Mechanism of Polycomb Group Gene Silencing
- Y. ZHANG,
- R. CAO,
- L. WANG, and
- R.S. JONES
This extract was created in the absence of an abstract.
Excerpt
The Drosophila trithorax-group (trxG) and Polycombgroup (PcG) proteins function in an antagonistic mannerto maintain the transcriptionally active and silence statesof target genes, respectively. Although they regulate numerous genes, mutant alleles of most trxG and PcG geneswere first identified on the basis of homeotic phenotypesresulting from misexpression of Hox genes of the Antennapedia and bithorax gene complexes. Drosophila Hoxgenes, which encode transcription factors that regulatenumerous downstream genes, must be continuously expressed in appropriate patterns throughout embryonic andlarval development in order to assign segmental identitiesto cells along the anterior–posterior body axis. The expression patterns of the Hox genes are initially established in early embryos by activators and repressors encoded by gap and pair rule genes, but soon after Hox geneexpression is initiated, these activators and repressors decay. It is during this window of time that trxG and PcGproteins somehow recognize the transcriptionally activeor repressed states of Hox genes and become responsiblefor maintaining their expression states in cell lineagesthroughout embryonic and larval development. Thus,trxG and PcG proteins serve as molecular memory systems central to the process of cellular determination(Francis and Kingston 2001; Simon and Tamkun 2002)...
