Stem-loop binding protein accumulates during oocyte maturation and is not cell-cycle-regulated in the early mouse embryo
Stem-loop binding protein accumulates during oocyte maturation and is not cell-cycle-regulated in the early mouse embryo
复制标题
DOI：
10.1242/jcs.00132
复制
发表时间：
2002-12-01
影响因子：
4
通讯作者：
Clarke, HJ
中科院分区：
文献类型：
--
作者：
Allard, P;Champigny, MJ;Clarke, HJ
茎环结合蛋白 (SLBP) 与组蛋白 mRNA 的 3' 端结合并参与新合成转录物的 3' 加工，从而保护它们免遭降解，并且可能还促进它们的翻译。在增殖细胞中，SLBP mRNA 的翻译从 G1/S 开始，蛋白质在 DNA 复制后被降解。这些转录后机制将 SLBP 表达与细胞周期的 S 期紧密结合，并在限制复制依赖性组蛋白合成至 S 期方面发挥关键作用。与体细胞相反，在卵母细胞和早期胚胎中，复制依赖性组蛋白 mRNA 的积累和翻译独立于 DNA 复制。我们在此报道，与体细胞相比，小鼠卵母细胞和早期胚胎中的 SLBP 表达和活性也有所不同。 SLBP 存在于停滞在 G2/M 前期的卵母细胞中，并集中在细胞核中。进入减数分裂成熟的 M 期后，SLBP 开始迅速积累，在停滞于中期 II 的成熟卵母细胞中达到非常高的水平。受精后，SLBP 在整个第一个细胞周期（包括 G1 和 G2 期）的细胞核和细胞质中保持丰富。它在第二和第三个细胞周期期间下降，到4细胞阶段后期达到相对较低的水平。 SLBP 可以在卵母细胞和早期胚胎细胞周期的所有阶段结合组蛋白 mRNA 茎环，并且它是这些细胞中唯一可检测到的茎环结合活性。我们还报道，SLBP 在进入减数分裂成熟的 M 期后通过对 roscovitine（一种细胞周期蛋白依赖性激酶抑制剂）敏感的机制迅速磷酸化。 SLBP 在受精或孤雌激活后迅速去磷酸化，并在有丝分裂的 M 期重新磷酸化。磷酸化不影响其茎环结合活性。这些结果表明，与爪蟾相反，小鼠卵母细胞和胚胎含有单一 SLBP。在卵母细胞和早期胚胎中，SLBP 的表达与 S 期脱钩，这表明在体细胞中强行细胞周期调节 SLBP 表达的机制在卵母细胞或第一个胚胎细胞周期中不起作用。这种独特的 SLBP 表达模式可能是精子染色质重塑和新合成的胚胎 DNA 组装成染色质所需的组蛋白积累所必需的。
The stem-loop binding protein (SLBP) binds to the 3' end of histone mRNA and participates in 3'-processing of the newly synthesized transcripts, which protects them from degradation, and probably also promotes their translation. In proliferating cells, translation of SLBP mRNA begins at G1/S and the protein is degraded following DNA replication. These post-transcriptional mechanisms closely couple SLBP expression to S-phase of the cell cycle, and play a key role in restricting synthesis of replication-dependent histones to S-phase. In contrast to somatic cells, replication-dependent histone mRNAs accumulate and are translated independently of DNA replication in oocytes and early embryos. We report here that SLBP expression and activity also differ in mouse oocytes and early embryos compared with somatic cells. SLBP is present in oocytes that are arrested at prophase of G2/M, where it is concentrated in the nucleus. Upon entry into M-phase of meiotic maturation, SLBP begins to accumulate rapidly, reaching a very high level in mature oocytes arrested at metaphase II. Following fertilization, SLBP remains abundant in the nucleus and the cytoplasm throughout the first cell cycle, including both G1 and G2 phases. It declines during the second and third cell cycles, reaching a relatively low level by the late 4-cell stage. SLBP can bind the histone mRNA-stem-loop at all stages of the cell cycle in oocytes and early embryos, and it is the only stem-loop binding activity detectable in these cells. We also report that SLBP becomes phosphorylated rapidly following entry into M-phase of meiotic maturation through a mechanism that is sensitive to roscovitine, an inhibitor of cyclindependent kinases. SLBP is rapidly dephosphorylated following fertilization or parthenogenetic activation, and becomes newly phosphorylated at M-phase of mitosis. Phosphorylation does not affect its stem-loop binding activity. These results establish that, in contrast to Xenopus, mouse oocytes and embryos contain a single SLBP. Expression of SLBP is uncoupled from S-phase in oocytes and early embryos, which indicates that the mechanisms that impose cell-cycle-regulated expression of SLBP in somatic cells do not operate in oocytes or during the first embryonic cell cycle. This distinctive pattern of SLBP expression may be required for accumulation of histone proteins required for sperm chromatin remodelling and assembly of newly synthesized embryonic DNA into chromatin.