4月22日，科技期刊《生殖生物学》（Biology of Reproduction）以“Histone H2A Has a Novel Variant in Fish Oocytes”为题在线发表了中科院水生生物所淡水生态与生物技术国家重点实验室桂建芳研究组的研究成果。
桂建芳研究组以银鲫为材料，在鱼类卵母细胞中发现了一种新的核心组蛋白H2A变体。他们在筛选到一个卵母细胞核心组蛋白H2A变体cDNA的基础上，首先分析确定了其卵母细胞特异表达的模式，接着观察到该蛋白在卵子发生过程中的磷酸化修饰作用。由于它是一个卵母细胞特异的H2A新变体，该变体基因被定名为h2af1o (H2A histone family, member 1, oocyte specific)。为了解这个新变体在核小体中的结合动力学特征，他们还从银鲫中克隆出另一个遍在的h2afx，并进一步采用体外过表达和FRAP实验方法比较分析了这两个组蛋白在染色质中的动态交换差异。有意思的是，H2af1o在核小体中比遍在的H2afx有更高的运动性，并且，与遍在的H2afx相比，H2af1o有更紧结合的C端和更弱结合的N端。这些结果表明，鱼类卵母细胞中有一个新的H2A变体，其更为游离的N端可能提供了更多的修饰位点，并能轻微降低核小体的稳定性，而其紧密结合的C端保证了核小体的中心区域的稳定。这些发现意味着H2af1o可能在鱼类卵子发生、卵母细胞成熟和早期卵裂中有改变染色质特性的能力。
该研究得到国家基础研究973计划等项目的资助，主要由博士研究生吴南等完成。据论文通讯作者桂建芳研究员介绍，组蛋白是核小体的重要成分，在基因表达模式的传输和核小体运动性的表观遗传调节中起了重要作用；组蛋白也存在许多变体，且这些变体在特定的细胞或特定的细胞周期阶段发挥了至关重要的转录调控作用。由于卵母细胞是高度特化的细胞，过去虽找到了一些卵母细胞特异的连接组蛋白，但迄今还未鉴定出卵母细胞特异的核心组蛋白。因此，这一新的鱼类卵母细胞特异的核心组蛋白H2A变体的发现对进一步研究鱼类卵子发生和卵母细胞成熟过程中的调控机制有重要意义。（生物谷Bioon.com）
生物谷推荐原始出处：
Biology of Reproduction，doi：10.1095/biolreprod.108.074955，Nan Wu，Jian-Fang Gui
Histone H2A Has a Novel Variant in Fish Oocytes
Nan Wu , Hua-Mei Yue , Bo Chen , and Jian-Fang Gui *
Abstract
Histone variants and their modifications play significant roles in many cellular processes. In this study, we have identified and characterized a histone H2A variant h2af1o in fish, and revealed its oocyte-specific expression pattern during oogenesis and embryogenesis. Moreover, a post-translational modification of H2af1o was observed, and the modification was demonstrated to result from the phosphorylation during oocyte maturation. To understand the binding dynamics of the novel core histone variant H2af1o in nucleosomes, we cloned another ubiquitous gibel carp h2afx as the conventional histone control, and investigated the dynamic exchange difference in chromatin by fluorescence recovery after photobleaching (FRAP). Significantly, H2af1o was revealed to confer relatively higher mobility in nucleosomes than that of ubiquitous H2afx. And, in comparison with ubiquitous H2afx, H2af1o has a tightly binding C terminus and a weak binding N terminus. The current data indicate that fish oocytes have a novel H2A variant that slightly destabilizes nucleosomes by protruding its N-terminal tail to a large extent, and stabilizes core particle by its tightly binding C-terminal tail. Our findings suggest that H2af1o might have the intrinsic ability to modify chromatin properties during fish oogenesis, oocyte maturation and early cleavage.
