Gene expression profiling reveals Cyp26b1 to be an activin regulated gene involved in ovarian granulosa cell proliferation

Immunolocalization of activin and inhibin at different stages of follicular development in the lizard Sceloporus torquatus

The activins and inhibins are glycoproteins with a role in the follicular development of vertebrates, that are found in follicular fluid and somatic follicular cells, with a different pattern among taxa. The principal function of activin (Act) is to modulate the follicle-stimulating hormone (FSH) synthesis and secretion, whereas inhibin (Inh) downregulates it. Both factors are modulators of intraovarian follicular recruitment, oocyte maturation, cell proliferation, and steroidogenic activity. Our aim was to characterize the immunolocalization of Act and Inh in the ovarian follicles during the reproductive cycle of the lizard Sceloporus torquatus. Act was detected in the granulosa cells and oocyte cortex in the different stages of follicular development. On the other hand, we identified Inh in the oocyte cortex and the cytoplasm of pyriform and small cells of previtellogenic follicles. Also, we found immunoreactivity in the oocyte cortex, theca, and small cells of vitellogenic and preovulatory follicles. Our data provide evidence that Act and Inh have changes related to the stage of follicular development. This dynamic appears to be conserved among vertebrates and is fundamental to ensure an adequate follicular development in this specie.

Comparative effects of retinoic acid, granulosa cells conditioned medium or forskolin in combination with granulosa cell co-culturing on mouse germ cell differentiation

BACKGROUND

Devising of an appropriate in vitro culture method for germ cells differentiation in the presence of soluble factors has attracted considerable attention, which results will provide new insight into reproductive biology. In this study, we compared the effects of forskolin, retinoic acid (RA) or granulosa cell-conditioned medium in the presence or absence of granulosa cell co-culturing on germ cell differentiation from embryonic stem cells (ESCs).

METHODS AND RESULTS

Embryonic stem cells were differentiated using embryoid bodies (EBs) for 5 days, and then EB-derived cells were co-cultured with or without adult mouse granulosa cells using monolayer protocol and treated with 50 µM forskolin, 1 µM RA and 50% granulosa cell-conditioned medium for 4 days. Granulosa cell-conditioned medium significantly increased the levels of Scp3, Rec8, Mvh and Gdf9 expression in the granulosa cell co-culture method compared to untreated cells. A significant elevation of Stra8, Rec8 and Mvh was observed after treatment with RA in the absence of granulosa cells and there was no significant increase in the levels of expression of germ cell-specific genes after treatment with forskolin compared to control. Furthermore, forskolin and RA significantly increased viability and proliferation of germ-like cells, compared with granulosa cell-conditioned medium.

CONCLUSIONS

Our study revealed that granulosa cell-conditioned medium and RA effectively can induce germ cell differentiation from ESCs, however combined application of granulosa cell-conditioned medium and co-culturing with granulosa cells had synergic effect on germ cell development in vitro as optimized protocol.

Nuclear receptors: Key regulators of somatic cell functions in the ovulatory process

The development of the ovarian follicle to its culmination by ovulation is an essential element of fertility. The final stages of ovarian follicular growth are characterized by granulosa cell proliferation and differentiation, and steroid synthesis under the influence of follicle-stimulating hormone (FSH). The result is a population of granulosa cells poised to respond to the ovulatory surge of luteinizing hormone (LH). Members of the nuclear receptor superfamily of transcription factors play indispensable roles in the regulation of these events. The key regulators of the final stages of follicular growth that precede ovulation from this family include the estrogen receptor beta (ESR2) and the androgen receptor (AR), with additional roles for others, including steroidogenic factor-1 (SF-1) and liver receptor homolog-1 (LRH-1). Following the LH surge, the mural and cumulus granulosa cells undergo rapid changes that result in expansion of the cumulus layer, and a shift in ovarian steroid hormone biosynthesis from estradiol to progesterone production. The nuclear receptor best associated with these events is LRH-1. Inadequate cumulus expansion is also observed in the absence of AR and ESR2, but not the progesterone receptor (PGR). The terminal stages of ovulation are regulated by PGR, which increases the abundance of the proteases that are directly responsible for rupture. It further regulates the prostaglandins and cytokines associated with the inflammatory-like characteristics of ovulation. LRH-1 regulates PGR, and is also a key regulator of steroidogenesis, cellular proliferation, and cellular migration, and cytoskeletal remodeling. In summary, nuclear receptors are among the panoply of transcriptional regulators with roles in ovulation, and several are necessary for normal ovarian function.

Shedding new light on early sex determination in zebrafish

In contrast to established zebrafish gene annotations, the question of sex determination has still not been conclusively clarified for developing zebrafish, Danio rerio, larvae, 28 dpf or earlier. Recent studies indicate polygenic sex determination (PSD), with the genes being distributed throughout the genome. Early genetic markers of sex in zebrafish help unravel co-founding sex-related differences to apply to human health and environmental toxicity studies. A qPCR-based method was developed for six genes: cytochrome P450, family 17, subfamily A, polypeptide 1 (cyp17a1); cytochrome P450, family 19, subfamily A, polypeptide 1a (cyp19a1a); cytochrome P450, family 19, subfamily A, polypeptides 1b (cyp19a1b); vitellogenin 1 (vtg1); nuclear receptor subfamily 0, group B, member 1 (nr0b1), sry (sex-determining region Y)-box 9b (sox9b) and actin, beta 1 (actb1), the reference gene. Sry-box 9a (Sox9a), insulin-like growth factor 3 (igf3) and double sex and mab-3 related transcription factor 1 (dmrt1), which are also known to be associated with sex determination, were used in gene expression tests. Additionally, Next-Generation-Sequencing (NGS) sequenced the genome of two adult female and male and two juveniles. PCR analysis of adult zebrafish revealed sex-specific expression of cyp17a1, cyp19a1a, vtg1, igf3 and dmrt1, the first four strongly expressed in female zebrafish and the last one highly expressed in male conspecifics. From NGS, nine female and four male-fated genes were selected as novel for assessing zebrafish sex, 28 dpf. Differences in transcriptomes allowed allocation of sex-specific genes also expressed in juvenile zebrafish.

