mRNAs for activin receptors II and IIB are expressed in 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 previously that in the mouse, activin beta A is expressed in the uterine decidua 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 embryonic ectoderm apparent at E5.5 and continuing through E8.5. These results support the hypothesis that activin derived from the decidua promotes development of mesoderm in the period E5.5-E6.5.