The effects of spermatozoal irradiation with X-rays on chromosome abnormalities and on development of mouse zygotes after delayed fertilization

Maturation/M-phase promoting factor regulates aging of porcine oocytes matured in vitro

Control of oocyte aging during manipulation of matured oocytes should have advantages for recently developed reproductive technologies, such as cloning after nuclear transfer. We have shown that the enhanced activation ability and fragmentation of porcine in vitro matured and aged oocytes bore a close relationship to the gradual decrease in maturation/M-phase promoting factor (MPF) activity and that porcine aged oocytes contained plenty of MPF, but it was in an inactive form, pre-MPF, as a result of phosphorylation of its catalytic subunit p34(cdc2) and, therefore, had low MPF activity. We incubated porcine oocytes with vanadate and caffeine, which affected the phosphorylation status and MPF activity, and evaluated their activation abilities and fragmentation frequencies. Incubation of nonaged oocytes with vanadate increased p34(cdc2) phosphorylation and reduced MPF activity to levels similar to those of aged oocytes and increased their parthenogenetic activation and fragmentation rates compared with those of the control oocytes. Conversely, treating aged oocytes with caffeine reduced p34(cdc2) phosphorylation and increased MPF activity. These oocytes showed significantly lower parthenogenetic activation and fragmentation rates than aged mature oocytes. These results suggest that MPF activity is a key mechanism of oocyte aging and controlling MPF activity by altering p34(cdc2) phosphorylation with these chemicals may enable oocyte aging to be manipulated in vitro. We expect those ideas will be applied practically to pig cloning.

Unprotected freezing of human spermatozoa exerts a detrimental effect on their oocyte activating capacity and chromosome integrity

The influence of unprotected freezing of mammalian spermatozoa on their oocyte activating capacity and chromosome integrity is unknown. However, this type of sperm treatment has been used in assisted reproduction by intracytoplasmic sperm injection in cattle and humans. The mouse oocyte injection test was used to analyse the influence of unprotected freezing of human spermatozoa on their reproductive characteristics. Mouse oocytes were microinjected with intact human spermatozoa or spermatozoa treated with two cycles of unprotected freeze-thawing. Oocytes surviving the injection were either cultured without further treatment or exposed to ethanol solution to induce parthenogenetic activation. Both injected and activated oocytes were used for sperm chromosome analysis. The results revealed a significant reduction in oocyte activating capacity and a tenfold increase in the incidence of structural chromosomal abnormalities in human spermatozoa treated by unprotected freezing. We conclude that unprotected freezing of human spermatozoa has a detrimental effect on their reproductive characteristics. Our data also provide a new perspective on the stability of mammalian spermatozoa to physical factors and demonstrate the importance of detailed analysis of the stability of sperm structures for successful development of new approaches in assisted reproduction.