Genetic background of the differences in timing of meiotic maturation in mouse oocytes: a study using recombinant inbred strains.

Recombinant inbred strains of mice derived from CBA and KE strains were used for studying the genetic background of the duration of the first meiotic cycle which differs in oocytes from progenitor strains. Oocytes were screened in vitro for the timing of germinal vesicle breakdown as well as for the timing of first polar body extrusion, and the approximate duration of the first meiotic M-phase was calculated. Although oocytes from progenitor strains did not differ in the duration of germinal vesicle breakdown, this characteristic segregated in recombinant strains showing involvement of at least two genes. Because of the similar duration of germinal vesicle breakdown in CBA and KE oocytes, the difference in timing of first polar body extrusion (9 h and 12 h for CBA and KE, respectively) reflects the difference in the duration of the first meiotic M-phase. The timing of germinal vesicle breakdown and the duration of M-phase in recombinant strains were negatively correlated (P < 0.01); in general, the more time needed for breakdown of the germinal vesicle, the shorter the M-phase. The timing of first polar body extrusion varied among strains: in some it was similar to one of the parental strains; in others it was intermediate between the two, which again shows the involvement of at least two genes in the control of this character. The linkage analysis suggests that one of the putative genes influencing the timing of first polar body extrusion may be situated near the Gpi-1 locus on chromosome 7, that is, in the region containing the locus for cyclin E. The possible involvement of cyclin E in the control of the timing of first meiosis in mouse oocytes is discussed.