Stem cells in sexual and asexual reproduction of botryllus schlosseri (ascidiacea, tunicata): An overview

Abstract

Botryllus schlosseri, a colonial ascidian reproducing both sexually and asexually, is an excellent model for the study of adult stem cells, since budding blastozooids are derived from a disc of stem cells at the parental atrial chamber and the overlying epidermis. At the colony level, adult zooids undergo cyclical generation changes during which the adults die, are resorbed and then replaced by their buds which reach functional maturity and start filtering. At the same time, blood cell renewal takes place thanks to a new haemopoietic wave. Several experimental manipulations were used to evaluate the behaviour of stem cells during bud morphogenesis under different developmental constraints. When all zooids and buds of a colony are extirpated, new developed zooids are derived from totipotent blood cells which aggregate on the walls of the blood vessels of the tunic. Stem cells can also be transferred from one colony to another through vasculature during fusion of allogeneic compatible colonies. Germ stem cells persist in a host colony so that heterochtonous offspring can be collected after many blastogenetic generations. The persistence of somatic stem cells alters the fusibility pattern of the colony. Pluripotent stem cells are also involved in the embryonic development of larval and juvenile organs; these embryonic cells were analysed and compared with bud stem cells for their potentials and gene expression. © 2009 Springer Netherlands.