<i>Nanos2</i> marks precursors of somatic lineages and is required for germline formation in the sea anemone <i>Nematostella vectensis</i>

In animals, stem cell populations of varying potency facilitate regeneration and tissue homeostasis. Notably, germline stem cells in both vertebrates and invertebrates express highly conserved RNA binding proteins, such as <i>nanos</i>, <i>vasa</i>, and <i>piwi</i>. In highly regenerative animals, these genes are also expressed in somatic stem cells, which led to the proposal that they had an ancestral role in all stem cells. In cnidarians, multi- and pluripotent interstitial stem cells have only been identified in hydrozoans. Therefore, it is currently unclear if cnidarian stem cell systems share a common evolutionary origin. We, therefore, aimed to characterize conserved stem cell marker genes in the sea anemone <i>Nematostella vectensis</i>. Through transgenic reporter genes and single-cell transcriptomics, we identify cell populations expressing the germline-associated markers <i>piwi1</i> and <i>nanos2</i> in the soma and germline, and gene knockout shows that Nanos2 is indispensable for germline formation. This suggests that <i>nanos</i> and <i>piwi</i> genes have a conserved role in somatic and germline stem cells in cnidarians.