This work was supported by The National Key Research and Development Program of China (2017YFA0104604), The General Program of National Natural Science Foundation of China (81772093), Military Logistics Research Project (AWS17J005), the Key Program of Shandong Province Natural Science Foundation (ZR2019ZD36) and The Key Research and Development Program of Shandong Province (2019GSF108107) to X.W. Guangdong Basic and Applied Basic Research Foundation (2019A1515110833) and The Fundamental Research Funds of Shandong University (2019GN043) to J.M.

The use of adult foreskin tissues in this protocol has been approved by the Human Research Ethics Committee (No.2015120401, date: May 12, 2015).
NOTE: Perform all the following procedures in a sterile environment to prevent contaminations of cells and cultures.
1. Preparations
<ol>
	<li>Gather fresh adult foreskin tissues from circumcision surgeries in 15 mL tubes containing 10 mL of phosphate buffer saline (PBS) and store in 4 &#176;C. 
	NOTE: Separate the tissues as detailed below within 24 h after their excision.</li>
	<li>Prepare reagents and culture medium.
	<ol>
		<li>Prepare 3% P/S (penicillin/streptomycin) as the washing solution. Mix 50 mL of PBS with 1.5 mL of penicillin (100 U/mL) and streptomycin (100 mg/L) (P/S).</li>
		<li>Prepare the termination solution (neutralization solution) for neutralization of enzymatic digestion. Supplement 1% P/S, 10% fetal bovine serum (FBS) into DMEM medium.</li>
		<li>Prepare TIVA medium to culture melanocytes: Ham&#8217;s F12; 10% FBS; 1x P&#8260;S&#8260;glutamine; 50 ng/mL 12-O-tetradecanoyl phorbol-13-acetate (TPA); 1 x 10-4 M 3-isobutyl-1-methyl xanthine (IBMX); 1 &#956;M Na3VO4; 1 x 10-3 M N-6,2&#8242;-O-dibutyryladenosine-3&#8242;,5&#8242;-cyclic monophosphate (dbcAMP).</li>
	</ol>
	</li>
</ol>
2. The conventional method
<ol>
	<li>Skin tissue pretreatment
	<ol>
		<li>Rinse each adult foreskin tissue once with 10 mL of 75% ethanol (alcohol) for 30 s, and then rinse twice with 10 mL of washing solution (3% P/S), for 5 min each. 
		NOTE: Wash foreskin tissues with 10 mL of PBS in the beginning if there is a lot of blood. All washes are prepared in 100 mm cell culture dishes.</li>
		<li>Scrape each foreskin tissue with a surgical blade to remove subcutaneous adipose tissues and loose connective tissues in the cover of a 100 mm cell culture dish. 
		NOTE: Use a scalpel to scrape the fat layers away until only the thin epidermis and the dense dermis remain.</li>
		<li>Transfer each adult foreskin into another 100 mm culture dish with the dermis side down. 
		NOTE: Cut each adult foreskin tissue into 3-4 mm wide strips using a scalpel blade to make the dispase work more efficiently.</li>
		<li>Add 2.5 mg/mL dispase to each 100 mm culture dish with adult foreskin tissues and incubate for 16 to 20 h at 4 &#176;C. 
		NOTE: Each gram of tissue is digested with 10 mL of dispase solution.</li>
	</ol>
	</li>
	<li>Separation of the epidermis from the adult foreskin tissue
	<ol>
		<li>After digestion for 16 to 20 h, separate the epidermis from the dermis using tweezers. Grab one side of the dermal edge of the tissue with one tweezer and the corresponding position of the epidermal part with another tweezer and gently peel off the epidermis.</li>
		<li>Wash the epidermis 3x with washing solution (3% P/S), and then transfer the epidermis into a tube.</li>
		<li>Submerge the epidermis by adding 5 mL of 0.05% trypsin into the tube and incubate in a water bath for 30 min at 37 &#176;C. 
		NOTE: Shake the tube to ensure the epidermis is completely submerged before incubation.</li>
	</ol>
	</li>
	<li>Collection and culture of primary cells
	<ol>
		<li>Add an equal volume of termination solution (10% FBS, 1% P/S in DMEM) to neutralize the trypsin and pipette the solution up and down 10-15 times to separate the epidermal cells.</li>
		<li>Pass the cell suspension into a new 50 mL tube through a 100 &#181;m mesh filter to remove debris.</li>
		<li>Centrifuge at 200 x g for 5 min.</li>
		<li>Remove the supernatant and add 10 mL of inoculation TIVA medium to resuspend the cells.</li>
		<li>Seed the resuspended cells into a 100 mm culture dish.</li>
		<li>Culture in a 37&#176; C incubator with 5% CO2.</li>
		<li>Change the medium every 2 days.</li>
		<li>Passage cells when they reach 80% confluence.</li>
	</ol>
	</li>
</ol>
3. The new method
NOTE: The procedure for tissue preparation and digestion in the new method is the same as described above for the conventional method, the only difference being that the isolated fresh cells are resuspended in 10 mL of TIVA medium containing 10 &#181;M Y-27632.
<ol>
	<li>Two days after seeding, replace the media with normal TIVA medium without Y-27632. After that, the culture conditions are the same between the new and the conventional methods.</li>
</ol>
4. Cell passaging
<ol>
	<li>Remove the TIVA medium and rinse each culture dish twice with PBS.</li>
	<li>Add 2 mL of 0.05% trypsin per 100 mm cell culture dish. 
	NOTE: Shake the dish to ensure adequate contact between digestive enzymes and the bottom of the dish.</li>
	<li>Digest in a 37 &#176;C incubator for 2 min.</li>
	<li>Use a microscope to check the cells, and make sure that most cells have dissociated from the cell culture dish. 
	NOTE: Gently tap the dish to release the cells to round up and float in the solution. Prolong the digestion time if most cells did not suspend after tapping, but no more than 5 more min.</li>
	<li>Transfer the melanocytes into a 15 mL tube after neutralizing the trypsin activity by adding 2 mL of termination solution. Centrifuge at 200 x g for 5 min.</li>
	<li>Resuspend each cell pellet with 10 mL of TIVA medium after slowly removing the supernatant, and then count the number of melanocytes.</li>
	<li>Plate about 1 x 106 melanocytes in 10 mL of TIVA medium per 100 mm cell culture dish.</li>
	<li>Renew the cell culture medium every 48 h.</li>
</ol>

