| Research Abstract |
To address molecular mechanisms underlying Polycomb group (PcG) -mediated repression of Hox gene expression, we have focused on how PcG proteins, Rnf2 (Ring1B), Edr1 (Rae28/Mph1), Ring1 (Ring1A) and Cbx2 (M33), and histone H3 acetylated on lysine 9 (H3K9) bind to flanking regions of the Hoxb8 gene. In 12.5 dpc embryos, association of Rnf2 to known Hoxb8 cis-acting regulatory elements was found predominantly in anterior embryonic tissues where transcription of this Hox gene is silent, whereas the presence of Edr1 and Cbx2 was observed irrespective of Hox transcriptional states. Conversely, acetylation of H3K9 at Hoxb8 was found in caudally increasing amounts in embryos, corresponding with the distribution of transcriptional activity. These results, and the developmental profile of Rnf2 association and H3K9 acetylation across the Hoxb cluster, suggest that inversely graded amounts of Rnf2-containing PcG complex and acetylated H3K9, may be involved in maintaining the anterior boundaries of Hox gene expression.
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