| Summary: | 博士 === 國立臺灣大學 === 分子與細胞生物學研究所 === 94 === Specific subcellular localization of maternal mRNAs in the oocyte during oogenesis is very important for proper embryonic patterning in Drosophila. For example, the deposition of oskar (osk) mRNA at the posterior pole of the oocyte is critical for both pole cells and abdomen formation.
Many mechanisms are involved in the posterior deposition of osk mRNA. In addition to those directly involved in the osk mRNA transportation, proteins participate in pre-mRNA splicing, such as Exon junction complex components, are implicated in osk mRNA transportation. Moreover, proteins that participate in mRNA translation, such as eIF4E and others related to translational initiation, can direct the posterior transportation of osk mRNA.
Except for the transportation, splicing, and translation machineries, the mRNA degradation machinery has not been reported to participate in the regulation of osk mRNA transport. Evidence presented here indicates that Drosophila decapping protein 1 (dDcp1) is required for not only the maternal mRNA degradation during early embryogenesis but also the posterior transportation of osk mRNA. As a component of osk mRNP complex, the mechanism of dDcp1-directed osk mRNA transportation and the possible roles of dDcp1 during oogenesis are discussed.
In both yeast and human cells, the sites of 5’ to 3’ mRNA degradation have been found to reside in specific cytoplasmic foci, named Processing bodies (P-bodies). P-bodies contain Decapping protein 1 (Dcp1), Decapping protein 2 (Dcp2), 5’ to 3’ exoribonuclease (Xrn1), and other proteins required for 5’ to 3’ mRNA degradation. In the oocyte, dDcp1 is localized at the posterior end and its localization is osk mRNA dosage- and position-dependent. In nurse cell cytoplasm, dDcp1 is localized in the cytosol and is colocalized with dDcp2, Drosophila 5’ to 3’ exoribonuclease (Pacman), and Me31B in discrete cytoplasmic foci. Evidence provided here indicates that these cytoplasmic dDcp1 bodies in nurse cells are Drosophila P-bodies.
The human homolog of Dcp1, hDcp1a, has been found to involve in the TGF-beta signaling pathway and is also named as SMIF (Smad4-interacting factor). In addition to the requirement of dDcp1 for the posterior transport of osk mRNA, the N-terminal of dDcp1 can interact with the MH1 domain of Medea (Drosophila Smad4 homolog). Besides, dDcp1 contains intrinsic transactivation activity in its C-terminal region and is able to translocate into the nucleus in response to the Dpp signaling. However, the possible roles of dDcp1 in the TGF-beta signaling during oogenesis remain to be clarified.
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