Restricted expression of WT1 messenger ribonucleic acid in immature ovarian follicles: uniformity in mammalian and avian species and maintenance during reproductive senescence

rno-miR-128-3p promotes apoptosis in rat granulosa cells (GCs) induced by norepinephrine through Wilms tumor 1 (WT1)

The mechanism related to ovarian follicular is complex, which has not been fully elucidated. Abundant reports have confirmed that the ovarian function development is closely related to sympathetic innervation. As one of the major neurotransmitters, norepinephrine (NE) is considered an effective regulator of ovarian functions like granulosa cell (GC) apoptosis. However, the mechanism between NE and GC apoptosis in rat is still unclear. In our study, GCs were isolated and cultured in vitro with NE treatment. The apoptosis of GCs was facilitated by NE. Wilms tumor 1 (WT1) was found to be significantly downregulated in GCs after NE treatment, and overexpression of WT1 repressed apoptosis in rat GCs induced by NE. rno-miR-128-3p was found to be significantly enhanced by NE in GCs, and inhibition of rno-miR-128-3p repressed apoptosis in rat GCs induced by NE. Mechanistically, rno-miR-128-3p interacted with WT1 and repressed its expression. In summary, inhibition of rno-miR-128-3p may enhance WT1 expression, and then repress NE-induced apoptosis in rat GCs. Our research may provide a new insight for the improvement of ovarian follicular development.

Wilms' tumor (WT1) (±KTS) variants decreases the progesterone secretion of bovine ovarian theca cells

Wilms' tumor gene WT1 encodes a nuclear transcriptional factor, which has been shown to regulate granulosa cell steroidogenesis in bovine; however, it is not known whether the functions of theca cells are regulated by WT1. Here, we determined the effects of this gene on theca cell proliferation, apoptosis, and steroidogenesis in vitro. In cultured bovine theca cells, the downregulation of WT1 increased the secretion of progesterone but had no effect on proliferation and apoptosis. WT1 includes the variants WT1(+KTS) and WT1(-KTS), which differ by 3 amino acids KTS (lysine, threonine, and serine). WT1(±KTS) upregulation increased the messenger RNA (mRNA) expression of STAR and CYP17A1 and decreased the progesterone secretion and CYP11A1 mRNA expression. In contrast to WT1(+KTS), WT1(-KTS) upregulation also decreased the mRNA expression of 3β-HSD. In both variants, WT1(-KTS) has more obvious effects. In conclusion, WT1 can decrease progesterone secretion, likely due in part to the inhibition of CYP11A1 and 3β-HSD.

Differential expression of Wilms' tumour 1 gene in porcine urogenital organs during development

Wilms' tumour 1 gene (WT1) is essential for the development of mammalian urogenital system. However, the expression pattern of WT1 in the development of porcine urogenital organs is still unclear. Here, we examined the expression of WT1 mRNA and protein in porcine kidneys, ovaries and testes from embryonic days 35 and 60 (E35d, E60d, n = 3) to the newborn (0d, n = 4) and adult (210d, n = 3) stages, using real-time PCR and immunofluorescent staining. Real-time PCR analysis showed that porcine kidneys, ovaries and testes all expressed high level of WT1 mRNAs, especially in adult testes (p < 0.05 or 0.01 vs. kidney and ovary, respectively). Morphologically, characteristic microstructures of the kidneys, ovaries and testes were observed and discerned at all four stages. Immunofluorescently, WT1 expression was detected in a dynamic and context-specific pattern during the development of these organs. Taken together, porcine urogenital organs express relatively high levels of WT1 mRNA. Dynamical and context-specific expression profile of WT1 in these organs occurs during their development, implying its close association with the development and function of porcine kidney, ovary and testis.

