Temporal and molecular separation of the kit receptor tyrosine kinase's roles in zebrafish melanocyte migration and survival.

The Kit receptor tyrosine kinase is required by vertebrate melanocytes for their migration and survival. The relationship between these developmental roles of Kit, however, remains poorly understood. Here, we use two genetic approaches to demonstrate that Kit's roles in the migration and survival of embryonic melanocytes in the zebrafish (Danio rerio) are temporally and functionally independent. We use a temperature-sensitive kit mutation to show that kit promotes melanocyte migration and survival during distinct stages of development. These experiments additionally reveal that melanocyte migration is neither necessary nor sufficient for subsequent survival. We also identify kit alleles that molecularly separate kits roles in migration and survival. These results suggest that the melanocyte changes its response to Kit receptor signaling and function during development, first to promote migration, then to promote survival through distinct Kit-dependent mechanisms.