Stem cell tumors in Drosophila melanogaster. Dividing the defects in asymmetric cell division

Abstract

Stem cells are the precursors of various tissues in multicellular organisms. Their unique ability to divide both symmetrically and asymmetrically enable them to expand cell populations and to generate various cell types. In the initial stages of tissue formation, stem cells divide symmetrically into two daughter stem cells to increase the progenitor pool. The stem cells are required to switch their division mode to asymmetry to provide differentiating daughter cells upon modeling of the tissues. In an asymmetric stem cell division, the differentiating daughter cell is budded off from a self-renewing stem cell. The balance between symmetric and asymmetric divisions is tightly regulated to control the levels of proliferating cells versus differentiating cells. Defects in the ability to generate a differentiating daughter results in an overpopulation of proliferating stem cell daughters, a phenomenon described as stem cell cancer. A lot of research was dedicated to understand the mechanisms of asymmetric division and the distribution of the different daughter fates. In this review, I will give an overview of the mechanisms involved in controlling asymmetry of a cell division, and the defects that have been unraveled up till now leading to stem cell tumor formation.