The Crystal Structure of the Drosophila Germline Inducer Oskar Identifies Two Domains with Distinct Vasa Helicase- and RNA-Binding Activities.

Mandy Jeske,Anne Ephrussi,Vladimir Rybin,Sandra Müller,Christoph W. Müller,Matteo Bordi,Sebastian Glatt

doi:10.1016/j.celrep.2015.06.055

Abstract

In many animals, the germ plasm segregates germline from soma during early development. Oskar protein is known for its ability to induce germ plasm formation and germ cells in Drosophila. However, the molecular basis of germ plasm formation remains unclear. Here, we show that Oskar is an RNA-binding protein in vivo, crosslinking to nanos, polar granule component, and germ cell-less mRNAs, each of which has a role in germline formation. Furthermore, we present high-resolution crystal structures of the two Oskar domains. RNA-binding maps in vitro to the C-terminal domain, which shows structural similarity to SGNH hydrolases. The highly conserved N-terminal LOTUS domain forms dimers and mediates Oskar interaction with the germline-specific RNA helicase Vasa in vitro. Our findings suggest a dual function of Oskar in RNA and Vasa binding, providing molecular clues to its germ plasm function.

Highlights

Propagation and survival of metazoan species depend on the maintenance of the germline
Oskar protein is known for its ability to induce germ plasm formation and germ cells in Drosophila
We show that Oskar is an RNA-binding protein in vivo, crosslinking to nanos, polar granule component, and germ cell-less mRNAs, each of which has a role in germline formation

Summary

Introduction

Propagation and survival of metazoan species depend on the maintenance of the germline. The germ plasm of Drosophila (pole plasm) forms during oogenesis at the posterior pole of the oocyte. In this organism, the process of germ cell formation is coupled to posterior patterning of the embryo and involves a series of mRNA and protein localization events. Abdominal patterning results from Oskar-dependent localization and translation of nanos mRNA and formation of a gradient of the posterior determinant Nanos (Ephrussi et al, 1991; Barker et al, 1992; Wang and Lehmann, 1991; Wang et al, 1994; Gavis and Lehmann, 1994)

Results

Discussion

Conclusion