Chromosomal constitution of mouse blastocysts derived from oocytes inseminated by multiple sperm insertion into the perivitelline space

Abstract

Our purpose was to evaluate the rate of chromosomal aberrations in mouse blastocysts obtained after microinjection of multiple spermatozoa under the zona pellucida of mature oocytes. Without detecting the appearance of pronuclei, the microinjected mouse oocytes containing two polar bodies were cultivated to the blastocyst stage and then analyzed cytogenetically. A chromosome study was carried out in a total of 109 blastocysts derived after microinjection of motile spermatozoa into the perivitelline space. Fifty-five blastocysts (50.5%) exhibited normal diploid chromosome complements, 30 (27.5%) showed different forms of mosaicism, and 24 (22%) exhibited haploidy caused by parthenogenetic activation. Compared to in vivo and in vitro control groups there was a significant increase in the parthenogenesis and mosaic forms of embryos produced by micromanipulation (P < 0.001). A total of 360 well-spread metaphases of 103 blastocysts was analyzed to determine whether the micromanipulation procedure increased the chance of aneuploidy. Aneuploid numbers of chromosomes were absent in all the metaphases analyzed. Mosaicism and parthenogenesis appear to be increased significantly following microinjection of multiple spermatozoa under the zona pellucida of mouse oocytes, and there was no evidence of aneuploidy.