dBRWD3在維持正常表觀遺傳體中的重要性

Abstract

In eukaryotes, DNA is organized into chromatin in a dynamic manner that enables it to be accessed for processes such as DNA repair and transcription. Many factors that control chromatin biology play key roles in essential nuclear functions. These factors belong to four broad classes: histone modifiers, chromatin remodelers, histone variants and histone chaperones. In addition to histone modifiers with enzymatic activities, co-modifiers could interpret the histone modification codes and trigger subsequent changes of chromatin configurations, helping cells to response to stimuli and function accordingly. Based on how they recognize histone codes, these indirect histone modifiers are characterized by the modifications-interacting domains such as bromodomain or chromodomain. dBRWD3, a human BRWD3 homologue in Drosophila melanogaster, is characterized by its N-terminal WD40 repeats and two C-terminal bromodomains, which imply dBRWD3 as a probable indirect histone modifier via binding to acetylated histone. Mutations in human BRWD3 cause X-linked mental retardation, suggesting an essential role of BRWD3 in the nervous system. We therefore hypothesize that dBRWD3 regulates gene expression. To better address this possibility, the difference of whole gene expression between the wild-type and the dBRWD3 hypomorphic mutant flies, we conducted genome wide RNA-Sequencing (RNA-seq) using RNA isolated from adult brains of wild-type flies and dBRWD3 trans-heterozygous mutant flies. In RNA-seq analysis, we identified numbers of differential expression genes (DEGs) that are directly or indirectly modulated by dBRWD3. Chromatin states analysis shows that these putative dBRWD3 target genes have a propensity to localize in transcriptionally silent intergeneic chromatin regions (state 9) and heterochromatin-like regions embedded in euchromatin (state 8). Chromatin immunoprecipitation (ChIP) reveals that the dysregulation of gene expression in dBRWD3 mutant flies may be due to the loss of repressive histone marks or loss of H3.3 occupancy at transcription start site in up-regulated DEGs or down-regulated DEGs, respectively. Thus, dBRWD3 may act as a histone reader that regulates histone modification and deposition on chromatin to maintain normal chromatin status and timely gene expression.