The prevalence of mRNAs coding for the sea urchin embryo regulatory factors P3A1 and P3A2 was measured by single-strand probe excess solution hybridization. P3A1 and P3A2 are not homologous proteins, though they both bind specifically to a particular cis-regulatory sequence. Interaction at this target site is known to be required for lineage-specific expression of an aboral ectoderm-specific gene and probably for several other genes as well. Genome blot hybridizations show that both factors are encoded by single-copy genes. Maternal mRNAs for both factors are present at less than 10(3) molecules per egg, which places them in the rare mRNA class. During development to the mesenchyme blastula stage, the amount of P3A1 mRNA (per embryo) increases severalfold while that of P3A2 remains approximately constant. Specification of the aboral ectoderm founder cells and of their initial patterns of gene expression must occur during early to mid-cleavage stage. Therefore, the regulatory proteins needed for this process must be produced by this stage. We show that the quantities of the P3A proteins that can be synthesized from the numbers of mRNA molecules present in the large blastomeres of the early embryo are sufficient to be functional, because these proteins will be accumulated in the nuclei. Thus maternal P3A1 or P3A2 proteins asre not required, nor were these detected in earlier studies. Furthermore, differential spatial (as well as temporal) distribution of both of these newly synthesized factor species could result from the unequal cleavage pattern utilized in the sea urchin egg.

译文

:通过单链探针过量溶液杂交测量编码海胆胚胎调节因子P3A1和P3A2的mRNA的发生率。尽管P3A1和P3A2都与特定的顺式调控序列特异性结合,但它们不是同源蛋白。已知该靶标位点的相互作用是特定于宗族的外胚层特异性基因的谱系表达所必需的,并且可能还需要其他几个基因。基因组印迹杂交显示这两个因子均由单拷贝基因编码。每个鸡蛋的母体mRNA均少于10(3)个分子,这使它们处于罕见的mRNA类中。在发育到间充质囊阶段期间,P3A1 mRNA(每个胚胎)的数量增加了几倍,而P3A2的数量则保持大致恒定。胎盘外胚层基础细胞及其基因表达的初始模式的规范必须在卵裂早期至中期进行。因此,必须在该阶段生产该过程所需的调节蛋白。我们表明,可以从早期胚胎的大型卵裂球中存在的mRNA分子数量合成的P3A蛋白数量足以发挥功能,因为这些蛋白将积聚在细胞核中。因此,不需要母体P3A1或P3A2蛋白,也不需要在早期研究中检测到这些蛋白。此外,这两种新合成的因子物种在空间(以及时间)上的差异分布可能是由于海胆卵中使用的不均等卵裂模式造成的。

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