TBP Dynamics during Mouse Oocyte Meiotic Maturation and Early Embryo Development

To maintain cell lineage, cells develop a mechanism which can transmit the gene activity information to the daughter cells. In mitosis, TBP (TATA-binding protein), a transcription factor which belongs to TFIID was associated with M phase chromosomes and was proved to be a bookmark for cellular memory. Although previous work showed that TBP was dispensable for mouse oocyte maturation and early embryo development, exogenous TBP protein was detected in the nuclear of oocytes and early embryos. It is still unknown whether exogenous TBP can associate with condensed chromosomes during meiosis and mouse early embryo development. In present study by the injection of GFP-tagged TBP mRNA we for the first time investigated TBP dynamics in mouse early embryos and confirmed its localization pattern in oocytes. The exogenous TBP enriched at germinal vesicle at GV stage but disappeared from the chromosomes after GVBD. Moreover, exogenous TBP was still dispersed from the chromosomes of somatic donor nuclear in oocytes by nuclear transfer (NT), further proving that oocyte has some mechanism to remove TBP. During mouse embryo development, the exogenous TBP was removed from the chromosomes of M phase zygotes, but was found to express weakly at the M phase of 2-cell. Moreover, in the blastocyst TBP was also detected at the M phase chromosomes. Overexpression of TBP caused the failure of oocyte maturation and embryo development. Our results supported the idea that TBP might be a marker for transmitting cellular memory to daughter cells.

为维持细胞谱系稳定，细胞演化出可将基因活性信息传递至子代细胞的机制。在有丝分裂过程中，属于转录因子IID（TFIID）的TATA结合蛋白（TATA-binding protein，TBP）可与M期染色体结合，被证实是细胞记忆的标记因子。尽管既往研究表明TBP对小鼠卵母细胞成熟及早期胚胎发育并非必需，但卵母细胞与早期胚胎细胞核中仍可检测到外源性TBP蛋白。目前尚不清楚外源性TBP能否在减数分裂及小鼠早期胚胎发育过程中与凝聚态染色体结合。本研究通过注射绿色荧光蛋白（GFP）标记的TBP mRNA，首次探究了小鼠早期胚胎中TBP的动态变化，并确认了其在卵母细胞中的定位模式：生发泡（GV）期时，外源性TBP富集于生泡内，而在生发泡破裂（GVBD）后则从染色体上解离消失。此外，通过细胞核移植（NT）将供体体细胞核注入卵母细胞后，外源性TBP仍会从供体染色体上弥散脱离，进一步证实卵母细胞存在清除TBP的调控机制。在小鼠胚胎发育进程中，M期合子的染色体上已无外源性TBP的分布，但在二细胞期M相阶段可检测到TBP的弱表达；囊胚期M期染色体上同样可检测到TBP。过表达TBP会导致卵母细胞成熟与胚胎发育失败。本研究结果支持“TBP可作为将细胞记忆传递给子代细胞的标记因子”这一假说。