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 division axis maintenance relies on their last-born daughter cell. We propose that, in addition to known intrinsic cues, stem cells in the developing fly brain are polarized by an extrinsic signal. We further find that division axis maintenance allows neuroblasts to maximize their contact area with glial cells known to provide protective and proliferative signals to neuroblasts.
Highlights
Controlling the orientation of cell division is important in the context of cell fate choices and tissue morphogenesis
Cytokinesis is linked to division orientation control in budding yeast, where the orientation of future divisions is biased by a landmark at the site of abscission[18]
To test our hypothesis that the orientation of NB division is under the influence of extrinsic cues provided by their daughter cells, we analysed the relationship of the orientation of NB division with the position of the last-born daughter cell (GMC)
Summary
Controlling the orientation of cell division is important in the context of cell fate choices and tissue morphogenesis. Embryonic neural stem cells (neuroblasts (NBs)) in Drosophila for instance can use spindle microtubules to deliver components of the microtubule anchoring machinery to the cortex[10] These cells can read extrinsic cues, orienting their division perpendicular to the overlying epithelium[11]. An ideal system to study mechanisms that orient cell division are the highly proliferative NBs of the Drosophila larva that divide over many cell cycles with very little deviation in the orientation of division between different cycles The mechanisms controlling this process are only partially understood. Contrary to embryonic NBs11, this occurs regardless of whether larval NBs reside within the brain or are in isolation in primary culture[31,32] This process is believed to occur through the apically localized centrosome and microtubules, which act as cell intrinsic polarizing cues[33]. This suggests that other polarizing cues contribute in parallel to maintain the orientation of the axis of NB division
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