Funding was provided by "Progetto a concorso Fondazione IRCCS Ospedale Maggiore Policlinico 2009-2010" to MD, and Associazione Bambino Nefropatico ABN Onlus, Milano

All animal experiments were performed according to the National and European current regulations regarding the protection of animals used for scientific purposes and were reviewed and approved by the ethical committee of Milan University.
1. Isolation of Primary Osteoblasts
The method, with minor modification, follows the procedure described by Dodig et al14.
<ol>
	<li>Prepare digesting medium, by adding 0.1% Collagenase P and 0.05% Trypsin (starting from 2.5% Trypsin 10X, no phenol red) to HBSS medium (Hanks Balanced Salt Solution, no calcium,&#160;magnesium, or&#160;phenol red).</li>
	<li>Use 3-4 day old mice (the procedure can be applied to as few as 1 mouse).</li>
	<li>Sacrifice by decapitation. Spray the head with 70% ethanol and keep on ice. Remove skin and muscle layers by tweezers and dissecting/surgical scissors.</li>
	<li>Gently remove the parietal bones and separate them by following the sagittal suture in two halves. Make sure bones are free of sutures and any adherent tissue and place individual bone pieces in well-plates containing HBSS medium until the procedure is completed.</li>
	<li>Discard HBSS and add to each well the digesting medium for 15 min at 37 &#176;C.</li>
	<li>Discard the supernatant.</li>
	<li>Add again the digesting medium for 15 min at 37 &#176;C.</li>
	<li>This time save the supernatant and place it in alpha-MEM (Minimum Essential Medium) supplemented with 10% FBS (Fetal Bovine Serum) and 1% streptomycin/penicillin.</li>
	<li>Repeat steps 1.7&#160;and 1.8&#160;2x.</li>
	<li>Pool the three collected fractions, spin cells by centrifuging at 425 g for 5 min, discard the supernatant, add 3 ml of supplemented alpha-MEM to resuspend the cell pellet, and transfer to a 25 cm2 flask.</li>
	<li>Change the medium after 24 hr to remove debris and dead cells.</li>
	<li>Add 50 &#181;g/ml ascorbic acid (AA) and 3 mM glycerol 2-phosphate disodium salt hydrate (GP) to the alpha-MEM medium.</li>
	<li>Thereafter, change the medium (alpha-MEM plus AA/GP) every other day.</li>
</ol>
2. ATRA Protocol
<ol>
	<li>Conduct all experiments with ATRA (All-Trans Retinoic Acid) in a darkened room to prevent inactivation.</li>
	<li>Prepare a 1X trypsin solution in HBSS medium and keep at 37 &#176;C until use.</li>
	<li>Remove the medium from subconfluent cells and carefully wash them with HBSS.</li>
	<li>Add 1 ml trypsin, gently rotate the flask to allow all cells to be covered by trypsin, and incubate for 3 min at 37 &#176;C.</li>
	<li>Check for the actual detachment of cells under an inverted microscope.</li>
	<li>Add 3 ml of alpha-MEM medium to inactivate trypsin.</li>
	<li>Recover the cells and centrifuge for 15 min at 425 g.</li>
	<li>Resuspend the cell pellet in fresh medium.</li>
	<li>Place a drop in a hemocytometer counting chamber, allow to settle for a few min&#160;and count the cell number.</li>
	<li>Place cells in 25 cm2 flasks at a density of 10,000 cells/cm2&#160;with alpha-MEM plus AA/GP. Be aware that cell density is relevant to the optimal development of cell processes and intercellular contacts. A starting density higher than 10,000 cells/cm2 impairs proper development of cell processes, but lower cell numbers result in premature cell death, due to the absence of intercellular contacts.</li>
	<li>Add&#160;5 &#181;M ATRA to the medium every 24 hr.</li>
	<li>Monitor the cells daily to assess morphology: morphological changes are generally observed after 48 hr. If, after the first 24-48 hr, cells are still proliferating, replate at the above density. A homogeneous population of mature osteocytes is present after 4-5 days. Depending on the needs, use cells at any time point, up to 12-15 days.</li>
	<li>When cells are plated on other supports (such as coverslips or well-plates), be sure that the above density is maintained and continue to add ATRA every 24 hr until use. Leave cells to adhere to the new support for at least 24 hr before the experiment.</li>
</ol>
3. Immunostaining
<ol>
	<li>For immunostaining, plate the cells on coverslips and follow established methodologies (see for instance Burry15).</li>
	<li>For example, for indirect immunofluorescence, fix in 4% paraformaldehyde or cold acetone, incubate sequentially with the primary antibody at RT for 1 hr in a humidified chamber, then with the secondary fluorescent-labeled antibody in the dark, at RT for 30 min, in a humidified chamber.</li>
	<li>Use DAPI or analogues for nuclear counterstaining, and mount in anti-fading medium.</li>
</ol>
4. Alizarin Red Staining and Extraction
<ol>
	<li>Plate the cells on coverslips.</li>
	<li>Fix the cells by immersing the coverslip in 70% ethanol for 10 min.</li>
	<li>Cover the cells with some drops of alizarin red staining solution (1 mg/ml, pH 5.5) for 30 min.</li>
	<li>Wash the coverslips with tap water. Mount with a drop of glycerol on glass slides and take images using an upright microscope at 10X and 20X magnification.</li>
	<li>After the above procedure, recover the coverslips by immersing the slides in tap water.</li>
	<li>Put each coverslip in a well plate.</li>
	<li>Add 60% perchloric acid (the quantity has to be enough to completely cover the cells) and leave O/N at 4 &#176;C with gentle agitation.</li>
	<li>Read the optical density of the supernatant by spectrophotometry at 450 nm wavelength.</li>
	<li>To normalize values for cell number, add Janus Green (0.2% solution in PBS) to cover the cell preparation for 10 min.</li>
	<li>Wash carefully with ultrapure water.</li>
	<li>Add 0.5 N HCl (the quantity has to be enough to cover all cells) and shake gently by hand for a few sec.</li>
	<li>Read the absorbance at 615 nm by spectrophotometry.</li>
</ol>