Sox9 and Sox8 protect the adult testis from male-to-female genetic reprogramming and complete degeneration

The new concept of mammalian sex maintenance establishes that particular key genes must remain active in the differentiated gonads to avoid genetic sex reprogramming, as described in adult ovaries after Foxl2 ablation. Dmrt1 plays a similar role in postnatal testes, but the mechanism of adult testis maintenance remains mostly unknown. Sox9 and Sox8 are required for postnatal male fertility, but their role in the adult testis has not been investigated. Here we show that after ablation of Sox9 in Sertoli cells of adult, fertile Sox8(-/-) mice, testis-to-ovary genetic reprogramming occurs and Sertoli cells transdifferentiate into granulosa-like cells. The process of testis regression culminates in complete degeneration of the seminiferous tubules, which become acellular, empty spaces among the extant Leydig cells. DMRT1 protein only remains in non-mutant cells, showing that SOX9/8 maintain Dmrt1 expression in the adult testis. Also, Sox9/8 warrant testis integrity by controlling the expression of structural proteins and protecting Sertoli cells from early apoptosis. Concluding, this study shows that, in addition to its crucial role in testis development, Sox9, together with Sox8 and coordinately with Dmrt1, also controls adult testis maintenance.

Low-density lipoprotein receptor affects the fertility of female mice

Low-density lipoprotein receptor (LDLR) has been demonstrated to play a central role in lipoprotein metabolism, with Ldlr-deficient (Ldlr–/–) mice developing severe dyslipidemia. In the present study we investigated whether Ldlr knockout could harm female reproduction and explored the mechanisms involved. The results indicate that although the number of litters born to Ldlr–/– mice did not differ significantly from that born to controls, the number of pups per litter was significantly lower in the former group. Interestingly, although Ldlr–/– mice were obese, the weight of their ovaries was lower than that in control mice. Serum cholesterol levels was significantly higher in Ldlr–/– mice than in their wild-type counterparts. In contrast, there were significant decreases in cholesterol, triglyceride and total lipid levels in ovaries of Ldlr–/– mice. Both ovarian lipid deposition, as detected by Oil red O staining, and lipid droplets, as evaluated by transmission electron microscopy, supported decreased lipid levels in ovaries from Ldlr–/– mice. In addition, Ldlr–/– mice had fewer ovarian follicles, more atretic follicles, lower oestrogen levels and spent significantly less time in oestrus than did the controls. Superovulation assays indicated immature Ldlr–/– mice ovulated fewer ova than controls. These results indicate that lack of Ldlr results in dyslipidaemia and poor fertility.

Wilms' tumor suppressor gene (WT1) suppresses apoptosis by transcriptionally downregulating BAX expression in immature rat granulosa cells

Background

The important role of WT1 in early folliculogenesis was evident from its restricted expression pattern in immature follicles and from its involvement in transcriptional control of inhibin-α and FSH receptor. There is also considerable evidence that WT1 is a potent inhibitor of apoptotic cell death in the developing kidney and male germ cells, suggesting that it could play a role in the regulation of follicle survival. Therefore, we evaluated if WT1 involves in cell survival of granulosa cells (GCs) during the FSH-independent stage.

Methods

GCs were obtained from small preantral follicles of immature rat ovary. Bax and bcl-2 mRNA and protein levels in GCs transfected with WT1 (−KTS) or WT1 (+KTS) were analyzed by Real-time RT-PCR and immune-blotting analysis. Cell viability was measured with MTT assays and apoptosis was analyzed with caspase 3/7 activity and TUNEL assay. The mechanism by which WT1 regulates Bax expression was investigated using Bax promoter-luciferase reporter assay and ChIP assays from GCs.

Results

Here, we showed that WT1 (−KTS) suppressed endogenous Bax transcript and protein expression, and this inhibition resulted from direct binding of WT1 in the Bax promoter region in vivo. In addition, anti-apoptotic effects of WT1 (−KTS) were demonstrated based on MTT assays, a sensitive bioluminescence caspase 3/7 assay and TUNEL assays. On the other hand, WT1 has no role on bcl-2 expression in GCs.

