Supplementary MaterialsSource data 1: Data values that have been depicted in the figures of the manuscript. work sheds light on the physical processes that underlie chiral morphogenesis in early development. nematode. The fully grown hermaphrodite worm consists of exactly 959 somatic cells that are essentially invariant both in terms of position and lineage (Sulston and Horvitz, 1977; Sulston et al., 1983; Schnabel et al., 2006; Li et al., 2019). Development is deterministic from the start: the one-cell embryo undergoes an asymmetric cell division that gives rise to the AB (somatic) lineage and the P lineage (Sulston et al., 1983; Bruce et al., 2002). While the anterior daughter cell, AB, undergoes a symmetric cell division into ABa and ABp, the posterior daughter cell, P1, divides asymmetrically into EMS forming DDPAC the endoderm and mesoderm, and P2 forming the germ line (Sulston et al., 1983). Appropriate cell-cell contacts are instrumental for development as they can determine cell identity (Priess, 2005; Artavanis-Tsakonas et al., 1999; Mango et al., 1994; Mello et al., 1994; Moskowitz et al., 1994). For example, reorientation of the ABa AHU-377 (Sacubitril calcium) and ABp cells AHU-377 (Sacubitril calcium) via pushing with a micro needle leads to an altered cell-cell contact pattern and an altered body plan with an inverted L/R body axis (Wood, 1991). Consequently, proper cell positioning, AHU-377 (Sacubitril calcium) perhaps mediated via repositioning of the mitotic spindle during cytokinesis, is crucial (Hennig et al., 1992). Here, we set out to investigate which of the cells of the early embryo undergo reorientations during cytokinesis, and by which mechanism they do so. Recently, a role for the actomyosin cell cortex in determining the cell division axis of early blastomeres was identified (Naganathan et al., 2014; Sugioka and Bowerman, 2018). The actomyosin cortex is a thin layer below the plasma membrane that consists mainly of actin filaments, actin binding proteins and myosin motor proteins (Pollard and Cooper, 1986). Collectively, these molecules generate contractile forces that can shape the cell, drive cortical flows during polarization and orchestrate other active processes such as cell division (Mayer et al., 2010; Pollard, 2017). Cell-cell contacts can impact on the activity of myosin and the generation of contractile stresses, and the resultant pattern of cortical flows can determine the orientation of the mitotic spindle at the onset of cytokinesis AHU-377 (Sacubitril calcium) (Sugioka and Bowerman, 2018). From a physical point of view, the actomyosin cortex can be thought of as a thin layer of a mechanically active fluid (Jlicher et al., 2007; Ramaswamy and Simha, 2006; Salbreux et al., 2009; Mayer et al., 2010) with myosin-driven active stress gradients generating cortical flows (Mayer et al., 2010). AHU-377 (Sacubitril calcium) Interestingly, actomyosin can also exhibit rotatory flows driven by active torque generation. These chiral rotatory cortical flows reorient the ABa cell and the ABp cell during cytokinesis, driving a cell skew of 20 during division (Naganathan et al., 2014). This skew results in a L/R asymmetric cell-cell contact pattern (Pohl and Bao, 2010), thus executing left-right (L/R) symmetry breaking in the entire organism. However, how general such reorientation events are, and how they are controlled, remains unclear. Furthermore, it remains poorly understood whether chiral flows are prevalent in other cell divisions as well, and if they play a prominent role in cell repositioning during early embryogenesis.