IMSc Webinar

Evolutionary diversification of actomyosin-driven early embryo morphogenesis

Teije Corneel Middelkoop

IMG, Prague

The shape of an animal arises gradually during embryonic development in a process referred to as ‘morphogenesis’. In nematodes, morphogenesis starts immediately after fertilization and requires a tight coordination of cell polarization, cell division and cellular-scale rotations. Biophysical studies have shown that all these processes depend on active forces and torques generated in the actomyosin cytoskeleton of embryonic cells. In recent years, much has been learned about the force generating mechanisms that drive early embryo morphogenesis in C. elegans. However, very little is known about whether and how these physical mechanisms have diversified during nematode evolution. To study this, we analyzed actomyosin-driven morphogenesis in a panel of related nematode species. We performed time lapse imaging of polarization and cell divisions up until the 4-cell stage. Subsequently, we quantitatively characterized intracellular actomyosin dynamics as well as cellular-scale morphogenetic rotations. We find striking differences in the dynamic behavior of the actomyosin cytoskeleton. For example, in C. elegans the actomyosin cytoskeleton undergoes intracellular chiral rotations that, in turn, drive cellular rotations. This rotatory actomyosin behavior was variable among species, with some displaying no rotatory behavior at all. Nonetheless, in agreement with earlier studies, we find that the overall pattern of polarization and cell orientation displays little variability among the nematodes analyzed. Altogether, these results are indicative of developmental systems drift, where different physical mechanisms give rise to a similar developmental outcome.


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