Structural chromosomal aberrations, aneuploidy, and mosaicism in early cleavage mouse embryos derived from spermatozoa exposed to γ-rays.

Purpose: To quantitatively and qualitatively investigate the changes in chromosomal aberrations during early cleavage in mouse embryos derived from γ-irradiated spermatozoa.

Materials And Methods: Mature males were exposed to 2 Gy or 4 Gy of ¹³⁷Cs γ-rays, and their spermatozoa were used to produce embryos via in vitro fertilisation (IVF). The metaphase chromosomes were prepared from one-cell, two-cell, and four-cell embryos. In the chromosome preparations from two-cell and four-cell embryos, the separation of the sister blastomeres was precluded by treatment of the embryos with concanavalin A. The incidence of embryos with structural chromosomal aberrations, aneuploidy, or mosaicism was estimated. The fates of the different types of γ-ray-induced structural chromosomal aberrations were also investigated in those embryos.

Results: The exposure of spermatozoa to 2 Gy or 4 Gy γ-rays caused structural chromosomal aberrations in 25.9% and 35.7% of the resultant one-cell embryos, respectively. At two-cell embryonic stage, the incidence of structural chromosomal aberrations was 17.4% in the 2 Gy group and 27.1% in the 4 Gy group. At the four-cell embryonic stage, although the incidence of control embryos with structural chromosomal aberrations was considerably high, the net incidence of embryos with radiation-induced structural chromosomal aberrations was similar to that at the one-cell stage. The incidence of aneuploidy was high in two-cell and four-cell embryos after both doses of γ-rays. The incidence of mosaicism increased significantly in dose- and embryonic-stage-dependent manners. Anaphase lag, and the degeneration and non-disjunction of the aberrant chromosomes were frequently observed in aneuploid and mosaic embryos.

Conclusions: Mouse sperm DNA is highly vulnerable to γ-rays. The structural chromosomal aberrations of sperm origin are unstable in their behaviour and structure during cleavage, and therefore cause secondary aneuploidy and mosaicism in the early cleavage embryos.