Conclusion

These findings suggest that activation of WT1 is necessary for maintenance of GC survival during early stage of follicles and WT1 can play a role in protecting apoptosis through the regulation of upstream activator (Bax), as well as through regulation of downstream effecter (caspases 3 and 7).

Expression profiles of Fsh-regulated ovarian genes during oogenesis in coho salmon

The function of follicle-stimulating hormone (Fsh) during oogenesis in fishes is poorly understood. Using coho salmon as a fish model, we recently identified a suite of genes regulated by Fsh in vitro and involved in ovarian processes mostly unexplored in fishes, like cell proliferation, differentiation, survival or extracellular matrix (ECM) remodeling. To better understand the role of these Fsh-regulated genes during oocyte growth in fishes, we characterized their mRNA levels at discrete stages of the ovarian development in coho salmon. While most of the transcripts were expressed at low levels during primary growth (perinucleolus stage), high expression of genes associated with cell proliferation (pim1, pcna, and mcm4) and survival (ddit4l) was found in follicles at this stage. The transition to secondary oocyte growth (cortical alveolus and lipid droplet stage ovarian follicles) was characterized by a marked increase in the expression of genes related to cell survival (clu1, clu2 and ivns1abpa). Expression of genes associated with cell differentiation and growth (wt2l and adh8l), growth factor signaling (inha), steroidogenesis (cyp19a1a) and the ECM (col1a1, col1a2 and dcn) peaked in vitellogenic follicles, showing a strong and positive correlation with transcripts for fshr. Other genes regulated by Fsh and associated with ECM function (ctgf, wapl and fn1) and growth factor signaling (bmp16 and smad5l) peaked in maturing follicles, along with increases in steroidogenesis-related gene transcripts. In conclusion, ovarian genes regulated by Fsh showed marked differences in their expression patterns during oogenesis in coho salmon. Our results suggest that Fsh regulates different ovarian processes at specific stages of development, likely through interaction with other intra- or extra-ovarian factors.

Contemporary genetic technologies and female reproduction

BACKGROUND

The Fifth Evian Annual Reproduction (EVAR) Workshop Meeting discussed knowledge regarding contemporary genetics in female reproduction.

METHODS

Specialist reproductive medicine clinicians and geneticists delivered presentations based on published literature and current research. The content of this report is based on the expert presentations and subsequent group discussions that took place during this Workshop.

RESULTS

Numerous ovarian genes with a role in infertility have been identified. Future challenges for genetic screening of patients, such as those with polycystic ovary syndrome, primary ovarian insufficiency or endometriosis, include the identification of high-throughput strategies and how to apply these findings to infertile patients. The identification of high-quality embryos in IVF using objective technologies remains a high priority in order to facilitate single-embryo transfer. Gene expression profiling of cumulus cells surrounding the oocyte, and proteomic and metabolomic approaches in embryo culture media may significantly improve non-invasive embryo quality assessment.

CONCLUSIONS

The way forward in advancing the knowledge of genes involved in reproduction was considered to be through genome-wide association studies involving large numbers of patients. Establishing international collaboration is required to enable the application of such technologies in sufficient numbers of patients.

Early avian follicular development is characterized by changes in transcripts involved in steroidogenesis, paracrine signaling and transcription