<ol>
	<li>Schneider, P., Meier, M., Wepf, R., M&#252;ller, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Towards+quantitative+3D+imaging+of+the+osteocyte+lacuno-canalicular+network.">Towards quantitative 3D imaging of the osteocyte lacuno-canalicular network.</a> Bone. 47 (5), 848-858 (2010).</li><li>Cheng, F., Hulley, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+osteocyte--a+novel+endocrine+regulator+of+body+phosphate+homeostasis.">The osteocyte--a novel endocrine regulator of body phosphate homeostasis.</a> Maturitas. 67 (4), 327-338 (2010).</li><li>Paic, F., 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=Identification+of+differentially+expressed+genes+between+osteoblasts+and+osteocytes.">Identification of differentially expressed genes between osteoblasts and osteocytes.</a> 45 (4), 682-692 (2009).</li><li>Dallas, S. L., Bonewald, L. F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Dynamics+of+the+transition+from+osteoblast+to+osteocyte.">Dynamics of the transition from osteoblast to osteocyte.</a> Ann N Y Acad Sci. 1192, 437-443 (2010).</li><li>van der Plas, A., Nijweide, P. J. <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+purification+of+osteocytes.">Isolation and purification of osteocytes.</a> J Bone Miner Res. 7 (4), 389-396 (1992).</li><li>Nijweide, P. J., van der Plas, A., Alblas, M. J., Klein-Nulend, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Osteocyte+isolation+and+culture.">Osteocyte isolation and culture.</a> Methods Mol Med. 80, 41-50 (2003).</li><li>Stern, A. R., Stern, M. M., Van Dyke, M. E., J&#228;hn, K., Prideaux, M., Bonewald, L. F. <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+culture+of+primary+osteocytes+from+the+long+bones+of+skeletally+mature+and+aged+mice.">Isolation and culture of primary osteocytes from the long bones of skeletally mature and aged mice.</a> Biotechniques. 52 (6), 361-373 .</li><li>Kalajzic, I., Matthews, B. G., Torreggiani, E., Harris, M. A., Divieti Pajevic, P., Harris, S. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=In+vitro+and+in+vivo+approaches+to+study+osteocyte.">In vitro and in vivo approaches to study osteocyte.</a> Bone. 54 (2), 296-206 .</li><li>Bonewald, L. F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Establishment+and+characterization+of+an+osteocyte-like+cell+line,+MLO-Y4.">Establishment and characterization of an osteocyte-like cell line, MLO-Y4.</a> J Bone Miner Metab. 17 (1), 61-65 (1999).</li><li>Mattinzoli, D., 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=A+novel+model+of+in+vitro+osteocytogenesis+induced+by+retinoic+acid+treatment.">A novel model of in vitro osteocytogenesis induced by retinoic acid treatment.</a> Eur Cell Mater. 24, 403-425 (2012).</li><li>Ross, S. A., McCaffery, P. J., Drager, U. C., De Luca, L. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Retinoids+in+embryonal+development.">Retinoids in embryonal development.</a> Physiol Rev. 80 (3), 1021-1054 (2000).</li><li>Clagett-Dame, M., McNeill, E. M., Muley, P. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Role+of+all-trans+retinoic+acid+in+neurite+outgrowth+and+axonal+elongation.">Role of all-trans retinoic acid in neurite outgrowth and axonal elongation.</a> J Neurobiol. 66 (7), 739-756 (2006).</li><li>Vaughan, M. R., 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=ATRA+induces+podocyte+differentiation+and+alters+nephrin+and+podocin+expression+in+vitro+and+in+vivo.">ATRA induces podocyte differentiation and alters nephrin and podocin expression in vitro and in vivo.</a> Kidney Int. 68 (1), 133-144 (2005).