Luk S K, Kilpatrick M, Kerr K, Macdonald P M
Department of Biological Sciences, Stanford University, California 94305-5020.
Genetics. 1994 Jun;137(2):521-30. doi: 10.1093/genetics/137.2.521.
Substantial insights into basic strategies for embryonic body patterning have been obtained from genetic analyses of Drosophila melanogaster. This knowledge has been used in evolutionary comparisons to ask if genes and functions are conserved. To begin to ask how highly conserved are the mechanisms of mRNA localization, a process crucial to Drosophila body patterning, we have focused on the localization of bcd mRNA to the anterior pole of the embryo. Here we consider two components involved in that process: the exuperantia (exu) gene, required for an early step in localization; and the cis-acting signal that directs bcd mRNA localization. First, we use the cloned D. melanogaster exu gene to identify the exu genes from Drosophila virilis and Drosophila pseudoobscura and to isolate them for comparisons at the structural and functional levels. Surprisingly, D. pseudoobscura has two closely related exu genes, while D. melanogaster and D. virilis have only one each. When expressed in D. melanogaster ovaries, the D. virilis exu gene and one of the D. pseudoobscura exu genes can substitute for the endogenous exu gene in supporting localization of bcd mRNA, demonstrating that function is conserved. Second, we reevaluate the ability of the D. pseudoobscura bcd mRNA localization signal to function in D. melanogaster. In contrast to a previous report, we find that function is retained. Thus, among these Drosophila species there is substantial conservation of components acting in mRNA localization, and presumably the mechanisms underlying this process.
通过对黑腹果蝇的遗传分析，我们已经获得了关于胚胎体模式形成基本策略的大量见解。这些知识已被用于进化比较，以探究基因和功能是否保守。为了开始研究mRNA定位机制（这对果蝇体模式形成至关重要）的保守程度有多高，我们聚焦于bcd mRNA定位于胚胎前极的过程。在此，我们考虑该过程中涉及的两个成分：定位早期步骤所需的exuperantia（exu）基因；以及指导bcd mRNA定位的顺式作用信号。首先，我们使用克隆的黑腹果蝇exu基因来鉴定果蝇 virilis和果蝇pseudoobscura的exu基因，并将它们分离出来进行结构和功能层面的比较。令人惊讶的是，果蝇pseudoobscura有两个密切相关的exu基因，而黑腹果蝇和果蝇virilis各只有一个。当在黑腹果蝇卵巢中表达时，果蝇virilis的exu基因和果蝇pseudoobscura的一个exu基因可以替代内源性exu基因来支持bcd mRNA的定位，这表明功能是保守的。其次，我们重新评估了果蝇pseudoobscura的bcd mRNA定位信号在黑腹果蝇中发挥作用的能力。与之前的一份报告相反，我们发现其功能得以保留。因此，在这些果蝇物种中，参与mRNA定位的成分以及推测该过程的潜在机制都有很大程度的保守性。
