Activins are expressed in preimplantation mouse embryos and in ES and EC cells and are regulated on their differentiation

RM Albano, N Groome, JC Smith - Development, 1993 - journals.biologists.com
RM Albano, N Groome, JC Smith
Development, 1993journals.biologists.com
Members of the activin family have been suggested to act as mesoderm-inducing factors
during early amphib-ian development. Little is known, however, about meso-derm formation
in the mammalian embryo, and as one approach to investigating this we have studied activin
expression during early mouse development. Activins are homo-or heterodimers of the βA or
βB subunits of inhibin, itself a heterodimer consisting of one of the β subunits together with
an α subunit. Our results indicate that the oocyte contains mRNA encoding all three …
Abstract
Members of the activin family have been suggested to act as mesoderm-inducing factors during early amphib- ian development. Little is known, however, about meso- derm formation in the mammalian embryo, and as one approach to investigating this we have studied activin expression during early mouse development.
Activins are homo- or heterodimers of the βA or βB subunits of inhibin, itself a heterodimer consisting of one of the β subunits together with an α subunit. Our results indicate that the oocyte contains mRNA encoding all three subunits, and antibody staining demonstrates the presence of both α and β protein chains. From the fer- tilized egg stage onwards, α subunit protein cannot be detected, so the presence of β subunits reflects the pres- ence of activin rather than inhibin.
Maternal levels of activin protein decline during early cleavage stages but increase, presumably due to zygotic transcription (see below), in the compacted morula. By 3.5 days, only the inner cell mass (ICM) cells of the blas- tocyst express activin, but at 4.5 days the situation is reversed; activin expression is confined to the trophec- toderm. Using reverse transcription-PCR, neither βA nor βB mRNA was detectable at the two-cell stage but transcripts encoding both subunits were detectable at the morula stage, with βB mRNA persisting into the blastocyst.
We have also analyzed activin and inhibin expression in ES and EC cells. Consistent with the observation that activins are expressed in the ICM of 3.5-day blastocysts, we find high levels of βA and βB mRNA in all eight ES cell lines tested. F9 EC cells express only activin βB, together with low levels of the inhibin αchain. When ES and EC cells are induced to differentiate, levels of activin fall dramatically. These results are consistent with a role for activins in mesoderm formation and other steps of early mouse development.
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