Molecular and functional analysis of the Polycomb group gene Sex comb on midleg (Scm) and its protein product.

摘要

First identified by mutations that caused derepression of homeotic genes in the fruit fly, Drosophila melanogaster, members of the Polycomb group (PcG) of transcriptional regulators now number greater than 15 and are likely to be involved in transcriptional regulation of more than 100 distinct genetic loci. Furthermore, homologues of most PcG genes have been discovered in diverse organisms ranging from the plants to mammals. Studies in mice have shown that of most of these genes show striking sequence conservation between flies and mammals, and more importantly, that the function of the gene products--regulation of Hox genes (homeotic genes in organisms other than Drosophila--is also conserved. Despite a great deal of attention in recent years, how these proteins achieve repression at target loci remains a mystery. Analysis of individual members of the PcG has given few clues as to the mechanism of repression. Thus, it is still not known how PcG proteins target the genes that they regulate, nor is it understood how they repress once they get there. Only recently has evidence supporting the hypothesis that PcG proteins assemble into complexes been forthcoming and, even so, the number and nature of such complexes remains to be elucidated. The goal of my research has been to study the contributions to repression made by a single member of the PcG, Sex comb on midleg, (Scm) in Drosophila melanogaster. To that end, I have cloned the Scm gene and, together with Ellen Miller, sequenced the gene. I have generated a rabbit polyclonal antibody to Scm protein, demonstrated its specificity, and used the antibody to investigate the in vivo behavior of both wild-type and mutant forms of Scm protein. I have also used an in-vitro assay to assess interactions between Scm protein and the protein product of another PcG gene, polyhomeotic, (ph), which shares a C-terminal domain with Scm protein. Since an Scm homologue has recently been discovered in humans, these studies will contribute not only to our knowledge of general repression mechanisms, but also have potential for application towards understanding of human development and disease.