Localized Translation of gurken/ TGF-α mRNA during Axis Specification Is Controlled by Access to Orb/CPEB on Processing Bodies

Summary

In Drosophila oocytes, gurken/TGF-α mRNA is essential for establishing the future embryonic axes. gurken remains translationally silent during transport from its point of synthesis in nurse cells to its final destination in the oocyte, where it associates with the edge of processing bodies. Here we show that, in nurse cells, gurken is kept translationally silent by the lack of sufficient Orb/CPEB, its translational activator. Processing bodies in nurse cells have a similar protein complement and ultrastructure to those in the oocyte, but they markedly less Orb and do not associate with gurken mRNA. Ectopic expression of Orb in nurse cells at levels similar to the wild-type oocyte dorso-anterior corner at mid-oogenesis is sufficient to cause gurken mRNA to associate with processing bodies and translate prematurely. We propose that controlling the spatial distribution of translational activators is a fundamental mechanism for regulating localized translation.

Graphical Abstract

Highlights

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  gurken mRNA is not silenced by known repressors during its transport

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  In nurse cells, gurken mRNA is not associated with processing bodies

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  In nurse cells, lack of sufficient Orb/CPEB silences gurken mRNA translation

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  In oocytes, gurken mRNA is associated with Orb on processing bodies and translated

Abstract

Localized transcripts that determine polarity are thought to be silenced during their transport by binding to translational repressors. Davidson et al. show that gurken mRNA, which sets up the primary Drosophila body axes, is instead regulated through lack of a translational activator, Orb, during its transport.