The aim of this project is to uncover the molecular mechanisms by which circulating mesenchymal cells are able to reconstruct a new individual. All ascidians possess undifferentiated mesenchymal cells named haemoblasts that circulate in their bloodstream. They participate in bud formation in different types of NED, and in the tissue and organ regeneration of solitary species. We showed that aggregates of hemoblasts proliferate at the onset of both B. schosseri vascular budding and preliminary data suggest their presence also in P. zorritensis NED. Hemoblasts are also present in solitary ascidians and are potentilly involved in their tissue regeneration. While an increasing amount of studies suggest that heamoblasts are toti/multipotent stem cells responsible of some forms of budding, no one assayed their degree of potency by tracking their fate and their dynamic during NED. We are currently describing (morphologically and molecularly) this cell population in P.zorritensis and we aim to test their potentiality by blocking and rescue of NED via single-cell transplantation.