Abstract: SAT 126

SMAD3 and SMAD4 Are Required for FSH Synthesis By Pituitary Gonadotrope Cells In Vivo

Presenter:


Abstract


Pituitary follicle-stimulating hormone (FSH) is an essential regulator of gonadal function and fertility in females and of quantitatively normal spermatogenesis in males. Pituitary-derived activins directly stimulate FSH synthesis by regulating transcription of the FSHβ subunit gene (Fshb) in gonadotrope cells. According to in vitro models, activins stimulate the formation of complexes of the signaling molecule SMAD3, its obligate co-factor SMAD4, and the forkhead transcription factor FOXL2. view more

Pituitary follicle-stimulating hormone (FSH) is an essential regulator of gonadal function and fertility in females and of quantitatively normal spermatogenesis in males. Pituitary-derived activins directly stimulate FSH synthesis by regulating transcription of the FSHβ subunit gene (Fshb) in gonadotrope cells. According to in vitro models, activins stimulate the formation of complexes of the signaling molecule SMAD3, its obligate co-factor SMAD4, and the forkhead transcription factor FOXL2. SMAD4 and FOXL2 bind adjacent cis-elements in the proximal Fshb promoter and the two proteins are linked through their mutual association with the C-terminal Mad homology 2 (MH2) domain of SMAD3. Consistent with this model, mice harboring loss of function mutations in Smad4 or Foxl2 specifically in gonadotropes are FSH deficient and subfertile. SMAD3’s role in vivo is less clear, however, as gonadotrope-specific Smad3 ‘knockout’ mice exhibit quantitatively normal FSH synthesis and fertility. Importantly, these mice may express a truncated form of the SMAD3 protein that lacks the N-terminal DNA binding MH1 domain but possesses the entirety of the MH2 domain. The latter represents the domain of the protein that is activated by activin receptors and mediates protein-protein interactions. Unfortunately, there are currently no mouse models that enable the complete and selective abrogation of SMAD3 function in gonadotropes or other cell types. However, based on the current in vitro model of activin induction of Fshb transcription, we reasoned that mice lacking both SMAD3 DNA binding activity and SMAD4 in gonadotropes (hereafter, S3/4 conditional knockout or cKO) should be FSH deficient and sterile. Indeed, S3/4cKO females are profoundly hypogonadal and have thread-like uteri. Furthermore, these females are acyclic and sterile, and their ovaries lack antral follicles and corpora lutea. S3/4cKO males have reduced testis mass and epididymal sperm counts compared with littermate controls, but are fertile. These phenotypes are consistent with those of Fshb knockout mice. Indeed, pituitary Fshb mRNA levels are significantly reduced in both male and female S3/4cKOs. In contrast, GnRH receptor (Gnrhr) mRNA levels are significantly elevated in cKOs in both sexes. Interestingly, other genes were altered in sex-specific fashion. Specifically, luteinizing hormone β subunit (Lhb) and common gonadotropin α subunit (Cga) mRNA expression are greatly elevated in S3/4cKO females, but significantly reduced in S3/4cKO males. The mechanisms underlying these sex differences are not yet clear, but might reflect differences in sex steroid milieu. Overall, our analyses suggest that: 1) SMAD3 is required for FSH synthesis in vivo and 2) residual FSH synthesis in Smad4-deficient mice likely reflects compensatory actions of SMAD3.
This research was supported by CIHR operating grant MOP-133394 and NSERC Discovery Grant 2015-05178 to DJB.

show less
Files:

Share this PosterTalk

About PosterTalks

PosterTalks allows meeting attendees the ability to view these presentations, download or bookmark their favorite presentations, download PDF versions of the posters, ask questions, leave comments, and share presentations with their colleagues – all from the convenience of a smart phone.

Contact Us

Have a question? Click here to contact us. Need technical support? Click here to email support.

© 2018 PosterTalks and Connect BioMed. All other content and data, including data entered into this website are copyrighted by their respective owners.