END-1 ENCODES AN APPARENT GATA FACTOR THAT SPECIFIES THE ENDODERM PRECURSOR IN CAENORHABDITIS-ELEGANS EMBRYOS

The endoderm in the nematode Caenorhabditis elegans is clonally derive d from the E founder cell. We identified a single genomic region (the endoderm-determining region, or EDR) that is required for the producti on of the entire C. elegans endoderm. In embryos lacking the EDR, the E cell gives rise to ectoderm and mesoderm instead of endoderm and app ears to adopt the fate of its cousin, the C founder cell. end-1, a gen e from the EDR, restores endoderm production in EDR deficiency homozyg otes. end-1 transcripts are first detectable specifically in the E cel l, consistent with a direct role for end-1 in endoderm development. Th e END-1 protein is an apparent zinc finger-containing GATA transcripti on factor. As GATA factors have been implicated in endoderm developmen t in other animals, our findings suggest that endoderm may be specifie d by molecularly conserved mechanisms in triploblastic animals. We pro pose that end-1, the first zygotic gene known to be involved in the sp ecification of germ layer and founder cell identity in C. elegans, may link maternal genes that regulate the establishment of the endoderm t o downstream genes responsible for endoderm differentiation.