September 5, 2008;
Highways for mRNA transport.
Two new studies reveal the role of microtubule polarity in the asymmetric localization of mRNAs. In this issue of Cell, Zimyanin et al. (2008) show that the asymmetric localization of oskar mRNA in fruit fly oocytes results from a slight bias in the direction of its transport. Meanwhile, Messitt et al. (2008) reporting in Developmental Cell find a subpopulation of microtubules that is critical for the asymmetric distribution of Vg1
mRNA in frog oocytes.
R01 GM084364-15A1 NIGMS NIH HHS
, R01 GM084364-16 NIGMS NIH HHS
, R01 GM084364-17 NIGMS NIH HHS
, R01 GM084364-18 NIGMS NIH HHS
, R01 GM084364 NIGMS NIH HHS
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Conserved Mechanisms for mRNA Localization in Oocytes
Microtubules are oriented in both directions in oocytes from the fruit fly Drosophila (upper left) and the frog Xenopus (upper right). Dual polarity of microtubules is a feature of neuronal dendrites as well. In such cases, granules containing mRNAs (turquoise) can move in either direction, but the predominant orientation of the microtubules determines the overall directional bias (see expanded view). In cases where the microtubule orientation that promotes the eventual mRNA localization is in the minority, an anchoring mechanism must remove mRNAs from the mobile pool. Several kinesins are responsible for this plus-end-directed movement (shown in pink and gold). It is likely that this anchoring mechanism (indicated by anchor icon) includes cortical actin (shown as filaments) and may also include Tropomyosin and Staufen. Translation then occurs after anchoring (ribosomes indicated).