Regulating Retinoic Acid Availability during Development and Regeneration: The Role of the CYP26 Enzymes

This review focuses on the role of the Cytochrome p450 subfamily 26 (CYP26) retinoic acid (RA) degrading enzymes during development and regeneration. Cyp26 enzymes, along with retinoic acid synthesising enzymes, are absolutely required for RA homeostasis in these processes by regulating availability of RA for receptor binding and signalling. Cyp26 enzymes are necessary to generate RA gradients and to protect specific tissues from RA signalling. Disruption of RA homeostasis leads to a wide variety of embryonic defects affecting many tissues. Here, the function of CYP26 enzymes is discussed in the context of the RA signalling pathway, enzymatic structure and biochemistry, human genetic disease, and function in development and regeneration as elucidated from animal model studies.

Biochemical and physiological importance of the CYP26 retinoic acid hydroxylases

The Cytochrome P450 (CYP) family 26 enzymes contribute to retinoic acid (RA) metabolism and homeostasis in humans, mammals and other chordates. The three CYP26 family enzymes, CYP26A1, CYP26B1 and CYP26C1 have all been shown to metabolize all-trans-retinoic acid (atRA) it's 9-cisRA and 13-cisRA isomers and primary metabolites 4-OH-RA and 4-oxo-RA with high efficiency. While no crystal structures of CYP26 enzymes are available, the binding of various ligands has been extensively explored via homology modeling. All three CYP26 enzymes are inducible by treatment with atRA in various prenatal and postnatal tissues and cell types. However, current literature shows that in addition to regulation by atRA, CYP26 enzyme expression is also regulated by other endogenous processes and inflammatory cytokines. In humans and in animal models the expression patterns of CYP26 enzymes have been shown to be tissue and cell type specific, and the expression of the CYP26 enzymes is believed to regulate the formation of critical atRA concentration gradients in various tissue types. Yet, very little data exists on direct disease associations of altered CYP26 expression or activity. Nevertheless, data is emerging describing a variety of human genetic variations in the CYP26 enzymes that are associated with different pathologies. Interestingly, some of these genetic variants result in increased activity of the CYP26 enzymes potentially leading to complex gene-environment interactions due to variability in dietary intake of retinoids. This review highlights the current knowledge of structure-function of CYP26 enzymes and focuses on their role in human retinoid metabolism in different tissues.

A Schwann cell-enriched circular RNA circ-Ankib1 regulates Schwann cell proliferation following peripheral nerve injury

Schwann cells (SCs) play an essential role in nerve injury repair. A striking feature of the cellular response to peripheral nerve injury is the proliferation of SCs. Circular (circ)RNAs are enriched in the nervous system and are involved in physiologic and pathologic processes. However, the potential role of circRNAs in SC proliferation post nerve injury remains largely unknown. Using a sciatic nerve crush model, we obtained an expression profiling of circRNAs in injured sciatic nerves in rats by RNA sequencing and bioinformatics analysis, and we further identified a circRNA [circ-ankyrin repeat and in-between Ring finger (IBR) domain containing 1 (Ankib1)] involved in SC proliferation by the transfection of specific small interfering RNAs. Overexpression of circ-Ankib1, which was specifically and highly enriched in SCs, impaired SC proliferation and axon regeneration following sciatic nerve injury. Mechanistically, increased expression of DEx/H-box helicase 9 (DHX9) postinjury might contribute to the down-regulation of circ-Ankib1, which further suppressed cytochrome P450, family 26, subfamily B, polypeptide 1 expression by sponging miR-423-5p, miR-485-5p, and miR-666-3p, leading to the induction of SC proliferation and nerve regeneration. Taken together, our results reveal a crucial role for circRNAs in regulating proliferation of SCs involved in sciatic nerve regeneration; as such, circRNAs may serve as a potential therapeutic avenue for nerve injury repair.-Mao, S., Zhang, S., Zhou, S., Huang, T., Feng, W., Gu, X., Yu, B. A Schwann cell-enriched circular RNA circ-Ankib1 regulates Schwann cell proliferation following peripheral nerve injury.

The role of FSH and TGF-β superfamily in follicle atresia

Most of the mammalian follicles undergo a degenerative process called “follicle atresia”. Apoptosis of granulosa cells is the main characteristic of follicle atresia. Follicle stimulating hormone (FSH) and the transforming growth factor β (TGF-β) superfamily have important regulatory functions in this process. FSH activates protein kinase A and cooperating with insulin receptor substrates, it promotes the PI3K/Akt pathway which weakens apoptosis. Both Smad or non-Smad signaling of the transforming growth factor β superfamily seem to be related to follicle atresia, and the effect of several important family members on follicle atresia is concluded in this article. FSH and TGF-β are likely to mutually influence each other and what we have already known about the possible underlying molecular mechanism is also discussed below.

