Turtle Lung Cells Produce a Melanization‐Stimulating Activity That Promotes Melanocytic Differentiation of Avian Neural Crest Cells

We found previously that neural crest cells in turtle embryos migrated into the lung buds and melanocytes were located in the lungs. The finding suggested to us that the lungs provide a stimulatory factor(s) to the differentiation of neural crest cells into melanocytes. We have established lung cell lines to facilitate analysis of the interactions of neural crest cells with the environment in melanocyte development. One cell line, TLC-2, was found to produce a putative melanization-stimulating activity (MSA), which promoted the melanocyte differentiation in vitro of avian neural crest cells. The TLC-2-derived MSA was different from that of basic fibroblast growth factor (bFGF), alpha-melanocyte stimulating hormone (alpha-MSH), and steel factor (SLF). Its molecular weight was estimated to be within the range of 150 kD. Our findings suggest that MSA may be a novel factor exercising a positive control over melanocyte differentiation.