The mechanisms associated with follicular activation and early growth are not well understood in avian species. Level of mRNA transcripts involved in steroidogenesis (STAR, HSD3B, CYP11A1, CYP19), paracrine signaling (AMH, BMP2, BMP4, BMP6, KITL, WNT4, and PCSK6) and transcription (SMAD1, SMAD2, SMAD3, SMAD5, SMAD9, FOXL3, FOXL2, NR5A1 (SF1), and WT1) were determined in small avian follicles 0.5, 1, and 2 mm in diameter after oocyte removal. STAR, HSD3B, CYP11A1, CYP19, PCSK6, FOXO3, and KITL mRNA increased 2- to 45-fold, while FOXL2, WT1, and WNT4 decreased 30-90% and NR5A1 did not change as follicles developed from 0.5 to 2 mm. Phosphorylated SMAD2, SMAD3, SMAD1/5/9 and FOXO3 proteins were found in both granulosa cells and oocytes of small (<0.5 mm) and larger (>1 mm) follicles. In contrast, non-phosphorylated FOXO3 protein was found in oocyte and granulosa cells of small follicles, but only in the oocyte of larger follicles. Culture of small avian follicles on the chorioallantoic membrane of chick embryos (in ovo) for 7 days caused changes in transcript levels that were similar to changes observed in vivo. The collective findings suggest that the growth of avian follicles from 0.5 to 2 mm is marked by an increase in steroidogenic capacity, and changes in paracrine signaling that may be important during early avian follicular development. Thus, a number of candidate marker genes were identified, and a method of follicle culture was developed to study early follicular development in a model avian species.

Sex determination in the Squalius alburnoides complex: an initial characterization of sex cascade elements in the context of a hybrid polyploid genome

Background

Sex determination processes vary widely among different vertebrate taxa, but no group offers as much diversity for the study of the evolution of sex determination as teleost fish. However, the knowledge about sex determination gene cascades is scarce in this species-rich group and further difficulties arise when considering hybrid fish taxa, in which mechanisms exhibited by parental species are often disrupted. Even though hybridisation is frequent among teleosts, gene based approaches on sex determination have seldom been conducted in hybrid fish. The hybrid polyploid complex of Squalius alburnoides was used as a model to address this question.

Methodology/Principal Findings

We have initiated the isolation and characterization of regulatory elements (dmrt1, wt1, dax1 and figla) potentially involved in sex determination in S. alburnoides and in the parental species S. pyrenaicus and analysed their expression patterns by in situ hybridisation. In adults, an overall conservation in the cellular localization of the gene transcripts was observed between the hybrids and parental species. Some novel features emerged, such as dmrt1 expression in adult ovaries, and the non-dimorphic expression of figla, an ovarian marker in other species, in gonads of both sexes in S. alburnoides and S. pyrenaicus. The potential contribution of each gene to the sex determination process was assessed based on the timing and location of expression. Dmrt1 and wt1 transcripts were found at early stages of male development in S. alburnoides and are most likely implicated in the process of gonad development.

Conclusions/Significance

For the first time in the study of this hybrid complex, it was possible to directly compare the gene expression patterns between the bisexual parental species and the various hybrid forms, for an extended set of genes. The contribution of these genes to gonad integrity maintenance and functionality is apparently unaltered in the hybrids, suggesting that no abrupt shifts in gene expression occurred as a result of hybridisation.

Regulation of Wilms' tumor gene expression by nerve growth factor and follicle-stimulating hormone in the immature mouse ovary

This study investigated the regulation of Wilms' tumor gene (WT1) in the ovary by nerve growth factor and FSH to better understand signals that initiate early follicular growth. Nerve growth factor showed a direct stimulatory effect on endogenous expression of WT1, whereas FSH attenuated basal and nerve growth factor-stimulated WT1 protein expression, which most likely depended on FSH responsiveness according to the follicle growth stage.

Wilms' tumor protein Wt1 is an activator of the anti-Müllerian hormone receptor gene Amhr2

