Molecular cloning and expression analysis of the complementary deoxyribonucleic acid for chicken inhibin/activin beta(B) subunit

Transcriptomic Diversification of Granulosa Cells during Follicular Development in Chicken

Granulosa cells play important roles in ovarian follicular development. To better understand the molecular mechanisms involved in this physiological process in chicken, high-throughput transcriptome analyses were performed to study the expression profiles of granulosa cells harvested from 6 mm white follicles, F5 follicles and F1 follicles. The analyses elucidated a clear tendency of granulosa cells in shifting its expression profile from proliferation to differentiation during follicular development. Transcripts down-regulated during this process were mainly associated with cell division, cell cycle and DNA replication while the up-regulated transcripts were related to ribosomal function, lipid metabolism and protein synthesis. Our study for the first time provides the complete gene expression profiles along follicular development supporting the active involvement of many genes characterized in cell signaling (AMH, Inhibins, Activins, BMPs) and transcription factors (SMAD3, SMAD5, ID1, ID2, ID3). Their temporal expression profiles support the notion of continual cross-talk between granulosa cells and its neighboring cells and shed light on the mechanisms behind avian follicular selection and pave the way to the better understanding of reproductive efficiency.

Occludin expression and regulation in small follicles of the layer and broiler breeder hen

Synchronized yolk accumulation and follicle development are essential for egg production in oviparous species. In birds, yolk is incorporated into the oocyte by an avian specific yolk receptor (LR8), and it has been suggested that occludin (OCLN), a tight junction protein, mediates transfer of yolk material to the oocyte surface. OCLN may be a key regulator of yolk accumulation and follicle growth, however, the expression and regulation of OCLN in granulosa cells during various stages of follicle development is unknown. In the first experiment, we found that LR8 and OCLN mRNA were highest in small follicles within the ovary. In addition, OCLN decreased with increasing follicle size. OCLN mRNA was more abundant in the germinal disc region of the granulosa cell layer than the non-germinal disc region. In addition, we found epidermal growth factor (EGF) and activin B, decreased OCLN mRNA, while activin A increased OCLN. In the second experiment, restricted fed (RF) broiler breeder hens were randomly divided into two groups and one group remained on RF and the other was fed ad libitum (FF). OCLN expression in granulosa cells of 3-5mm follicles of FF hens was lower compared to RF hens and yolk weights were higher in the FF group, however, LR8 mRNA in small whole follicles (<3mm) did not differ between groups. In conclusion, the level of feed intake is related to or may directly regulate OCLN mRNA expression or may have an indirect effect through paracrine or autocrine factors in the ovary.

Intra-ovarian growth factors regulating ovarian function in avian species: a review

There is now overwhelming evidence that the avian ovary is a site of production and action of several growth factors that have also been implicated in the functioning of the mammalian ovary. Several members of the Insulin-like growth factor family (IGF), the Epidermal growth factor family (EGF), the Transforming growth factor-beta family (TGF-beta), Fibroblast growth factors (FGF), the Tumour necrosis factor-alpha (TNF-alpha), and others, have been identified either in the granulosa and/or theca compartments of ovarian follicles and in the embryonic and juvenile ovary. Some have been specifically localized to the germinal disc area containing the oocyte. The mRNAs and proteins of the growth factors, receptor proteins and binding proteins of some of the members of each group have been reported in the chicken, turkey, quail and duck. The intra-ovarian roles reported for the different growth factors include regulation of cell proliferation, steroidogenesis, follicle selection, modulation of gonadotrophin action, control of ovulation rate, cell differentiation, production of growth factors, etc. The aim of this paper is to provide a review of the current knowledge of avian ovarian growth factors and their biological activity in the ovary. The review covers the detection of the growth factor proteins, the receptor proteins, binding proteins, their spatial and temporal distribution in embryonic, juvenile and adult ovaries and their regulation. The paper also discusses their roles in each follicular compartment during follicular development. Greater emphasis is given to the major growth factors that have been studied to greater detail and others are discussed very briefly.

