).</li><li>Kanczler, J. M., Smith, E. L., Roberts, C. A., Oreffo, R. O. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+novel+approach+for+studying+the+temporal+modulation+of+embryonic+skeletal+development+using+organotypic+bone+cultures+and+microcomputed+tomography.">A novel approach for studying the temporal modulation of embryonic skeletal development using organotypic bone cultures and microcomputed tomography.</a> Tissue Engineering. Part C, Methods. 18 (10), 747-760 (2012).</li><li>Houston, D. A., Staines, K. A., MacRae, V. E., Farquharson, C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Culture+of+Murine+Embryonic+Metatarsals:+A+Physiological+Model+of+Endochondral+Ossification.">Culture of Murine Embryonic Metatarsals: A Physiological Model of Endochondral Ossification.</a> Journal of Visualized Experiments. (118), (2016).</li><li>Abubakar, A. A., Noordin, M. M., Azmi, T. I., Kaka, U., Loqman, M. Y. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+use+of+rats+and+mice+as+animal+models+in+ex+vivo+bone+growth+and+development+studies.">The use of rats and mice as animal models in ex vivo bone growth and development studies.</a> Bone &amp; Joint Research. 5 (12), 610-618 (2016).</li><li>Lui, J. 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=Differential+aging+of+growth+plate+cartilage+underlies+differences+in+bone+length+and+thus+helps+determine+skeletal+proportions.">Differential aging of growth plate cartilage underlies differences in bone length and thus helps determine skeletal proportions.</a> PLoS Biology. 16 (7), e2005263 (2018).</li><li>Agoston, H., 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=C-type+natriuretic+peptide+regulates+endochondral+bone+growth+through+p38+MAP+kinase-dependent+and+-independent+pathways.">C-type natriuretic peptide regulates endochondral bone growth through p38 MAP kinase-dependent and -independent pathways.</a> BMC Developmental Biology. 7, 18 (2007).</li><li>Rosello-Diez, A., Madisen, L., Bastide, S., Zeng, H., Joyner, A. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Cell-nonautonomous+local+and+systemic+responses+to+cell+arrest+enable+long-bone+catch-up+growth+in+developing+mice.">Cell-nonautonomous local and systemic responses to cell arrest enable long-bone catch-up growth in developing mice.</a> PLoS Biology. 16 (6), e2005086 (2018).</li><li>Marino, S., Staines, K. A., Brown, G., Howard-Jones, R. A., Adamczyk, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Models+of+ex+vivo+explant+cultures:+applications+in+bone+research.">Models of ex vivo explant cultures: applications in bone research.</a> BoneKEy Reports. 5, 818 (2016).</li><li>Okubo, 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=Prolonged+bioluminescence+monitoring+in+mouse+ex+vivo+bone+culture+revealed+persistent+circadian+rhythms+in+articular+cartilages+and+growth+plates.">Prolonged bioluminescence monitoring in mouse ex vivo bone culture revealed persistent circadian rhythms in articular cartilages and growth plates.</a> PloS One. 8 (11), e78306 (2013).</li><li>Hirota, K., 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=Live+imaging+analysis+of+the+growth+plate+in+a+murine+long+bone+explanted+culture+system.">Live imaging analysis of the growth plate in a murine long bone explanted culture system.</a> Scientific Reports. 8 (1), 10332 (2018).</li><li>Romereim, S. M., Conoan, N. H., Chen, B., Dudley, A. 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The authors have nothing to disclose.

Bone ex vivo culture methods have been used for some time to assess the biology of bone growth28, but have been seldom applied to murine long bones. With the development of imaging techniques, ex vivo bone culture offers an attractive way to study bone growth in real time in a setting closely resembling the in vivo conditions. In this scenario, it is important to define the conditions in which the growth of long bones is comparable to their growth in vivo.
In the presen...

