Abstract
Control of mRNA translation is a key mechanism by which the differentiated oocyte transitions to a totipotent embryo. In Drosophila, the PNG kinase complex regulates maternal mRNA translation at the oocyte-to-embryo transition. We previously showed that the GNU activating subunit is crucial in regulating PNG and timing its activity to the window between egg activation and early embryogenesis (Hara et al., 2017). In this study, we find associations between GNU and proteins of RNP granules and demonstrate that GNU localizes to cytoplasmic RNP granules in the mature oocyte, identifying GNU as a new component of a subset of RNP granules. Furthermore, we define roles for the domains of GNU. Interactions between GNU and the granule component BIC-C reveal potential conserved functions for translational regulation in metazoan development. We propose that by binding to BIC-C, upon egg activation GNU brings PNG to its initial targets, translational repressors in RNP granules.
Highlights
The transition from oocyte to embryo marks the onset of development for most metazoans
We find that GNU forms a complex with translational repressors in mature oocytes
Does GNU interact with the known components of oocyte RNP granules, ME31B and BIC-C, it co-localizes with these two proteins as well as TRAL in large cytoplasmic structures
Summary
The transition from oocyte to embryo marks the onset of development for most metazoans. Egg activation triggers this transition and results in, amongst other changes, completion of the meiotic program in the oocyte and restoration of a totipotent cell state (Aviles-Pagan and Orr-Weaver, 2018; Krauchunas and Wolfner, 2013) This transition is regulated exclusively by post-transcriptional mechanisms, as it occurs in the absence of new transcription and depends on translational control of stockpiled maternal mRNAs as well as proteolysis and posttranslational modification of proteins. In Drosophila, egg activation triggers the disassembly of these ‘oocyte’ granules (Weil et al, 2012), and they reform as ‘embryonic’ RNP complexes in early embryos (Wang et al, 2017), consistent with roles for these complexes in the regulation of maternal mRNAs at this time. We discuss new models of activation of the PNG complex and control of mRNA translation during egg activation based on these findings
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