The Wilms' tumor protein Wt1 plays an essential role in mammalian urogenital development. WT1 mutations in humans lead to a variety of disorders, including Wilms' tumor, a pediatric kidney cancer, as well as Frasier and Denys-Drash syndromes. Phenotypic anomalies in Denys-Drash syndrome include pseudohermaphroditism and sex reversal in extreme cases. We have used cDNA microarray analyses on Wt1 knockout mice to identify Wt1-dependent genes involved in sexual development. The gene most dramatically affected by Wt1 inactivation was Amhr2, encoding the anti-Müllerian hormone (Amh) receptor 2. Amhr2 is an essential factor for the regression of the Müllerian duct in males, and mutations in AMHR2 lead to the persistent Müllerian duct syndrome, a rare form of male pseudohermaphroditism. Here we show that Wt1 and Amhr2 are coexpressed during urogenital development and that the Wt1 protein binds to the promoter region of the Amhr2 gene. Inactivation and overexpression of Wt1 in cell lines was followed by immediate changes of Amhr2 expression. The identification of Amhr2 as a Wt1 target provides new insights into the role of Wt1 in sexual differentiation and indicates, in addition to its function in early gonad development and sex determination, a novel function for Wt1, namely, in Müllerian duct regression.

Novel trends in follicular development, atresia and corpus luteum regression: a role for apoptosis

During ovarian follicular development in humans, only a limited number of follicles mature and ovulate. The vast majority of follicles stop developing after the formation of an antrum and then undergo atresia. The few that are selected to become ovulatory follicles are transformed into corpora lutea following ovulation. The lifespan of the corpus luteum is also limited. In each oestrus/menstrual cycle, corpora lutea regress and are eliminated by a progress called luteolysis. During atresia and luteolysis, granulosa and lutein cells undergo apoptosis. It is believed that there are many signal transduction pathways that control apoptosis in order to suppress full maturation of too many follicles and to protect the dominant follicle from the apoptotic process prior the ovulation. Such interplay between different factors, some of them produced in the ovary, may modulate apoptosis of corpus luteum cells, in order to preserve the function of the corpus luteum during pregnancy or to eliminate the old corpora lutea of the previous cycle. The present review reports a number of factors that regulate follicular atresia and corpus luteum regression, via apoptotic pathways. Elucidation of apoptotic mechanisms may lead to prevention of female infertility or other pathological conditions.

Subcellular and molecular mechanisms regulating anti-Müllerian hormone gene expression in mammalian and nonmammalian species

Anti-Müllerian hormone (AMH) is best known for its role as an inhibitor of the development of female internal genitalia primordia during fetal life. In the testis, AMH is highly expressed by Sertoli cells of the testis from early fetal life to puberty, when it is downregulated by the action of testosterone, acting through the androgen receptor, and meiotic spermatocytes, probably acting through TNFalpha. Basal expression of AMH is induced by SOX9; GATA4, SF1, and WT1 enhance SOX9-activated expression. When the hypothalamic-pituitary axis is active and the negative effect of androgens and germ cells is absent, for example, in the fetal and neonatal periods or in disorders like androgen insensitivity, FSH upregulates AMH expression through a nonclassical cAMP-PKA pathway involving transcription factors AP2 and NFkappaB. The maintenance and hormonal regulation of AMH expression in late fetal and postnatal life requires distal AMH promoter sequences. In the ovary, granulosa cells express AMH from late fetal life at low levels; DAX1 and FOG2 seem to be responsible for negatively modulating AMH expression. Particular features are observed in AMH expression in nonmammalian species. In birds, AMH is expressed both in the male and female fetal gonads, and, like in reptiles, its expression is not preceded by that of SOX9.