</li><li>Dodig, 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=Identification+of+a+TAAT-containing+motif+required+for+high+level+expression+of+the+COL1A1+promoter+in+differentiated+osteoblasts+of+transgenic+mice.">Identification of a TAAT-containing motif required for high level expression of the COL1A1 promoter in differentiated osteoblasts of transgenic mice.</a> J Biol Chem. 271 (27), 16422-16429 (1996).</li><li>Burry, R. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Immunocytochemistry.">Immunocytochemistry.</a> A practical guide for biomedical research. , (2010).</li><li>Woo, S. M., Rosse, r. J., Dusevich, V., Kalajzic, I., Bonewald, L. F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Cell+line+IDG-SW3+replicates+osteoblast-to-late-osteocyte+differentiation+in+vitro+and+accelerates+bone+formation+in+vivo.">Cell line IDG-SW3 replicates osteoblast-to-late-osteocyte differentiation in vitro and accelerates bone formation in vivo.</a> J Bone Miner Res. 26 (11), 2634-2646 (2011).</li><li>Gu, G., Nars, M., Hentune, n. T. A., Metsikk&#246;, K., V&#228;&#228;n&#228;nen, H. K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Isolated+primary+osteocytes+express+functional+gap+junctions+in+vitro.">Isolated primary osteocytes express functional gap junctions in vitro.</a> Cell Tissue Res. 323 (2), 263-271 (2006).</li><li>Boukhechba, F., 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=Human+primary+osteocyte+differentiation+in+a+3D+culture+system.">Human primary osteocyte differentiation in a 3D culture system.</a> J Bone Miner Res. 24 (11), 1927-1935 (2009).</li><li>Krishnan, V., Dhurjati, R., Vogler, E. A., Mastro, A. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Osteogenesis+in+vitro:+from+pre-osteoblasts+to+osteocytes:+a+contribution+from+the+Osteobiology+Research+Group,+The+Pennsylvania+State+University.">Osteogenesis in vitro: from pre-osteoblasts to osteocytes: a contribution from the Osteobiology Research Group, The Pennsylvania State University.</a> In Vitro Cell Dev Biol Anim. 46 (1), 28-35 .</li><li>Irie, K., Ejiri, S., Sakakura, Y., Shibui, T., Yajima, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Matrix+mineralization+as+a+trigger+for+osteocyte+maturation.">Matrix mineralization as a trigger for osteocyte maturation.</a> J Histochem Cytochem. 56 (6), 561-567 .</li><li>Hirao, 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=Oxygen+tension+is+an+important+mediator+of+the+transformation+of+osteoblasts+to+osteocytes.">Oxygen tension is an important mediator of the transformation of osteoblasts to osteocytes.</a> J Bone Miner Metab. 25 (5), 266-276 (2007).</li><li>Brounais, B., 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=Long+term+oncostatin+M+treatment+induces+an+osteocyte-like+differentiation+on+osteosarcoma+and+calvaria.">Long term oncostatin M treatment induces an osteocyte-like differentiation on osteosarcoma and calvaria.</a> Bone. 44 (5), 830-839 (2009).</li><li>Gupta, R. R., Yoo, D. J., Hebert, C., Niger, C., Stains, J. P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Induction+of+an+osteocyte-like+phenotype+by+fibroblast+growth+factor-2.">Induction of an osteocyte-like phenotype by fibroblast growth factor-2.</a> Biochem Biophys Res Commun. 402 (2), 258-264 (2010).</li><li>Poole, K. E., 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=Sclerostin+is+a+delayed+secreted+product+of+osteocytes+that+inhibits+bone+formation.">Sclerostin is a delayed secreted product of osteocytes that inhibits bone formation.</a> FASEB J. 19 (13), 1842-1844 (2005).</li><li>Dallas, S. L., Prideaux, M., Bonewald, L. F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+Osteocyte:+An+Endocrine+Cell+and+More.">The Osteocyte: An Endocrine Cell and More.</a> Endocr Rev. 34 (5), 658-690 (2013).</li></ol>