<ol>
	<li>Costin, G. E., Hearing, V. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Human+skin+pigmentation:+melanocytes+modulate+skin+color+in+response+to+stress.">Human skin pigmentation: melanocytes modulate skin color in response to stress.</a> FASEB Journal. 21 (4), 976-994 (2007).</li><li>Battyani, Z., Xerri, L., Hassoun, J., Bonerandi, J. J., Grob, J. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Tyrosinase+gene+expression+in+human+tissues.">Tyrosinase gene expression in human tissues.</a> Pigment Cell Research. 6 (6), 400-405 (1993).</li><li>Michaloglou, 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=BRAFE600-associated+senescence-like+cell+cycle+arrest+of+human+naevi.">BRAFE600-associated senescence-like cell cycle arrest of human naevi.</a> Nature. 436 (7051), 720-724 (2005).</li><li>Hu, F., Staricco, R. J., Pinkus, H., Fosnaugh, R. P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Human+melanocytes+in+tissue+culture.">Human melanocytes in tissue culture.</a> Journal of Investigative Dermatology. 28 (1), 15-32 (1957).</li><li>Eisinger, M., Marko, O. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Selective+proliferation+of+normal+human+melanocytes+in+vitro+in+the+presence+of+phorbol+ester+and+cholera+toxin.">Selective proliferation of normal human melanocytes in vitro in the presence of phorbol ester and cholera toxin.</a> Proceedings of the National Academy of Sciences of the United States of America. 79 (6), 2018-2022 (1982).</li><li>Hirobe, T. <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+keratinocyte-derived+factors+involved+in+regulating+the+proliferation+and+differentiation+of+mammalian+epidermal+melanocytes.">Role of keratinocyte-derived factors involved in regulating the proliferation and differentiation of mammalian epidermal melanocytes.</a> Pigment Cell Research. 18 (1), 2-12 (2005).</li><li>Halaban, 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=Basic+fibroblast+growth+factor+from+human+keratinocytes+is+a+natural+mitogen+for+melanocytes.">Basic fibroblast growth factor from human keratinocytes is a natural mitogen for melanocytes.</a> Journal of Cell Biology. 107 (4), 1611-1619 (1988).</li><li>Kunisada, T., 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=Keratinocyte+expression+of+transgenic+hepatocyte+growth+factor+affects+melanocyte+development,+leading+to+dermal+melanocytosis.">Keratinocyte expression of transgenic hepatocyte growth factor affects melanocyte development, leading to dermal melanocytosis.</a> Mechanisms of Development. 94 (1-2), 67-78 (2000).</li><li>Hirobe, T., Shinpo, T., Higuchi, K., Sano, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Life+cycle+of+human+melanocytes+is+regulated+by+endothelin-1+and+stem+cell+factor+in+synergy+with+cyclic+AMP+and+basic+fibroblast+growth+factor.">Life cycle of human melanocytes is regulated by endothelin-1 and stem cell factor in synergy with cyclic AMP and basic fibroblast growth factor.</a> Journal of Dermatological Science. 57 (2), 123-131 (2010).</li><li>Wen, J., Zu, T., Zhou, Q., Leng, X., Wu, X. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Y-27632+simplifies+the+isolation+procedure+of+human+primary+epidermal+cells+by+selectively+blocking+focal+adhesion+of+dermal+cells.">Y-27632 simplifies the isolation procedure of human primary epidermal cells by selectively blocking focal adhesion of dermal cells.</a> Journal of Tissue Engineering and Regenerative Medicine. 12 (2), 1251-1255 (2018).</li><li>Liu, Z., 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+simplified+and+efficient+method+to+isolate+primary+human+keratinocytes+from+adult+skin+tissue.">A simplified and efficient method to isolate primary human keratinocytes from adult skin tissue.</a> Journal of Visualized Experiments. (138), e7862 (2018).</li><li>Terunuma, A., Limgala, R. P., Park, C. J., Choudhary, I., Vogel, J. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Efficient+procurement+of+epithelial+stem+cells+from+human+tissue+specimens+using+a+Rho-associated+protein+kinase+inhibitor+Y-27632.">Efficient procurement of epithelial stem cells from human tissue specimens using a Rho-associated protein kinase inhibitor Y-27632.</a> Tissue Engineering Part A. 16 (4), 1363-1368 (2010).</li><li>Cerqueira, M. T., Frias, A. M., Reis, R. L., Marques, A. P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Interfollicular+epidermal+stem+cells:+boosting+and+rescuing+from+adult+skin.">Interfollicular epidermal stem cells: boosting and rescuing from adult skin.</a> Methods in Molecular Biology. 989, 1-9 (2013).</li><li>Zhou, Q., 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=ROCK+inhibitor+Y-27632+increases+the+cloning+efficiency+of+limbal+stem/progenitor+cells+by+improving+their+adherence+and+ROS-scavenging+capacity.">ROCK inhibitor Y-27632 increases the cloning efficiency of limbal stem/progenitor cells by improving their adherence and ROS-scavenging capacity.</a> Tissue Engineering Part C, Methods. 19 (7), 531-537 (2013).</li><li>Yokoyama, 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=Pharmacologic+suppression+of+MITF+expression+via+HDAC+inhibitors+in+the+melanocyte+lineage.">Pharmacologic suppression of MITF expression via HDAC inhibitors in the melanocyte lineage.</a> Pigment Cell &amp; Melanoma Rresearch. 21 (4), 457-463 (2008).</li><li>Mi, 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=A+ROCK+inhibitor+promotes+keratinocyte+survival+and+paracrine+secretion,+enhancing+establishment+of+primary+human+melanocytes+and+melanocyte-keratinocyte+co-cultures.">A ROCK inhibitor promotes keratinocyte survival and paracrine secretion, enhancing establishment of primary human melanocytes and melanocyte-keratinocyte co-cultures.</a> Pigment Cell &amp; Melanoma Research. 33 (1), 16-19 (2020).</li></ol>

