Abstract
ABSTRACTMouse zygote morphokinetics were measured during interphase, the mitotic period, cytokinesis, and two-cell stage. Sequences of rounder–distorted–rounder shapes were revealed, as were changing patterns of cross section area. A calcium chelator and an actin-disrupting agent inhibited the area changes that occurred between pronuclear envelope breakdown and cytokinesis. During cell division, two vortices developed in each nascent cell and they rotated in opposite directions at each end of the cell, a pattern that sometimes persisted for up to 10 h. Exchange with the environment may have been promoted by these shape and area cycles and persisting circulation in the cytoplasm may have a similar function between a cell's interior and periphery. Some of these movements were sporadically also seen in human zygotes with abnormal numbers of pronuclei and the two-cell stages that developed from these compromised human zygotes.
Highlights
The purpose of the present paper was to search for movements of the zygote and two-cell stage that might increase exchange between the embryo and its environment in culture.The emphasis is on the changing space between the cell membrane and acellular matrix of the zona pellucida (ZP) because alterations here give strong flow in a closed hydraulic system
Similar shape changes were seen in some human embryos that developed from zygotes with abnormal numbers of pronuclei (Supplementary Material)
The main methods for measuring and analysing cell shape and cytoplasm movement were the development of bespoke software that outlined the zygote membrane, calculated the centre of area (CoA), and the length of 36 radii and 18 diameters at 10° of rotation around CoA
Summary
The purpose of the present paper was to search for movements of the zygote and two-cell stage that might increase exchange between the embryo and its environment in culture (see Discussion). The emphasis is on the changing space between the cell membrane and acellular matrix of the zona pellucida (ZP) because alterations here give strong flow in a closed hydraulic system. The disposition of this space was already known to alter in the zygote and two-cell stage (Ajduk et al, 2011; Deguchi et al, 2000; Gardner and Davies, 2003; Kurotaki et al, 2007; Waksmundzka et al, 1984). Inside each cell of the two-cell stage bulk cytoplasm flows were noticed and these flows differed from most movements of cytokinesis in that there were vortices at both ends of each nascent cell, and vorticity sometimes persisted for up to 10 h into the two-cell stage, invertebrate cytokinesis reviewed (Rappaport, 1996)
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