ALK4-SMAD2/3-SMAD4 signaling mediates the activin A-induced suppression of PTX3 in human granulosa-lutein cells

As one of the members of the transforming growth factor-β (TGF-β) superfamily, activin A plays an important role in regulating follicular development and oocyte maturation. Pentraxin 3 (PTX3) is the key component that promotes the process of cumulus expansion during mammalian ovulation. At present, the regulation of PTX3 expression in human granulosa cells remains largely unknown. This study aimed to examine the effects of activin A on the expression of PTX3 in human granulosa-lutein (hGL) cells and to investigate the underlying molecular mechanisms. Using an established immortalized hGL cell line (SVOG) and primary hGL cells as study models, we demonstrated that activin A significantly increased the phosphorylation of SMAD2 and SMAD3, which suppressed the expression of PTX3 at both the mRNA and protein levels. Additionally, these effects induced by activin A were completely reversed by pretreatment with the TGF-β type I receptor inhibitor SB431542 and knockdown of ALK4. Furthermore, knockdown of SMAD2, SMAD3, or SMAD4 completely reversed the activin A-induced suppressive effects on PTX3 expression. Notably, the ChIP analyses demonstrated that phosphorylated SMADs could bind to human PTX3 promoter. Collectively, our results showed that the ALK4-SMAD2/3-SMAD4 signaling pathway most likely mediates the suppressive effect of activin A on PTX3 expression in hGL cells.

Association of RBP-4 gene polymorphisms with follicular cysts in large white sows

Follicular cysts, which is a common infertility disease, can cause financial losses in pig breeding programmes. The pathogenesis and mechanisms of the formation of follicular cysts are not understood clearly. In our previous study, the concentration of retinol-binding protein 4 (RBP-4) in the follicular fluid (FF) of the ovary with follicular cysts was found to be significantly higher than that of normal ovary, thereby suggesting that RBP-4 may be a candidate biomarker for porcine follicular cysts. To study the association of RBP-4 and follicular cysts further, we detected the polymorphisms of the RBP-4 gene and the presence of follicular cysts by PCR-Restriction fragment length polymorphism (RFLP) assay. In this study, we screened the mutations of RBP-4 gene in 79 sows with follicular cysts and 100 normal sows without cysts. Results showed that +249-63G>C polymorphisms were significantly associated with follicular cysts, and sows with CC genotype in RBP-4 gene had a high risk of developing follicular cysts. Hence, our findings further proved that RBP-4 may be a novel biomarker for follicular cysts, which may be valuable for the diagnosis of follicular cysts and molecular breeding of pigs.

Retinoic acid signaling in ovarian folliculogenesis and steroidogenesis

Retinoids are essential for reproduction. Most research has focused on the role of retinoic acid signaling in the regulation of meiosis during early fetal germ cell development. However, less attention has been paid to the possible effects of retinoic acid signaling in adult female gonads. Retinoic acid, its receptors, and the key enzymes required for retinoic acid synthesis are expressed in the ovaries and they are involved in the regulation of folliculogenesis and steroidogenesis. Exposure to compounds that can interfere with normal retinoic acid signaling is associated with adverse ovarian outcomes, including altered steroidogenesis and reduction in indicators of ovarian reserve in women and laboratory animal models. These observations call for more attention to retinoids as regulators of adult ovarian physiology and as possible targets of endocrine disruption by environmental chemicals. In this review, we summarize the current knowledge of retinoids in folliculogenesis and steroidogenesis in post-pubertal mammalian ovaries.

Putative Loci Causing Early Embryonic Mortality in Duroc Swine

Lethal recessive alleles that act prenatally may be detected from the absence of homozygous individuals in a population. However, these alleles may be maintained at relatively low frequencies in populations as heterozygotes. In pigs, they may reduce litter size. This study aimed to detect putative lethal variants in the Duroc breed. Phenotypes for the numbers of piglets born (TNB), born live (BA), alive at 24 h (L24), stillborn (SB), and born as mummified fetuses (MM) were available from 5340 recorded litters which resulted from mating of 192 genotyped boars with sows of unknown genotype (dataset 1). An additional 50 litters were produced from parents that were both genotyped (dataset 2). Imputed genotypes of 650K SNPs for 1359 Duroc boars were used in this study. One significant SNP (Bonferroni corrected P = 5.5E-06) was located on SSC14 with 45.3 homozygous individuals expected but none observed. This SNP was significant for mummified fetuses. One hundred fifty two haplotypes were also found to potentially harbor recessive lethal mutations. Twenty-one haplotypes had a significant harmful effect on at least one trait. Two regions, located on SSC8 (144.9–145.5 Mb) and SSC9 (19–19.4 Mb) had significant effects on fertility traits in both datasets. Additionally, regions on SSC1 (82.0–82.8 Mb), SSC3 (73.3–73.7 and 87.1–87.5 Mb) and SSC12 (35.8–36.2 and 50.0–50.5 Mb) had significant deleterious effects on TNB or BA or L24 in dataset 1. Finally, a region on SSC17 (28.7–29.3 Mb) had significant effects on TNB, BA and L24 in dataset 2. A few candidate genes identified within these regions were described as being involved in spermatogenesis and male fertility (TEX14, SEP4, and HSF5), or displayed recessive lethality (CYP26B1, SCD5, and PCF11) in other species. The putative loci detected in this study provide valuable information to potentially increase Duroc litter size by avoiding carrier-by-carrier matings in breeding programs. Further study of the identified candidate genes responsible for such lethal effects may lead to new insights into functions regulating pig fertility.

