Serano T L, Cohen R S
Department of Biochemistry, University of Kansas, Lawrence 66045, USA.
Development. 1995 Nov;121(11):3809-18. doi: 10.1242/dev.121.11.3809.
The establishment of dorsoventral polarity in the Drosophila oocyte and future embryo is dependent on the efficient transport of K10 mRNA from nurse cells into the oocyte. To investigate the cis-requirements of K10 mRNA transport, we used a transgenic fly assay to analyze the expression patterns of a series of K10 deletion variants. Such studies identify a 44 nucleotide sequence within the K10 3' untranslated region that is required and sufficient for K10 mRNA transport and subsequent localization to the oocyte's anterior cortex. An inspection of the 44 nucleotide transport/localization sequence (TLS) reveals a strong potential for the formation of a stem-loop secondary structure. Nucleotide substitutions that interfere with the predicted base-pairing of the TLS block mRNA transport and anterior localization. Conversely, mutations that alter the base composition of the TLS while maintaining predicted base-pairing do not block mRNA transport or anterior localization. We conclude that K10 mRNA transport and anterior localization is mediated by a 44 nucleotide stem-loop structure. A similar putative stem-loop structure is found in the 3' untranslated region of the Drosophila orb mRNA, suggesting that the same factors mediate the transport and anterior localization of both K10 and orb mRNAs. Apart from orb, the K10 TLS is not found in any other localized mRNA, raising the possibility that the transport and localization of other mRNAs, e.g., bicoid, oskar and gurken, are mediated by novel sets of cis- and trans-acting factors. Moreover, we find that the K10 TLS overrides the activity of oskar cis-regulatory elements that mediate the late stage movement of the mRNA to the posterior pole. We propose the existence of a family of cis-regulatory elements that mediate mRNA transport into the oocyte, only some of which are compatible with the elements that mediate late stage movements.
果蝇卵母细胞及未来胚胎中背腹极性的建立依赖于K10 mRNA从滋养细胞向卵母细胞的有效转运。为了研究K10 mRNA转运的顺式需求，我们使用转基因果蝇检测法来分析一系列K10缺失变体的表达模式。此类研究确定了K10 3'非翻译区内一个44个核苷酸的序列，该序列对于K10 mRNA的转运以及随后定位于卵母细胞的前皮质是必需且充分的。对44个核苷酸的转运/定位序列（TLS）进行检查发现，其具有形成茎环二级结构的强大潜力。干扰TLS预测碱基配对的核苷酸替换会阻断mRNA的转运和前定位。相反，改变TLS碱基组成但维持预测碱基配对的突变不会阻断mRNA的转运或前定位。我们得出结论，K10 mRNA的转运和前定位是由一个44个核苷酸的茎环结构介导的。在果蝇orb mRNA的3'非翻译区发现了一个类似的假定茎环结构，这表明相同的因子介导了K10和orb mRNA的转运和前定位。除了orb之外，在任何其他定位的mRNA中都未发现K10 TLS，这增加了其他mRNA（如bicoid、oskar和gurken）的转运和定位由新的顺式和反式作用因子介导的可能性。此外，我们发现K10 TLS会覆盖介导mRNA后期向后极移动的oskar顺式调控元件的活性。我们提出存在一类顺式调控元件，它们介导mRNA向卵母细胞的转运，其中只有一些与介导后期移动的元件兼容。