The authors have nothing to disclose.

In the last years the osteocyte has emerged as the most central cell in the bone. Research advances are progressively revealing a number of previously unsuspected or unproven osteocyte properties, which are of enormous value for designing novel and better treatment for a variety of bone diseases. However, investigation of osteocyte biology has been suffering from the limited availability of in vitro models to such an extent that osteoblasts have been used as surrogate cells over a long period before the osteocyt...

Osteocytes, the most abundant bone cell type, are terminally differentiated, highly ramified cells deeply located within the skeleton. The cell body of mature osteocytes are contained in bone lacunae and have diverse shapes; osteocytes with elongated cell bodies are found in the cortical bone, whereas rounded osteocytes are more frequent in the trabecular bone1. Branched dendrites extend from the cell body and reside in tiny channels called canaliculi, forming an intricate web that makes multiple contacts not only with other osteocytes, but also with other bone cell types, bone marrow, blood vessels and associated pericytes. Through the interstitial fluid contained in lacunae and canaliculi, osteocytes are also ultimately connected to the circulating system, therefore they can influence not only local but also systemic events, and vice versa their behavior can be regulated by both local and systemic changes2.
The study of osteocytes has recently gained momentum, thanks to several technical advances, such as the generation of tissue- and cell-specific transgenic animals, the use of powerful microscopy techniques and of high-throughput molecular screening3,4. However, knowledge of these cells is still incomplete, mainly due to the relative scarcity of adequate in vitro models. Actually, osteocytes have been always difficult to obtain and maintain in culture because of the deep location, and the low level of proliferation that characterizes such a differentiated cell type.
Along the years, a number of methods have been developed to isolate primary osteocytes5-7, though they generally produce low cell yields and carry the risk that even a few contaminating fibroblasts will rapidly overgrow the osteocytes8. For this reason, most experimental in vitro work has been conducted so far on the well-established osteocyte cell line MLO-Y4&#160;9.
Additional in vitro methodologies could enhance the possibility of studying these cells and could improve the analysis of osteocyte biology and pathophysiology. To be largely adopted, such methods should be easy to reproduce, and would not require special instrumentation or very long times to reach cell maturation. Importantly, if applicable to primary cells, they would make it possible to take advantage of transgenic animals.&#160; We recently described that treatment of the osteoblast cell line MC3T3-E1 and of primary osteoblasts with retinoic acid induces a rapid phenotype change leading to the development of a homogeneous population of ramified cells bearing morphological and molecular features of osteocytes10.
All-trans retinoic acid (ATRA) is an active metabolic product of vitamin A which regulates gene transcription by binding the nuclear retinoic acid receptors (RARs). RARs bind to DNA as heterodimers with the retinoid X receptors (RXRs), ultimately leading to modulation of retinoic acid (RA)-responsive target genes11. ATRA has been shown to modulate differentiation and maturation of several cell types, among them other ramified cells such as neuronal cells12 and podocytes13.
The method here described is based on addition of ATRA to primary osteoblasts. To be effective, ATRA has to be added at a precise maturation stage on cells plated at a defined density; in our experience these conditions are critical to obtain the phenotype switch from osteoblasts to osteocytes.

<table border="0" cellpadding="0" cellspacing="0" style="width:923px;" width="923">
	<colgroup>
		<col />
		<col />
		<col />
		<col />
	</colgroup>
	<tbody>
		<tr height="20">
			<td height="20" style="height:20px;width:283px;">Name</td>
			<td style="width:239px;">Company</td>
			<td style="width:219px;">Cat #</td>
			<td style="width:183px;">comments</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Collagenase P</td>
			<td>Roche Applied Science</td>
			<td>11213857001</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Trypsin</td>
			<td>Gibco, Life Technologies</td>
			<td>15400054</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">HBSS</td>
			<td>Gibco, Life Technologies</td>
			<td>14175129</td>
			<td>Pre-warm at 37&#176;C before use</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Alpha-MEM</td>
			<td>Invitrogen, Life Technologies</td>
			<td>22571038</td>
			<td>Pre-warm at 37&#176;C before use</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">FBS</td>
			<td>Sigma-Aldrich</td>
			<td>F4135</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Streptomycin/Penicillin</td>
			<td>Sigma-Aldrich</td>
			<td>P4333</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Ascorbic acid</td>
			<td>Sigma-Aldrich</td>
			<td>A4403</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">glycerol 2-phosphate disodium salt hydrate</td>
			<td>Sigma-Aldrich</td>
			<td>G9422</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">ATRA</td>
			<td>Sigma-Aldrich</td>
			<td>R2625</td>
			<td>Protect ATRA from light</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">paraformaldehyde</td>
			<td>Sigma-Aldrich</td>
			<td>P6148</td>
			<td>Dissolve in PBS and filter before use. Work always under a chemical hood.</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">DAPI</td>
			<td>Sigma-Aldrich</td>
			<td>32670</td>
			<td>Can be added to the secondary antibody</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Alizarin red</td>
			<td>Sigma-Aldrich</td>
			<td>A5533</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Janus Green</td>
			<td>Sigma-Aldrich</td>
			<td>201677</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Perchloric acid</td>
			<td>Sigma-Aldrich</td>
			<td>176745</td>
			<td>Use with caution (skin and eye protection are recommended)</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">HCl</td>
			<td>Sigma-Aldrich</td>
			<td>320331</td>
			<td>Use with caution (skin and eye protection are recommended)</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">glycerol</td>
			<td>Sigma-Aldrich</td>
			<td>G5516</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">fluorsave</td>
			<td>Calbiochem - Merck</td>
			<td>345789</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;"></td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Economy Tweezers #7, 0.40 x 0.5mm tips</td>
			<td>World Precision Instruments</td>
			<td>501981</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Economy Tweezers #4, 0.40 x 0.45mm tips</td>
			<td>World Precision Instruments</td>
			<td>501978</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Dissecting Scissors, straight,10cm curved</td>
			<td>World Precision Instruments</td>
			<td>14394</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Surgical Scissors, 14 cm, straight, S/S</td>
			<td>World Precision Instruments</td>
			<td>501218</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;"></td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Culture flasks</td>
			<td>Corning</td>
			<td>430168</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Well-plates</td>
			<td>Corning</td>
			<td>3335</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Thermanox coverslips</td>
			<td>Thermo Scientific Nunc</td>
			<td>12-565-27</td>
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			<td>Zeiss Apotome</td>
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			<td height="20" style="height:20px;">spectrometer</td>
			<td>Safas Xenius</td>
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application of retinoic acid to obtain osteocytes cultures from primary mouse osteoblasts

