MESSENGER-RNAS FOR ACTIVIN RECEPTOR-II AND RECEPTOR-IIB ARE EXPRESSEDIN MOUSE OOCYTES AND IN THE EPIBLAST OF PREGASTRULA AND GASTRULA STAGE MOUSE EMBRYOS

Activin is a potent inducer of mesoderm in frog embryos. We showed pre viously that in the mouse, activin PA is expressed in the uterine deci dua near the embryo before and during the first appearance of mesoderm (E4.5-E6.5). Here, using Northern blotting and in situ hybridization, we show that mouse oocytes, E6.5 and E7.5 embryos, and E6.5 and E7.5 decidua contain mRNAs for both activin receptors type II and IIB. The expression of activin receptor type IIB is particularly strong in embr yonic ectoderm apparent at E5.5 and continuing through E8.5. These res ults support the hypothesis that activin derived from the decidua prom otes development of mesoderm in the period E5.5-E6.5.