In an effort to understand the genetic events that lead to the formation of the intestine, we are investigating the network of regulatory factors expressed during gut development. Here, we describe our studies of three such factors: the GATA-type transcription factor, ELT-7, and two ODD-SKIPPED-like factors, ODD-1 (formerly EEL-1) and ODD-2.
elt-7::gfp is expressed continuously in the E lineage beginning at the 2E cell stage. This expression pattern is identical to that of ELT-2, suggesting that these GATA factors may perform overlapping roles in gut development. Thus, ELT-2 and -7 might act redundantly and immediately downstream of the END-1 and END-3 GATA factors, which redundantly specify E cell identity. However,
elt-7(RNAi) embryos show no discernible phenotype, and the degraded gut phenotype of the
elt-2(0) mutation does not appear to be enhanced by RNAi of
elt-7. This contrasts with
end-1/end-3 double RNAi, which results in a penetrant loss of gut not seen with each RNAi alone. Ectopic
elt-7 expressed from a heat-shock promoter results in gut differentiation throughout the embryo, showing that ELT-7 is able to activate gut development. Ian Hope's expression screen identified
odd-1 as a gut-specific gene.
odd-2 was discovered through its similarity to
odd-1. Each encodes a 3 zinc finger protein similar to Drosophila ODD-SKIPPED family members.
odd-1::gfp is expressed in two phases. The first phase corresponds to E lineage expression from the 4E cell stage through mid-elongation (about 1.5-fold). In the second phase, expression is continuous throughout development after elongation in intestinal-rectal valve cells and in a decreasing posterior to anterior gradient in the gut, with increased expression again in the four anterior (
int1) cells. Expression of
odd-2::lacZ::gfp is similar to the second phase of
odd-1::gfp expression, albeit at lower levels and with somewhat altered kinetics. Both
odd-1(0) and
odd-2(RNAi) animals die as L1 larva, with no obvious effect on gut development. We are further characterizing the function of these genes to understand their action and regulatory interrelationships during development of the intestine.