Follicle-stimulating hormone (FSH) promotes retinol uptake and metabolism in the mouse ovary

BACKGROUND

Retinoids (retinol and its derivatives) are required for the development and maintenance of normal physiological functions of the ovary. However, the mechanisms underlying the regulation of ovarian retinoid homeostasis during follicular development remain unclear.

METHODS

The present study determined retinoid levels and the expression levels of genes involved in the retinol uptake and its metabolic pathway in the ovaries of follicle-stimulating hormone (FSH)-treated mice and in granulosa cells treated with FSH using ultra performance liquid chromatography (UPLC) combined with quadrupole time-of-flight high-sensitivity mass spectrometry (Q-TOF/HSMS) and real-time PCR analysis.

RESULTS

The levels of total retinoids and retinoic acid (RA) and expressions of retinol-oxidizing enzyme genes alcohol dehydrogenase 1 (Adh1) and aldehyde dehydrogenase (Aldh1a1) are increased in the ovaries of mice treated with FSH; in contrast, the retinyl ester levels and retinol-esterifying enzyme gene lecithin: retinol acyltransferase (Lrat) expression are diminished. In FSH-treated granulosa cells, the levels of retinyl esters, retinaldehyde, and total retinoids are augmented; and this is coupled with an increase in the expressions of stimulated by retinoic acid 6 (Stra6) and cellular retinol-binding protein 1 (Crbp1), genes in the retinol uptake pathway, and Adh1, Adh7, and Aldh1a1 as well as a diminution in Lrat expression.

CONCLUSIONS

These data suggest that FSH promotes retinol uptake and its conversion to RA through modulating the pathways of retinol uptake and metabolism in the mouse ovary. The present study provides a possible mechanism for the regulation of endogenous RA signaling in the developing follicles.

Regulation by FSH of the dynamic expression of retinol-binding protein 4 in the mouse ovary

BACKGROUND

Ovarian retinoid homeostasis plays an important role in the physiological function of the ovary. Retinol-binding protein 4 (RBP4) acts as the mediator for the systemic and intercellular transport of retinol and is heavily involved in cellular retinol influx, efflux, and exchange. However, the expression patterns and regulatory mechanisms of Rbp4 in the ovary remain unclear.

METHODS

The expression pattern of ovarian Rbp4 was examined in immature mice during different developmental stages and in adult mice during different stages of the estrous cycle. The potential regulation and mechanisms of ovarian Rbp4 expression by estrogen and related gonadotropins in mouse ovaries were also investigated.

RESULTS

The present study demonstrated that the ovarian expression of Rbp4 remained constant before puberty and increased significantly in the peripubertal period. In adult female mice, the expression of Rbp4 increased at proestrus and peaked at estrus at both the mRNA and protein levels. The protein distribution of RBP4 was mainly localized in the granulosa cell and theca cell layer in follicles. In addition, the expression of Rbp4 was significantly induced by follicle-stimulating hormone (FSH) or FSH + luteinizing hormone (LH) in combination in immature mouse (3 weeks old) ovaries in vivo and in granulosa cells cultured in vitro, both at the mRNA and protein levels. In contrast, treatment with LH or 17β-estradiol did not exhibit any observable effects on ovarian Rbp4 expression. Transcription factors high-mobility group AT-hook 1 (HMGA1), steroidogenic factor 1 (SF-1), and liver receptor homolog 1 (LRH-1) (which have been previously shown to be involved in activation of Rbp4 transcription), also responded to FSH stimulation. In addition, H-89, an inhibitor of protein kinase A (PKA), and the depletion of HMGA1, SF-1, and LRH-1 by small interfering RNAs (siRNAs), resulted in a dramatic loss of the induction of Rbp4 expression by FSH at both the mRNA and protein levels.

CONCLUSIONS

These data indicate that the dynamic expression of Rbp4 is mainly regulated by FSH through the cAMP-PKA pathway, involving transcriptional factors HMGA1, SF-1, and LRH-1, in the mouse ovary during different stages of development and the estrous cycle.

MicroRNA dynamics at the onset of primordial germ and somatic cell sex differentiation during mouse embryonic gonad development

In mammals, commitment and specification of germ cell lines involves complex programs that include sex differentiation, control of proliferation, and meiotic initiation. Regulation of these processes is genetically controlled by fine-tuned mechanisms of gene regulation in which microRNAs (miRNAs) are involved. We have characterized, by small-RNA-seq and bioinformatics analyses, the miRNA expression patterns of male and female mouse primordial germ cells (PGCs) and gonadal somatic cells at embryonic stages E11.5, E12.5, and E13.5. Differential expression analyses revealed differences in the regulation of key miRNA clusters such as miR-199-214, miR-182-183-96, and miR-34c-5p, whose targets have defined roles during gonadal sexual determination in both germ and somatic cells. Extensive analyses of miRNA sequences revealed an increase in noncanonical isoforms on PGCs at E12.5 and dramatic changes of 3' isomiR expression and 3' nontemplate nucleotide additions in female PGCs at E13.5. Additionally, RT-qPCR analyses of genes encoding proteins involved in miRNA biogenesis and 3' nucleotide addition uncovered sexually and developmentally specific expression, characterized by the decay of Drosha, Dgcr8, and Xpo5 expression along gonadal development. These results demonstrate that miRNAs, their isomiRs, and miRNA machinery are differentially regulated and participate actively in gonadal sexual differentiation in both PGCs and gonadal somatic cells.

