Analysis of litter size and weight in mice differing in Ped gene phenotype and the Q region of the H-2 complex.

A gene has been described, Ped (Preimplantation embryo development), that influences the rate of cleavage of preimplantation mouse embryos. Previous studies of linkage of Ped gene phenotype (fast or slow embryo development) and H-2 haplotype (H-2b or H-2k) in backcross embryos from the C57BL/10Sn and B10.BR congenic strains have shown that the Ped gene is located in the H-2 complex, the major histocompatibility complex (MHC) of the mouse. The present study was undertaken to localize the Ped gene to a particular subregion of the H-2 complex. Analysis of the B6.K1 and B6.K2 congenic strains, which differ at only the Q subregion of the MHC, was undertaken to test whether the Ped gene is located in the Q subregion of the MHC. Qa-2 antigen expression was used as a marker for the Q subregion and fast or slow development was used to assess Ped gene phenotype in backcross embryos generated from the mating of (B6.K1 x B6.K2)F1 and B6.K1 mice. The results showed linkage of Ped gene phenotype and Qa-2 antigen expression, which strongly supports the idea that the Ped gene is located in the Q subregion of the MHC. In a further set of experiments, litter size and weight were investigated in the B6.K1 and B6.K2 mice. Pure line and reciprocal crosses were made using sires and dams of both the B6.K1 and B6.K2 genotypes. Traits measured on pups included birth weight, weaning weight and weight per day of age from birth to weaning. Litter traits measured were number born and weaned and survivability. Sex effects existed for weaning weight and weight gain per day of age. Males gained more and were heavier than female pups (P less than 0.05). Pups whose sire or dam were B6.K2 were significantly (P less than 0.05) heavier at birth than those pups whose sire or dam were B6.K1, and B6.K2 homozygous pups were significantly (P less than 0.001) heavier than all others. Litters whose dams were B6.K2 had significantly more pups at birth (P less than 0.05) than those litters whose dams were B6.K1. Results suggest that pups that are heterozygous or homozygous B6.K2 are more apt to be heavier at birth and be in larger litters suggesting that genes in the Q region of the H-2 complex are advantageous to reproductive performance.