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An explanation for the mysterious distribution of melanin in human skin ‐ a rare example of asymmetric (melanin) organelle distribution during mitosis of basal layer progenitor keratinocytes
Joly-Tonetti, Nicolas Wibawa, J.I.D. Bell, M. Tobin, Desmond J.
Joly-Tonetti, Nicolas
Wibawa, J.I.D.
Bell, M.
Tobin, Desmond J.
Publication Date
2018-11
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© 2018 Wiley
This is the peer reviewed version of the following article: Joly-Tonetti N, Wibawa JID, Bell M et al (2018) An explanation for the mysterious distribution of melanin in human skin ‐ a rare example of asymmetric (melanin) organelle distribution during mitosis of basal layer progenitor keratinocytes. British Journal of Dermatology. 179(5): 1115-1126, which has been published in final form at https://doi.org/10.1111/bjd.16926. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving.
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2018-05-28
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Abstract
Background: Melanin is synthesized by melanocytes in the basal layer of the epidermis. When transferred to surrounding keratinocytes it is the key UVR-protective biopolymer responsible for skin pigmentation. Most melanin is observable in the proliferative basal layer of the epidermis, and only sparsely distributed in the stratifying/differentiating epidermis. The latter has been explained, despite formal evidence, to ‘melanin degradation’ in supra-basal layers.
Objectives: Our aim was to re-evaluate this currently-accepted basis for melanin distribution in the human skin epidermis, and whether this pattern is altered after a regenerative stimulus.
Methods: Normal epidermis of adult human skin, at rest and after tape-stripping, was analysed by a range of (immuno)histochemical and high-resolution microscopy techniques. In vitro models of melanin granule uptake by human keratinocytes were attempted.
Results: We propose a wholly different fate for melanin in the human epidermis. Our evidence indicates that the bulk of melanin is inherited only by the non-differentiating daughter cell post mitosis in progenitor keratinocytes, via asymmetric organelle inheritance. Moreover, this preferred pattern of melanin distribution can switch to a symmetric or equal daughter cell inheritance mode under conditions of stress including regeneration.
Conclusions: We provide in this preliminary report a plausible and histologically-supportable explanation for how human skin pigmentation is efficiently organized in the epidermis. Steady state epidermis pigmentation may involve much less redox-sensitive melanogenesis than previously thought, and at least some pre-made melanin may be available for re-use. The epidermal-melanin unit may be an excellent example to study organelle distribution via asymmetric or symmetric inheritance in response to micro-environment and tissue demands.
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Joly-Tonetti N, Wibawa JID, Bell M et al (2018) An explanation for the mysterious distribution of melanin in human skin ‐ a rare example of asymmetric (melanin) organelle distribution during mitosis of basal layer progenitor keratinocytes. British Journal of Dermatology. 179(5): 1115-1126.
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