Effect of activin A and inhibin A on expression of the inhibin/activin beta-B-subunit and gonadotropin receptors in granulosa cells of the hen

Activin A has been shown to be abundant in the theca layer of the large pre-ovulatory follicles of the hen whereas inhibin A is produced in the granulosa layer. The purpose of this study was to investigate the effects of activin A and inhibin A on granulosa cell expression of inhibin beta-B-subunit, FSH receptor (FSHR), and LH receptor (LHR). Granulosa cells were isolated from the F1, F3+F4, and small yellow follicles (SYF; 6-12 mm diameter) of laying hens and pooled according to size. The cells were dispersed and plated in the presence of 0, 10, or 50 ng/ml recombinant human activin A (n=5 replicate cultures). RNA was subsequently extracted from the cells and Northern blots performed. Cell proliferation was determined for all treatments. An identical set of experiments was performed in which the granulosa cells were treated with recombinant human inhibin A (n=4 replicate cultures). Treatment with activin A at 50 ng/ml significantly (p<0.05) increased expression of beta-B-subunit for granulosa cells from all follicles. This dose also significantly increased expression of FSHR in granulosa cells from all follicles (p<0.05) and increased expression of LHR in cells from F1 and F3+F4 follicles (p<0.01) with no significant effect on cells from the SYF. Overall, activin A treatment significantly (p<0.05) decreased cell proliferation at the 50 ng/ml dose. Inhibin A had no significant effect on expression of beta-B-subunit, FSHR or LHR at any dose. There was a moderate stimulatory effect of inhibin A on granulosa cell proliferation. These results suggest that activin A may have an important role in regulating granulosa cell responsiveness to gonadotropins while also modulating follicle development by attenuating cell proliferation.

Pattern of secretion of immunoreactive inhibin/activin subunits by avian granulosa cells

The messenger RNA expression for the inhibin/activin subunits in the granulosa layer of avian follicles of different developmental stages has previously been reported. In the present study, we examined the pattern of secretion of these protein subunits from cultured granulosa cells (GC) of avian follicles of defined maturity. Laying hens were euthanized and the F1, F2, F3, F4, small yellow follicles (SYF; 6-10 mm) and large white follicles (LWF; 3-5 mm) were removed. GC were isolated from the follicles, plated by size at a density of 6.25 x 10(5)cells per well (3 wells per follicle size) and cultured for 48 h in medium 199 with 5% FBS, antibiotics, and 1.0 microg/ml bovine insulin. After 48 h, the cultures were terminated and the media were saved (n = 6 replications). Proteins were precipitated from media, reconstituted for electrophoresis (SDS-PAGE), and analyzed by Western blot. Progesterone was also measured in the medium. For detection of the inhibin alpha-subunit, a rabbit antibody against the chicken inhibin alpha-subunit (1-26 aa) was used. The betaA-subunit was detected with rabbit anti-betaA-subunit (81-113 aa) and the betaB-subunit was detected with rabbit anti-betaB-subunit (80-112 aa). Under reduced conditions, GC from the larger follicle sizes (F1-F4) secreted the most (p < 0.05) immunoreactive inhibin alpha-subunit compared to smaller follicle sizes. Under non-reduced conditions, a band at approximately 32 kDa was detected by both the alpha-subunit antibody and by the betaA-subunit antibody in media from GC of the F1-F4 follicles, suggesting secretion of intact inhibin A. Immunoreactive alpha-subunit and betaB-subunit were detected under reduced conditions in media from the GC of the SYF, suggesting that this follicle population may secrete intact inhibin B. In addition, under non-reduced conditions, cells from the SYF secreted the greatest amount of intact inhibin B (p < 0.05) at a size of approximately 32 kDa. Cells from the LWF expressed low levels of all inhibin subunits. Progesterone concentration in the media from the F1 follicle was greatest and was decreased in media from smaller follicles. It is suggested that the largest follicles in the hierarchy are the source of most circulating intact inhibin A while the small follicles are the source of intact inhibin B.

