A degron-based approach to manipulate Eomes functions in the context of the developing mouse embryo.

The T-box transcription factor Eomesodermin (Eomes), also known as Tbr2, plays essential roles in the early mouse embryo. Loss-of-function mutant embryos arrest at implantation due to Eomes requirements in the trophectoderm cell lineage. Slightly later, expression in the visceral endoderm promotes anterior visceral endoderm formation and anterior-posterior axis specification. Early induction in the epiblast beginning at day 6 is necessary for nascent mesoderm to undergo epithelial to mesenchymal transition (EMT). Eomes acts in a temporally and spatially restricted manner to sequentially specify the yolk sac haemogenic endothelium, cardiac mesoderm, definitive endoderm, and axial mesoderm progenitors during gastrulation. Little is known about the underlying molecular mechanisms governing Eomes actions during the formation of these distinct progenitor cell populations. Here, we introduced a degron-tag and mCherry reporter sequence into the Eomes locus. Our experiments analyzing homozygously tagged embryonic stem cells and embryos demonstrate that the degron-tagged Eomes protein is fully functional. dTAG (degradation fusion tag) treatment in vitro results in rapid protein degradation and recapitulates the Eomes-null phenotype. However in utero administration of dTAG resulted in variable and lineage-specific degradation, likely reflecting diverse cell type-specific Eomes expression dynamics. Finally, we demonstrate that Eomes protein rapidly recovers following dTAG wash-out in vitro. The ability to temporally manipulate Eomes protein expression in combination with cell marking by the mCherry-reporter offers a powerful tool for dissecting Eomes-dependent functional roles in these diverse cell types in the early embryo.

The transcriptional repressor Blimp1/PRDM1 regulates the maternal decidual response in mice.

The transcriptional repressor Blimp1 controls cell fate decisions in the developing embryo and adult tissues. Here we describe Blimp1 expression and functional requirements within maternal uterine tissues during pregnancy. Expression is robustly up-regulated at early post-implantation stages in the primary decidual zone (PDZ) surrounding the embryo. Conditional inactivation results in defective formation of the PDZ barrier and abnormal trophectoderm invasion. RNA-Seq analysis demonstrates down-regulated expression of genes involved in cell adhesion and markers of decidualisation. In contrast, genes controlling immune responses including IFNγ are up-regulated. ChIP-Seq experiments identify candidate targets unique to the decidua as well as those shared across diverse cell types including a highly conserved peak at the Csf-1 gene promoter. Interestingly Blimp1 inactivation results in up-regulated Csf1 expression and macrophage recruitment into maternal decidual tissues. These results identify Blimp1 as a critical regulator of tissue remodelling and maternal tolerance during early stages of pregnancy.