Complete in vitro oogenesis: retrospects and prospects

Precise control of mammalian oogenesis has been a traditional focus of reproductive and developmental biology research. Recently, new reports have introduced the possibility of obtaining functional gametes derived in vitro from stem cells. The potential to produce functional gametes from stem cells has exciting applications for regenerative medicine though still remains challenging. In mammalian females ovulation and fertilization is a privilege reserved for a small number of oocytes. In reality the vast majority of oocytes formed from primordial germ cells (PGCs) will undergo apoptosis, or other forms of cell death. Removal occurs during germ cell cyst breakdown and the establishment of the primordial follicle (PF) pool, during the long dormancy at the PF stage, or through follicular atresia prior to reaching the ovulatory stage. A way to solve this limitation could be to produce large numbers of oocytes, in vitro, from stem cells. However, to recapitulate mammalian oogenesis and produce fertilizable oocytes in vitro is a complex process involving several different cell types, precise follicular cell-oocyte reciprocal interactions, a variety of nutrients and combinations of cytokines, and precise growth factors and hormones depending on the developmental stage. In 2016, two papers published by Morohaku et al. and Hikabe et al. reported in vitro procedures that appear to reproduce efficiently these conditions allowing for the production, completely in a dish, of a relatively large number of oocytes that are fertilizable and capable of giving rise to viable offspring in the mouse. The present article offers a critical overview of these results as well as other previous work performed mainly in mouse attempting to reproduce oogenesis completely in vitro and considers some perspectives for the potential to adapt the methods to produce functional human oocytes.

Mechanisms controlling germline cyst breakdown and primordial follicle formation

In fetal females, oogonia proliferate immediately after sex determination. The progress of mitosis in oogonia proceeds so rapidly that the incompletely divided cytoplasm of the sister cells forms cysts. The oogonia will then initiate meiosis and arrest at the diplotene stage of meiosis I, becoming oocytes. Within each germline cyst, oocytes with Balbiani bodies will survive after cyst breakdown (CBD). After CBD, each oocyte is enclosed by pre-granulosa cells to form a primordial follicle (PF). Notably, the PF pool formed perinatally will be the sole lifelong oocyte source of a female. Thus, elucidating the mechanisms of CBD and PF formation is not only meaningful for solving mysteries related to ovarian development but also contributes to the preservation of reproduction. However, the mechanisms that regulate these phenomena are largely unknown. This review summarizes the progress of cellular and molecular research on these processes in mice and humans.

Retinoic acid signaling is dispensable for somatic development and function in the mammalian ovary

Retinoic acid (RA) is a potent inducer of cell differentiation and plays an essential role in sex-specific germ cell development in the mammalian gonad. RA is essential for male gametogenesis and hence fertility. However, RA can also disrupt sexual cell fate in somatic cells of the testis, promoting transdifferentiation of male Sertoli cells to female granulosa-like cells when the male sexual regulator Dmrt1 is absent. The feminizing ability of RA in the Dmrt1 mutant somatic testis suggests that RA might normally play a role in somatic cell differentiation or cell fate maintenance in the ovary. To test for this possibility we disrupted RA signaling in somatic cells of the early fetal ovary using three genetic strategies and one pharmaceutical approach. We found that deleting all three RA receptors (RARs) in the XX somatic gonad at the time of sex determination did not significantly affect ovarian differentiation, follicle development, or female fertility. Transcriptome analysis of adult triple mutant ovaries revealed remarkably little effect on gene expression in the absence of somatic RAR function. Likewise, deletion of three RA synthesis enzymes (Aldh1a1-3) at the time of sex determination did not masculinize the ovary. A dominant-negative RAR transgene altered granulosa cell proliferation, likely due to interference with a non-RA signaling pathway, but did not prevent granulosa cell specification and oogenesis or abolish fertility. Finally, culture of fetal XX gonads with an RAR antagonist blocked germ cell meiotic initiation but did not disrupt sex-biased gene expression. We conclude that RA signaling, although crucial in the ovary for meiotic initiation, is not required for granulosa cell specification, differentiation, or reproductive function.

Php4 Is a Key Player for Iron Economy in Meiotic and Sporulating Cells

Meiosis is essential for sexually reproducing organisms, including the fission yeast Schizosaccharomyces pombe In meiosis, chromosomes replicate once in a diploid precursor cell (zygote), and then segregate twice to generate four haploid meiotic products, named spores in yeast. In S. pombe, Php4 is responsible for the transcriptional repression capability of the heteromeric CCAAT-binding factor to negatively regulate genes encoding iron-using proteins under low-iron conditions. Here, we show that the CCAAT-regulatory subunit Php4 is required for normal progression of meiosis under iron-limiting conditions. Cells lacking Php4 exhibit a meiotic arrest at metaphase I. Microscopic analyses of cells expressing functional GFP-Php4 show that it colocalizes with chromosomal material at every stage of meiosis under low concentrations of iron. In contrast, GFP-Php4 fluorescence signal is lost when cells undergo meiosis under iron-replete conditions. Global gene expression analysis of meiotic cells using DNA microarrays identified 137 genes that are regulated in an iron- and Php4-dependent manner. Among them, 18 genes are expressed exclusively during meiosis and constitute new putative Php4 target genes, which include hry1⁺ and mug14⁺ Further analysis validates that Php4 is required for maximal and timely repression of hry1⁺ and mug14⁺ genes. Using a chromatin immunoprecipitation approach, we show that Php4 specifically associates with hry1⁺ and mug14⁺ promoters in vivo Taken together, the results reveal that in iron-starved meiotic cells, Php4 is essential for completion of the meiotic program since it participates in global gene expression reprogramming to optimize the use of limited available iron.

