Cytoplasmic flows in starfish oocytes are fully determined by cortical contractions
Fig 8
Mixing hypothesis and polar body formation.
A: A particle starting at the dot follows the shown line during the SCW. Most trajectories end approximately at their starting point and follow similar paths as their neighbouring ones. Therefore mixing of the cytoplasm can be excluded as a function of the SCW. B,C: It has been suggested that the polar body is pushed out by the SCW due to build up of high internal pressure. Our hydrodynamic model shows that the SCW leads to a locally higher pressure at the animal pole of several hundred μPa. If the polar body was pushed out by a blebbing mechanism, the pressure difference between inside and outside would need to be of the order of several hundred Pa at the animal pole. Therefore the pressure due to the SCW can be excluded as a mechanism for polar body extrusion. D: Both the deformation speed and the internal flows of a blebbistatin-treated cell are much weaker than in the wild type cell. E: A polar body is formed even with blebbistatin-treatment. Full videos are given as S9 and S10 Videos. F: A potential mechanism for polar body extrusion is local actin polymerisation. The actin of the oocyte was labelled with utrophin which makes a local accumulation of actin visible at the position of the polar body (S11 Video).