Biology of Polycomb and Trithorax Group Proteins

Transcriptional interference: an unexpected layer of complexity in gene regulation

“…maintenance element that is the binding site for Polycomb and trithorax group (PcG and trxG) proteins that respectively maintain the repressed and activated states of Hox genes in different parasegments (Breiling et al, 2007;Grimaud et al, 2006;Ringrose and Paro, 2007).…”

Does cohesin regulate developmental gene expression in Drosophila ?

“…Reduced dose of Pc (PcϪ/ϩ) and of several other PcG genes leads to ectopic activation of homeotic genes in body segments in which they would normally be silent, leading to morphological transformations. For example, ''sex combs'' (patches of long, thick bristles) are present on the first tarsal segment of all six legs in Pc 4 /ϩ males, instead of on just the anteriormost pair of legs, as in wild-type males (11)(12)(13).…”

“…Their findings indicate that mutations in the gene encoding the Rad21 cohesin subunit interact with mutations in hedgehog (hh), a signal-transduction gene with multiple developmental roles (10), and in Polycomb (Pc), which encodes a component of a chromatin complex responsible for silencing expression of multiple homeotic genes during development. These phenotypes are characteristic of mutations in trithorax-group (trxG) genes, which encode a diverse group of chromatin proteins required to counteract Polycomb group (PcG)-mediated silencing and maintain appropriate expression of several genes important for proper identity of Drosophila segments and other developmental processes (11)(12)(13). Thus, the findings of Hallson et al (9) suggest that cohesin may play a fundamental role in developmental gene regulation in addition to its established role in chromosome segregation.…”

Molecular Genetic Analysis of Suppressor 2 of zeste Identifies Key Functional Domains

“…It stands in stark contrast to Psc, which has been the focus of extensive genetic, molecular, and biochemical analyses for many years. Psc is a member of the Polycomb group (PcG) of genes, many of which function at the level of chromatin as part of at least two PcG repressive complexes, called PRC1 and PRC2 (reviewed by Brock and Fisher 2005;Breiling et al 2007;Schuettengruber et al 2007;Pirrotta 2007, 2008;MateosLangerak and Cavalli 2008). PRC2 contains the Enhancer of zeste [E(z)] protein, which provides a histone methyltransferase activity that methylates histone H3 on lysine 27 (reviewed by Cao and Zhang 2004).…”

“…For example, Psc and Su(z)2 alleles differ with respect to their lethal phases and cuticular phenotypes ( Jü rgens 1985; Adler et al 1989Adler et al , 1991Wu and Howe 1995) as well as with respect to their interactions with trithorax group genes, which act in opposition to PcG genes (reviewed by Brock and Fisher 2005;Breiling et al 2007;Schuettengruber et al 2007;Pirrotta 2007, 2008). Given the structural similarities and partial functional redundancy between Psc and Su(z)2, these differences suggest that Su(z)2 has roles beyond those associated with prototypical PcG genes.…”