Retinoic acid enhances progesterone production via the cAMP/PKA signaling pathway in immature rat granulosa cells

Retinoic acid (RA) is a metabolite of vitamin A and has important roles in development, differentiation, and reproduction. Activin has been shown to regulate the RA pathway and affect granulosa cell (GC) proliferation, suggesting that RA is important for early follicle development. However, little is known about the effects of RA on GC functions, particularly steroidogenesis, during the early follicle stage. The aim of this study was to investigate the effects of all-trans-RA (atRA) on progesterone production in immature rat GCs cultured without gonadotropin. Our results demonstrated that atRA enhanced progesterone production by upregulating the levels of steroidogenic acute regulatory protein (StAR) and cytochrome P450scc (Cyp11a1) mRNAs, but not 3β-hydroxysteroid dehydrogenase mRNA in immature rat GCs. Additionally, analysis of the mechanisms through which atRA upregulated StAR and Cyp11a1 mRNAs revealed that atRA enhanced intracellular cAMP accumulation and phosphorylation of cAMP response-element binding protein (CREB). In addition, H-89, an inhibitor of protein kinase A (PKA), abolished the stimulatory effects of atRA, indicating that atRA enhanced progesterone synthesis through cAMP/PKA signaling. In conclusion, our data demonstrated that atRA has a crucial role in progesterone synthesis in rat GCs during the early follicle stage.

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atRA upregulated StAR and Cyp11a1 and enhanced progesterone production.

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atRA enhanced intracellular cAMP accumulation and phosphorylation of CREB.

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Inhibition of PKA abolished the stimulatory effects of atRA.

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atRA mediated progesterone synthesis in rat GCs during the early follicle stage.

De Novo-Synthesized Retinoic Acid in Ovarian Antral Follicles Enhances FSH-Mediated Ovarian Follicular Cell Differentiation and Female Fertility

Retinoic acid (RA) is the active form of vitamin A and is synthesized from retinol by two key enzymes, alcohol dehydrogenase (ADH) and acetaldehyde dehydrogenase (ALDH). As the physiological precursor of RA, retinol impacts female reproductive functions and fertility. The expression of Adh1 and Adh5 as well as Aldh1a1 and Aldh1a7 are significantly increased in the ovaries of mice treated with equine chorionic gonadotropin/FSH. The RA receptor is expressed and localized in granulosa cells and is activated by endogenous RA as indicated by LacZ expression in granulosa cells of RA-responsive transgene-LacZ transgenic mice (RA reporter mice). Coinjection of the ADH inhibitor, 4-methylpyrazole, with equine chorionic gonadotropin significantly decreases the number and developmental competence of oocytes ovulated in response to human chorionic gonadotropin/LH as compared with controls. Injections of RA completely reverse the effects of the inhibitor of ovulation and oocyte development. When mice were fed a retinol-free, vitamin A-deficient diet that significantly reduced the serum levels of retinol, the expression of the LH receptor (Lhcgr) was significantly lower in the ovaries of the vitamin A-deficient mice, and injections of human chorionic gonadotropin failed to induce genes controlling ovulation. These results indicate that ovarian de novo biosynthesis of RA is required for the follicular expression of Lhcgr in granulosa cells and their ability to respond to the ovulatory LH surge.

Change in the Gastro-Intestinal Tract by Overexpressed Activin Beta A

Originally, activins were identified as stimulators of FSH release in reproduction. Other activities, including secondary axis formation in development, have since been revealed. Here, we investigated the influence of activin βA on the body, including the gastro-intestinal (GI) tract. Initially, the activin βA protein was detected in the serum proportional to the amount of pCMV-rAct plasmid injected. The induced level of activin βA in muscle was higher in female than male mice. Subsequent results revealed that stomach and intestine were severely damaged in pCMV-rAct-injected mice. At the cellular level, loss of parietal cells was observed, resulting in increased pH within the stomach. This phenomenon was more severe in male than female mice. Consistent with damage of the stomach and intestine, activin βA often led to necrosis in the tip of the tail or foot, and loss of body weight was observed in pCMV-rAct-injected male but not female mice. Finally, in pCMV-rAct-injected mice, circulating activin βA led to death at supraphysiological doses, and this was dependent on the strain of mice used. Taken together, these results indicate that activin βA has an important role outside of reproduction and development, specifically in digestion. These data also indicate that activin βA must be controlled within a narrow range because of latent lethal activity. In addition, our approach can be used effectively for functional analysis of secreted proteins.