The need for osteocyte cultures is well known to the community of bone researchers; isolation of primary osteocytes is difficult and produces low cell numbers. Therefore, the most widely used cellular system is the osteocyte-like MLO-Y4 cell line.
The method here described refers to the use of retinoic acid to generate a homogeneous population of ramified cells with morphological and molecular osteocyte features.
After isolation of osteoblasts from mouse calvaria, all-trans retinoic acid (ATRA) is added to cell medium, and cell monitoring is conducted daily under an inverted microscope. First morphological changes are detectable after 2 days of treatment and differentiation is generally complete in 5 days, with progressive development of dendrites, loss of the ability to produce extracellular matrix, down-regulation of osteoblast markers and up-regulation of osteocyte-specific molecules.
Daily cell monitoring is needed because of the inherent variability of primary cells, and the protocol can be adapted with minimal variation to cells obtained from different mouse strains and applied to transgenic models. 
The method is easy to perform and does not require special instrumentation, it is highly reproducible, and rapidly generates a mature osteocyte population in complete absence of extracellular matrix, allowing the use of these cells for unlimited biological applications.

Results were obtained from 5 to 10 independent experiments.
Cell Morphology
AA/GP treated primary cells have mostly cobblestone-like features, characteristic of mature osteoblasts. Interspersed ramified cells (as indicated by red arrows in Figure 1A) can be found, which likely represent some osteocytes.
With ATRA treatment, cells rapidly start displaying ramifications, which are generally observed after 2 days. As shown in <str...

Watch this Scientific Journal Video about Application of Retinoic Acid to Obtain Osteocytes Cultures from Primary Mouse Osteoblasts at JoVE.com

Application of Retinoic Acid to Obtain Osteocytes Cultures from Primary Mouse Osteoblasts

Treatment of primary mouse osteoblasts with retinoic acid produces a homogeneous population of ramified cells bearing morphological and molecular features of osteocytes. The method overcomes the difficulty of obtaining and maintaining primary osteocytes in culture, and can be advantageous to study cells derived from transgenic models.&#160;

The need for osteocyte cultures is well known to the community of bone researchers; isolation of primary osteocytes is difficult and produces low cell ...

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Biology

13.3K Views.  Fondazione IRCCS Ca' Granda Ospedale Maggiore Policlinico. Treatment of primary mouse osteoblasts with retinoic acid produces a homogeneous population of ramified cells bearing morphological and molecular features of osteocytes. The method overcomes the difficulty of obtaining and maintaining primary osteocytes in culture, and can be advantageous to study cells derived from transgenic models. 

Video: Application of Retinoic Acid to Obtain Osteocytes Cultures from Primary Mouse Osteoblasts

Primary Neuronal Cultures from the Brains of Late Stage Drosophila Pupae

In this video, we demonstrate the preparation of primary neuronal cultures from the brains of late stage Drosophila pupae. The procedure begins with the removal of brains from animals at 70-78 hrs after puparium formation. The isolated brains are shown after brief incubation in papain followed by several washes in serum-free growth medium. The process of mechanical dissociation of each brain in a 5 ul drop of media on a coverslip is illustrated. The axons and dendrites of the post-mitotic neurons are sheered off near the soma during dissociation but the neurons begin to regenerate processes within a few hours of plating. Images show live cultures at 2 days. Neurons continue to elaborate processes during the first week in culture. Specific neuronal populations can be identified in culture using GAL4 lines to drive tissue specific expression of fluorescent markers such as  GFP or RFP. Whole cell recordings have demonstrated the cultured neurons form functional, spontaneously active cholinergic and GABAergic synapses. A short video segment illustrates calcium dynamics in the cultured neurons using Fura-2 as a calcium indicator dye to monitor spontaneous calcium transients and nicotine evoked calcium responses in a dish of cultured neurons. These pupal brain cultures are a useful model system in which genetic and pharmacological tools can be used to identify intrinsic and extrinsic factors that influence formation and function of central synapses.

