Jellyfish germ cell development and the evolution of the animal germ line – JERMLINE

Original ERC Resumé (ERC-StG-2025): Germ cells play a critical role in the protection and fidelity of genome inheritance, and there is a longstanding historical interest in their developmental origins. Traditionally, germ cells were considered to arise from a distinct cell lineage - the germline - during early embryogenesis. Across animals, however, definitive segregation of the germline and soma during embryogenesis is far from universal. In cnidarians, for example, such as the powerful emerging laboratory model jellyfish Clytia hemisphaerica, germ cells derive continuously from “adult” stem cell populations. The time is thus ripe to exploit Clytia to redefine the paradigms of germline development and, by comparing across species, to trace their evolution. The specific aim of this project is to define in Clytia the timing and regulation of the successive developmental transitions leading through embryogenesis, sex determination, and the generation of distinct stem cell populations, to the formation of male and female germ cells. To do this, I will deploy complementary approaches: Transcriptomic analyses, alongside live and fixed imaging, will identify and track distinct somatic, stem cell and putative germ line populations; Experimental manipulations of embryos and adults will determine the origins and the interconvertibility of these lineages; Gene knockdown techniques will identify the regulators and molecular pathways underlying germ cell development; A combination of ‘omics, imaging and gene knockdown techniques will uncover genetic and environmental mechanisms of sex determination that specify male vs female stem cells. This comprehensive study will define mechanisms of stem cell and germ cell development in a new cnidarian system. It has the potential to deliver new insights into germline specifications across the animal kingdom, enabling the germline concept to be redefined.