DBRWD3 抑制 Polycomb Group 突變導致之異位基因表現

Abstract

Epigenetic regulation involves chromatin remodeling, nucleosome assembly, replacement of histone variants and DNA methylation. Histone modification alter the compaction of chromatin, thereby affecting transcription factors binding to gene regions. One of the well-known enzymes that catalyze histone modifications, Polycomb group (PcG) proteins, are reported to write the repressive histone marks, H3K27me3 and H2AK118ub, to keep the targeted gene silenced. On the other hand, the incorporation of histone variants is another regulatory mechanism of epigenetics. In the previous studies, we found that incorporation of histone variants could be regulated negatively. The incorporation of histone 3 variant, H3.3, could be negatively regulated by dBRWD3 (Drosophila Bromodomain and WD repeat domain containing 3) through a HIRA/YEM-dependent pathway. Here, we found when we depleted one of the PcG protein, Pc, in Drosophila larval nervous system, Ubx and Antp, two Hox genes, expressed ectopically (into the brain. Interestingly, this ectopic gene expression could be suppressed by dBRWD3 depletion. dBRWD3 depletion also suppressed the ectopic gene expression caused by the depletion of E(z), encoding the histone methyltransferase that catalyzes the modification of H3K27me3. Moreover, when we depleted the general transcription factors, Cdk7, CycH, TAF5 or TAF7, the ectopic expression of Ubx or Antp was also suppressed. Interestingly, there was no alteration of orthotopic gene expression by dBRWD3 depletion. To dissect the mechanisms underlying the suppression of ectopic gene expression by dBRWD3 depletion. First, we focused on the effect of dBRWD3 on RNA polymerase II. We utilized DamID (DNA adenine methyltransferase identification) to study the frequency of Pol II occupying on the target genes (Ubx, Antp). The results showed that dBRWD3 depletion might maintain Pol II-Dam on promoter and 5' regions of Antp and then affect the initial stage of transcription.. Second, we wondered if the repressive histone mark added by PcGs would be rescued by dBRWD3 depletion. We utilized ChIP of H3K27me3 or H2AK118ub, and found that additional dBRWD3 depletion had no effect on these marks when E(z) or Pc was depleted. In the process to investigate the role of dBRWD3in ectopic gene expression, we unexpectedly provided a new insights into the differences between the ectopic and orthotopic gene expression.