Estrogen actions on follicle formation and early follicle development

Estradiol-17beta (E(2)) affects late follicular development, whereas primordial follicle differentiation and early activation are believed to be independent of E(2). To test this hypothesis we compared numbers of primordial and primary follicles in wild-type and E(2)-deficient, aromatase knockout (ArKO) mice, and the immunohistochemical staining or mRNA expression of Mullerian inhibiting substance (MIS), Wilms tumor 1 (WT-1), and growth differentiation factor (GDF9), which are known to effect early follicular differentiation. Proliferating cell nuclear antigen (PCNA) staining was a marker of proliferative index. The effects of E(2) replacement for 3 wk in 7-wk-old ArKO and wild-type mice on these parameters were also tested. ArKO mice had reduced numbers of primordial and primary follicles compared with wild-type mice (63%, P < 0.001 and 60%, P = 0.062, respectively). This reduction was not corrected by E(2) treatment, suggesting that E(2) affects the initial formation or activation of primordial follicles. There was a significant increase in the diameters of the oocytes in primordial follicles of ArKO mice compared with mice of the wild type. There were no differences in the immunostaining of MIS, WT-1, and PCNA in primordial and primary follicles between wild-type and ArKO mice. The only difference was as a consequence of Sertoli and Leydig cells that develop in ovaries of ArKO mice. GDF9 mRNA expression was markedly increased in ArKO ovaries. E(2) treatment restored the ovarian follicular morphology in ArKO mice, and consequently the immunostaining patterns, but had no effect on early follicle numbers. In conclusion, E(2) has a role in controlling the size of the oocyte and primordial follicle pool in mice.

Up-regulation of alpha-inhibin expression in the fetal ovary of estrogen-suppressed baboons is associated with impaired fetal ovarian folliculogenesis

We recently demonstrated that the number of primordial follicles was significantly reduced in the ovaries of near-term baboon fetuses deprived of estrogen in utero and restored to normal in animals administered estradiol. Although the baboon fetal ovary expressed estrogen receptors alpha and beta, the mechanism(s) of estrogen action remains to be determined. It is well established that inhibin and activins function as autocrine/paracrine factors that impact adult ovarian function. However, our understanding of the expression of these factors in the primate fetal ovary is incomplete. Therefore, we determined the expression of alpha-inhibin, activin beta(A), activin beta(B), and activin receptors in fetal ovaries obtained at mid and late gestation from untreated baboons and at late gestation from animals in which fetal estrogen levels were reduced by >95% by maternal administration of the aromatase inhibitor CGS 20267 or restored to 30% of normal by treatment with CGS 20267 and estradiol benzoate. Immunocytochemical expression of alpha-inhibin was minimal to nondetectable in fetal ovaries from untreated baboons. In contrast, in baboons depleted of estrogen, alpha-inhibin was abundantly expressed in pregranulosa cells of interfollicular nests and granulosa cells of primordial follicles. Thus, the number (mean +/- SEM) per 0.08 mm2 of fetal ovarian cells expressing alpha-inhibin, determined by image analysis, was similar at mid and late gestation and increased approximately 8-fold (P < 0.01) near term in baboons treated with CGS 20267 and was restored (P < 0.01) to normal in baboons treated with CGS 20267 plus estradiol. Activin beta(A) was detected in oocytes and pregranulosa cells at midgestation and in oocytes and granulosa cells of primordial follicles at late gestation. Activin beta(B) was also expressed in pregranulosa cells and granulosa cells at mid and late gestation, respectively, but was not detected in oocytes. Neither the pattern nor the apparent level of expression of activin beta(A) or beta(B) were altered in fetal ovaries of baboons treated with CGS 20267 or CGS 20267 and estrogen. Activin receptors IA, IB, IIA, and IIB were detected by Western blot analysis in fetal ovaries at mid and late gestation, and expression was not altered by treatment with CGS 20267 or CGS 20267 and estrogen. Activin receptors IB and IIA were localized to oocytes and pregranulosa cells at midgestation and to granulosa cells and oocytes of primordial follicles at late gestation. Thus, the decrease in the number of follicles in the primate fetal ovary of baboons deprived of estrogen in utero was associated with increased expression of alpha-inhibin. Therefore, we propose that estrogen regulates fetal ovarian follicular development by controlling alpha-inhibin expression and, thus, the intraovarian inhibin:activin ratio.

