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Dr Rippei Hayashi (Photo: ANU Media)

Pushing the envelope: survival mechanism of infectious retrotransposons in metazoans

Hosted by: Professor Leonie Quinn

Abstract

Retrotransposons acquire a gene that encodes a membrane fusion protein, called envelope, to become infectious. Env acquisition happened most famously to vertebrate retroviruses that behave as exogenous viruses today. Less famously, it also occurred to Ty3/gypsy retrotransposons in Drosophila. However, it has long been thought that they independently acquired the env gene. By examining the small RNA-based transposon defence mechanism and an in silico survey of the genomic copy of env-carrying retrotransposons, we show that similar elements are widespread across metazoan phyla and their divergence closely follows that of the host species. Our finding challenges the current assumption of the origin of vertebrate retroviruses and suggests that the genomic version of retroviruses has a hidden life cycle in which they infect the germ line cells to vertically transmit their copies.

Biography

Dr Rippei Hayashi is a group leader and senior lecturer at the John Curtin School of Medical Research. Hayashi earned his PhD from the University of Tokyo in 2007 before becoming a world traveller. In his first postdoc in the UK with the late Dr David Ish-Horowicz, Hayashi studied the mechanism of microtubule-dependent mRNA localisation in Drosophila oocytes and conducted an EMS mutagenesis screen, from which he unexpectedly identified a number of mutants in the piRNA pathway, the evolutionarily conserved transposon defence mechanism. Hayashi followed up these mutants and revealed key mechanisms of piRNA biosynthesis during his second postdoc in Vienna with Dr Julius Brennecke. Hayashi came to ANU in 2018 to start his own lab. He continues to study aspects of piRNA biogenesis as well as mRNA splicing and cell type-specific transcription that govern the germ line development in animals.