Chromosome aberrations in mouse embryos and fetuses produced by assisted reproductive technology

The occurrence of structural chromosome aberrations in mouse one-cell embryos produced by intracytoplasmic sperm injection (ICSI) with mature spermatozoa was dependent on the type of sperm incubation medium and sperm incubation time. When cauda epididymal spermatozoa were used following incubation in bicarbonate-buffered TYH medium for 0h (no incubation) and 0.5h, the chromosome aberration rates (6.9% and 7.4%, respectively) in the resultant embryos were significantly higher than that (2.3%) in the IVF embryos. However, when the spermatozoa were incubated for 2-2.5h and 6h in the same medium, the chromosome aberration rates were reduced to the IVF embryo level (3.8% and 4.3%, respectively). When spermatozoa incubated in Hepes-buffered H-mCZB and phosphate-buffered PB1 media were used for ICSI, chromosome aberration rates in embryos were significantly high (8.6-28.1%) and increased in a time-dependent manner. On the other hand, when immature testicular spermatozoa were incubated in those three media for 0.5h and 6h, the incidences of resultant embryos with structural chromosome aberrations ranged between 7.4% and 11.7%, and there was no medium- and time-dependent change in these aberration rates. To evaluate transmissible risk of chromosome aberrations to offspring, two- or four-cell embryos derived from cauda epididymal spermatozoa were transferred into the oviducts of pseudopregnant females and chromosomes of live fetuses were examined on gestational day 16. One (2.0%) mosaic fetus was found when spermatozoa were incubated in TYH for 2-2.5h, and there were four (6.7%) fetuses displaying a structurally abnormal karyotype when spermatozoa were incubated in H-mCZB for 2-2.5h, indicating that structural chromosome aberrations generated in ICSI one-cell embryos are transmissible to offspring. The causal mechanism of structural chromosome aberrations in ICSI one-cell embryos is discussed in relation to the acrosomal plasma membrane cholesterol and the acrosome.