| Summary: | 博士 === 國立臺灣大學 === 分子與細胞生物學研究所 === 106 === During oogenesis in the fruit fly (Drosophila melanogaster), oskar mRNA is delivered and localized to the posterior, and thereby also promotes the assembly of germ plasm, which is a specialized cytoplasm for germ-cell formation. Processing bodies (P-bodies) of mRNA are sites that 5’ to 3’ mRNA degradation happens, including the removal of 5’ cap on mRNA and mRNA exonuclease activity. In a previous study, the Drosophila decapping protein 1 (dDcp1) has been found as a component of the oskar messenger ribonucleoprotein (mRNP), directing its posterior localization. In this study, I aimed to the three components of a decapping complex (dDcp1, Drosophila decapping protein 2 (dDcp2) and dGe-1) cooperating with Drosophila moesin (Dmoesin) participates in the transport and anchoring of oskar mRNP in the oocyte.
First, I found that the trimeric complex forming by dDcp1, dDcp2, and dGe-1 stands along the oocyte cortex and is required for the posterior localization of oskar mRNA. Moreover, the presence of dDcp2 plays a critical role in sustaining the cortical localizations of dDcp1 and dGe-1 in oocytes. Second, previous studies point out that microtubule cytoskeleton is responsible for the oskar mRNA transport and F-actin microfilaments facilitate the oskar mRNA anchorage. I found that dDcp2, except the mRNA decapping activity, shows a positive regulation both on the microtubule growth and F-actin proper formation in oocytes. Third, Dmoesin is a crosslinker connecting the membrane and F-actin along the cortex. dDcp2 and Dmoesin show a mutually-dependent adherecne along the oocyte cortex. Lastly, the phosphorylation status of Dmoeisn determines the allocation of dDcp2 in the oocyte. Overexpression of phospho-Dmoesin accumulates the cortical dDcp2, whereas overexpression of nonphospho-Dmoeisn draws dDcp2 into the ooplasm.
Hence, we propose that from stage 6 dDcp2 and phospho-Dmoesin form a pre-localized anchor for locate oskar mRNA along the cortex. And Dmoesin-dDcp2 recruit oskar mRNA-dDcp1-dGe-1 to be the anchoring complex. nonphospho-Dmoe and dDcp2 organize a transporting complex to move oskar mRNA-dDcp1 from the cortex. At the posterior, phosphorylation status exchange the components of the two complex and oskar mRNA can be anchored properly.
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