Transcriptional Repressor Erf Determines Extraembryonic Ectoderm Differentiation

Abstract

Extraembryonic ectoderm differentiation and chorioallantoic attachment are fibroblast growth factor (FGF)- and transforming growth factor β-regulated processes that are the first steps in the development of the placenta labyrinth and the establishment of the fetal-maternal circulation in the developing embryo. Only a small number of genes have been demonstrated to be important in trophoblast stem cell differentiation. Erf is a ubiquitously expressed Erk-regulated, ets domain transcriptional repressor expressed throughout embryonic development and adulthood. However, in the developing placenta, after 7.5 days postcoitum (dpc) its expression is restricted to the extraembryonic ectoderm, and its expression is restricted after 9.5 dpc in a subpopulation of labyrinth cells. Homozygous deletion of Erf in mice leads to a block of chorionic cell differentiation before chorioallantoic attachment, resulting in a persisting chorion layer, a persisting ectoplacental cone cavity, failure of chorioallantoic attachment, and absence of labyrinth. These defects result in embryo death by 10.5 dpc. Trophoblast stem cell lines derived from Erf^dl1/dl1 knockout blastocysts exhibit delayed differentiation and decreased expression of spongiotrophoblast markers, consistent with the persisting chorion layer, the expanded giant cell layer, and the diminished spongiotrophoblast layer observed in vivo. Our data suggest that attenuation of FGF/Erk signaling and consecutive Erf nuclear localization and function is required for extraembryonic ectoderm differentiation, ectoplacental cone cavity closure, and chorioallantoic attachment.

SUPPLEMENTAL MATERIAL

We are grateful to the IMBB animal facility personnel for keeping of the mice, S. O'Gorman of Case Western Reserve University for the PC3 ES cells, G. Kollias of the BSRC “Alexander Fleming” for his support, Ling Wang of the BIMR Mouse Molecular Genetics Shared Resource for blastocyst isolation, and Laura Virgilio for helpful discussions.

This work was supported by EU grant HPRN-CT-2000-00083, PYTHAGORAS II grant KA2091, and GSRT grant PENED99 to G.M. and in part by RO1CA098778, PO1CA102583, and Cancer Center Support Grant CA 30199 from the National Cancer Institute.