<em>Drosophila</em> RISC Component VIG and Its Homolog Vig2 Impact Heterochromatin Formation

Heterochromatin formation plays an important role in gene regulation and the maintenance of genome integrity. Here we present results from a study of the D. melanogaster gene vig, encoding an RNAi complex component and its homolog vig2 (CG11844) that support their involvement in heterochromatin formation and/or maintenance. Protein null mutations vigEP812 and vig2PL470 act as modifiers of Position Effect Variegation (PEV). VIG and Vig2 are present in polytene chromosomes and partially overlap with HP1. Quantitative immunoblots show depletion of HP1 and HP2 (large isoform) in isolated nuclei from the vigEP812 mutant. The vig2PL470 mutant strain demonstrates a decreased level of H3K9me2. Pull-down experiments using antibodies specific to HP1 recovered both VIG and Vig2. The association between HP1 and both VIG and Vig2 proteins depends on an RNA component. The above data and the developmental profiles of the two genes suggest that Vig2 may be involved in heterochromatin targeting and establishment early in development, while VIG may have a role in stabilizing HP1/HP2 chromatin binding during later stages.异染色质（Heterochromatin）的形成在基因调控与基因组完整性维持中发挥着重要作用。本研究针对黑腹果蝇（D. melanogaster）的vig基因（编码RNAi复合物组分）及其同源基因vig2（CG11844）展开分析，实验结果证实二者参与异染色质的形成与维持过程。蛋白无效突变体vigEP812与vig2PL470可作为位置效应花斑（Position Effect Variegation, PEV）的修饰因子。VIG与Vig2蛋白定位于多线染色体，且与异染色质蛋白1（HP1）存在部分共定位。定量免疫印迹实验显示，vigEP812突变体的分离细胞核中，HP1与HP2（大亚型）的表达水平显著下调。vig2PL470突变株的组蛋白H3赖氨酸9二甲基化（H3K9me2）水平明显降低。采用HP1特异性抗体进行的下拉实验可同时富集到VIG与Vig2蛋白。HP1与VIG、Vig2蛋白之间的相互作用依赖于RNA组分。综合上述实验数据与两个基因的发育表达谱，研究提示Vig2可能参与发育早期的异染色质靶向与建立过程，而VIG则可能在发育后期发挥稳定HP1/HP2染色质结合的作用。