Organ growth has to be tightly tuned to prevent the appearance of growth disorders, and involves the regulation of multiple cell types, molecular pathways and crosstalk among different parts of the body. Imaging techniques are essential to address the changes occurring over time in a growing embryo, both in normal conditions, as well as after a perturbation is induced in the system. Embryos with intrauterine development, such as the widely used rodent models, present an additional challenge for live imaging and drug treatment, which can be partially overcome by using ex vivo culture techniques. To successfully recapitulate the in vivo processes and obtain meaningful results, it becomes crucial to find the right culturing conditions for each organ or tissue.
Most bones of the mammalian skeleton grow through endochondral ossification, where the embryonic cartilage (composed of cells called chondrocytes) drives longitudinal growth and is gradually replaced by bone. This process happens at the growth plates, located at the end of the long bones, where three zones can be distinguished: resting, proliferative, and hypertrophic1,2. First, the round progenitor chondrocytes in the resting zone transition into the cycling columnar chondrocytes in the proliferative zone. During the next stage of differentiation, these chondrocytes become hypertrophic and start secreting type X collagen. Hypertrophic chondrocytes orchestrate the subsequent steps of ossification: they secrete key signaling molecules, such as connective tissue growth factor, bone morphogenetic proteins and Indian hedgehog, and direct the mineralization of the matrix, recruit blood vessels to the central part of the bone, and, upon apoptosis, allow osteoblasts (bone-forming cells) to invade the matrix to form the primary ossification center3,4. The mineralized matrix facilitates the penetration of blood vessels through which osteoblasts migrate to replace this degraded cartilage with a bone matrix5. Most osteoblasts invade the cartilage matrix from the perichondrium, a fibrous layer that wraps the cartilage6. Alternatively, a proportion of hypertrophic chondrocytes are able to survive and transdifferentiate to osteoblasts7,8,9. The final length of the bone is due to the accumulated growth of the transient cartilage, whose growth rate in turn depends on the number and size of the hypertrophic chondrocytes, and their matrix production10. Additionally, it was recently shown that the duration of the last hypertrophy phase correlates with the final length of the bone11. Therefore, tight regulation of the proliferation and differentiation of these cells is required to ensure proper bone size.
Despite of the substantial knowledge acquired over the years on the organization and development of the growth plates, most of these conclusions are based on the observation of fixed histological sections. Tissue sectioning provides valuable information about this process, but can be ridden with technical artifacts, so it cannot be always reliably used to estimate morphological or size changes between different stages. Additionally, as bone growth is a dynamic process, the static two-dimensional (2D) images offer a limited insight into the movement of the cells in the growth plate, while time-lapse imaging on live tissue could offer valuable information on the behavior of the chondrocytes in the growth plate.
All these limitations can be potentially resolved using ex vivo bone cultures. While bone culture protocols have been developed some time ago, they were limitedly applied to murine long bones. Most of the studies use chick bones due to the technical advantages offered by the chick model12,13. Organotypic cultures (air/liquid interface) were applied to chick embryonic femurs, which were maintained in culture for 10 days14. The sophisticated genetic tools available in mouse make this model very appealing to be used in ex vivo bone culture. The studies that used mice to look into bone growth worked mostly with metatarsal bones15, probably due to their small size and greater numbers obtained per embryo16. Although traditionally considered long bones, metatarsi enter senescence (characterized by reduced proliferation and involution of the growth plate17) earlier than other long bones in vivo, and therefore their continuous growth ex vivo does not really recapitulate the in vivo process. For the purposes of this article, we will use the term long bones for bones from the proximal and intermediate limb regions. Several previous studies used long murine bones, such as tibia, in ex vivo cultures and observed a substantial growth of the cartilage but little ossification18. We also used tibial cultures recently, mainly to study chondrocyte dynamics19. Other studies used femoral heads from young mice20 or only the distal part of the femur for culture21. Some more recent works successfully combine the ex vivo culture of full bones with time-lapse imaging to acquire three-dimensional (3D) movies of chondrocytes in living mouse tissue22,23. The authors managed to observe previously unnoticed events in the rearrangement of chondrocytes to the proliferative zone23 in a good example of the potential application of bone ex vivo culture. The alternative, i.e., analyzing static images, requires indirect and complex techniques. This was exemplified by a recent study assessing the importance of transversally-oriented clones for cartilage growth, where genetic tracing with multicolor reporter mouse strains coupled with mathematical modeling were used24. Therefore, ex vivo culture might help gain insight into dynamic processes in a faster and more straightforward way.
Here, we present a method for murine long bones culture, which can be combined with different molecular treatments and/or with time-lapse live imaging. This protocol adapts the methods used in previous reports15,18,25, but addresses some additional issues and focuses on long bones such as the tibia, rather than metatarsal bones. Finally, it explores the potential of using statistically powerful paired comparisons by culturing left and right bones separately in the presence of different substances.

