Abstract
Melanin is a black/brown pigment present in abundance in human skin. Its main function is photo-protection of underlying tissues from harmful UV light. Natural sources of isolated human melanin are limited; thus, in vitro cultures of human cells may be a promising source of human melanin. Here, we present an innovative in vitro differentiation protocol of induced pluripotent stem cells (iPS) into melanin-producing cells, delivering highly pigmented cells in quantity and quality incomparably higher than any other methods previously described. Pigmented cells constitute over 90% of a terminally differentiated population and exhibit features characteristic for melanocytes, i.e., expression of specific markers such as MITF-M (microphthalmia-associated transcription factor isoform M), TRP-1 (tyrosinase-related protein 1), and TYR (tyrosinase) and accumulation of black pigment in organelles closely resembling melanosomes. Black pigment is unambiguously identified as melanin with features corresponding to those of melanin produced by typical melanocytes. The advantage of our method is that it does not require any sophisticated procedures and can be conducted in standard laboratory conditions. Moreover, our protocol is highly reproducible and optimized to generate high-purity melanin-producing cells from iPS cells; thus, it can serve as an unlimited source of human melanin for modeling human skin diseases. We speculate that FGF-8 might play an important role during differentiation processes toward pigmented cells.
Highlights
Invented in 2006 by Shinya Yamanaka et al, induced pluripotent stem cells [1]opened a new chapter in the potential application of stem cells in regenerative medicine for many disorders
The morphology of cells changes through each differentiation step, as depicted in cell differentiation through the suppression of a self-renewal and stemness-supporting environment
Among the acquired cells, a subpopulation became markedly loaded with black pigment, which appeared to be localized in intracellular granules (Figure 2G)
Summary
Invented in 2006 by Shinya Yamanaka et al, induced pluripotent stem (iPS) cells [1]opened a new chapter in the potential application of stem cells in regenerative medicine for many disorders. Melanin is a dark pigment found predominantly in the skin whose main role is photoprotection [6]. It is produced in specialized cells called melanocytes, within which the melanin is contained in dedicated membranous organelles called melanosomes [7]. Knowledge of human melanin structure, function, and synthesis is limited mainly due to scarce sources of the pigment. Among these sources, invasive skin biopsies and hair samples are the most common; they are limited and may deliver melanin in a highly photo-degraded and dehydrated state, as the skin and hair of adult donors have been exposed to a lifetime of sunlight and are deprived of water [6]
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