Mechanisms for reaching the differentiated state: Insights from neural crest-derived melanocytes

Abstract

Black pigment cells, or melanocytes, are the major contributing cells to pigmentation in vertebrate organisms. Although the function of these cells is distinct depending on the organism, the events involved in their development are remarkably similar. Here, we review the mechanisms involved in the early development of melanocytes from neural crest, many of which are conserved in organisms as diverse as zebrafish, birds and humans. We also discuss recent studies that provide further insight into how melanocyte differentiation is achieved and maintained.

Figure 1. Extrinsic and intrinsic factors involved in melanophore development and function in zebrafish

A) Unpigmented, specified melanoblasts expressing mRNA for the melanin producing enzyme, Dct. The blue product reveals the locations of dct transcript. (white arrow, e; eye) B) Melanophores in the early stages of melanin production (~30 hours post fertilizatioyn). Cell morphology is highly dendritic at this stage. C) Mature melanophore at 2 days post fertilization. Cells have accumulated high levels of melanin and have taken on a flattened morphology. D). Alteration in melanophore appearance in response to environmental cues. Melanophores are capable of aggregating (black arrow) and dispersing (black arrowhead) melanin containing organelles, melanosomes. Here, both events are observed simultaneously in this zebrafish melanophore mutant. E) Regulated survival of melanophores. Without Kit signaling, larval melanophores undergo apoptosis. Characteristic morphologies of apoptosing melanophores include cell rounding and clumping.