All authors declare no interest of conflict.

The protocol described here was based on a recent publication16. Some attention should be paid to the following critical steps to achieve the best results with the new method. First, successful separation of the epidermis and the dermis is crucial. Cut the adult foreskin tissues into 3-4 mm wide strips using a scalpel blade to make the dispase work more thoroughly and easily to separate the epidermis from the dermis. Second, when separating those two layers, contamination of the dermis should be a...

The goal of this study was to develop a simple and effective protocol to isolate melanocytes from the epidermis of adult skin for biological research and clinical applications. Melanocytes, which are located in the basal epidermis of the skin and in hair follicles, play an important role in pigmentation of the skin and hair by producing melanin1. The resulting skin pigmentation from epidermal melanocytes acts as an ultraviolet radiation &#64257;lter that reduces/prevents DNA damage to underlying cells in the skin2. The abnormal proliferation of melanocytes in the skin is quite common, such as in the formation of benign nevi (moles) in which melanocytes potentially transform to oncogenic growth followed by cellular senescence3.
Since 1957, the isolation and subsequent culture of human primary melanocytes has been possible4, but only since 1982 has there been an efficient method that can reproducibly establish cultures of human melanocytes from the epidermis5. The conventional method to isolate primary melanocytes from the epidermis involves a two-step enzymatic digestion. Briefly, the skin is initially digested with dispase to separate the epidermis from the dermis, after which the epidermis is digested with trypsin to produce suspensions containing melanocytes and keratinocytes, which can then be selectively grown in different media. Currently, the initial culture usually takes about 3 to 4 weeks for melanocytes to reach confluency using the conventional method, which is likely due to the low efficiency of their isolation. Therefore, increasing the initial production of melanocytes from adult skin tissues would be quite helpful for both laboratory research and clinical applications.
Many growth factors, most of which have been shown to be secreted by keratinocytes (e.g., &#945;-MSH, ACTH, bFGF, NGF, ET-1, GM-CSF, HGF, LIF and SCF)5-8, regulate the differentiation and proliferation of mammalian melanocytes. In the absence of feeder layers, the lack of those growth factors leads to the decreased proliferation of melanocytes and their increased apoptosis9. The co-culture of keratinocytes as feeder cells and melanocytes could lead to accelerated melanocyte proliferation and reduced apoptosis. However, the co-culture method not only demands more skin tissues to prepare keratinocytes, which is not practical, but also could not work efficiently because the culture conditions required by melanocytes does not favor keratinocyte growth, and vice-versa.
Previous studies have reported that the addition of Y-27632, a ROCK inhibitor, into the growth medium can enhance the yield of human primary epidermal cells from skin tissues10-14. Therefore, it would be interesting to test whether the isolation of human primary melanocytes would benefit from the presence of Y-27632. Indeed, the addition of Y-27632 into the inoculation TIVA medium15, which contains TPA, IBMX, Na3VO4 and dbcAMP, significantly increased the yield of primary melanocytes isolated from foreskin tissues in the initial cultures16. Compared to the conventional protocol, this new protocol is significantly more efficient in increasing the yield of melanocytes16. Therefore, this protocol describes the new method in detail using adult skin tissues based on a previous study16 in order to promote its application in basic and applied biological research.