Developmental Profiles of Activin βA, βB, and Follistatin Expression in the Zebrafish Ovary: Evidence for Their Differential Roles During Sexual Maturation and Ovulatory Cycle1

Our recent experiments showed that gonadotropin(s) stimulated activin betaA and follistatin expression through the cAMP-PKA pathway but suppressed betaB via a cAMP-dependent but PKA-independent pathway in cultured zebrafish follicle cells. Given that pituitary gonadotropins are the major hormones controlling the development and function of the ovary, the differential expression of activin betaA and betaB as well as follistatin in response to gonadotropin(s) raises an interesting question about the temporal expression patterns of these molecules in vivo during sexual maturation and ovulatory cycle. Three experiments were performed in the present study. In the first experiment using sexually immature zebrafish, we followed the expression of activin betaA, betaB, and follistatin at the whole ovary level during a 10-day period in which the ovary developed from the primary growth stage to the one with nearly full-grown follicles. Activin betaA expression was very low at the primary growth stage but significantly increased with the growth of the ovary, and its rise was accompanied by an increase in follistatin expression. In contrast, the expression of activin betaB could be easily detected in the ovary of all stages; however, it did not exhibit an obvious trend of variation during the development. The second experiment examined the stage-dependent expression of activin betaA, betaB, and follistatin at the follicle level in the adult mature zebrafish. The expression of activin betaA was again low in the follicles during the primary growth stage, but exhibited a phenomenal increase after the follicles entered vitellogenesis with the peak level reached at midvitellogenic stage; in contrast, activin betaB mRNA could be easily detected at all stages with a slight increase during follicle growth. The expression of follistatin, on the other hand, also increased significantly during vitellogenesis; however, its level dropped sharply after reaching the peak at the midvitellogenic stage. In the third experiment, we investigated the dynamic changes of the ovarian activin betaA, betaB, and follistatin expression during the daily ovulatory cycle. The expression of activin betaA and follistatin gradually increased from 1800 h onward and reached the peak level around 0400 h when the germinal vesicles had migrated to the periphery in the full-grown oocytes. In contrast, activin betaB expression steadily declined, although not statistically significant, during the same period, but increased sharply at 0700 h when mature oocytes started to appear in most of the ovaries collected. In conclusion, activin betaA and betaB exhibit distinct expression patterns during the development of the ovary and the daily ovarian cycle of the zebrafish. It seems that activin betaA is involved in promoting ovary and follicle growth, whereas activin betaB may have a tonic role throughout follicle development but becomes critical at the late stage of oocyte maturation and/or ovulation.

Developmental changes in inhibin α and inhibin/activin βA and βB mRNA levels in the gonads during post-hatch prepubertal development of male and female chickens

Dimeric inhibins and activins are barely detectable in the plasma during prepubertal development of male and female chickens. This may be misconstrued to indicate that the proteins are not produced in the gonads and have no functional significance during this period. Very few studies have actually determined the mRNA expression profile of the inhibin and activin subunits in the gonads prior to puberty in order to establish their secretion at the local level and postulate potential roles for the inhibin and activins at this developmental stage. In this study, the expression of the mRNA for the alpha-, betaA-, and betaB-subunits was determined in the ovary and testis of chickens during prepubertal development. Gene expression was determined at 3, 5, 6, 8, 10, 12, 16, and 18 weeks of age by RT-PCR. Messenger RNA level was quantified by competitive RT-PCR at 3, 6, 12, and 18 weeks of age in order to detect any changes with development, suggest potential relationship to the profile of dimeric inhibins and activins reported previously and to suggest potential paracrine and endocrine roles for them. The results show that all the inhibin/activin subunit mRNAs are expressed in the testis of the chicken throughout the period of prepubertal development up to 18 weeks of age. However, in the ovary, only the betaA- and betaB-subunits were detected at all ages whereas the alpha-subunit mRNA could only be detected just before puberty. Quantification of the mRNA levels showed variation of each subunit with age. These temporal changes suggest relationship with paracrine functional role in the ovary or the testis. Quantitative changes in expression levels also suggests that there may be some relationship between mRNA levels and the type and amount of dimeric inhibins and activins produced at any developmental stage. There are major differences between the male and female gonads in the timing of the expression of different subunits. In conclusion, the expression of the mRNA subunits in the testis and ovary suggests that inhibins and activins are being produced but may be principally involved in autocrine/paracrine function within the gonads.

