Department of Molecular Biosciences, The University of Texas at Austin, Austin, Texas, United States of America.
Department of Molecular Genetics, University of Toronto, Toronto, Canada.
PLoS Genet. 2021 Apr 2;17(4):e1009500. doi: 10.1371/journal.pgen.1009500. eCollection 2021 Apr.
Localization of oskar mRNA includes two distinct phases: transport from nurse cells to the oocyte, a process typically accompanied by cortical anchoring in the oocyte, followed by posterior localization within the oocyte. Signals within the oskar 3' UTR directing transport are individually weak, a feature previously hypothesized to facilitate exchange between the different localization machineries. We show that alteration of the SL2a stem-loop structure containing the oskar transport and anchoring signal (TAS) removes an inhibitory effect such that in vitro binding by the RNA transport factor, Egalitarian, is elevated as is in vivo transport from the nurse cells into the oocyte. Cortical anchoring within the oocyte is also enhanced, interfering with posterior localization. We also show that mutation of Staufen recognized structures (SRSs), predicted binding sites for Staufen, disrupts posterior localization of oskar mRNA just as in staufen mutants. Two SRSs in SL2a, one overlapping the Egalitarian binding site, are inferred to mediate Staufen-dependent inhibition of TAS anchoring activity, thereby promoting posterior localization. The other three SRSs in the oskar 3' UTR are also required for posterior localization, including two located distant from any known transport signal. Staufen, thus, plays multiple roles in localization of oskar mRNA.
osk 基因 mRNA 的定位包括两个明显的阶段：从滋养细胞到卵母细胞的运输，这一过程通常伴随着卵母细胞中的皮质锚定，随后在卵母细胞内进行后定位。指导运输的osk 基因 3'UTR 内的信号各自较弱，这一特征先前被假设为促进不同定位机制之间的交换。我们表明，改变包含osk 运输和锚定信号（TAS）的 SL2a 茎环结构会消除抑制作用，使得体外由 RNA 运输因子平等主义者的结合增加，体内从滋养细胞到卵母细胞的运输也增加。卵母细胞内的皮质锚定也得到增强，干扰了后定位。我们还表明，Staufen 识别结构（SRSs）的突变，预测了 Staufen 的结合位点，破坏了 oskar mRNA 的后定位，就像在 staufen 突变体中一样。SL2a 中的两个 SRSs，一个与平等主义者结合位点重叠，被推断介导 Staufen 依赖性抑制 TAS 锚定活性，从而促进后定位。osk 基因 3'UTR 中的另外三个 SRSs 也需要后定位，包括两个位于任何已知运输信号都很远的位置。因此，Staufen 在 oskar mRNA 的定位中发挥多种作用。