Expression of wilms' tumor gene and protein localization during ovarian formation and follicular development in sheep

Wilms' tumor protein (WT1) is a transcriptional repressor essential for the development of mammalian kidneys and gonads. To gain insight into possible roles of WT1 in ovarian formation and follicular function, we studied patterns of mRNA and protein localization throughout fetal gonadal development and in ovaries of 4-wk-old and adult sheep. At Day 24 after conception, strong expression of WT1 mRNA and protein was observed in the coelomic epithelial region of the mesonephros where the gonad was forming. By Day 30, expression was observed in the surface epithelium and in many mesenchymal and endothelial cells of the gonad. Epithelial cells continued to express WT1 throughout gonadal development, as did pregranulosa cells during the process of follicular formation. However, WT1 expression was not observed in germ cells. During follicular growth, granulosa cells expressed WT1 from the type 1 (primordial) to the type 4 stages, but thereafter expression was reduced in type 5 (antral) follicles, consistent with the differentiation of granulosa cells into steroid-producing cells. The possible progenitor cells for the theca interna (i.e., the cell streams in the ovarian interstitium) expressed WT1 heterogeneously. However, differentiated theca cells in antral follicles did not express WT1. Strong expression of WT1 was observed during gonadal development, which is consistent with a role for WT1 in ovarian and follicular formation in the ewe. WT1 was identified in many cells of the neonatal and adult ovaries, including granulosa cells, suggesting that this factor is important for preantral follicular growth. However, the decline in WT1 expression in antral follicles suggests that WT1 may prevent premature differentiation of somatic cells of the follicle during early follicular growth.

Different patterns of anti-Müllerian hormone expression, as related to DMRT1, SF-1, WT1, GATA-4, Wnt-4, and Lhx9 expression, in the chick differentiating gonads

In mammals, anti-Müllerian hormone (AMH) is produced by Sertoli cells from the onset of testicular differentiation and by granulosa cells after birth. In birds, AMH starts to be expressed in indifferent gonads of both sexes at a similar level and is later up-regulated in males. We previously demonstrated that, unlike in mammals, the onset of AMH expression occurs in chick embryo in the absence of SOX9. We looked for potential factors that might be involved in regulating AMH expression at different stages of chick gonad differentiation by comparing its expression pattern in embryos and young chicken with that of DMRT1, SF-1, WT1, GATA-4, Wnt-4, and Lhx9, by in situ hybridization. The results allowed us to distinguish different phases. (1) In indifferent gonads of both sexes, AMH is expressed in dispersed medullar cells. SF-1, WT1, GATA-4, Wnt-4, and DMRT1 are transcribed in the same region of the gonads, but none of these factors has an expression strictly coincident with that of AMH. Lhx9 is present only in the cortical area. (2) After this period, AMH is up-regulated in male gonads. The up-regulation is concomitant with the beginning of SOX9 expression and a sex dimorphic level of DMRT1 transcripts. It is followed by the aggregation of the AMH-positive cells (Sertoli cells) into testicular cords in which AMH is coexpressed with DMRT1, SF-1, WT1, GATA-4, and SOX9. (3) In the females, the low level of dispersed medullar AMH expression is conserved. With development of the cortex in the left ovary, cells expressing AMH accumulate in the juxtacortical part of the medulla, whereas they remain dispersed in the right ovary. At this stage, AMH expression is not strictly correlated with any of the studied factors. (4) After hatching, the organization of left ovarian cortex is characterized by the formation of follicles. Follicular cells express AMH in conjunction with SF-1, WT1, and GATA-4 and in the absence of SOX9, as in mammals. In addition, they express Lhx9 and Wnt-4, the latter being also found in the oocytes. (5) Moreover, unlike in mammals, the chicken ovary retains a dispersed AMH expression in cortical interstitial cells between the follicles, with no obvious correlation with any of the factors studied. Thus, the dispersed type of AMH expression in indifferent and female gonads appears to be bird-specific and not controlled by the same factors as testicular or follicular AMH transcription.

