Activation of paternally derived regulatory mechanism in early mouse embryo

A stage-specific occurrence of retrovirus-like elements (intracisternal particles) is regularly observed within the endoplasmic reticulum of early mouse embryos. A quantitative electron microscopic study was carried out on hybrid embryos issued from the matings between high- and low-producer mouse strains of intracisternal particles. The low-producer character behaved as dominant in all these crosses, and this enabled us to demonstrate the activation of paternally introduced regulatory mechanism in two-cell embryos and morulae. There was no sign of maternal effect in the results of reciprocal crosses.