Drosophila asymmetric division, polarity and cancer.

A limited number of adult stem cells (SCs) maintain the homoestasis of different tissues through the lifetime of the individual by generating differentiating daughters and renewing themselves. Errors in the SC division rate or in the fine balance between self-renewal and differentiation might result in tissue overgrowth or depletion, two potentially lethal conditions. A few types of SCs have been identified in Drosophila. These include the SCs of the adult intestine and malpighian tubes, (Micchelli and Perrimon, 2006; Ohlstein and Spradling, 2006; Singh et al., 2007), the prohematocytes that maintain the population of cells involved in the immunoresponse (Lanot et al., 2001; Lemaitre and Hoffmann, 2007), the SC of the follicle epithelia in the ovary (Nystul and Spradling, 2007), germ line SCs (GSCs) of both sexes (Fuller and Spradling, 2007) and neuroblasts (NBs), the fly neural SCs (Yu et al., 2006; Chia et al., 2008; Knoblich, 2008). Drosophila SCs have proved a fruitful model system to unveil some aspects of the molecular logic that sustains SC function. This review focuses on results obtained in the last few years from the study of NBs, particularly from the standpoint of the possible functional connection between asymmetric SC division and cancer.