Melanogenesis in cultures of peripheral nervous tissue: II. Environmental factors determining the fate of pigment-forming cells

Abstract

Spinal ganglia from 4- to 7-day [Stage 23–30; Hamburger and Hamilton (1951) J. Morphol. 88, 49–92 ] chicken embryos were cultured in vitro to investigate the effect of various environmental conditions on cell differentiation. Culture morphology (i.e., degree of dispersion of the explanted ganglia, survival of neurons, and outgrowth of axons) was observed to depend upon several factors including: (1) the age of the explanted ganglia, (2) the presence or absence of nerve growth factor (NGF), and (3) the nature of the substratum on which the cultured tissue resides. These observations enabled us to disturb the association of neurons with the other cells in ganglion cultures and thereby modulate the differentiation of adventitious melanocytes. Thus, in medium permissive for melanogenesis, melanocytes appear when the association between neurons and small stellate nonneuronal cells in the ganglion is disrupted. This disruption is most extensive (1) when young (Stage 26–27, 5-day) ganglia are explanted on plastic substrata, in the initial absence of NGF, and (2) when cells from enzyme-dissociated ganglia are cultured on plastic substrata. In comparable media, pigment cell differentiation is not observed when the association between neurons and small stellate cells is preserved. Such associations tend to endure (1) in developmentally older (Stage 30+, 7- to 8-day) ganglia or (2) when ganglia are cultured on agar or fibroblast substrata. We conclude that loss of association between neurons and the nonneuronal cells in young ganglia is necessary for the latter to undergo melanogenesis in vitro.