We are studying the regulation of gut esterase (
ges-1) gene expression in developing C. elegans embryos.
ges-1 is first expressed when the gut lineage has only 4-8 cells and the embryo has 150 cells. The C. elegans
ges-1 (
Ce-ges-1) gene is expressed solely in the gut. However, deletion of a 36 bp fragment containing two tandem WGATAR sites from the upstream
Ce-ges-1 promoter switches expression off in the gut and on in the pharynx and tail. We have previously shown that this gut-to-pharynx/tail switch changes
Ce-ges-1 expression from the E lineage into portions of the digestive tract derived from the ABa, ABp, and MS lineages. Further deletions have identified the putative pharynx activator element within 68 bp upstream from the
ges-1 initiator methionine. Thus,
Ce-ges-1 appears to be controlled by a complex regulatory mechanism involving the entire digestive tract. How could such a complex control mechanism have evolved? One possible model is that the ancestral
ges-1 gene was expressed throughout the digestive tract but was later restricted to the gut as
ges-1 expression became unnecessary, or detrimental, in the pharynx and rectum. To test this model, we are looking at expression of
ges-1 homologues in two related species, C. briggsae and Panagrellus redivivus. C. briggsae
ges-1 (
Cb-ges-1) is 75% identical to the
Ce-ges-1 coding sequence but flanking sequences are not well conserved overall. However,
Cb-ges-1 has two upstream tandem WGATAR sites that when deleted lead to the same gut to pharynx/tail expression switch seen in C. elegans. Interestingly, the putative pharynx/tail activator element in
Cb-ges-1 appears to be at the 3 end of the gene, whereas the
Ce-ges-1 pharynx/tail activator is at the 5 end.. Further characterization of the
Cb-ges-1 regulatory elements are underway. P. redivivus embryos have a major esterase activity expressed throughout their gut and pharynx. Preliminary analysis suggests that this major esterase could indeed be the P. redivivus
ges-1 homologue. Two esterases have been cloned that show significant levels of identity to the active site regions of both Ce-GES-1 and Cb-GES-1. These esterases are being characterized to determine the best candidate for
Pr-ges-1. Our plans are to reintroduce
Pr-ges-1 into C. elegans to investigate how the pharynx and gut expression is controlled.