This video demonstrates the preparation of primary neuronal cultures from the brains of late stage Drosophila pupae. Views of live cultures show neurite outgrowth and imaging of calcium levels using Fura-2.

In this video, we demonstrate the preparation of primary neuronal cultures from the brains of late stage Drosophila pupae. The procedure begins with the ...

Primary Dissociated Midbrain Dopamine Cell Cultures from Rodent Neonates

The ability to create primary cell cultures of dopamine neurons allows for the study of the presynaptic characteristics of dopamine neurons in isolation from systemic input from elsewhere in the brain. In our lab, we use these neurons to assess dopamine release kinetics using carbon fiber amperometry, as well as expression levels of dopamine related genes and proteins using quantitative PCR and immunocytochemistry. In this video, we show you how we generate these cultures from rodent neonates.
The process involves several steps, including the plating of cortical glial astrocytes, the conditioning of neuronal cell culture media by the glial substrate, the dissection of the midbrain in neonates, the digestion, extraction and plating of dopamine neurons and the addition of neurotrophic factors to ensure cell survival.
The applications suitable for such a preparation include electrophysiology, immunocytochemistry, quantitative PCR, video microscopy (i.e., of real-time vesicular fusion with the plasma membrane), cell viability assays and other toxicological screens.

Primary dissociated midbrain dopamine cell cultures allow for the study of presynaptic characteristics of dopamine neurons. They can be used to monitor real-time dopamine release kinetics and protein/mRNA levels of regulators of dopamine exocytosis. Here, we show you how to generate these cultures from rodent neonates.

The ability to create primary cell cultures of dopamine neurons allows for the study of the presynaptic characteristics of dopamine neurons in isolation ...

The Preparation of Primary Hematopoietic Cell Cultures From Murine Bone Marrow for Electroporation

It is becoming increasingly apparent that electroporation is the most effective way to introduce plasmid DNA or siRNA into primary cells. The Gene Pulser MXcell  electroporation system and Gene Pulser  electroporation buffer were specifically developed to transfect nucleic acids into mammalian cells and difficult-to-transfect cells, such as primary and stem cells.This video demonstrates how to establish primary hematopoietic cell cultures from murine bone marrow, and then prepare them for electroporation in the MXcell system. We begin by isolating femur and tibia. Bone marrow from both femur and tibia are then harvested and cultures are established. Cultured bone marrow cells are then transfected and analyzed.

This procedure describes how to establish primary hematopoietic cell cultures from murine bone marrow and is followed by transfection using the Gene Pulser MXCell electroporation system.

It is becoming increasingly apparent that electroporation is the most effective way to introduce plasmid DNA or siRNA into primary cells. The Gene Pulser ...

Establishing Primary Adult Fibroblast Cultures From Rodents

The importance of using primary cells, rather than cancer cell lines, for biological studies is becoming widely recognized. Primary cells are preferred in studies of cell cycle control, apoptosis, and DNA repair, as cancer cells carry mutations in genes involved in these processes. Primary cells cannot be cultured indefinitely due to the onset of replicative senescence or aneuploidization. Hence, new cultures need to be established regularly. The procedure for isolation of rodent embryonic fibroblasts is well established, but isolating adult fibroblast cultures often presents a challenge. Adult rodent fibroblasts isolated from mouse models of human disease may be a preferred control when comparing them to fibroblasts from human patients. Furthermore, adult fibroblasts are the only available material when working with wild rodents where pregnant females cannot be easily obtained. Here we provide a protocol for isolation and culture of adult fibroblasts from rodent skin and lungs. We used this procedure successfully to isolate fibroblasts from over twenty rodent species from laboratory mice and rats to wild rodents such as beaver, porcupine, and squirrel.

This article describes a protocol for isolation and maintenance of primary fibroblast cultures from skin and lung tissue of wild rodents.

The importance of using primary cells, rather than cancer cell lines, for biological studies is becoming widely recognized.  Primary cells are preferred ...

Primary Cell Cultures from Drosophila Gastrula Embryos

Here we describe a method for preparing and culturing primary cells dissociated from Drosophila gastrula embryos. In brief, a large amount of staged embryos from young and healthy flies are collected, sterilized, and then physically dissociated into a single cell suspension using a glass homogenizer. After being plated on culture plates or chamber slides at an appropriate density in culture medium, these cells can further differentiate into several morphologically-distinct cell types, which can be identified by their specific cell markers. Furthermore, we present conditions for treating these cells with double stranded (ds) RNAs to elicit gene knockdown. Efficient RNAi in Drosophila primary cells is accomplished by simply bathing the cells in dsRNA-containing culture medium. The ability to carry out effective RNAi perturbation, together with other molecular, biochemical, cell imaging analyses, will allow a variety of questions to be answered in Drosophila primary cells, especially those related to differentiated muscle and neuronal cells.

