Macdonald P M, Struhl G
Howard Hughes Medical Institute, Columbia University College of Physicians and Surgeons, New York, N.Y. 10032.
Nature. 1988 Dec 8;336(6199):595-8. doi: 10.1038/336595a0.
The anterior body pattern of Drosophila melanogaster is specified in large part by the protein product of the bicoid (bcd) gene which functions as a graded morphogen with its peak of expression at the anterior pole of the embryo. Formation of the gradient is dependent on prior localization of bcd messenger RNA at the anterior pole of the egg cell during oogenesis. Here we demonstrate that a discrete portion of the bcd mRNA is necessary for anterior localization of the bcd transcript and is sufficient to cause localization of heterologous transcripts. The sequences responsible for localization appear to span an interval of about 625 base pairs in the 3' untranslated portion of the bcd mRNA and to include regions capable of forming extensive secondary structure. Transcripts from bcd are synthesized predominantly, if not exclusively, in the nurse cells and then transported to the oocyte by connections at the prospective anterior pole. Our findings support the proposal that bcd transcripts are selectively recognized and trapped as they enter the anterior tip of the oocyte, and suggest that this localization process is mediated by anchored sequence-specific receptors in the oocyte cytoplasm.
黑腹果蝇的前体模式很大程度上由双尾（bcd）基因的蛋白质产物所决定，该蛋白质作为一种梯度形态发生素，在胚胎的前极表达量达到峰值。这种梯度的形成依赖于在卵子发生过程中bcd信使核糖核酸（mRNA）预先定位于卵细胞的前极。在这里，我们证明bcd mRNA的一个离散部分对于bcd转录本的前位定位是必需的，并且足以导致异源转录本的定位。负责定位的序列似乎在bcd mRNA的3'非翻译部分跨越约625个碱基对的区间，并且包括能够形成广泛二级结构的区域。bcd的转录本主要（如果不是唯一的话）在滋养细胞中合成，然后通过预期前极处的连接运输到卵母细胞。我们的发现支持这样的提议，即bcd转录本在进入卵母细胞的前尖端时被选择性识别和捕获，并表明这种定位过程是由卵母细胞细胞质中锚定的序列特异性受体介导的。
