Activation of hypodermal differentiation in the Caenorhabditis elegans embryo by GATA transcription factors ELT-1 and ELT-3

The Caenorhabditis elegans GATA transcription factor genes elt-1 and elt-3 are expressed in the embryonic hypodermis (also called the epidermis). elt- l is expressed in precursor cells and is essential for the production of mo st hypodermal cells (22). elt-3 is expressed in all of the major hypodermal cells except the lateral seam cells, and expression is initiated immediate ly after the terminal division of precursor lineages (13). Although this ex pression pattern suggests a role for ELT-3 in hypodermal development, no fu nctional studies have yet been performed. In the present paper, we show tha t either elt-3 or elt-1 is sufficient, when force expressed in early embryo nic blastomeres, to activate a program of hypodermal differentiation even i n blastomeres that are not hypodermal precursors in wild-type embryos. We h ave deleted the elt-3 gene and shown that ELT-3 is not essential for either hypodermal cell differentiation or the viability of the organism. We showe d that ELT-3 can activate hypodermal gene expression in the absence of ELT- 1 and that, conversely, ELT-1 can activate hypodermal gene expression in th e absence of ELT-3. Overall, the combined results of the mutant phenotypes, initial expression times, and our forced-expression experiments suggest th at ELT-3 acts downstream of ELT-1 in a redundant pathway controlling hypode rmal cell differentiation.