Activin A accelerates the progression of fetal oocytes throughout meiosis and early oogenesis in the mouse

Activins can exert several roles in ovary development. However, little is known about their involvement in early mammalian oogenesis. In this study, we reported that activin receptors (including ActRIA, ActRIB, ActRIIA, and ActRIIB) are expressed throughout the development of the mouse ovaries from 12.5 days postcoitum (dpc) to 21 days postparturition (dpp). Moreover, we found that in vitro, the addition of activin A (ActA) to the culture medium of 12.5 dpc ovarian tissues accelerated the progression of oocytes throughout meiotic prophase I stages. This result was reproduced in vivo following administration of ActA to pregnant mice. The in vitro effect of ActA was associated with increased expression of premeiotic and meiotic genes (including Dazl, Spo11, Stra8, Scp3, and Rec8) in the ovarian tissues. Mechanistically, ActA-dependent SMAD3 signaling modulated the expression of members of the retinoic acid (RA) system, including the RA degradation CYP26B1 enzyme and the RA receptors. Finally, ActA promoted the survival and growth of fetal and early postnatal oocytes and primordial follicle assembly both in vitro and in vivo. In conclusion, the present study identifies new roles of ActA in early oogenesis and suggested that ActA and RA might cooperate in promoting meiosis in female germ cells.

Inhibition of retinoic acid synthesis disrupts spermatogenesis and fecundity in zebrafish

Timing of germ cell entry into meiosis is sexually dimorphic in mammals. However it was recently shown that germ cells initiate meiosis at the same time in male and female zebrafish. Retinoic acid (RA) has been shown to be critical for mammalian spermatogenesis. Inhibition of RA synthesis by WIN 18,446 has been reported to inhibit spermatogenesis in a wide variety of animals including humans and was once used as a contraceptive in humans. In this study we explored the role of RA in zebrafish spermatogenesis. In silico analysis with Internal coordinate mechanics docking software showed that WIN 18,446 can bind to the rat, human and zebrafish Aldh1a2 catalytic domain with equivalent potency. RA exposure resulted in up-regulation of the RA metabolizing enzyme genes cyp26a1, cyp26b1 and cyp26c1 in vitro and in vivo. Exposure to WIN 18,446 resulted in down-regulation of Aldh1a2, cyp26a1 and cyp26b1 in vivo. WIN 18,446 was effective in disrupting spermatogenesis and fecundity in zebrafish but the reduction in sperm count and fecundity was only observed when zebrafish were maintained on a strict Artemia nauplii diet which is known to contain low levels of vitamin A. This study shows that RA is involved in spermatogenesis as well as oocyte development in zebrafish. As the zebrafish Aldh1a2 structure and function is similar to the mammalian counterpart, Aldh1a2 inhibitor screening using zebrafish as a model system may be beneficial in the discovery and development of new and safe contraceptives for humans.

A role for retinoids in human oocyte fertilization: regulation of connexin 43 by retinoic acid in cumulus granulosa cells

Retinoids are essential for ovarian steroid production and oocyte maturation in mammals. Oocyte competency is known to positively correlate with efficient gap junction intercellular communication (GJIC) among granulosa cells in the cumulus-oocyte complex. Connexin 43 (C x 43) is the main subunit of gap junction channels in human cumulus granulosa cells (CGC) and is regulated by all-trans retinoic acid (ATRA) in other hormone responsive cell types. The objectives of this study were to quantify retinoid levels in human CGC obtained during IVF oocyte retrievals, to investigate the potential relationship between CGC ATRA levels and successful oocyte fertilization, and to determine the effects of ATRA on C x 43 protein expression in CGC. Results showed that CGC cultures actively metabolize retinol to produce ATRA. Grouped according to fertilization rate tertiles, mean ATRA levels were 2-fold higher in pooled CGC from women in the highest versus the lowest tertile (P < 0.05). ATRA induced a rapid dephosphorylation of C x 43 in CGC and granulosa cell line (KGN) cultures resulting in a >2-fold increase in the expression of the functional non-phosphorylated (P0) species (P < 0.02). Similar enhancement of P0 by ATRA was shown in CGC and KGN cultures co-treated with LH or hCG which, by themselves, enhanced the protein levels of C x 43 without altering its phosphorylation profile. Correspondingly, the combination of ATRA+hCG treatment of KGN caused a significant increase in GJIC compared with single agent treatments (P < 0.025) and a doubling of GJIC from that seen in untreated cells (P < 0.01). These findings indicate that CGC are a primary site of retinoid uptake and ATRA biosynthesis. Regulation of C x 43 by ATRA may serve an important role in folliculogenesis, development of oocyte competency, and successful fertilization by increasing GJIC in CGC.

Exogenous supplementation of Activin A enhances germ cell differentiation of human embryonic stem cells

Human embryonic stem cells (hESCs) derived in the presence of Activin A (ActA) demonstrate an increased differentiation propensity toward the germ cell lineage. In addition, mouse epiblast stem cells and mouse epiblast-like cells are poised toward germ cell differentiation and are derived in the presence of ActA. We therefore investigated whether supplementation with ActA enhances in vitro hESC differentiation toward germ cell lineage. ActA up-regulated early primordial germ cell (PGC) genes STELLA/DPPA3 (developmental pluripotency associated 3) and tyrosine kinase receptor cKIT in both ActA-derived and standard-derived hESCs indicating its role in priming hESCs toward the PGC lineage. Indeed, ActA plus bone morphogenic protein 4 (BMP4) strongly increased germ cell differentiation potential of hESCs based on the high expression of late PGC markers DAZL (deleted in azoospermia-like) and VASA/DDX4 (DEAD-box polypeptide 4) at mRNA and protein level. Hence, the combination of ActA with BMP4 provides an additional boost for hESCs to develop into postmigratory germ cells. Together with increased VASA expression in the presence of ActA and BMP4, we also observed up-regulation of endoderm-specific genes GATA4 (GATA binding protein 4) and GATA6. Finally, we were able to further mature these in vitro-derived PGC-like cells (PGCLCs) by culturing them in in vitro maturation (IVM) medium, resulting in the formation of germ cell-like clusters and induction of meiotic gene expression. In conclusion, we demonstrate for the first time a synergism between ActA and BMP4 in facilitating germ cell-directed differentiation of hESCs, which is enhanced by extended culture in IVM medium, as shown by cytoplasmic VASA-expressing PGCLCs. We propose a novel relationship between the endoderm and germ cell lineage during hESC differentiation.

