CD34 defines melanocyte stem cell subpopulations with distinct regenerative properties.

Melanocyte stem cells (McSCs) are the undifferentiated melanocytic cells of the mammalian hair follicle (HF) responsible for recurrent generation of a large number of differentiated melanocytes during each HF cycle. HF McSCs reside in both the CD34+ bulge/lower permanent portion (LPP) and the CD34- secondary hair germ (SHG) regions of the HF during telogen. Using Dct-H2BGFP mice, we separate bulge/LPP and SHG McSCs using FACS with GFP and anti-CD34 to show that these two subsets of McSCs are functionally distinct. Genome-wide expression profiling results support the distinct nature of these populations, with CD34- McSCs exhibiting higher expression of melanocyte differentiation genes and with CD34+ McSCs demonstrating a profile more consistent with a neural crest stem cell. In culture and in vivo, CD34- McSCs regenerate pigmentation more efficiently whereas CD34+ McSCs selectively exhibit the ability to myelinate neurons. CD34+ McSCs, and their counterparts in human skin, may be useful for myelinating neurons in vivo, leading to new therapeutic opportunities for demyelinating diseases and traumatic nerve injury. Author summary The hair follicle (HF) undergoes three different stages, anagen, catagen, and telogen during each hair cycle. In anagen, melanocyte stem cells (McSCs) give rise to differentiated melanocytes which are responsible for coloration of hair. In catagen, melanocytes undergo apoptosis while McSCs are retained. In the resting telogen HF, McSCs are identified as non-proliferating and quiescent populations. Interestingly, in a mouse model, we identified McSCs in both CD34+ bulge and CD34- secondary hair germ (SHG) compartments of telogen HFs. In this study, we separated and characterized McSC subpopulations from these two distinct compartments of telogen HFs. Using Dct-H2BGFP mice, bulge and SHG McSCs were separated using CD34. Based on genomic approaches and functional assays we found that CD34- McSCs (SHG) are primed for melanocyte differentiation and CD34+ McSCs (bulge) exhibit broader neural crest stem cell properties and demonstrate ability to differentiate into glia and myelinate neurons. Our results thus reveal functional heterogeneity of McSC subtypes.