Meyer Wibke J, Schreiber Silke, Guo Yi, Volkmann Thorsten, Welte Michael A, Müller H Arno J
Institut für Genetik, Heinrich-Heine Universität, Düsseldorf, Germany.
PLoS Genet. 2006 Aug 25;2(8):e134. doi: 10.1371/journal.pgen.0020134. Epub 2006 Jul 13.
Argonaute proteins are essential components of the molecular machinery that drives RNA silencing. In Drosophila, different members of the Argonaute family of proteins have been assigned to distinct RNA silencing pathways. While Ago1 is required for microRNA function, Ago2 is a crucial component of the RNA-induced silencing complex in siRNA-triggered RNA interference. Drosophila Ago2 contains an unusual amino-terminus with two types of imperfect glutamine-rich repeats (GRRs) of unknown function. Here we show that the GRRs of Ago2 are essential for the normal function of the protein. Alleles with reduced numbers of GRRs cause specific disruptions in two morphogenetic processes associated with the midblastula transition: membrane growth and microtubule-based organelle transport. These defects do not appear to result from disruption of siRNA-dependent processes but rather suggest an interference of the mutant Ago2 proteins in an Ago1-dependent pathway. Using loss-of-function alleles, we further demonstrate that Ago1 and Ago2 act in a partially redundant manner to control the expression of the segment-polarity gene wingless in the early embryo. Our findings argue against a strict separation of Ago1 and Ago2 functions and suggest that these proteins act in concert to control key steps of the midblastula transition and of segmental patterning.
AGO蛋白是驱动RNA沉默的分子机制的重要组成部分。在果蝇中，AGO蛋白家族的不同成员已被分配到不同的RNA沉默途径。虽然AGO1是miRNA功能所必需的，但AGO2是在siRNA触发的RNA干扰中RNA诱导沉默复合体的关键组成部分。果蝇AGO2含有一个不寻常的氨基末端，带有两种功能未知的不完全富含谷氨酰胺的重复序列（GRR）。在这里，我们表明AGO2的GRR对该蛋白的正常功能至关重要。GRR数量减少的等位基因会在与囊胚中期转换相关的两个形态发生过程中引起特异性破坏：膜生长和基于微管的细胞器运输。这些缺陷似乎不是由siRNA依赖过程的破坏引起的，而是表明突变的AGO2蛋白干扰了AGO1依赖的途径。使用功能缺失等位基因，我们进一步证明AGO1和AGO2以部分冗余的方式发挥作用，以控制早期胚胎中节段极性基因无翅基因的表达。我们的发现反对AGO1和AGO2功能的严格分离，并表明这些蛋白协同作用以控制囊胚中期转换和节段模式形成的关键步骤。
