High impact information on Psc

• Psc is a member of the Polycomb-group gene family, which is required to maintain the repression of homeotic genes that regulate the identities of Drosophila segments [1].
• Drosophila genes Posterior Sex Combs and Suppressor two of zeste encode proteins with homology to the murine bmi-1 oncogene [2].
• Sequence similarity between the mammalian bmi-1 proto-oncogene and the Drosophila regulatory genes Psc and Su(z)2 [3].
• Posterior sex combs (PSC), a subunit of dPCC, inhibits chromatin remodeling and transcription efficiently but requires assembly with dRING1 to recruit chromatin [4].
• One subunit, PSC, can also inhibit chromatin remodeling on its own [5].

Biological context of Psc

• There is an excellent correlation between the in vivo phenotypes of mutant Psc alleles and the structure and in vitro activities of the corresponding proteins, suggesting that the in vitro activities of PRC1 reflect essential functions of Psc in vivo [6].
• We have analyzed the domains required for the association of Psc with ph and Pc by using the yeast two-hybrid system and an in vitro protein-binding assay [7].
• We find evidence for transformations along both the anterior-posterior and dorsal-ventral axes in embryos of a variety of genotypes that include a null mutation in Psc [8].
• On polytene chromosomes, we find Psc at 45 chromosomal loci where two other Pc-G proteins are present [9].
• There exist suppressor and enhancer mutations that modify the z1 eye color, and this paper summarizes our studies of those belonging to the Suppressor 2 of zeste complex [Su(z)2-C] [10].

Anatomical context of Psc

• We have examined mutant embryos derived from a mutant maternal germ line and found a stronger mutant phenotype, indicating that the weak zygotic phenotype of Psc is due to maternal rescue [9].
• We have found that Psc RNA accumulates in developing oocytes and this maternal RNA is presumably responsible for the maternal rescue [9].
• Antibody staining of salivary gland polytene chromosomes showed that after heat shock induction of hs-Psc, Psc protein binds ectopically to hundreds of polytene chromosome loci [11].
• Immunocytochemistry localized both Pc1 and Psc1 protein in blastomere nuclei [12].

Physical interactions of Psc

• We show that ph and Psc coprecipitate with Pc from nuclear extracts [7].

Other interactions of Psc

• The Drosophila polycomb group protein Psc contacts ph and Pc through specific conserved domains [7].
• Finally, we show that the CCF protein binds to specific sites on polytene chromosomes, many of which are shared with the Posterior sex combs Pc-G protein [13].
• Furthermore, Polyhomeotic and Posterior Sex Combs are also associated with expressed genes [14].
• Severe defects in sister chromatid segregation and nuclear fallout, but not condensation are exhibited by Polycomb, Posterior sex combs and Additional sex combs [15].

Analytical, diagnostic and therapeutic context of Psc

• On northern blots, we find evidence for two Psc mRNAs and, on western blots, we find evidence for two Psc proteins that are altered either in abundance or size in Psc mutants [9].

References