Post-Embryonic Nerve-Associated Precursors to Adult Pigment Cells: Genetic Requirements and Dynamics of Morphogenesis and Differentiation
(A) Hypothesized lineage relationships, showing neural crest (NC) cells in the early embryo that give rise to Schwann cells and pigment cells of the early larva as well as erbb3b-dependent progenitors to metamorphic glial and pigment cell lineages (mGP). mGP are maintained in association with peripheral nerves and ganglia, express foxd3, and their population expands (multiple arrowheads) in a tuba8l3a-dependent manner. During pigment pattern metamorphosis (met), some mGP differentiate as metamorphic Schwann cells (S) and the expansion of this lineage likely requires erbb3b (not shown). Other mGP become specified for metamorphic pigment cell lineages, as marked by mitfa::GFP expression. Some mitfa::GFP+ cells will give rise to melanophores or iridophores and are initially extra-hypodermally located in peripheral nerves and ganglia (M/I-e) but then migrate to the hypodermis (M/I-h). The expansion of this population requires ednrb1 . Some M/I-h will differentiate as metamorphic iridophores (I), other M/I-h expand their population in a tuba8l3a- and kita-dependent manner and ultimately differentiate as metamorphic melanophores (M). Individual M/I-e or M/I-h may be bipotent for melanophore and iridophore fates, as in embryos , or their respective populations may harbor precursors already specified for either the melanophore or iridophore fate. csf1r-dependent metamorphic xanthophores (X) presumably arise from a different precursor population (dashed line) and promote the survival of metamorphic melanophores (orange arrow) , , . Some mGP persist into the adult and have a limited re-population potential. (B) Schematic of metamorphic larva illustrating sources and migratory pathways of metamorphic melanophore and iridophore precursors. Shown are mGP and M/I-e (colors as in A) associated with nerves and beneath the dorsal fin (f). M/I-e enter the hypodermis (arrows) from the dorsal or ventral margins of the myotomes (m), or after migrating along nerves associated with the the vertical myosepta (vm) or the horizontal myoseptum (hm). Others may arise from the lateral line nerve (ll). Once in the hypodermis, these cells differentiate as melanophores (green cell with heavy black outline) or iridophores (not shown). sc, spinal cord. Additional populations of precursors that may give rise to LM melanophores and scale melanophores are not shown (see text).