C. elegans
fkh-1 is a homolog of the Drosophila forkhead and rodent HNF-3 genes with greater than 75% identity within the DNA binding domains. We are interested in determining whether
fkh-1 has an important developmental role in endoderm formation, like the Drosophila and rodent genes. Northerns show that
fkh-1 transcripts are expressed at highest levels in embryos. In situ hybridization shows that these transcripts are present both in the gut and pharynx of pre-morphogenic embryos. By the comma stage, transcripts are found only in the pharynx and in a spot in the tail. lacZ reporter fusions also show embryonic expression in the gut and pharynx, along with a second phase of expression in the somatic gonad of L2-L4 larvae. Thus, the embryonic expression patterns have similarities to the expression patterns found in Drosophila and rodents. The mutant phenotype of
fkh-1 is of foremost interest. We have so far failed to find an imprecise excision of a Tc1 insertion in a fkh- 1 intron, and are currently screening for lethal mutants rescued by a transforming array carrying
fkh-1 genomic DNA and a
rol-6 marker. We are also analyzing the
fkh-1 promoter in order to identify embryonic regulatory factors that also might have important roles in the determination of the gut and pharynx. Uni-directional and internal deletions of the
fkh-1 promoter reveal regions important for gut and somatic gonad specific expression. Within a region of the
fkh-1 promoter important for gut expression, there is clear sequence similarity to the GATA element containing region essential for the gut expression of the
ges-1 gene. Indeed, GATA elements also may be important for
fkh-1 regulation: we have shown that heat shock expression of the ELT-2 GATA factor is capable of inducing the
fkh-1 reporter construct throughout the entire embryo (see abstract by Fukushige et al.). In the future, we plan to identify
fkh-1 promoter binding factors, as well as to determine ELT-2's role in
fkh-1 regulation. We will then be able to compare the regulation of
fkh-1 in C. elegans to the regulation of
fkh-1 homologs in other organisms.