<table><tbody><tr><td>Alexa fluor-594 donkey anti-mouse IgG</td><td>Thermo Fisher Scientific</td><td>A21203</td><td>For Immunofluorescence</td></tr><tr><td>Alexa fluor-594 donkey anti-rabbit IgG</td><td>Thermo Fisher Scientific</td><td>R37119</td><td>For Immunofluorescence</td></tr><tr><td>Cell Culture Dish</td><td>Eppendorf</td><td>30702115</td><td>For cell culture</td></tr><tr><td>Cell Strainer</td><td>Corning incorporated</td><td>431792</td><td>Cell filtration</td></tr><tr><td>15 mL Centrifuge Tube</td><td>KIRGEN</td><td>171003</td><td>For cell centrifuge</td></tr><tr><td>50 mL Centrifuge Tube</td><td>KIRGEN</td><td>171003</td><td>For cell centrifuge</td></tr><tr><td>CO2 Incubator</td><td>Thermo Scientific</td><td>51026333</td><td>For cell incubating</td></tr><tr><td>Constant Temperature Shaker</td><td>Shanghai Boxun</td><td>150036</td><td>For water bath</td></tr><tr><td>DAPI</td><td>Abcam</td><td>ab104139</td><td>For Immunofluorescence</td></tr><tr><td>Dispase</td><td>Gibco</td><td>17105-041</td><td>For melanocyte isolation</td></tr><tr><td>DMEM</td><td>Thermo Scientific</td><td>C11995500</td><td>Component of neutralization medium</td></tr><tr><td>Fetal Bovine Serum</td><td>Biological Industries</td><td>04-001-1AC5</td><td>Component of neutralization medium</td></tr><tr><td>Fluorescence microscope</td><td>Olympus</td><td>5E44316</td><td>For Immunofluorescence</td></tr><tr><td>Forskolin</td><td>MCE</td><td>HY-15371</td><td>Induce pigmentation</td></tr><tr><td>Glutamine</td><td>Thermo Fisher Scientific</td><td>25030081</td><td>melanocyte culture medium</td></tr><tr><td>Ham&#039;s F12</td><td>Thermo Scientific</td><td>11330032</td><td>melanocyte culture medium</td></tr><tr><td>Inverted microscope</td><td>Olympus</td><td>5C42258</td><td>For cell microscopic observation</td></tr><tr><td>3-isobutyl-1-methyl xanthine (IBMX)</td><td>Sigma</td><td>17018</td><td>melanocyte culture medium</td></tr><tr><td>mouse anti-human MITF</td><td>Abcam</td><td>ab12039</td><td>For Immunofluorescence</td></tr><tr><td>Na&lt;sub&gt;3&lt;/sub&gt;VO&lt;sub&gt;4&lt;/sub&gt;</td><td>Sigma</td><td>S6508</td><td>melanocytes culture medium</td></tr><tr><td>N6,2&#039;-O-dibutyryladeno-sine 3&#039;,5&#039;-cyclic monophosphate (dbcAMP)</td><td>Sigma</td><td>D0627</td><td>melanocyte culture medium</td></tr><tr><td>12-O-tetradecanoyl phorbol-13-acetate (TPA)</td><td>Sigma</td><td>79346</td><td>melanocyte culture medium</td></tr><tr><td>Penicillin Streptomycin</td><td>Thermo Scientific</td><td>15140-122</td><td>Antibiotics</td></tr><tr><td>rabbit anti-human Ki-67</td><td>Abcam</td><td>ab15580</td><td>For Immunofluorescence</td></tr><tr><td>Phosphate buffered solution</td><td>Solarbio Life Science</td><td>P1020-500</td><td>Washing solution</td></tr><tr><td>Sorvall ST 16R Centrifuge</td><td>Thermo Scientific</td><td>75004380</td><td>Cell centrifugation</td></tr><tr><td>TC20TM automated cell counter</td><td>Bio-Rad</td><td>1450102</td><td>Automatic cell counting</td></tr><tr><td>0.05% Trypsin</td><td>Life Technologies</td><td>25300-062</td><td>For melanocyte dissociation</td></tr><tr><td>Y-27632</td><td>Sigma</td><td>Y0503</td><td>For melanocyte isolation</td></tr></tbody></table>

