RT Journal Article SR Electronic T1 Spatiotemporally controlled Myosin relocalization and internal pressure cause biased cortical extension to generate sibling cell size asymmetry JF bioRxiv FD Cold Spring Harbor Laboratory SP 311852 DO 10.1101/311852 A1 Tri Thanh Pham A1 Arnaud Monnard A1 Jonne Helenius A1 Erik Lund A1 Nicole Lee A1 Daniel J. Müller A1 Clemens Cabernard YR 2018 UL http://biorxiv.org/content/early/2018/05/01/311852.abstract AB Metazoan cells can generate unequal sized sibling cells during cell division. This form of asymmetric cell division depends on spindle geometry and Myosin distribution but the underlying mechanics are unclear. Here, we use atomic force microscopy and live cell imaging to elucidate the biophysical forces involved in the establishment of physical asymmetry in Drosophila neural stem cells. We show that the force driving initial apical membrane expansion is provided by hydrostatic pressure, peaking shortly after anaphase onset, and enabled by a relieve of actomyosin contractile tension on the apical cell cortex. The subsequent increase in contractile forces at the cleavage furrow, combined with the relocalization of basally located Myosin results in basal membrane extension and sustained apical expansion. We propose that spatiotemporally controlled actomyosin contractile tension and hydrostatic pressure enables stereotypic biased membrane expansion to generate sibling cell size asymmetry.