Follistatin expression in ES and F9 cells and in preimplantation mouse embryos.

Activins are thought to play a role in mesoderm induction in amphibian development. Studies of the expression patterns of activin during mouse embryogenesis are consistent with the proposal that they are also involved in mesoderm formation in mammals. Activins are expressed both maternally and zygotically at preimplantation stages, and at postimplantation stages transcripts are present at high levels in the deciduum, suggesting that mesoderm is induced by maternally-derived activin. The functions of activin can be modulated by follistatin. At postimplantation stages follistatin is expressed in the deciduum in a pattern reciprocal to that of activin. In the embryo proper, follistatin transcripts are localized to the primitive streak region during gastrulation and later in the somites and in rhombomeres 2, 4 and 6 of the hindbrain. In this paper we show that follistatin, like activin, is expressed throughout pre-implantation mouse development. Transcripts are present at low levels in undifferentiated F9 and ES cells, but they increase greatly on differentiation of both cell types. Expression of activin mRNA is decreased in differentiated F9 and ES cells, and the simultaneous increase in follistatin may create an efficient and rapid means of decreasing levels of functional activin.