Evolutionary mechanisMS of asymmetric spindle positioning in nematode embyos

Abstract

Asymmetric cell division is essential for generating cellular diversity, which leads to two unequal daughter cells with different cellular fates. In most of the animal cells, asymmetric spindle positioning is the key factor which leads to the first asymmetric cell division and decides the size of the daughter cells. Although the process of asymmetric positioning of spindle is conserved in most of the species, but not much is known about the robustness of the mechanisms which lead to this evolutionarily conserved phenomenon. We recorded the first embryonic division three nematode species such as Caenorhabditis elegans, Oscheius tipulae and Diploscapter sp.JU359 to study the biophysical properties of spindle positioning and the mechanical parameters those can affect the spindle positioning. We hypothesized that viscosity could be one of the parameters which might affect the different mechanisms which govern the asymmetric spindle positioning. So, by using microrheology methods we tried calculating viscosity values of the cytoplasm of these nematode species by tracking the lipid granules in the cytoplasm. The results showed us that, Diploscapter sp.JU359 which has the least movement of spindle has the highest viscosity values and all the three species show higher viscosity values than water.