Programming of pluripotency and the germ line co-evolved from a Nanog ancestor

Francois Jacob proposed that evolutionary novelty arises through incremental tinkering with pre-existing genetic mechanisms. Vertebrate evolution was predicated on pluripotency, the ability of embryonic cells to form somatic germ layers and primordial germ cells (PGCs). The origins of pluripotency remain unclear, as key regulators, such as Nanog, are not conserved outside of vertebrates. Given NANOG's role in mammalian development, we hypothesized that NANOG activity might exist in ancestral invertebrate genes. Here, we find that Vent from the hemichordate Saccoglossus kowalevskii exhibits NANOG activity, programming pluripotency in Nanog^-/- mouse pre-induced pluripotent stem cells (iPSCs) and NANOG-depleted axolotl embryos. Vent from the cnidarian Nematostella vectensis showed partial activity, whereas Vent from sponges and vertebrates had no activity. VENTX knockdown in axolotls revealed a role in germline-competent mesoderm, which Saccoglossus Vent could rescue but Nematostella Vent could not. This suggests that the last deuterostome ancestor had a Vent gene capable of programming pluripotency and germline competence.