y-27632 enriches the yield of human melanocytes from adult skin tissues

The isolation and culture of primary melanocytes from skin tissues is very important for biological research and has been widely used for clinical applications. Isolating primary melanocytes from skin tissues by the conventional method usually takes about 3 to 4 weeks to passage sufficiently. More importantly, the tissues used are usually newborn foreskins and it is still a challenge to efficiently isolate primary melanocytes from adult tissues. We recently developed a new isolation method for melanocytes that adds Y-27632, a Rho kinase inhibitor, to the initial culture medium for 48 h. Compared with the conventional protocol, this new method dramatically increases the yield of melanocytes and shortens the time required to isolate melanocytes from foreskin tissues. We now describe this new method in more detail using adult epidermis to efficiently culture primary melanocytes. Importantly, we show that melanocytes obtained from adult tissues prepared by this new method can function normally. This new protocol will significantly benefit studies of pigmentation defects and melanomas using primary melanocytes prepared from easily accessed adult skin tissues.

Figure 1 shows a schematic diagram comparing the conventional and the new methods. The procedure for tissue preparation and digestion with the new method is the same as the procedure for the conventional method, the only difference being that the isolated cells are resuspended in 10 mL of TIVA medium in the presence of 10 &#181;M Y-27632. Two days after seeding, replace the media with normal TIVA medium without Y-27632. The conventional method of isolating primary melanocytes from skin tissu...

Watch this Scientific Journal Video about Y-27632 Enriches the Yield of Human Melanocytes from Adult Skin Tissues at JoVE.com

Y-27632 Enriches the Yield of Human Melanocytes from Adult Skin Tissues

This paper reports that the addition of Y-27632 to TIVA medium can significantly increase the yield of melanocytes from adult skin tissues.

The isolation and culture of primary melanocytes from skin tissues is very important for biological research and has been widely used for clinical ...

y-27632-enriches-yield-human-melanocytes-from-adult-skin

Research

JoVE Journal

Biology

5.5K Views.  Shandong University & Shandong Key Laboratory of Oral Tissue Regeneration & Shandong Engineering Laboratory for Dental Materials and Oral Tissue Regeneration. This paper reports that the addition of Y-27632 to TIVA medium can significantly increase the yield of melanocytes from adult skin tissues.

Video: Y-27632 Enriches the Yield of Human Melanocytes from Adult Skin Tissues

The Three-Dimensional Human Skin Reconstruct Model: a Tool to Study Normal  Skin and Melanoma Progression

Most in vitro studies in experimental skin biology have been done in 2-dimensional (2D) monocultures, while accumulating evidence suggests that cells behave differently when they are grown within a 3D extra-cellular matrix and also interact with other cells (1-5). Mouse models have been broadly utilized to study tissue morphogenesis in vivo. However mouse and human skin have significant differences in cellular architecture and physiology, which makes it difficult to extrapolate mouse studies to humans. Since melanocytes in mouse skin are mostly localized in hair follicles, they have distinct biological properties from those of humans, which locate primarily at the basal layer of the epidermis. The recent development of 3D human skin reconstruct models has enabled the field to investigate cell-matrix and cell-cell interactions between different cell types. The reconstructs consist of a "dermis" with fibroblasts embedded in a collagen I matrix, an "epidermis", which is comprised of stratified, differentiated keratinocytes and a functional basement membrane, which separates epidermis from dermis. Collagen provides scaffolding, nutrient delivery, and potential for cell-to-cell interaction. The 3D skin models incorporating melanocytic cells recapitulate natural features of melanocyte homeostasis and melanoma progression in human skin. As in vivo, melanocytes in reconstructed skin are localized at the basement membrane interspersed with basal layer keratinocytes. Melanoma cells exhibit the same characteristics reflecting the original tumor stage (RGP, VGP and metastatic melanoma cells) in vivo. Recently, dermal stem cells have been identified in the human dermis (6). These multi-potent stem cells can migrate to the epidermis and differentiate to melanocytes.