Primary Cell Cultures from Drosophila Gastrula Embryos

We provide a detailed protocol for preparing primary cells dissociated from Drosophila embryos. The ability to carry out the effective RNAi perturbation, together with other molecular, biochemical and cell imaging methods will allow a variety of questions to be addressed in Drosophila primary cells.

Here we describe a method for preparing and culturing primary cells dissociated from Drosophila gastrula embryos.   In brief, a large amount of staged ...

Isolating Primary Melanocyte-like Cells from the Mouse Heart

We identified a novel population of melanocyte-like cells (also known as cardiac melanocytes) in the hearts of mice and humans that contribute to atrial arrhythmia triggers in mice. To investigate the electrical and biological properties of cardiac melanocytes we developed a procedure to isolate them from mouse hearts that we derived from those designed to isolate neonatal murine cardiomyocytes. In order to obtain healthier cardiac melanocytes suitable for more extensive patch clamp or biochemical studies, we developed a refined procedure for isolating and plating cardiac melanocytes based on those originally designed to isolate cutaneous melanocytes. The refined procedure is demonstrated in this review and produces larger numbers of healthy melanocyte-like cells that can be plated as a pure population or with cardiomyocytes.

In this protocol, we identified a novel population of melanocyte-like cells (also known as cardiac melanocytes) in the hearts of mice and humans that contribute to atrial arrhythmia triggers in mice.&#160;

We identified a novel population of melanocyte-like cells (also known as cardiac melanocytes) in the hearts of mice and humans that contribute to atrial ...

Na&iuml;ve Adult Stem Cells Isolation from Primary Human Fibroblast Cultures

Over the last decade, several adult stem cell populations have been identified in human skin 1-4. The isolation of multipotent adult dermal precursors was first reported by Miller F. D laboratory 5, 6. These early studies described a multipotent precursor cell population from adult mammalian dermis 5. These cells--termed SKPs, for skin-derived precursors-- were isolated and expanded from rodent and human skin and differentiated into both neural and mesodermal progeny, including cell types never found in skin, such as neurons 5. Immunocytochemical studies on cultured SKPs revealed that cells expressed vimentin and nestin, an intermediate filament protein expressed in neural and skeletal muscle precursors, in addition to fibronectin and multipotent stem cell markers 6. Until now, the adult stem cells population SKPs have been isolated from freshly collected mammalian skin biopsies.
Recently, we have established and reported that a population of skin derived precursor cells could remain present in primary fibroblast cultures established from skin biopsies 7. The assumption that a few somatic stem cells might reside in primary fibroblast cultures at early population doublings was based upon the following observations: (1) SKPs and primary fibroblast cultures are derived from the dermis, and therefore a small number of SKP cells could remain present in primary dermal fibroblast cultures and (2) primary fibroblast cultures grown from frozen aliquots that have been subjected to unfavorable temperature during storage or transfer contained a small number of cells that remained viable 7. These rare cells were able to expand and could be passaged several times. This observation suggested that a small number of cells with high proliferation potency and resistance to stress were present in human fibroblast cultures 7.
We took advantage of these findings to establish a protocol for rapid isolation of adult stem cells from primary fibroblast cultures that are readily available from tissue banks around the world (Figure 1). This method has important significance as it allows the isolation of precursor cells when skin samples are not accessible while fibroblast cultures may be available from tissue banks, thus, opening new opportunities to dissect the molecular mechanisms underlying rare genetic diseases as well as modeling diseases in a dish.

Na&amp;#239;ve Adult Stem Cells Isolation from Primary Human Fibroblast Cultures

We report a method to isolate na&#239;ve multipotent skin-derived precursor (SKP) cells from primary human fibroblast cultures. We show that these SKPs derived from fibroblast cultures share similar stem cell properties to the ones derived directly from human skin biopsies. These cells express the neural crest marker, nestin, in addition to the multipotent markers such as OCT4 and Nanog.

Over the last decade, several adult stem cell  populations have been identified in human skin 1-4.  The isolation of multipotent adult dermal precursors ...