<table border="0" cellpadding="0" cellspacing="0" style="width:868px;" width="869">
	<tbody>
		<tr height="21">
			<td height="21" style="height:21px;width:451px;">5-Ethynyl-2&#39;-deoxyuridine</td>
			<td style="width:132px;">Santa Cruz</td>
			<td style="width:119px;">CAS 61135-33-9</td>
			<td style="width:167px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">5-Bromo-2&#8242;-deoxyuridine</td>
			<td style="width:132px;">Sigma</td>
			<td>B5002</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">50mL Conical Centrifuge Tubes</td>
			<td style="width:132px;">Falcon</td>
			<td>352070</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">60 mm TC-treated Center Well Organ Culture Dish, 20/Pack, 500/Case, Sterile</td>
			<td style="width:132px;">Falcon</td>
			<td>353037</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Adobe Photoshop</td>
			<td style="width:132px;">Adobe</td>
			<td>CS4</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:451px;">Ascorbic acid</td>
			<td style="width:132px;">Sigma</td>
			<td>A92902</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:451px;">Base unit for the scope</td>
			<td style="width:132px;">Zeiss</td>
			<td>435425-9100-000</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:451px;">Betaglycerophosphate</td>
			<td style="width:132px;">Sigma</td>
			<td style="width:119px;">G9422</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:451px;">Binocular scope</td>
			<td style="width:132px;">Zeiss</td>
			<td style="width:119px;">STEMI-2000</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:451px;">Bovine Serum Albumin (BSA) fraction v</td>
			<td style="width:132px;">Roche/Sigma</td>
			<td style="width:119px;">10735086001</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:451px;">DigiRetina 500 camera</td>
			<td style="width:132px;">Aunet</td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:451px;">Dissection kit</td>
			<td style="width:132px;">Cumper Robbins</td>
			<td style="width:119px;">PFS00034</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:451px;">DMEM</td>
			<td style="width:132px;">Gibco</td>
			<td style="width:119px;">11960044</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:451px;">DMSO</td>
			<td style="width:132px;">Sigma</td>
			<td style="width:119px;">D8418</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:451px;">Eppendorf 2-mL tubes</td>
			<td style="width:132px;">Eppendorf</td>
			<td style="width:119px;">0030120094</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:451px;">Ethanol 96%</td>
			<td style="width:132px;">Merk</td>
			<td style="width:119px;">159010</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:451px;">Forceps Dumont#5 Inox08</td>
			<td style="width:132px;">Fine Science Tools</td>
			<td style="width:119px;">T05811</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:451px;">Heracell 150 CO2 incubator</td>
			<td style="width:132px;">Thermo Fisher</td>
			<td style="width:119px;">51026282</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:451px;">Minimum Essential Medium Eagle</td>
			<td style="width:132px;">Sigma</td>
			<td style="width:119px;">M2279</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:451px;">Multiwell 24 well</td>
			<td style="width:132px;">Falcon</td>
			<td style="width:119px;">353047</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:451px;">Paraformaldehyde</td>
			<td style="width:132px;">Sigma</td>
			<td style="width:119px;">158127</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:451px;">Penicillin-Streptomycin (10,000 U/mL)</td>
			<td style="width:132px;">Gibco</td>
			<td style="width:119px;">15140-122</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:451px;">Plastic pipettes 1mL Sterile Individually wrapped</td>
			<td style="width:132px;">Thermo</td>
			<td style="width:119px;">273</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:451px;">Syringe filter 0.2 um&#160;</td>
			<td style="width:132px;">Life Sciences</td>
			<td style="width:119px;">PN4612</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:451px;">Terumo syringe 20 mL</td>
			<td style="width:132px;">Terumo</td>
			<td style="width:119px;">DVR-5174</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:451px;">Tretinoin (retinoic acid)</td>
			<td style="width:132px;">Sigma</td>
			<td style="width:119px;">PHR1187-3X</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:451px;">Trinocular scope</td>
			<td style="width:132px;">Aunet</td>
			<td style="width:119px;">AZS400T</td>
			<td></td>
		</tr>
	</tbody>
</table>

culturing and measuring fetal and newborn murine long bones

Long bones are complex and dynamic structures, which arise from endochondral ossification via a cartilage intermediate. The limited access to healthy human bones makes particularly valuable the use of mammalian models, such as mouse and rat, to look into different aspects of bone growth and homeostasis. Additionally, the development of sophisticated genetic tools in mice allows more complex studies of long bone growth and asks for an expansion of techniques used to study bone growth. Here, we present a detailed protocol for ex vivo murine bone culture, which allows the study of bone and cartilage in a tightly controlled manner while recapitulating most of the in vivo process. The method described allows the culture of a range of bones, including tibia, femur, and metatarsal bones, but we have focused mainly on tibial culture here. Moreover, it can be used in combination with other techniques, such as time-lapse live imaging or drug treatment.

Bone culture can be performed starting from different stages. In Figure 1A-D, a comparison between cultured tibia and freshly extracted ones at equivalent stages is shown. The first observation is that up to two days of culture the size achieved is comparable to the in vivo bone growth for both cartilage and mineralized bone (Figure 1A,B,D). Longer culture periods lead to bigger differences betwe...

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Culturing and Measuring Fetal and Newborn Murine Long Bones

Here, we present a method for ex vivo culture of long murine bones at both fetal and newborn stages, suitable for analyzing bone and cartilage development and homeostasis in controlled conditions while recapitulating the in vivo process.

Long bones are complex and dynamic structures, which arise from endochondral ossification via a cartilage intermediate. The limited access to healthy ...

