Possible causal factors of structural chromosome aberrations in intracytoplasmic sperm injection of the mouse

Incidence of structural chromosome aberrations in mouse one‐cell embryos produced by intracytoplasmic sperm injection (ICSI) with mature epididymal spermatozoa were influenced by sperm incubation medium and time. When spermatozoa were incubated in bicarbonate‐buffered TYH for ≤0.5 h, the embryo aberration rates were significantly higher than in vitro fertilization (IVF) embryos. However, after the incubation of spermatozoa in the same medium for ≥2 h, the aberration rates were close to the IVF embryo level. When spermatozoa were incubated in bicarbonate‐buffered mCZB, hepes‐buffered H‐TYH and H‐mCZB, and phosphate‐buffered PB1, the increased incidences of aberrations were observed at any incubation time. In the case of sperm incubation in H‐TYH, H‐mCZB and PB1, the aberration rates increased in a time‐dependent manner. Chromosome aberrations generated by ICSI were transmissible to offspring. On the other hand, the aberration rate in embryos derived from testicular spermatozoa was independent of the medium type and incubation time. Thus, the incubation media appears to have no effect on sperm chromatin. TYH can effectively induce capacitation and acrosome reaction, while H‐TYH, H‐mCZB and PB1 never induce these spermatozoal events. It is probable that the cholesterol‐rich plasma membrane and intact acrosome injected into the ooplasm affect sperm chromatin remodeling, thus resulting in the generation of chromosome damage in ICSI embryos.