Hemoblasts in colonial tunicates: Are they stem cells or tissue-restricted progenitor cells?
Article first published online: 5 NOV 2009
© 2009 The Authors. Journal compilation © 2009 Japanese Society of Developmental Biologists
Development, Growth & Differentiation
Special Issue: Comparative Aspects of Stem Cells
Volume 52, Issue 1, pages 69–76, January 2010
How to Cite
Kawamura, K. and Sunanaga, T. (2010), Hemoblasts in colonial tunicates: Are they stem cells or tissue-restricted progenitor cells?. Development, Growth & Differentiation, 52: 69–76. doi: 10.1111/j.1440-169X.2009.01142.x
- Issue published online: 11 JAN 2010
- Article first published online: 5 NOV 2009
- Received 8 March 2009; revised 9 March 2009; accepted 9 March 2009.
- germ line;
- progenitor cell;
- stem cell
Colonial tunicates have hemoblasts, which are undifferentiated coelomic cells that play a key role in tissue renewal during reproduction and regeneration. Some hemoblasts differentiate into somatic lineage cells such as endodermal multipotent epithelial, cardiac and body-wall muscle, and blood cells. There is no well established evidence that somatic hemoblasts are stem cells. Rather, like tissue-restricted progenitor cells, some peripheral hemoblasts give rise to terminally differentiated cells, while other hemoblasts differentiate into germ cells and accessory cells. Unlike somatic lineage cells, germ cells and their precursors express vasa homologues in common. In some colonial tunicates, vasa is indispensable for germ cell development. All vasa-positive hemoblasts appear to differentiate into germ cells, suggesting that most of them are tissue-restricted progenitor cells. When a colony is naturally or experimentally depleted of vasa-expressing cells, vasa and vasa-expressing germ cells can reappear in the colony. We speculate that, in addition to tissue-restricted progenitor cells, highly potent stem cells which regulate the activities of blastogenesis and gametogenesis and eventually cause soma-germ conflict in colonial tunicates may exist in colonial tunicates.