Involvement of cyclic adenosine 3',5'-monophosphate in the differential regulation of activin betaA and betaB expression by gonadotropin in the zebrafish ovarian follicle cells

Activin is a dimeric protein consisting of two similar but distinct beta-subunits, betaA and betaB. In our previous studies, both activin A (betaAbetaA) and activin B (betaBbetaB) have been demonstrated to stimulate oocyte maturation and promote oocyte maturational competence in the zebrafish. Follistatin, a specific activin-binding protein, can block both activin- and gonadotropin-induced final oocyte maturation in vitro, suggesting that activin is likely a downstream mediator of gonadotropin actions in the zebrafish ovary. In the present study, a full-length cDNA encoding zebrafish ovarian activin betaA was cloned and sequenced. The precursor of zebrafish activin betaA consists of 395 amino acids and its mature region exhibits about 78% homology with that of mammals. Using an in vitro primary culture of the ovarian follicle cells and semiquantitative RT-PCR assays, we examined the regulation of activin betaA and betaB expression by human chorionic gonadotropin (hCG) and its intracellular signal transduction mechanisms. hCG (15 IU/ml) increased the mRNA level of activin betaA-subunit; however, it significantly down-regulated the steady-state expression level of activin betaB in a time- and dose-dependent manner. The differential regulation of the two beta-subunits by hCG could be mimicked by 3-isobutyl-1-methylxanthine, forskolin, and dibutyryl-cAMP, suggesting involvement of the intracellular cAMP pathway. Interestingly, H89 (a specific inhibitor of protein kinase A, PKA) could effectively block hCG- and forskolin-stimulated activin betaA expression at 10 micro M, but it was unable to reverse the inhibitory effects of hCG and forskolin on betaB expression. This suggests that the hCG-stimulated activin betaA expression is dependent on the activation of the cAMP-PKA pathway, whereas the inhibitory effect of hCG on activin betaB expression is likely mediated by PKA-independent pathway(s).

Estradiol regulation of follistatin and inhibin alpha- and beta(B)-subunit mRNA in avian granulosa cells

Estradiol modulation of granulosa cell growth and regulation of follistatin and inhibin alpha- and beta(B)-subunit mRNA were investigated in cultured chicken granulosa cells. Granulosa cells were isolated and pooled according to size from the F(4) + F(5), small yellow (SYF), and large white (LWF) follicles. Isolated and dispersed granulosa cells were then cultured in the absence or presence of 1 x 10(-5) M 17 beta-estradiol. In Experiment 1 (n = 4 replications) the effect of estradiol on the growth of granulosa cells from the different-sized follicles was examined at 24 and 48 h of culture. Untreated and treated granulosa cells from all three follicle sizes proliferated during culture, and cell viability for all cultures was over 95% throughout the experiment. After 48 h the untreated cultures for all follicle types had 1.6 to 2.2 times (P < 0.05) more cells than the estradiol-treated cultures. In Experiment 2 (n = 3 replications), the cultures were terminated at 4 and 24 h after plating. Follistatin mRNA levels were higher in estradiol-treated cells at 24 h in F(4) + F(5) follicles, at 4 and 24 h in the SYF, and at 4 h in the LWF. beta(B)-subunit mRNA levels were also increased by estradiol at 4 h in F(4) + F(5) cells and at 4 and 24 h in the LWF. Steady state mRNA levels for the alpha-subunit were higher (P < 0.05) in estradiol-treated cultures at 4 and 24 h in F(4) + F(5) follicles and at 24 h in the SYF. Immunoreactive alpha-subunit protein, however, was not increased by estradiol treatment. Thus, whereas estradiol inhibited granulosa cell growth, it exerted a generally stimulatory effect on the expression of FS and the inhibin alpha- and beta(B)-subunit mRNA.