An analysis of melanogenesis in cultured chick embryo spinal ganglia

Abstract

When sensory ganglia are removed from the 4-day chicken embryo and cultured in vitro, some cells appear after several days in culture which contain melanin pigment. Pigment cell differentiation occurs less frequently in cultures of slightly older ganglia, and does not occur at all in cultures of ganglia explanted from embryos older than 6 days. From these results and other considerations, we conclude that some cells in the nascent ganglion produce pigment in vitro when they would not normally do so in situ. It has been suggested that the degree of dispersion may influence the differentiation of pluripotent neural crest cells ( Weston and Butler, 1966). The facts (1) that conditions in culture promote the disruption of the structural integrity of the explanted ganglion and the dispersion of its cells, and (2) that pigment usually appears in the peripheral outgrowths of such cultures, are consistent with this suggestion. The mechanism by which dispersion might effect expression of the pigment phenotype is not known. Ganglion cultures were treated with actinomycin D (AD) and cytosine arabinoside (CA) to discriminate between the possibilities (1) that the capacity to make pigment existed in some cells of the ganglion at the time of explanation and (2) that this capability arose in some of these cells as a consequence of the environmental conditions in vitro. The appearance of pigment cells in cultures of young sensory ganglia is sensitive to AD and CA during the first few days in culture, but becomes relatively insensitive to such treatment later in the culture period. These results suggest that some developmentally significant events, presumably involving DNA synthesis and perhaps some DNA-dependent RNA synthesis, must occur during the first few days in culture before the pigment phenotype may be expressed by cells in the cultured ganglion.