In this report, we describe the three-dimensional skin reconstruct model which mimics human skin in architecture and composition. Melanocyte physiology, melanoma progression and the fate of dermal stem cells have been investigated using the skin reconstruct model. The model is also useful as a preclinical tool for drug assessment.

Most in vitro studies in experimental skin biology have been done in 2-dimensional (2D) monocultures, while accumulating evidence suggests that cells ...

Bioengineering

Feeder-free Derivation of Melanocytes from Human Pluripotent Stem Cells

Human pluripotent stem cells (hPSCs) represent a platform to study human development in vitro under both normal and disease conditions. Researchers can direct the differentiation of hPSCs into the cell type of interest by manipulating the culture conditions to recapitulate signals seen during development. One such cell type is the melanocyte, a pigment-producing cell of neural crest (NC) origin responsible for protecting the skin against UV irradiation. This protocol presents an extension of a currently available in vitro Neural Crest differentiation protocol from hPSCs to further differentiate NC into fully pigmented melanocytes. Melanocyte precursors can be enriched from the Neural Crest protocol via a timed exposure to activators of WNT, BMP, and EDN3 signaling under dual-SMAD-inhibition conditions. The resultant melanocyte precursors are then purified and matured into fully pigmented melanocytes by culture in a selective medium. The resultant melanocytes are fully pigmented and stain appropriately for proteins characteristic of mature melanocytes.

This work describes an in vitro differentiation protocol to produce pigmented, mature melanocytes from human pluripotent stem cells via a neural crest and melanoblast intermediate stage using a feeder-free, 25 day protocol.

Human pluripotent stem cells (hPSCs) represent a platform to study human development in vitro under both normal and disease conditions. Researchers can ...

Developmental Biology

Rapid Generation of Primary Murine Melanocyte and Fibroblast Cultures

Defects in fibroblast or melanocyte function are associated with skin diseases, including poor barrier function, defective wound healing, pigmentation defects and cancer. Vital to the understanding and amelioration of these diseases are experiments in primary fibroblast and melanocyte cultures. Nevertheless, current protocols for melanocyte isolation require that the epidermal and dermal layers of the skin are trypsinized and manually disassociated. This process is time consuming, technically challenging and contributes to inconsistent yields. Furthermore, methods to simultaneously generate pure fibroblast cultures from the same tissue sample are not readily available. Here, we describe an improved protocol for isolating melanocytes and fibroblasts from the skin of mice on postnatal days 0-4. In this protocol, whole skin is mechanically homogenized using a tissue chopper and then briefly digested with collagenase and trypsin. Cell populations are then isolated through selective plating followed by G418 treatment. This procedure results in consistent melanocyte and fibroblast yields from a single mouse in less than 90 min. This protocol is also easily scalable, allowing researchers to process large cohorts of animals without a significant increase in hands-on time. We show through flow cytometric assessments that cultures established using this protocol are highly enriched for melanocytes or fibroblasts.

This protocol outlines a rapid method to simultaneously generate melanocyte and fibroblast cultures from the skin of 0-4 day old mice. These primary cultures can be maintained and manipulated in vitro to study a variety of physiologically relevant processes, including skin cell biology, pigmentation, wound healing and melanoma.

Defects in fibroblast or melanocyte function are associated with skin diseases, including poor barrier function, defective wound healing, pigmentation ...

