The control of cell shape during cytokinesis requires a precise regulation of mechanical properties of the cell cortex. Only few studies have addressed the mechanisms underlying the robust production of unequal-sized daughters during asymmetric cell division. Here we report that unequal daughter-cell sizes resulting from asymmetric sensory organ precursor divisions in Drosophila are controlled by the relative amount of cortical branched Actin between the two cell poles. We demonstrate this by mistargeting the machinery for branched Actin dynamics using nanobodies and optogenetics. We can thereby engineer the cell shape with temporal precision and thus the daughter-cell size at different stages of cytokinesis. Most strikingly, inverting cortical Actin asymmetry causes an inversion of daughter-cell sizes. Our findings uncover the physical mechanism by which the sensory organ precursor mother cell controls relative daughter-cell size: polarized cortical Actin modulates the cortical bending rigidity to set the cell surface curvature, stabilize the division and ultimately lead to unequal daughter-cell size.

胞质分裂过程中细胞形状的控制需要精确调节细胞皮层的机械特性。只有少数研究解决了在不对称细胞分裂过程中大量产生不等大小子代的潜在机制。在这里，我们报告了果蝇中不对称的感觉器官前体分裂导致的不等子细胞大小由两个细胞极之间皮质分支肌动蛋白的相对量控制。我们通过使用纳米体和光遗传学错误定位分支肌动蛋白动力学的机制来证明这一点。因此，我们可以设计具有时间精度的细胞形状，从而设计细胞分裂不同阶段的子细胞大小。最引人注目的是，反转皮质肌动蛋白不对称会导致子细胞大小反转。我们的研究结果揭示了感觉器官前体母细胞控制相对子细胞大小的物理机制：极化皮质肌动蛋白调节皮质弯曲刚度以设定细胞表面曲率，稳定分裂并最终导致不平等的子细胞大小。