Postnatal compensatory growth of manipulated mouse embryos.

As an extension of the biometrical analysis of data described in an earlier paper (Papaioannou et al., 1989, Development, 106, 817-827), we have examined the extent of postnatal compensatory growth in body weight and tail length of genetically identical F1 mice from the following groups: controls--the natural offspring of timed matings; transferred controls--offspring from embryos flushed at the 2-cell stage and transferred to recipient foster mothers; and transferred half embryos--offspring developing from one blastomere from the 2-cell stage transferred to recipient foster mothers. There was little difference between the postnatal growth curves of transferred controls and mice produced from half embryos, indicating regulation during prenatal development is complete and that halving an embryo at the beginning of gestation has no lasting effects on its size or postnatal growth rate. In contrast, embryo transfer itself had a significant effect, resulting in smaller litters and larger, more variable animals after birth. There was then a period of postnatal compensatory growth in body weight and tail length after 4 weeks of age. We have provided direct evidence that animals that become relatively large during early growth curtail their growth rate compared to small animals as they approach maximum size and the reverse occurs with small animals. A similar phenomenon was observed for tail length. Although the overall variance of embryo transfer mice is high during postnatal growth, the intraclass correlation coefficient is also high, making them useful for comparative experiments.