Cancer Research

Quantification of Hypopigmentation Activity In Vitro

This study presents laboratory methods for the quantification of hypopigmentation activity in vitro. Melanin, the major pigment in melanocytes, is synthesized in response to multiple cellular and environmental factors. Melanin protects skin cells from ultraviolet damage, but also has biophysical and biochemical functions. Excessive production or accumulation of melanin in melanocytes can cause dermatological problems, such as freckles, dark spots, melasma, and moles. Therefore, the control of melanogenesis with hypopigmentation agents is important in individuals with clinical or cosmetic needs. Melanin is primarily synthesized in the melanosomes of melanocytes in a complex biochemical process called melanogenesis, which is influenced by extrinsic and intrinsic factors, such as hormones, inflammation, age, and ultraviolet light exposure. We describe three methods to determine the hypopigmentation activity of chemicals or natural substances in melanocytes: measurement of the 1) cellular tyrosinase activity and 2) melanin content, and 3) staining and quantifying cellular melanin with image analysis.
In melanogenesis, tyrosinase catalyzes the rate-limiting step that converts L-tyrosine into 3,4-dihydroxyphenylalanine (L-DOPA) and then into dopaquinone. Therefore, the inhibition of tyrosinase is a primary hypopigmentation mechanism. In cultured melanocytes, tyrosinase activity can be quantified by adding L-DOPA as a substrate and measuring dopaquinone production by spectrophotometry. Melanogenesis can also be measured by quantifying the melanin content. The melanin-containing cellular fraction is extracted with NaOH and melanin is quantified spectrophotometrically. Finally, the melanin content can be quantified by image analysis following Fontana-Masson staining of melanin. Although the results of these in vitro assays may not always be reproduced in human skin, these methods are widely used in melanogenesis research, especially as the initial step to identify potential hypopigmentation activity. These methods can also be used to assess melanocyte activity, growth, and differentiation. Consistent results with the three different methods ensure the validity of the effects.

We describe three experimental methods for evaluating the hypopigmentation activity of chemicals in vitro: quantification of 1) cellular tyrosinase activity and 2) melanin content, and 3) measurement of melanin by cellular melanin staining and image analysis.

This study presents laboratory methods for the quantification of hypopigmentation activity in vitro. Melanin, the major pigment in melanocytes, is ...

Biochemistry

Spatial and Temporal Control of Murine Melanoma Initiation from Mutant Melanocyte Stem Cells

Cutaneous melanoma is well known as the most aggressive skin cancer. Although the risk factors and major genetic alterations continue to be documented with increasing depth, the incidence rate of cutaneous melanoma has shown a rapid and continuous increase during recent decades. In order to find effective preventative methods, it is important to understand the early steps of melanoma initiation in the skin. Previous data has demonstrated that follicular melanocyte stem cells (MCSCs) in the adult skin tissues can act as melanoma cells of origin when expressing oncogenic mutations and genetic alterations. Tumorigenesis arising from melanoma-prone MCSCs can be induced when MCSCs transition from a quiescent to active state. This transition in melanoma-prone MCSCs can be promoted by the modulation of either hair follicle stem cells&#39; activity state or through extrinsic environmental factors such as ultraviolet-B (UV-B). These factors can be artificially manipulated in the laboratory by chemical depilation, which causes transition of hair follicle stem cells and MCSCs from a quiescent to active state, and by UV-B exposure using a benchtop light. These methods provide successful spatial and temporal control of cutaneous melanoma initiation in the murine dorsal skin. Therefore, these in vivo model systems will be valuable to define the early steps of cutaneous melanoma initiation and could be used to test potential methods for tumor prevention.

The following procedure describes a method for spatial and temporal control of melanocytic tumor initiation in murine dorsal skin, using a genetically engineered mouse model. This protocol describes macroscopic as well as microscopic cutaneous melanoma initiation.

Cutaneous melanoma is well known as the most aggressive skin cancer. Although the risk factors and major genetic alterations continue to be documented ...

Pharmacologic Induction of Epidermal Melanin and Protection Against Sunburn in a Humanized Mouse Model

Fairness of skin, UV sensitivity and skin cancer risk all correlate with the physiologic function of the melanocortin 1 receptor, a Gs-coupled signaling protein found on the surface of melanocytes. Mc1r stimulates adenylyl cyclase and cAMP production which, in turn, up-regulates melanocytic production of melanin in the skin. In order to study the mechanisms by which Mc1r signaling protects the skin against UV injury, this study relies on a mouse model with "humanized skin" based on epidermal expression of stem cell factor (Scf). K14-Scf transgenic mice retain melanocytes in the epidermis and therefore have the ability to deposit melanin in the epidermis. In this animal model, wild type Mc1r status results in robust deposition of black eumelanin pigment and a UV-protected phenotype. In contrast, K14-Scf animals with defective Mc1r signaling ability exhibit a red/blonde pigmentation, very little eumelanin in the skin and a UV-sensitive phenotype. Reasoning that eumelanin deposition might be enhanced by topical agents that mimic Mc1r signaling, we found that direct application of forskolin extract to the skin of Mc1r-defective fair-skinned mice resulted in robust eumelanin induction and UV protection 1. Here we describe the method for preparing and applying a forskolin-containing natural root extract to K14-Scf fair-skinned mice and report a method for measuring UV sensitivity by determining minimal erythematous dose (MED). Using this animal model, it is possible to study how epidermal cAMP induction and melanization of the skin affect physiologic responses to UV exposure.

