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Kate L. Loveland, Sirisha Mendis, Sarah J. Meachem, Mai A. Sarraj, Martin M. Matzuk, Activin A Balances Sertoli and Germ Cell Proliferation in the Fetal Mouse Testis., Biology of Reproduction, Volume 83, Issue Suppl_1, 1 November 2010, Page 20, https://doi.org/10.1093/biolreprod/83.s1.20
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Activin is important for male reproduction, and its role in the postnatal mouse testis has been extensively studied. This study defines the inverse relationship between activin actions on Sertoli cells and gonocytes in the fetal mouse testis, demonstrating the mechanisms by which physiological levels of activin A mediate normal testis growth. We began by investigating the normal activin signalling machinery that is present between the time of sex determination (E12.5) and birth (0 dpp). The mRNA encoding activin A (Inhba) is selectively upregulated in the testis from E12.5, followed closely by increased inhibin alpha (Inha) mRNA by E14.5. Quantitative PCR analyses revealed changes in activin receptor transcript levels: Acvr1 was significantly higher, while Acvr2b was lower in the 0 dpp testis compared with E13.5 and E15.5 timepoints. Transcript levels of Smads1, 3 and 4 were higher compared with E13.5 and E15.5, while Smads2, 5 and 7 were lower. Immunohistochemistry demonstrated phosphorylated SMAD2/3 (P-SMAD 2/3) in nearly all cell nuclei in the testis at E13.5, E15.5 and 0 dpp, indicating the widespread presence of active signalling by TGFbeta and/or activin ligands. Activin knockout (inhba-/-) mice have significantly smaller testes at birth relative to wild type littermates. This was attributed to decreased Sertoli cell proliferation from E13.5 using PCNA immunohistochemistry, and results in a 50% reduction in Sertoli cell number at birth. In contrast, the inhba-/- testis contained double the wild type number of gonocytes at birth, with some germ cells appearing to bypass quiescence prior to birth. The presence of P-SMAD 2/3 in nearly all cells in inhba-/- samples indicates the contribution of other TGFbeta superfamily ligands to fetal testis growth. Real time PCR interrogation of inhba+/+, inhba+/- and inhba-/- mouse testes at E13.5, E15.5 and at birth identified changes in activin signalling machinery and specific cell cycle regulators in relationship to inhba gene dosage that can be directly correlated with changes in the number of germ cells and Sertoli cells. This demonstrates the contribution of activin to establishing the balance between Sertoli and germ cell numbers that is required for male fertility in adulthood.
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