Becker Matthias, Becker Antje, Miyara Faiçal, Han Zhiming, Kihara Maki, Brown David T, Hager Gordon L, Latham Keith, Adashi Eli Y, Misteli Tom
National Cancer Institute, National Institutes of Health, Bethesda, MD 20892, USA.
Mol Biol Cell. 2005 Aug;16(8):3887-95. doi: 10.1091/mbc.e05-04-0350. Epub 2005 Jun 8.
The embryonic genome is formed by fusion of a maternal and a paternal genome. To accommodate the resulting diploid genome in the fertilized oocyte dramatic global genome reorganizations must occur. The higher order structure of chromatin in vivo is critically dependent on architectural chromatin proteins, with the family of linker histone proteins among the most critical structural determinants. Although somatic cells contain numerous linker histone variants, only one, H1FOO, is present in mouse oocytes. Upon fertilization H1FOO rapidly populates the introduced paternal genome and replaces sperm-specific histone-like proteins. The same dynamic replacement occurs upon introduction of a nucleus during somatic cell nuclear transfer. To understand the molecular basis of this dynamic histone replacement process, we compared the localization and binding dynamics of somatic H1 and oocyte-specific H1FOO and identified the molecular determinants of binding to either oocyte or somatic chromatin in living cells. We find that although both histones associate readily with chromatin in nuclei of somatic cells, only H1FOO is capable of correct chromatin association in the germinal vesicle stage oocyte nuclei. This specificity is generated by the N-terminal and globular domains of H1FOO. Measurement of in vivo binding properties of the H1 variants suggest that H1FOO binds chromatin more tightly than somatic linker histones. We provide evidence that both the binding properties of linker histones as well as additional, active processes contribute to the replacement of somatic histones with H1FOO during nuclear transfer. These results provide the first mechanistic insights into the crucial step of linker histone replacement as it occurs during fertilization and somatic cell nuclear transfer.
胚胎基因组由母本基因组和父本基因组融合而成。为了在受精卵中容纳由此产生的二倍体基因组，必须发生剧烈的全基因组重组。体内染色质的高级结构严重依赖于染色质结构蛋白，其中连接组蛋白家族是最关键的结构决定因素之一。虽然体细胞含有多种连接组蛋白变体，但小鼠卵母细胞中仅存在一种，即H1FOO。受精后，H1FOO迅速占据引入的父本基因组，并取代精子特异性组蛋白样蛋白。在体细胞核移植过程中引入细胞核时也会发生同样的动态替换。为了理解这种动态组蛋白替换过程的分子基础，我们比较了体细胞H1和卵母细胞特异性H1FOO的定位和结合动力学，并确定了在活细胞中与卵母细胞或体细胞染色质结合的分子决定因素。我们发现，虽然这两种组蛋白都能很容易地与体细胞细胞核中的染色质结合，但只有H1FOO能够在生发泡期卵母细胞核中正确地与染色质结合。这种特异性是由H1FOO的N端和球状结构域产生的。对H1变体体内结合特性的测量表明，H1FOO比体细胞连接组蛋白与染色质的结合更紧密。我们提供的证据表明，连接组蛋白的结合特性以及其他活跃过程都有助于在核移植过程中用H1FOO替换体细胞组蛋白。这些结果为受精和体细胞核移植过程中发生的连接组蛋白替换这一关键步骤提供了首个机制性见解。