Epidermal melanin is induced by topical application of forskolin in a murine model of the fair-skinned UV-sensitive human. Pharmacologic manipulation of cAMP levels in the skin and epidermal darkening strongly protect against UV-mediated inflammation (sunburn) as measured by the minimum erythematous dose (MED) assay.

Fairness of skin, UV sensitivity and skin cancer  risk all correlate with the physiologic function of the melanocortin 1  receptor, a Gs-coupled signaling ...

Medicine

A Simplified and Efficient Method to Isolate Primary Human Keratinocytes from Adult Skin Tissue

Primary human keratinocytes isolated from fresh skin tissues and their expansion in vitro have been widely used for laboratory research and for clinical applications. The conventional isolation method of human keratinocytes involves a two-step sequential enzymatic digestion procedure, which has been proven to be inefficient in generating primary cells from adult tissues due to the low cell recovery rate and reduced cell viability. We recently reported an advanced method to isolate human primary epidermal progenitor cells from skin tissues that utilizes the Rho kinase inhibitor Y-27632 in the medium. Compared with the traditional protocol, this new method is simpler, easier, and less time-consuming, and increases epithelial stem cell yield and enhances their stem cell characteristics. Moreover, the new methodology does not require the separation of the epidermis from the dermis, and, therefore, is suitable for isolating cells from different types of adult tissues. This new isolation method overcomes the major shortcomings of conventional methods and is more suitable for producing large numbers of epidermal cells with high potency both for laboratory and for clinical applications. Here, we describe the new method in detail.

Here we present a protocol to efficiently isolate primary human keratinocytes from adult skin tissues. This method simplifies the conventional procedure by using the ROCK Inhibitor Y-27632 in the inoculation medium to spontaneously separate epidermal cells from dermal cells.

Primary human keratinocytes isolated from fresh skin tissues and their expansion in vitro have been widely used for laboratory research and for clinical ...

Direct Reprogramming of Mouse Fibroblasts into Melanocytes

The loss of function of melanocytes leads to vitiligo, which seriously affects the physical and mental health of the affected individuals. Presently, there is no effective long-term treatment for vitiligo. Therefore, it is imperative to develop a convenient and effective treatment for vitiligo. Regenerative medicine technology for direct reprogramming of skin cells into melanocytes seems to be a promising novel treatment of vitiligo. This involves the direct reprogramming of the patient's skin cells into functional melanocytes to help ameliorate the loss of melanocytes in patients with vitiligo. However, this method needs to be first tested on mice. Although direct reprogramming is widely used, there is no clear protocol for direct reprogramming into melanocytes. Moreover, the number of available transcription factors is overwhelming. 
Here, a concentrated lentivirus packaging system protocol is presented to produce transcription factors selected for reprogramming skin cells to melanocytes, including Sox10, Mitf, Pax3, Sox2, Sox9, and Snai2. Mouse embryonic fibroblasts (MEFs) were infected with the concentrated lentivirus for all these transcription factors for the direct reprogramming of the MEFs into induced melanocytes (iMels) in vitro. Furthermore, these transcription factors were screened, and the system was optimized for direct reprogramming to melanocytes. The expression of the characteristic markers of melanin in iMels at the gene or protein level was significantly increased. These results suggest that direct reprogramming of fibroblasts to melanocytes could be a successful new therapeutic strategy for vitiligo and confirm the mechanism of melanocyte development, which will provide the basis for further direct reprogramming of fibroblasts into melanocytes in vivo.

Here, we describe an optimized direct reprogramming system for melanocytes and a high-efficiency, concentrated virus packaging system that ensures smooth direct reprogramming.

The loss of function of melanocytes leads to vitiligo, which seriously affects the physical and mental health of the affected individuals. Presently, ...

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 ...

Rapid Culturing of Primary Murine Melanocytes and Fibroblasts: Isolating Melanocytes and Fibroblasts from Whole Murine Skin Sample

Source: Murphy, B. M. et al. <a href="https://www.jove.com/v/59468"> Rapid Generation of Primary Murine Melanocyte and Fibroblast Cultures</a>. J. Vis. Exp. (2019)
This video describes the rapid method to isolate and culture the melanocytes and fibroblast simultaneously from the postnatal mouse pup&#8217;s skin. These cells can be maintained and manipulated in vitro to study skin cell biology, wound healing, and melanoma.

Source: Murphy, B. M. et al.  Rapid Generation of Primary Murine Melanocyte and Fibroblast Cultures. J. Vis. Exp. (2019)
This video describes the rapid ...