Drosophila neural stem cells are polarized by their daughter cells

Abstract

Controlling the orientation of cell division is important in the context of cell fate choices and tissue morphogenesis. However, the mechanisms providing the required positional information remain incompletely understood. Here we use stem cells of the Drosophila larval brain that stably maintain their axis of polarity and division between cell cycles to identify cues that orient cell division. Using live cell imaging of cultured brains, laser ablation and genetics we reveal that these cells use the position of their last-born daughter cell as a polarizing cue. Remarkably, this daughter cell derived signal received at one pole of the stem cell has an effect on the opposite pole influencing where apical will be in the next mitosis, thereby directing the orientation of division. Therefore, in addition to known intrinsic cues, stem cells in the developing fly brain are polarized by an extrinsic signal that acts upstream of apico-basal polarity establishment.