The Ggnbp2 null mutant embryos died in utero between Embryonic Days 13.5 to 15.5 with dysmorphic placentae, characterized by excessive nonvascular cell nests consisting of proliferative trophoblastic tissue and abundant trophoblast stem cells (TSCs) in the labyrinth. Lethality of Ggnbp2 null embryos was caused by insufficient placental perfusion as a result of remarkable decreases in both fetal and maternal blood vessels in the labyrinth. These defects were accompanied by a significant elevation of c-Met expression and phosphorylation and its downstream effector Stat3 activation. Knockdown of Ggnbp2 in wild-type TSCs in vitro provoked the proliferation but delayed the differentiation with an upregulation of c-Met expression and an enhanced phosphorylation of c-Met and Stat3. In contrast, overexpression of Ggnbp2 in wild-type TSCs exhibited completely opposite effects compared to knockdown TSCs. These results suggest that loss of GGNBP2 in the placenta aberrantly overactivates c-Met-Stat3 signaling, alters TSC proliferation and differentiation, and ultimately compromises the structure of placental vascular labyrinth. Our studies for the first time demonstrate that GGNBP2 is an essential factor for pregnancy success acting through the maintenance of a balance of TSC proliferation and differentiation during placental development.

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There is no consensus whether Sertoli cells express estrogen receptor 1 (Esr1). Reverse transcription-polymerase chain reaction, Western blot, and immunofluorescence demonstrated that mouse Sertoli cell lines, TM4, MSC-1, and 15P-1, and purified primary mouse Sertoli cells (PSCs) contained Esr1 messenger RNA and proteins. Incubation of Sertoli cells with 17b-estradiol (E2) or ESR1 agonist stimulated the expression of an estrogen responsive gene Greb1, which was prevented by ESR inhibitor or ESR1 antagonist. Overexpression of Esr1 in MSC-1 enhanced E2-induced Greb1 expression, while knockdown of Esr1 by small interfering RNA in TM4 attenuated the response. Furthermore, E2-induced Greb1 expression was abolished in the PSCs isolated from Amh-Cre/Esr1-floxed mice in which Esr1 in Sertoli cells were selectively deleted. Chromatin immunoprecipitation assays indicated that E2-induced Greb1 expression in Sertoli cells was mediated by binding of ESR1 to estrogen responsive elements. In summary, ligand-dependent nuclear ESR1 was present in mouse Sertoli cells and mediates a classical genomic action of estrogens.

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