THE ZEBRAFISH HOMOLOG OF THE RET RECEPTOR AND ITS PATTERN OF EXPRESSION DURING EMBRYOGENESIS

The c-ret proto-oncogene, a member of the receptor tyrosine kinase gen e superfamily, plays a critical role in the development of the excreto ry system and the enteric and autonomic nervous systems of mammalian e mbryos. To study the potential function of the c-vet locus in lower ve rtebrates, we have isolated its zebrafish homologue, ret1 and establis hed its expression pattern during embryogenesis. Ret1 mRNA first appea rs during early somitogenesis in the presumptive brain, spinal cord an d excretory system. Within the CNS, expression of ret1 is detected in primary motor and sensory (Rohon-Beard) neurons. Ret1 transcripts are also expressed in subsets of neural crest cells and cranial ganglia as well as in the enteric nervous system. In the excretory system, expre ssion is detected in the developing nephric duct and the pronephros. O ur findings reveal a remarkable similarity in the expression pattern o f c-ret between higher and lower vertebrates, suggesting that the func tion of this locus has been conserved throughout vertebrate evolution. Furthermore, the conservation of ret1 expression in cell types which remain unaffected by the mammalian c-vet mutations, such as motor and sensory neurons, suggests a function of this receptor in these cell li neages.