Histochemical Demonstration of Activin/lnhibin βA-βB and α-Subunits in Early Embryos and Oviducts of Different Strains of Mice

Spontaneous arrest of cleavage takes place at the 2-cell stage (the 2-cell block) in vitro, in some mouse strains (the “blocking strains”), whereas in others, no such arrest has been recorded (the “non-blocking strains”). We found that activin A releases the 2-cell block, and stimulates the early embryogenesis in mice of the blocking strains (Lu etal. 1990). In this paper, presence of activin/inhibin subunits in zygotes, 2-cell embryos, and oviductal epithelial cells was demonstrated immunohistochemically, using the blocking (CD-1 and DBA/2NJcl) and the non-blocking (C57BL/6NCrj) strains of mice. Strong immunoreactivity for the and βe-subunits of activins/inhibins was detected, in the cytoplasm of 1-cell and 2-cell embryos of the 3 strains. Staining intensities with the βA-subunit was higher during the 2-cell stage than during the 1-cell stage in the blocking strains. In the non-blocking strains, no such increase was observed. In contrast with the case of βA-subunit, immunoreactivity of the embryos to the βB-subunit decreased in the blocking strains, while in the non-blocking strain, it stayed at the same level between the two stages. Possible role played by activin AB in the early embryogenesis, was discussed. The immunohistochemically detected activin/inhibin subunits in the zona, probably represented those transferred passively from the oviductal fluid.