Melanin Distribution in Human Skin: Influence of Cytoskeletal, Polarity, and Centrosome-Related Machinery of Stratum basale Keratinocytes.

Irene Castellano-Pellicena,Clare O’Connor,Ciaran G Morrison,Desmond J Tobin,Mike Bell

doi:10.3390/ijms22063143

Abstract

Melanin granules cluster within supra-nuclear caps in basal keratinocytes (KCs) of the human epidermis, where they protect KC genomic DNA against ultraviolet radiation (UVR) damage. While much is known about melanogenesis in melanocytes (MCs) and a moderate amount about melanin transfer from MC to KC, we know little about the fate of melanin once inside KCs. We recently reported that melanin fate in progenitor KCs is regulated by rare asymmetric organelle movement during mitosis. Here, we explore the role of actin, microtubules, and centrosome-associated machinery in distributing melanin within KCs. Short-term cultures of human skin explants were treated with cytochalasin-B and nocodazole to target actin filaments and microtubules, respectively. Treatment effects on melanin distribution were assessed by the Warthin–Starry stain, on centrosome-associated proteins by immunofluorescence microscopy, and on co-localisation with melanin granules by brightfield microscopy. Cytochalasin-B treatment disassembled supra-nuclear melanin caps, while nocodazole treatment moved melanin from the apical to basal KC domain. Centrosome and centriolar satellite-associated proteins showed a high degree of co-localisation with melanin. Thus, once melanin granules are transferred to KCs, their preferred apical distribution appears to be facilitated by coordinated movement of centrosomes and centriolar satellites. This mechanism may control melanin’s strategic position within UVR-exposed KCs.

Highlights

Melanin is predominantly restricted to the basal layer of the human epidermis, where it is found in both melanocytes (MCs), the cells that make melanin, and in nearby keratinocytes (KCs), the cells of the epidermis that accept melanin
We recently reported that melanin granule distribution in human skin is regulated primarily within in the Stratum (S.) basale of the epidermis, where they accumulate via an asymmetric mode of organelle distribution [4]
We aimed to explore the role of the MT/actin cytoskeleton and associated centrosomal machinery in melanin distribution and localisation within KCs of the human epidermis, with a primary focus on the role of S. basale KC polarity in melanin distribution in human skin

Summary

Introduction

Melanin is predominantly restricted to the basal layer (or Stratum basale) of the human epidermis, where it is found in both melanocytes (MCs), the cells that make melanin, and in nearby keratinocytes (KCs), the cells of the epidermis that accept melanin. We recently reported that melanin granule distribution in human skin is regulated primarily within in the Stratum (S.) basale of the epidermis, where they accumulate (and are largely, and remarkably, retained) via an asymmetric mode of organelle distribution [4]. This view challenged a long-held dogma, which explained a histologically apparent “depletion” of melanin in the epidermis above the S. basale as “degradation” of the melanin biopolymer, for which no convincing biochemical evidence has yet been advanced [5,6]. Only a minor portion of melanin transits to the

Objectives

Results

Conclusion