MODULATION OF GENE-EXPRESSION IN THE EMBRYONIC DIGESTIVE-TRACT OF C-ELEGANS

The Caenorhabditis elegans digestive tract is composed of four distinc t modules derived from separate cell lineages: anterior pharynx from t he ABa lineage, posterior pharynx from the MS lineage, gut from tile E lineage, and rectum from the ABp lineage. The C. elegans gut esterase gene (ges-1) is normally expressed in the embryonic gut or E lineage. However, expression of ges-1 can be switched into cells of the embryo nic pharynx and tail by virtue of deleting a tandem pair of WGATAR sit es in the ges-1 promoter, Here, we use both laser ablation experiments and genetic analysis to show that cells expressing the WGATAR-deleted ges-1 transgene belong to all three nongut lineages of the digestive tract: ABa, MS, and ABp. We also show that the molecular size and spat ial distribution of ges-1 mRNA transcripts produced by either the WGAT AR-deleted ges-1 transgene or the undeleted ges-l control transgene ap pear correctly regulated, suggesting that the spatial switch in ges-1 expression occurs at the level of transcription initiation. We further show that both the WGATAR-deleted and the undeleted ges-1 transgenes respond appropriately to mutations in a series of maternal effect gene s (skn-1, mex-1, pie-1, and pop-1) that alter early blastomere fate. M oreover, the pharynx/tail expression of the WGATAR-deleted ges-1 trans gene is abolished by mutations in the zygotic gene pha-4. Finally, we use imprecise transposon excision to produce two independent C, elegan s strains with 1- to 2-kb deletions that remove the tandem WGATAR site s from the promoter of the endogenous chromosomal I gene: in both of t hese strains, ges-1 is not expressed in the embryonic gut but is expre ssed in cells of the embryonic pharynx; pharynx expression is weak but incontrovertible, Overall, our results validate previous transgenic a nalysis of ges-1 control and show further that ges-1 appears to be reg ulated in a system-specific, rather than a lineage-specific, manner. T he multiple facets of ges-l expression provide an opportunity to inves tigate how a multicomponent organ system such as the digestive tract i s established from diverse cell lineages. (C) 1996 Academic Press, Inc .