Normal gonadotropin production and fertility in gonadotrope-specific Bmpr1a knockout mice

Abstract

Pituitary FSH synthesis is regulated by TGFβ superfamily ligands; most notably the activins and inhibins. Bone morphogenetic proteins (BMPs) also regulate FSHβ subunit (Fshb) expression in immortalized murine gonadotrope-like LβT2 cells and in primary murine or ovine primary pituitary cultures. BMP2 signals preferentially via the BMP type I receptor, BMPR1A, to stimulate murine Fshb transcription in vitro. Here, we used a Cre-lox approach to assess BMPR1A’s role in FSH synthesis in mice in vivo. Gonadotrope-specific Bmpr1a knockout animals developed normally and had reproductive organ weights comparable to those of controls. Knockouts were fertile, with normal serum gonadotropins and pituitary gonadotropin subunit mRNA expression. Cre-mediated recombination of the floxed Bmpr1a allele was efficient and specific, as indicated by PCR analysis of diverse tissues and isolated gonadotrope cells. Furthermore, BMP2 stimulation of inhibitor of DNA binding 3 expression was impaired in gonadotropes isolated from Bmpr1a knockout mice, confirming the loss of functional receptor protein in these cells. Treatment of purified gonadotropes with small molecule inhibitors of BMPR1A (and the related receptors BMPR1B and ACVR1) suppressed Fshb mRNA expression, suggesting that an autocrine BMP-like molecule might regulate FSH synthesis. However, deletion of Bmpr1a and Acvr1 in cultured pituitary cells did not alter Fshb expression, indicating that the inhibitors had off-target effects. In sum, BMPs or related ligands acting via BMPR1A or ACVR1 are unlikely to play direct physiological roles in FSH synthesis by murine gonadotrope cells.

Transcription factor GATA2 may potentiate follicle-stimulating hormone production in mice via induction of the BMP antagonist gremlin in gonadotrope cells

“…Gremlin is a BMP antagonist, and BMPs were previously reported to regulate Fshb expression in different contexts ( 45 , 48 , 51 ). Nevertheless, mice lacking canonical BMP type II (BMPR2) ( 34 ) or type I receptors (ACVR1 and BMPR1A) ( 52 ) in gonadotropes produce FSH normally. Therefore, BMPs do not appear to signal directly in gonadotropes to regulate FSH production in mice.…”

“…Eventually, given that cKO females had normal fertility, Gata2 fx/fx ; Gnrhr GRIC/+ females were mated to Gata2 fx/fx males so that all progeny could be used for experiments (50% control, 50% cKO). Genotyping and assessment of genomic recombination were conducted as previously described ( 52 ) (primers listed in Table 1 ). Animals were housed ad libitum on a 12L:12D cycle (lights on at 7:00, lights off at 19:00).…”

Impaired LH surge amplitude in gonadotrope-specific progesterone receptor knockout mice

“…Controls for FACS were generated by crossing Rosa26 mTmG/mTmG and GRIC mice to generate Pgr +/+ ;Gnrhr GRIC/+ ;Rosa26 mTmG/+ progeny. Genotyping and assessment of genomic recombination were conducted as previously described (Zhou et al 2016) (primers listed in Table 1). All animal experiments were performed in accordance with institutional and federal guidelines and were approved by the McGill University and Goodman Cancer Centre Facility Animal Care Committee (Protocol 5204).…”

Cellular interactions in the pituitary stem cell niche

“…There have been no compelling studies from mouse, that analyse the postnatal role of FGFs or BMPs within the anterior pituitary, despite emerging data from sequencing studies that ligands continue to be expressed after morphogenesis and into adulthood [ 69 , 70 ]. BMPR1A is detected in mouse gonadotroph cell lines and enables signalling of BMP2 [ 71 ], however efficient murine genetic deletion of Bmpr1a in gonadotrophs did not result in a phenotype [ 72 ]. Mutations activating the MAPK signalling pathway result in tumour formation, showing an increase in proliferation of SOX2+ cells and impairment of differentiation [ 73 ].…”