Isolation of Primary Myofibroblasts from Mouse and Human Colon Tissue

The myofibroblast is a stromal cell of the gastrointestinal (GI) tract that has been gaining considerable attention for its critical role in many GI functions. While several myofibroblast cell lines are commercially available to study these cells in vitro, research results from a cell line exposed to experimental cell culture conditions have inherent limitations due to the overly reductionist nature of the work. Use of primary myofibroblasts offers a great advantage in terms of confirming experimental findings identified in a cell line. Isolation of primary myofibroblasts from an animal model allows for the study of myofibroblasts under conditions that more closely mimic the disease state being studied. Isolation of primary myofibroblasts from human colon tissue provides arguably the most relevant experimental data, since the cells come directly from patients with the underlying disease. We describe a well-established technique that can be utilized to isolate primary myofibroblasts from both mouse and human colon tissue. These isolated cells have been characterized to be alpha-smooth muscle actin and vimentin-positive, and desmin-negative, consistent with subepithelial intestinal myofibroblasts. Primary myofibroblast cells can be grown in cell culture and used for experimental purposes over a limited number of passages.

The myofibroblast is an influential stromal cell of the gastrointestinal tract that regulates important physiologic processes in both normal and disease states. We describe a technique that allows for the isolation of primary myofibroblasts from both mouse and human colon tissue, which can be utilized for in vitro experimentation.

The myofibroblast is  a stromal cell of the gastrointestinal (GI) tract that has been gaining  considerable attention for its critical role in many GI ...

Preparation of Primary Myogenic Precursor Cell/Myoblast Cultures from Basal Vertebrate Lineages

Due to the inherent difficulty and time involved with studying the myogenic program in vivo, primary culture systems derived from the resident adult stem cells of skeletal muscle, the myogenic precursor cells (MPCs), have proven indispensible to our understanding of mammalian skeletal muscle development and growth. Particularly among the basal taxa of Vertebrata, however, data are limited describing the molecular mechanisms controlling the self-renewal, proliferation, and differentiation of MPCs. Of particular interest are potential mechanisms that underlie the ability of basal vertebrates to undergo considerable postlarval skeletal myofiber hyperplasia (i.e.&#160;teleost fish) and full regeneration following appendage loss (i.e.&#160;urodele amphibians). Additionally, the use of cultured myoblasts could aid in the understanding of regeneration and the recapitulation of the myogenic program and the differences between them. To this end, we describe in detail a robust and efficient protocol (and variations therein) for isolating and maintaining MPCs and their progeny, myoblasts and immature myotubes, in cell culture as a platform for understanding the evolution of the myogenic program, beginning with the more basal vertebrates. Capitalizing on the model organism status of the zebrafish (Danio rerio), we report on the application of this protocol to small fishes of the cyprinid clade Danioninae. In tandem, this protocol can be utilized to realize a broader comparative approach by isolating MPCs from the Mexican axolotl (Ambystomamexicanum) and even laboratory rodents. This protocol is now widely used in studying myogenesis in several fish species, including rainbow trout, salmon, and sea bream1-4.

In vitro culture systems have proven indispensible to our understanding of vertebrate myogenesis. However, much remains to be learned about nonmammalian skeletal muscle development and growth, particularly in basal taxa. An efficient and robust protocol for isolating the adult stem cells of this tissue, the myogenic precursor cells (MPCs), and maintaining their self-renewal, proliferation, and differentiation in a primary culture setting allows for the identification of conserved and divergent regulatory mechanisms throughout the vertebrate lineages.

Due to the inherent difficulty and time involved with studying the myogenic program in vivo, primary culture systems derived from the resident adult stem ...

Determination of Fatty Acid Oxidation and Lipogenesis in Mouse Primary Hepatocytes

Lipid metabolism in liver is complex. In addition to importing and exporting lipid via lipoproteins, hepatocytes can oxidize lipid via fatty acid oxidation, or alternatively, synthesize new lipid via de novo lipogenesis. The net sum of these pathways is dictated by a number of factors, which in certain disease states leads to fatty liver disease. Excess hepatic lipid accumulation is associated with whole body insulin resistance and coronary heart disease. Tools to study lipid metabolism in hepatocytes are useful to understand the role of hepatic lipid metabolism in certain metabolic disorders.
In the liver, hepatocytes regulate the breakdown and synthesis of fatty acids via &#946;-fatty oxidation and de novo lipogenesis, respectively. Quantifying metabolism in these pathways provides insight into hepatic lipid handling. Unlike in vitro quantification, using primary hepatocytes, making measurements in vivo is technically challenging and resource intensive. Hence, quantifying &#946;-fatty acid oxidation and de novo lipogenesis in cultured mouse hepatocytes provides a straight forward method to assess hepatocyte lipid handling. 
Here we describe a method for the isolation of primary mouse hepatocytes, and we demonstrate quantification of &#946;-fatty acid oxidation and de novo lipogenesis, using radiolabeled substrates.

De novo lipogenesis and &#946;-fatty acid oxidation constitute key metabolic pathways in hepatocyte, pathways that are perturbed in several metabolic disorders, including fatty liver disease. Here we demonstrate isolation of mouse primary hepatocytes and describe quantification of &#946;-fatty acid oxidation and lipogenesis.