2000 West Coast Worm Meeting abstract 58
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| 1 | Department of MCD Biology, University of California, Santa Barbara, CA |
| 2 | Department of Chemistry, University of Virginia, Charlottesville, VA |
end-1 encodes a GATA type transcription factor that is sufficient to specify the endoderm progenitor, E. end-1 is activated in the E lineage by the combined action of SKN-1 and the Wnt/MAP kinase-activated form of POP-1 (see abstract by Kasmir et al.). It is repressed in MS, the sister of E, by POP-1 in the absence of the Wnt/MAPK signal.
We are taking a biochemical approach to characterize additional factors that activate end-1 in the E lineage and repress it in MS. We developed procedures for isolating factors from early developing C. elegans embryos that bind key regulatory elements in end-1. Mass spectrometry of affinity-purified proteins identified several end-1 binding factors, one of which, encoded by the plp-1 gene, is an apparent homologue of a mammalian transcription factor called pur alpha, whose in vivo function is unknown.
We performed RNAi to examine the role of PLP-1 in mesendoderm development. Less than 10% of plp-1(RNAi) embryos arrest before hatching. A fraction of these contain extra intestinal cells and show a concomitant loss of MS-derived (posterior) pharynx. This phenotype appears to result from an MS to E transformation, consistent with our finding that end-1 is sometimes expressed in MS and its descendants in plp-1(RNAi) embryos. Thus, plp-1 appears to function in part to repress end-1 expression in the MS lineage. As such, it may act as a corepressor with POP-1.
Paradoxically, we also observe an impenetrant (<5%) absence of gut in plp-1(RNAi) embryos, suggesting that PLP-1 might also function in the E lineage to activate endoderm development. Indeed, the possible collaboration of plp-1 and the Wnt pathway in endoderm specification is supported by our finding that plp-1(RNAi) enhances a mutation in the Wnt receptor-encoding mom-5 gene: while 5% of mom-5(or57) embryos lack gut, ~35% of mom-5(or57); plp-1(RNAi) embryos lack gut.
Our findings demonstrate the efficacy of biochemical approaches toward identifying additional factors in early blastomere specification and suggest that PLP-1 may function with POP-1 to regulate the fates of both E and MS, perhaps by alternately acting as a corepressor and coactivator for end gene expression respectively.