In Vivo Imaging of oskar mRNA Transport Reveals the Mechanism of Posterior Localization

Vitaly L Zimyanin,Katsiaryna Belaya,Jacques Pecreaux,Michael J Gilchrist,Alejandra Clark,Ilan Davis,Daniel St Johnston

doi:10.1016/j.cell.2008.06.053

Vitaly L Zimyanin, Katsiaryna Belaya + Show 5 more

Open Access

https://doi.org/10.1016/j.cell.2008.06.053

Copy DOI

Abstract

Summaryoskar mRNA localization to the posterior of the Drosophila oocyte defines where the abdomen and germ cells form in the embryo. Although this localization requires microtubules and the plus end-directed motor, kinesin, its mechanism is controversial and has been proposed to involve active transport to the posterior, diffusion and trapping, or exclusion from the anterior and lateral cortex. By following oskar mRNA particles in living oocytes, we show that the mRNA is actively transported along microtubules in all directions, with a slight bias toward the posterior. This bias is sufficient to localize the mRNA and is reversed in mago, barentsz, and Tropomyosin II mutants, which mislocalize the mRNA anteriorly. Since almost all transport is mediated by kinesin, oskar mRNA localizes by a biased random walk along a weakly polarized cytoskeleton. We also show that each component of the oskar mRNA complex plays a distinct role in particle formation and transport.

Highlights

MRNA localization is a common mechanism for targeting proteins to specific regions of a cell and plays an important role in axis formation in many organisms, where localized mRNAs function as cytoplasmic determinants
This has been extensively studied in Drosophila, where both main body axes are defined by the localization of bicoid, oskar, and gurken mRNAs to distinct regions of the oocyte (Bashirullah et al, 1998; St Johnston, 2005). osk mRNA moves to the posterior of the oocyte during stages 8–10 of oogenesis and is translated as soon as it is localized to the posterior pole, where Oskar protein nucleates the polar granules, which contain the abdominal and germline determinants (Ephrussi et al, 1991; Kim-Ha et al, 1991, 1995; Markussen et al, 1995)
The role of the Kinesin heavy chain (Khc) suggests a simple model for osk mRNA localization, in which this plus end-directed motor is linked to the mRNA by HRP48, the EJC, and Stau and transports the mRNA along microtubules to the posterior pole

Summary

SUMMARY

Oskar mRNA localization to the posterior of the Drosophila oocyte defines where the abdomen and germ cells form in the embryo. This localization requires microtubules and the plus end-directed motor, kinesin, its mechanism is controversial and has been proposed to involve active transport to the posterior, diffusion and trapping, or exclusion from the anterior and lateral cortex. By following oskar mRNA particles in living oocytes, we show that the mRNA is actively transported along microtubules in all directions, with a slight bias toward the posterior. We show that each component of the oskar mRNA complex plays a distinct role in particle formation and transport

INTRODUCTION

RESULTS

DISCUSSION