The effect of in-vitro ageing on mouse sperm chromosomes

In-vitro ageing has long been suspected to affect adversely the ability of spermatozoa to fertilize and produce viable zygotes. A comparison of the first cleavage chromosome complement of 824 mouse embryos fertilized with fresh spermatozoa and 656 embryos fertilized with spermatozoa aged for 12, 24 or 48 h is reported herein. The chromosome analysis of first-cleavage embryos allows us to study directly the paternal and maternal chromosome complements which contribute to the embryo. Both chromosome clusters remain separate when an antimitotic agent is used to prevent metaphase synchronization, allowing identification of maternal and paternal chromosomes. We show that after sperm ageing, there is a decrease in the fertilization rate from 75% in the controls to 57.5% (12 h of ageing), 63.5% (24h of ageing) and 4.4% (48 h of ageing). Simultaneously, the level of chromosome structural abnormalities increase from 1.3% in the controls to 16.5% after 12 h of ageing, 18.8% after 24 h of ageing and 59% after 48 h of ageing. The incidence of aneuploidy and polyploidy is not affected by ageing of the spermatozoa. Most of the structural abnormalities are paternal in origin and are presumably induced by the ageing of spermatozoa.