This method adapts the metatarsal culture protocol to bigger bones, allowing direct bone manipulation to be combined with complex genetic models to address processes related to bone development. This technique allows manipulation and analysis of bone growth that are not possible in vivo, such as live imaging or direct physical and pharmacological manipulation. This ex vivo culture method allows the specific study of the local effects of the genetic inset in the bone separating it from the systemic effect the treatment has on the organism.Begin by sterilizing the abdominal region of a pregnant gestational day 14.5 to 18.5 mouse with 80%ethanol and using small scissors to open the skin and abdominal muscles to access the uterine horns. To extract the uterus from the abdominal cavity, remove the mesometrium and cut the base of the horns. Then, transfer the uterus to a 60 millimeter petri dish containing ice-cold dissection medium on ice.In a biosafety cabinet cut between the sacks with scissors to separate the individual fetuses, and transfer an individual sack into a new 60 millimeter dish with fresh dissection medium under a dissection stereo microscope. Use tweezers to separate the fetuses from the placentas and to clean the fetuses from the membranes. Use a trimmed plastic pipette to transfer the body into a new 60 millimeter dish, and decapitate the embryo before further dissection.Then use tweezers to remove the skin, starting from the back and peeling out to the toes. Use the tweezers to cut close to the spine and separate the hind limbs from the body. Transfer the hind limbs to a clean dish containing ice-cold dissection medium, and insert the tweezers between the surface cartilage of the distal femur and the proximal tibia to separate the tibia from the femur.Remove the hip bones from the proximal femur and the calcaneus bone and the fibula from the tibia. Carefully nip and pull the soft tissues from the femurs and tibias and use a sterile one-milliliter pipette to transfer all four leg bones into the first well of a 24-well plate containing fresh dissection medium. It is important to show that the soft tissue that connects the pulse of the bone is removed.Otherwise, the bone will bend and not achieve proper growth. When the bones have been dissected from the appropriate experimental number of fetuses, image the bones in each well at times zero under a light microscope with a good contrast and replace the dissection medium in each well with one milliliter of culture medium per well taking extra care not to aspirate the bones. To observe the effect of growth inhibition in the culture conditions, treat the left tibias with 500 nanomolar retinoic acid and incubate the right tibias with an equivalent volume of vehicle as a control.Then, place the plate in a cell culture incubator under standard cell culture conditions. After two days, treat the bones with an appropriate thymidine analog for one to two hours to assess bone cell proliferation before transferring the bones to individual two-milliliter tubes of 4%paraformaldehyde for 10 minutes. Then, transfer the bones to PBS to image the bones at the final time point before returning the samples to the paraformaldehyde for overnight fixation at four degrees Celsius.To measure the length and mineralized region of the bones, open an appropriate imaging software program, and taking into account the scale of the image, measure both the total length of the bone, and the mineralized region. Starting the measurements from the first dark cells at one end until the last dark cells at the other end. To calculate the growth rate which is defined as the average increase in length per day, divide the difference between the final length of the bone and the initial length by the number of days in culture.Here, a comparison between cultured tibia and freshly-extracted tibia at equivalent stages is shown. After up to two days of culture, the size achieved is comparable to the in vivo bone growth for both the cartilage and mineralized bone. Longer culture periods lead to bigger differences between the cultured bones and freshly extracted bones.Note, the tibia grown with an incomplete removal of the soft tissue can result in bending of the cultured tibia. Treatment with retinoic acid has a robust effect on the tibial growth as early as after two days of treatment. Although there is a consistent increase in the total length of the tibia after two days in culture, this growth corresponds to an approximate increase of only nine to 29%from initial length.Less than the bone growth increase that would be observed in vivo. Indeed, thymidine analog labeling shows fewer positive cells in this region after culture compared to freshly extracted bones of an equivalent stage. Further, in in vitro cultured tibia, the total length of the skeletal element increases substantially, while almost no increase in the mineralized region is observed.In addition to histological and molecular analysis, clearing and 3D imaging can be performed after the culture to characterize cellular effect of the treatments applied to the cultured bones. The technique allows us to address questions related to interorganal communication. For example, by co-culturing bones from the different genetic models in some sort of pain-free parabiosis experiment.

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Research

JoVE Journal

Developmental Biology

8.0K vistas.  Monash University. Este método adapta el protocolo de cultivo metatarsiano a huesos más grandes, permitiendo combinar la manipulación ósea directa con modelos genéticos complejos para abordar procesos relacionados con el desarrollo óseo. Esta técnica permite la manipulación y el análisis del crecimiento óseo que no son posibles in vivo, como imágenes en vivo o manipulación física y farmacológica directa. Este método de cultivo ex vivo permite el estudio específico de los efectos locales de la in...