Fig. 1. Lack of melanocyte differentiation in Ednrb^lacZ/Ednrb^lacZ neural crest cells in culture. Primary cultures from embryos of the indicated genotypes were established and kept in the presence of EDN3 for 2 weeks before fixation. X-gal staining was then performed and the cultures were photographed in bright field to show melanin and ß-gal staining. (A) Ednrb^lacZ/+ cultures show melanin-positive cells, many of which co-express ß-gal (arrow) although some lack clear ß-gal staining (arrowhead). (B) Ednrb^lacZ/Ednrb^lacZ cultures lack melanin-positive cells, although ß-gal-positive cells are present (arrow).