Worrad D M, Schultz R M
Department of Biology, University of Pennsylvania, Philadelphia 19104-6018, USA.
Mol Reprod Dev. 1997 Mar;46(3):268-77. doi: 10.1002/(SICI)1098-2795(199703)46:3<268::AID-MRD5>3.0.CO;2-N.
Activation of the embryonic genome during preimplantation mouse development entails a dramatic reprogramming of the pattern of gene expression. The complement of transcription factors that are present in the early embryo and that must intrinsically be involved in this reprogramming is essentially uncharacterized. We and others have demonstrated that transcription factor Sp1 is present in the mouse oocyte and early cleavage stage preimplantation embryo. Due to Sp1's prominent role in regulating the expression of a vast array of genes that are involved in cell proliferation and differentiation, as well as in general housekeeping functions, we characterized the temporal and spatial patterns of Sp1 expression during preimplantation development. The relative abundance of Sp1 transcripts, as well as transcripts for the TATA box-binding protein TBP, decreases during oocyte maturation and reaches a minimum level in the two-cell stage, after which time the abundance of these transcripts increases progressively to the blastocyst stage. Immunoblotting experiments detect Sp1 species of Mr = 95,000 and 105,000 at all stages of preimplantation development. The amount of Sp1 increases about 8-fold during preimplantation development, and an alpha-amanitin-insensitive increase is observed between G1 and G2 of the one-cell embryo; this increase may reflect the mobilization of a maternal Sp1 transcript. Immunocytochemical experiments also reveal a similar increase in the amount of Sp1 during preimplantation; the nuclear concentration of Sp1 is greater in the trophectoderm cells than in the inner cell mass cells. Finally, gel-shift experiments document an increase during preimplantation development of a DNA-binding activity that is likely due to Sp1. These increases in the abundance of the Sp1 protein and an Sp1-like DNA-binding activity parallel increases in the rate of transcription that occur during preimplantation development.
在小鼠植入前发育过程中，胚胎基因组的激活需要对基因表达模式进行剧烈的重编程。早期胚胎中存在的、必然内在地参与这种重编程的转录因子组成基本上尚未明确。我们和其他人已经证明转录因子Sp1存在于小鼠卵母细胞和早期卵裂阶段的植入前胚胎中。由于Sp1在调节大量参与细胞增殖和分化以及一般管家功能的基因表达中起着重要作用，我们对植入前发育过程中Sp1表达的时空模式进行了表征。Sp1转录本以及TATA盒结合蛋白TBP转录本的相对丰度在卵母细胞成熟过程中降低，并在二细胞阶段达到最低水平，此后这些转录本的丰度逐渐增加至囊胚阶段。免疫印迹实验在植入前发育的所有阶段都检测到分子量为95,000和105,000的Sp1蛋白。在植入前发育过程中，Sp1的量增加了约8倍，并且在单细胞胚胎的G1和G2之间观察到对α-鹅膏蕈碱不敏感的增加；这种增加可能反映了母体Sp1转录本的动员。免疫细胞化学实验也揭示了植入前Sp1量的类似增加；滋养外胚层细胞中Sp1的核浓度高于内细胞团细胞。最后，凝胶迁移实验证明在植入前发育过程中一种可能归因于Sp1的DNA结合活性增加。Sp1蛋白丰度和类似Sp1的DNA结合活性的这些增加与植入前发育过程中发生的转录速率增加平行。
