Transforming growth factor β (TGF-β) and related growth factors are secreted pleiotropic factors that play critical roles in embryogenesis and adult tissue homeostasis by regulating cell proliferation, differentiation, death, and migration. The TGF-β family members signal via heteromeric complexes of type I and type II receptors, which activate members of the Smad family of signal transducers. The main attribute of the TGF-β signaling pathway is context-dependence. Depending on the concentration and type of ligand, target tissue, and developmental stage, TGF-β family members transmit distinct signals. Deregulation of TGF-β signaling contributes to developmental defects and human diseases. More than a decade of studies have revealed the framework by which TGF-βs encode a context-dependent signal, which includes various positive and negative modifiers of the principal elements of the signaling pathway, the receptors, and the Smad proteins. In this review, we first introduce some basic components of the TGF-β signaling pathways and their actions, and then discuss posttranslational modifications and modulatory partners that modify the outcome of the signaling and contribute to its context-dependence, including small noncoding RNAs.

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TGF-β Signaling from Receptors to Smads.

Transforming growth factor beta (TGF-beta) family members signal via heterotetrameric complexes of type I and type II dual specificity kinase receptors. The activation and stability of the receptor ...

/pdf/signaling-receptors-for-tgf-b-family-members-2wl9tw60r2.pdf

Signaling Receptors for TGF-β Family Members

MicroRNAs (miRNAs) are transcriptional and posttranscriptional regulators involved in nearly all known biological processes in distant eukaryotic clades. Their discovery and functional characterization have broadened our understanding of biological regulatory mechanisms in animals and plants. They show both evolutionary conserved and unique features across Metazoa. Here, we present the current status of the knowledge about the role of miRNA in development, growth, and physiology of teleost fishes, in comparison to other vertebrates. Infraclass Teleostei is the most abundant group among vertebrate lineage. Fish are an important component of aquatic ecosystems and human life, being the prolific source of animal proteins worldwide and a vertebrate model for biomedical research. We review miRNA biogenesis, regulation, modifications, and mechanisms of action. Specific sections are devoted to the role of miRNA in teleost development, organogenesis, tissue differentiation, growth, regeneration, reproduction, endocrine system, and responses to environmental stimuli. Each section discusses gaps in the current knowledge and pinpoints the future directions of research on miRNA in teleosts.

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microRNA in teleost fish

Although much progress has been made in the genetic dissection of biological networks involved in follicular/luteal development in the mammalian ovary, the gene regulation mechanisms involved are still poorly understood. Over the last 10 years, miRNAs have emerged as master regulators of tissue growth and differentiation in animals. However, compared with other body tissues, little is still known about the functional involvement of miRNAs in the ovary. Several studies have identified miRNA populations specifically associated with the development of follicles and corpora lutea, particularly in relation to the follicular-luteal transition, and the functional involvement of some of these miRNAs has been characterised in vitro and/or in vivo. Specifically, three different miRNAs, miR-224, miR-378 and miR-383, have shown to be involved in regulating aromatase expression during follicle development. In addition, miR-21 has been identified as promoting follicular cell survival during ovulation, and pro-angiogenic miR-17-5p and let-7b were shown to be necessary for normal development of the corpus luteum. Experimental evidence for the involvement of several other miRNAs in different aspects of follicle/luteal development has also been obtained. In addition, many of these studies exemplify the challenges associated with identifying physiologically relevant targets of ovarian miRNAs. Continuous advances in this field will be considerably facilitated by progress in understanding miRNA physiology in other body systems and will eventually lead to a much better understanding of the control of follicular/luteal development. In turn, through the potential offered by miRNA diagnostics and miRNA therapeutics, this new knowledge should bring considerable benefits to reproductive medicine.

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Involvement of miRNAs in ovarian follicular and luteal development

MicroRNAs as therapeutic targets in chemoresistance

Activin, a member of the transforming growth factor-β superfamily, promotes the growth of preantral follicles and the proliferation of granulosa cells. However, little is known about the role of microRNAs in activin-mediated granulosa cell proliferation. Here, we reported a dose- and time-dependent suppression of microRNA-181a (miR-181a) expression by activin A in mouse granulosa cells (mGC). Overexpression of miR-181a in mGC suppressed activin receptor IIA (acvr2a) expression by binding to its 3′-untranslated region (3′-UTR), resulting in down-regulation of cyclin D2 and proliferating cell nuclear antigen expression, leading to inhibition of the cellular proliferation, while overexpression of acvr2a attenuated the suppressive effect of miR-181a on mGC proliferation. Consistent with the inhibition of acvr2a expression, miR-181a prevented the phosphorylation of the activin intracellular signal transducer, mothers against decapentaplegic homolog 2 (Smad2), leading to the inactivation of activin signaling pathway. Interestingly, we found that miR-181a expression decreased in ovaries of mice at age of 8, 12, and 21 days, as compared with that in ovaries of 3-day old mice, and its level was reduced in preantral and antral follicles of mice compared with that in primary ones. Moreover, the level of miR-181a in the blood of patients with premature ovarian failure was significantly increased compared with that in normal females. This study identifies an interplay between miR-181a and acvr2a, and reveals an important role of miR-181a in regulating granulosa cell proliferation and ovarian follicle development.

