POTENTIAL OF CD34 IN THE REGULATION OF SYMMETRICAL AND ASYMMETRICAL DIVISIONS BY HEMATOPOIETIC PROGENITOR CELLS

¹ Department of Haematology, Imperial College Faculty of Medicine, London, United Kingdom

^* To whom correspondence should be addressed. E-mail: myrtle.gordon{at}imperial.ac.uk.

	Abstract

The control of symmetric and asymmetric division in the hematopoietic stem/progenitor cell population is critically important for the regulation of blood cell production. Asymmetric divisions depend on cell polarisation, which may be conferred by location and/or interaction with neighbouring cells. In this study we sought evidence for polarisation in CD34+ cells which interact by binding to one another. In these cells, surface molecules became redistributed by mechanisms that included transport by lipid rafts and the interacting cells were able to communicate via gap junctions. These changes were accompanied by modulation of cell cycle regulating proteins (p16^Ink-4a, p27^kip1, cyclins D and the retinoblastoma (Rb) pathway proteins) and a reduction in progenitor cell proliferation in vitro. These results are consistent with an increase in asymmetric cell division kinetics. Accordingly, we found that interaction between CD34+ cells influenced the plane of cell division in a way that suggests unequal sharing of Notch-1 between daughter cell progeny. We conclude that interaction between CD34+ cells may co-ordinate cell function participate in the control of hematopoietic stem/progenitor cell division kinetics.