Eukaryotic Chromatin Structure and Gene Regulation

我们的团队继续研究染色质结构和真核生物基因表达的调控。我们在了解果蝇核小体重塑因子（NURF）对atp依赖性染色质重塑的机制方面取得了重大进展。为了阐明nurf诱导核小体滑动的生物学意义，我们分离并广泛表征了果蝇nurf301的突变。我们证实，NURF是多种对体内发育和细胞信号传导重要的基因转录调控所必需的。值得注意的是，NURF亚基的突变体表现出幼虫血细胞的肿瘤转化，诱导黑色素瘤的形成。这些结果表明，NURF不仅是参与应激反应和发育的基因的适当调控所必需的，而且也是肿瘤抑制所必需的。我们已经将这种疾病的表型追溯到JAK-STAT信号通路的失调，并正在对受影响的靶基因进行分子分析。INO80和SWR1复合物的研究也取得了很好的进展，它们是染色质重塑酶SWI2/SNF2超家族的新成员。我们进行了遗传和生化实验来阐明复合物的机制和生理功能。INO80复合物含有一定量的肌动蛋白和三种肌动蛋白相关蛋白（Arp4、Arp5和Arp8）。Arp4和肌动蛋白对细胞存活至关重要，但Arp5和Arp8零突变体的生存能力使我们能够进一步研究它们的功能作用。我们通过对零突变体的生化分析，揭示了Arp5和Arp8在染色质重塑中的功能。此外，酵母SWR1复合物已被发现催化组蛋白H2AZ变体的交换。鉴于组蛋白变异与染色质结合的机制至今仍不清楚，我们的发现极大地改变了人们对染色质重塑酶的认识，并为未来的研究提供了令人兴奋的新途径。

Our group has continued studies of chromatin structure and the regulation of eukaryotic gene expression. We have made significant progress towards understanding the mechanism of ATP-dependent chromatin remodeling by Drosophila NURF (Nucleosome Remodeling Factor). To elucidate the biological significance of NURF-induced nucleosome sliding, we have isolated and extensively characterized mutations for Drosophila nurf301. We confirm that NURF is required for transcriptional regulation of a variety of genes important for development and cell signalling in vivo. Stikingly, mutants in NURF subunits exhibit neoplastic transformation of larval blood cells that induces melanotic tumor formation. These results reveal that NURF is required not only for proper regulation of genes involved in the stress response and development, but also for tumor suppression. We have traced this disease phenotype to a dysregulation of the JAK-STAT signalling pathway, and are conducting a molecular analysis of the affected target genes. We are also making excellent progress on studies of INO80 and SWR1 complexes, which are new members of the SWI2/SNF2 superfamily of chromatin remodeling enzymes. We have conducted genetic and biochemical experiments to elucidate the mechanism and physiological functions of the complexes. The INO80 complex contains stoichiometric amounts of actin and three actin related proteins (Arp4, Arp5, and Arp8). Arp4 and actin are essential for cell survival, but the viability of null mutants for Arp5 and Arp8 allowed us to further investigate their functional roles. We uncovered functions of Arp5 and Arp8 in chromatin remodeling by biochemical analysis of the null mutants. Moreover, the yeast SWR1 complex has been found to catalzye the exchange of the histone H2AZ variant. Given that the mechanism of incorporation of histone variants into chromatin has been obscure until now, our findings have dramatically changed perceptions of chromatin remodeling enzymes, and have provided an exciting new avenue for future investigations.