Gonad-specific expression of two novel chicken complementary DNA isoforms

Differential display reverse transcription polymerase chain reaction was used to isolate a novel cDNA clone (C47) that was initially shown to be downregulated in senescent chicken embryo fibroblast cells. In a tissue environment, C47 transcripts were only detected in gonadal tissue. The expression of the larger isoform (C47L) was essentially restricted to the ovary, and the smaller isoform (C47S) was predominately expressed in the testis. Although levels of the C47L mRNA were relatively high in both the small white and the developing larger follicles, there was very low expression in regressed and postovulated follicles. Nucleotide sequence analysis indicated that two different transcripts of the single-copy C47 gene were generated by differential polyadenylation in the 3' untranslated region. As a result of a single nucleotide deletion, the C47L mRNA produced a smaller 48-kDa protein, and the C47S mRNA generated a larger 57-kDa protein when both were translated in vitro. Both protein isoforms were shown to contain conserved C2H2 Zn finger motifs and nuclear localization signals suggestive of being putative transcription factors. These results suggest that the C47L and C47S isoforms might play an important role in the regulation and maintenance of ovarian and testicular functions, respectively, in the chicken.

Ovarian steroidogenic responsiveness to exogenous gonadotropin stimulation in young and middle-aged female rats

Reproductive aging in the female rat is associated with gradual declines in LH secretion and ovarian progesterone (P) production. This study examined whether the influences of aging on P levels reflect decreased ovarian responsiveness to gonadotropin stimulation, as opposed to changes in gonadotropin release. Young and middle-aged regularly cyclic female rats received sodium pentobarbital to block endogenous proestrous luteinizing hormone (LH) surges, followed by administration of various doses of human chorionic gonadotropin (hCG). Similar treatments were performed in middle-aged acyclic persistent-estrous (PE) females. Injection of hCG resulted in equivalent plasma hCG levels in each treatment group. At the lowest hCG dose tested, a significant rise in plasma P levels was observed in middle-aged cyclic rats, but not in young cyclic or middle-aged PE females. This unexpected finding may reflect accelerated follicular development in middle-aged cyclic females, as suggested by a previous study. At the intermediate dose, young and middle-aged cyclic but not PE rats displayed significantly increased P in response to hCG. At the highest dose tested, all three groups of rats displayed increased P levels after hCG stimulation. However, P concentrations were significantly lower in middle-aged PE than regularly cyclic females. Northern and slot blot hybridization analyses revealed that ovarian mRNA levels for cytochrome P450 side-chain cleavage, the rate-limiting enzyme in P synthesis, were markedly reduced in PE rats following hCG stimulation. These findings indicate that ovarian responsiveness to gonadotropin stimulation is impaired in middle-aged PE, but not regularly cyclic rats, and suggest influences of cycle status on the biochemical and molecular mechanisms regulating ovarian steroid production. Furthermore, these findings reveal that attenuated P production in middle-aged proestrous rats is due to attenuated preovulatory LH surges, rather than decreased ovarian sensitivity to LH.

Initial and cyclic recruitment of ovarian follicles

Mammalian ovaries consist of follicles as basic functional units. The total number of ovarian follicles is determined early in life, and the depletion of this pool leads to reproductive senescence. Each follicle develops to either ovulate or, more likely, to undergo degeneration. The dynamics of ovarian follicle development have interested endocrinologists and developmental biologists for many years. With the advent of assisted reproductive techniques in humans, the possibility of regulating follicle development in vivo and in vitro has gained clinical relevance. In this review, we focus upon key branching points during the development of ovarian follicles as well as factors involved in determining the eventual destiny of individual follicles. We discuss inconsistencies in the literature regarding the definitions of follicle recruitment and selection and propose to name the two major steps of follicle development as initial and cyclic recruitment, respectively. Because some of these disparities have arisen due to differences in the animal systems studied, we also compare the development of the ovarian follicles of both humans and rats. We also review the status of knowledge of several puzzling clinical issues that may provide important clues toward unlocking the mechanisms of follicle development.