Stauber Michael, Lemke Steffen, Schmidt-Ott Urs
Max-Planck-Institut für Biophysikalische Chemie, Abt. Molekulare Entwicklungsbiologie, Am Fassberg 11, 37077, Göttingen, Germany.
Dev Genes Evol. 2008 Feb;218(2):81-7. doi: 10.1007/s00427-008-0204-5. Epub 2008 Jan 24.
The homeobox gene caudal (cad) regulates posterior development in Drosophila. In early embryos, the cad protein (CAD) is expressed in a posterior-to-anterior concentration gradient, which contributes polarity to the developing embryo. The CAD gradient is complementary to and dependent on the anterior pattern organizer Bicoid (BCD), which represses the translation of ubiquitous maternal cad transcripts in the anterior embryo through a direct interaction with the cad 3' untranslated region (UTR). Here, we show that early embryos of the lower cyclorrhaphan fly Megaselia express the putative cad orthologue Mab-cad throughout the posterior three quarters of the blastoderm but lack maternal transcripts. In transgenic blastoderm embryos of Drosophila, Mab-cad cis-regulatory DNA drives the expression of a reporter gene in a similar pattern, while Mab-cad 3' UTR fails to mediate translational repression of a ubiquitously transcribed reporter. For another lower cyclorrhaphan fly (Lonchoptera) and two related outgroup taxa of Cyclorrhapha (Empis, Haematopota), we report maternal cad expression in ovarian follicles. Together, our results suggest that BCD is not required for the translational repression of Mab-cad, and that maternal cad expression was lost in the Megaselia lineage.
同源异型框基因尾端（cad）调控果蝇的后部发育。在早期胚胎中，cad蛋白（CAD）以从后到前的浓度梯度表达，这为发育中的胚胎赋予了极性。CAD梯度与前部模式组织者双尾（BCD）互补且依赖于它，BCD通过与cad 3'非翻译区（UTR）直接相互作用，抑制前部胚胎中普遍存在的母体cad转录本的翻译。在此，我们表明，低等环裂蝇大跗蝇的早期胚胎在胚盘的后四分之三区域均表达推定的cad直系同源基因Mab-cad，但缺乏母体转录本。在果蝇的转基因胚盘胚胎中，Mab-cad顺式调控DNA以类似模式驱动报告基因的表达，而Mab-cad 3'UTR未能介导对普遍转录的报告基因的翻译抑制。对于另一种低等环裂蝇（长角蝇）以及环裂蝇的两个相关外类群分类单元（长足虻、角虻），我们报告了卵巢卵泡中母体cad的表达。总之，我们的结果表明，Mab-cad的翻译抑制不需要BCD，并且在大跗蝇谱系中母体cad的表达已经丧失。
