Characterization of the genetic network of endoderm formation in the nematode Caenorhabditis elegans

The goal of developmental biology is to understand the events that occur throughout the life of an organism at the morphological, genetic and molecular levels and to use that knowledge to further understand how all organisms are related to each other. One component of this goal is the characterization of the differentiation of an embryonic germ layer into organs and tissues. In the nematode C. elegans, the intestine, or gut, is the sole derivative of the endoderm germ layer, making it an ideal system to characterize the genetic events that occur during organogenesis and the development of a germ layer. GATA transcription factors have a well-established role in endoderm formation. elt-7 encodes a GATA factor that is expressed continuously in the intestine beginning shortly after the endoderm progenitor is born, similar to another GATA factor gene, elt-2. elt-7 is sufficient to cause non-gut cells of early embryos to express terminal intestinal markers. All intestine-specific GATA factors genes, including elt-7, are sufficient to drive expression of elt-7::LacZ::GFP in non-gut cells in early embryos. elt-7(RNAi) animals do not have any obvious phenotype. However, ELT-7 and ELT-2 collaborate to regulate the expression of a number of terminal gut genes and other factors that contribute to intestinal morphogenesis. elt-2( ca15); elt-7(RNAi) L1 larvae do not contain a discernible gut lumen. In addition, the boundary between the intestine and adjacent cells in the digestive tract may be compromised, possibly leading to a partial transformation of differentiated intestine into connecting valve cells. odd-1 and odd-2 encode zinc finger proteins related to the Odd-Skipped family of proteins that are used throughout the metazoa. Reporter constructs for odd-1 and odd-2 show similar, but not identical, expression and appear to be regulated differently by ELT-2 and ELT-7. odd-1( RNAi) animals do not have an obvious phenotype. Severely affected odd-2(RNAi) animals arrest and die as L1 larvae with a blocked intestine. While our results indicate that ELT-7 plays a similar role in endoderm development to endoderm GATA factors in other animals, odd-1 and odd-2 may have roles in development that are both similar to and different than other known Odd-Skipped genes.