A cytogenetic study of in-vitro matured murine oocytes after ICSI by human sperm.

BACKGROUND The purpose of this study was to investigate the chromosomal complement and developmental potential of in-vitro matured murine oocytes following ICSI by human sperm. METHODS Heterologous ICSI fertilization between mouse oocytes and human sperm was employed in order to overcome the reduced fertilization rates observed after conventional IVF due to zona hardening during in-vitro maturation, and to assess separately maternal and paternal chromosome complements. Cytogenetic analyses were performed in four types of oocytes: (i) in-vitro matured metaphase II (MII) oocytes; (ii) in-vivo matured MII oocytes; (iii) in-vitro matured oocytes after ICSI; (iv) in-vivo matured oocytes after ICSI. RESULTS Activation rates after ICSI of in-vitro matured oocytes was lower than that of in-vivo matured oocytes (69.9 versus 97.2%, P < 0.01), and premature chromosomal condensation was only observed in in-vitro matured oocytes. However, there were no significant differences in developmental rates after successful activation between in-vivo and in-vitro matured ICSI oocytes (69.7 versus 76.6%). The incidences of aneuploidy and structural aberrations were similar between the ICSI embryos and non-ICSI (MII) oocytes. Furthermore, the frequency of chromosomal aberrations was not associated with in-vitro or in-vivo maturation. Similar analyses of paternal chromosomes indicated that there were no significant differences in the incidence of chromosomal aberrations between the embryos derived from in-vitro and in-vivo matured oocytes. CONCLUSIONS These results suggest that in-vitro matured oocytes following ICSI do not lead to an increase in the frequency of aneuploidy and structural aberrations when human sperm are injected into mouse oocytes.