Abstract
BackgroundDimethyl sulfoxide (DMSO) is used extensively as a permeable cryoprotectant and is a common solvent utilized for several water-insoluble substances. DMSO has various biological and pharmacological activities; however, the effect of DMSO on mouse oocyte meiotic maturation remains unknown.ResultsIn DMSO-treated oocytes, we observed abnormal MII oocytes that contained large polar bodies, including 2-cell–like MII oocytes, during in vitro maturation. Oocyte polarization did not occur, due to the absence of actin cap formation and spindle migration. These features are among the primary causes of abnormal symmetric division; however, analysis of the mRNA expression levels of genes related to asymmetric division revealed no significant difference in the expression of these factors between the 3% DMSO-treated group and the control group. After each “blastomere” of the 2-cell–like MII stage oocytes was injected by one sperm head respectively, the oocytes still possessed the ability to extrude the second polar body from each “blastomere” and to begin cleavage. However, MII oocytes with large polar bodies developed to the blastocyst stage after intracytoplasmic sperm injection (ICSI). Furthermore, other permeable cryoprotectants, such as ethylene glycol and glycerol, also caused asymmetric division failure.ConclusionPermeable cryoprotectants, such as DMSO, ethylene glycol, and glycerol, affect asymmetric division. DMSO disrupts cytokinesis completion by inhibiting cortical reorganization and polarization. Oocytes that undergo symmetric division maintain the ability to begin cleavage after ICSI.
Highlights
Dimethyl sulfoxide (DMSO) is used extensively as a permeable cryoprotectant and is a common solvent utilized for several water-insoluble substances
DMSO treatment causes disruption of asymmetric division In vitro-maturing oocytes were exposed to DMSO, which resulted in abnormal metaphase II (MII) oocytes with large polar
By the MII stage, several oocytes had formed a 2-cell–like structure (Figure 2). These results indicate that spindle migration and actin cap formation were disrupted after DMSO treatment
Summary
Dimethyl sulfoxide (DMSO) is used extensively as a permeable cryoprotectant and is a common solvent utilized for several water-insoluble substances. Mouse oocyte maturation is a precise and orderly multistage process [1,2]. During this process, the oocyte is transformed into a highly polarized large metaphase II (MII)-arrested oocyte with a small polar body that extrudes from the oocyte, which is essential for the retention of maternal components necessary for early development [3]. Mouse oocyte meiotic maturation is characterized by a unique asymmetric division process. To ensure asymmetry in each division, the meiotic spindle has to be positioned near one side of the cortex. The spindle migrates along its long axis to the cortex in an actin-dependent manner, which
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