/pdf/microrna-181a-suppresses-mouse-granulosa-cell-proliferation-1bb6jui1hu.pdf

MicroRNA-181a Suppresses Mouse Granulosa Cell Proliferation by Targeting Activin Receptor IIA

https://febs.onlinelibrary.wiley.com/doi/pdf/10.1016/j.febslet.2013.06.023

MicroRNA-133b stimulates ovarian estradiol synthesis by targeting Foxl2

https://febs.onlinelibrary.wiley.com/doi/pdf/10.1016/j.febslet.2012.06.048

MicroRNA-145 suppresses mouse granulosa cell proliferation by targeting activin receptor IB.

Estrogen synthesis is an important function of the mammalian ovary. Estrogen plays important roles in many biological processes, including follicular development, oocyte maturation and endometrial proliferation, and dysfunctions in estrogen synthesis contribute to the development of polycystic ovary syndrome and premature ovarian failure. Classical signaling cascades triggered by follicle-stimulating hormone induce estrogen synthesis via the upregulation of Cyp19a1 in granulosa cells (GCs). This study aimed to determine the effect of microRNA-132 (miR-132) on estradiol synthesis in GCs. Primary mouse GCs were collected from ovaries of 21-day-old immature ICR mice through follicle puncture. GCs were cultured and treated with the stable cyclic adenosine monophosphate analog 8-Br-cAMP or transfected with miR-132 mimics, Nurr1-specific small interfering RNA oligonucleotides and Flag-Nurr1 plasmids. Concentrations of estradiol and progesterone in culture medium were determined by an automated chemiluminescence-based assay. Quantitative real time PCR and western blot were performed to identify the effect of miR-132 on Cyp19a1, Cyp11a1 and an orphan nuclear receptor-Nurr1 expression in GCs. Direct suppression of Nurr1 via its 3'-untranslated region by miR-132 were further verified using luciferase reporter assays. The expression level of miR-132 in cultured mouse GCs was significantly elevated during 48 h of treatment with 8-Br-cAMP. The synthesis of estradiol increased after the overexpression of miR-132 in mouse GCs. The real-time PCR results demonstrated that miR-132 induced the expression of Cyp19a1 significantly. Nurr1, an orphan nuclear receptor that suppresses Cyp19a1 expression, was found to be a direct target of miR-132. Nurr1 was suppressed by miR-132, as indicated by a luciferase assay and Western blotting. The knockdown of Nurr1 primarily elevated the synthesis of estradiol and partially attenuated the miR-132-induced estradiol elevation, and the ectopic expression of Flag-Nurr1 abrogated the stimulatory effect of miR-132 on estradiol synthesis in mouse GCs. Our findings suggest that miR-132 is involved in the cAMP signaling pathway and promotes estradiol synthesis via the translational repression of Nurr1 in ovarian GCs.

/pdf/microrna-132-promotes-estradiol-synthesis-in-ovarian-3f96ewf43k.pdf

MicroRNA-132 promotes estradiol synthesis in ovarian granulosa cells via translational repression of Nurr1.

The androgen receptor (AR) is a nuclear receptor that is expressed in growing follicles and involved in folliculogenesis and follicle growth. The orphan nuclear receptor, Nur77, also has an important role in steroid signaling and follicle maturation. We hypothesized that AR levels and androgen signaling through AR are regulated by Nur77 in the ovary. In the ovaries of Nur77 knockout mice (n = 5), real-time PCR results showed that the mRNA levels of AR and an androgen signaling target gene, Kitl, were decreased by 35% and 24%, respectively, relative to wild-type mice (n = 5), which suggested transcriptional regulation of AR by Nur77 in vivo. In cultured mouse granulosa cells and a steroidogenic human ovarian granulosa-like tumor cell line, KGN, mRNA and protein expression levels of AR were increased by overexpressing Nur77 but decreased by knocking down endogenous Nur77. Consistent with increased AR expression, chromatin immunoprecipitation showed that Nur77 bound to the NGFI-B response element (NBRE) in the AR promoter sequence. AR promoter activity was stimulated by Nur77 in HEK293T cells and attenuated in Nur77 knockout mouse granulosa cells (luciferase assay). Overexpression of Nur77 enhanced the androgenic induction of Kitl (200 nM; 48h), while knockout of Nur77 attenuated this induction. These results demonstrate that AR is regulated by Nur77 in the ovaries, and they suggest that the participation of Nur77 in androgen signaling may be essential for normal follicular development.

/pdf/orphan-nuclear-receptor-nur77-regulates-androgen-receptor-4dfwc3louy.pdf

Ting Fang

Papers

MicroRNA-181a Suppresses Mouse Granulosa Cell Proliferation by Targeting Activin Receptor IIA

MicroRNA-133b stimulates ovarian estradiol synthesis by targeting Foxl2

MicroRNA-145 suppresses mouse granulosa cell proliferation by targeting activin receptor IB.

MicroRNA-132 promotes estradiol synthesis in ovarian granulosa cells via translational repression of Nurr1.

Orphan Nuclear Receptor Nur77 Regulates Androgen Receptor Gene Expression in Mouse Ovary