Mode of redifferentiation and melanogenesis of melanocytes in mouse hair follicles

Changes in Different Melanocyte Populations During Hair Follicle Involution (Catagen)

“…Our study also revealed that during early-mid catagen TUNEL-negative melanocytes concentrate in the outer root sheath and follicular papilla and during late catagen become visible in the secondary hair germ (Figs 1 and 2, Table I). Lack of proliferation in the follicular melanocytes during catagen ( Fig 2M) suggests that secondary hair germ of late catagen HF is most likely repopulated by melanocytes arising from the outer root sheath or follicular papilla of early/mid-catagen HF, as it was proposed previously by others (Sugiyama, 1979;Tobin et al, 1999), These data are consistent with our previous observations, which revealed that during HF regression induced by chemotherapy, only a few hair bulb melanocytes undergo apoptosis, whereas the others show previously unrecognized capability to survive (Sharov et al, 2003a). In contrast to the HF regression induced by chemotherapy (Sharov et al, 2003a), melanocytes during physiological catagen, however, do not proliferate and do not repopulate the interfollicular epidermis (Figs 1 and 2).…”

“…Our data also reveal that a subset of the bulbar melanocytes became visible in the follicular papilla during early-mid catagen (Figs 1 and 2), raising a hypothesis about their migration from the melanogenic area of the HF and dedifferentiation into ''amelanotic'' forms (Sugiyama, 1979;Tobin et al, 1999). It was shown previously that SCF stimulates melanocyte migration in vivo and that cultured follicular papilla cells secrete chemotactic factor(s) for melanocytes (Kunisada et al, 1998a, b;Jordan and Jackson, 2000;Ideta et al, 2002).…”

Human hair pigmentation – biological aspects

“…Conditions that support the production of high amounts of l ‐tyrosine from l ‐phenylalanine include high levels of 6BH 4 , GTP‐cyclohydrolase 1 and phenylalanine hydroxylase (PAH). These three exist at high levels from the commencement of anagen through to anagen III – the start of melanogenesis [19, 20, 28, 38]. Thereafter, the activities of all three drop significantly and remain low until the next telogen.…”

“…Melanocytes in the S or DNA synthesis phase of the cell cycle have been reported as early as anagen II and a burst of melanocyte mitosis occurs a little later in anagen III [38]. Hair bulb melanocytes continue to increase in number until anagen VI (or full anagen characterized by maximal hair fibre production) and also to produce more of the cellular machinery needed for melanogenesis.…”

Behavior of Hair Follicles in Vitiligo: Clinical Presentation and Discussion

“…Melanocytes of the hair bulb are known to have potential proliferation power and are not as indolent as epidermal melanocyte lacking completely this power of renewal. The hair bulb melanocyte system has been perceived as selfperpetuating whereby melanocytes involved in the pigmentation of one generation are also involved in the pigmentation of the next wave [5,6]. Follicular melanogenesis is characteristically cyclic in nature, as opposed to the continuous melanogenesis of epidermal pigmentation [7].…”