Influence of activin A supplementation during human embryonic stem cell derivation on germ cell differentiation potential

Human embryonic stem cells (hESCs) are more similar to "primed" mouse epiblast stem cells (mEpiSCs). mEpiSCs, which are derived in Activin A, show an increased propensity to form primordial germ cell (PGC)-like cells in response to bone morphogenic protein 4 (BMP4). Hence, we hypothesized that hESCs derived in the presence of Activin A may be more competent in differentiating towards PGC-like cells after supplementation with BMP4 compared to standard hESC lines. We were able to successfully derive two hESC lines in the presence of Activin A, which were pluripotent and showed higher base levels of STELLA and cKIT compared to standard hESC lines derived without Activin A addition. Furthermore, upon differentiation as embryoid bodies in the presence of BMP4, we observed upregulation of VASA at day 7, both at the transcript and protein level compared to standard hESC lines, which appeared to take longer time for PGC specification. Unlike other hESC lines, nuclear pSMAD2/3 presence confirmed that Activin signalling was switched on in Activin A-derived hESC lines. They were also responsive to BMP4 based on nuclear detection of pSMAD1/5/8 and showed endodermal differentiation as a result of GATA-6 expression. Hence, our results provide novel insights into the impact of hESC derivation in the presence of Activin A and its subsequent influence on germ cell differentiation potential in vitro.

MicroRNA-181a suppresses mouse granulosa cell proliferation by targeting activin receptor IIA

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.

Discovery of novel protein partners of the transcription factor FOXL2 provides insights into its physiopathological roles

FOXL2 transcription factor is responsible for the Blepharophimosis Ptosis Epicantus inversus Syndrome (BPES), a genetic disease involving craniofacial malformations often associated with ovarian failure. Recently, a somatic FOXL2 mutation (p.C134W) has been reported in >95% of adult-type granulosa cell tumors. Here, we have identified 10 novel FOXL2 partners by yeast-two-hybrid screening and co-immunoprecipitation. Most BPES-inducing mutated FOXL2 proteins display aggregation in cultured cells. Here, we show that two of the partners (NR2C1 and GMEB1) can be sequestered in such aggregates. This co-aggregation can contribute to the pathogenesis of FOXL2 mutations. We have also measured the effects of FOXL2 interactants on the transcriptional regulation of a series of target promoters. Some of the partners (CXXC4, CXXC5, BANF1) were able to repress FOXL2 activity indistinctively of the promoter. Interestingly, CREM-τ2α, which acted as a repressor on most promoters, increased wild-type (WT) FOXL2 activity on two promoters (PTGS2 and CYP19A1), but was unable to increase the activity of the oncogenic mutant p.C134W. Conversely, GMEB1, which also acted as a repressor on most promoters and increased WT FOXL2 activity on the Per2 promoter, increased to a greater extent the activity of the p.C134W variant. Interestingly, partners with intrinsic pro-apoptotic effect were able to increase apoptosis induction by WT FOXL2, but not by the p.C134W mutant, whereas partners with an anti-apoptotic effect decreased apoptosis induction by both FOXL2 versions. Altogether, these results suggest that the p.C134W mutated form fails to integrate signals through protein-protein interactions to regulate target promoter subsets and in particular to induce cell death.

The effects of FSH and activin A on follicle development in vitro

Numerous studies have reported on the roles of activins in gonadal regulation; however, little is known about their specific roles in early folliculogenesis. Ovarian follicular growth was investigated in 10-day cultures of day 4 postnatal whole ovaries treated with activin A (ActA; 50 ng/ml), with or without FSH (100 ng/ml) in vitro. We hypothesized that treatment with ActA±FSH would affect rates of growth and atresia in follicles. None of the treatments affected primordial follicle activation, and antral follicles were not observed after 10 days in culture. Primordial follicle numbers from all treatment groups were ∼20% of those in day 4 fresh ovaries, indicating that activation had occurred. In the presence of ActA, preantral follicle numbers increased significantly (P<0.0001). ActA alone decreased the proportion of atretic follicles in the primary and preantral classes, whereas the combined treatment of ActA+FSH increased the proportion of atretic preantral oocytes. Real-time PCR analysis revealed that follistatin, FSH receptor, and activin βA and βB subunits were all expressed at significantly higher levels in the ActA-only treated group but not in the ActA+FSH group. Here, we report novel findings supporting the role of FSH in primordial follicle survival through an action on apoptosis and a stimulatory role of ActA in the primordial to primary and preantral stages of follicle development, suggesting an inhibitory action of activin on oocyte apoptosis.

Cytochrome P450s in the regulation of cellular retinoic acid metabolism

The active metabolite of vitamin A, retinoic acid (RA), is a powerful regulator of gene transcription. RA is also a therapeutic drug. The oxidative metabolism of RA by certain members of the cytochrome P450 (CYP) superfamily helps to maintain tissue RA concentrations within appropriate bounds. The CYP26 family--CYP26A1, CYP26B1, and CYP26C1--is distinguished by being both regulated by and active toward all-trans-RA (at-RA) while being expressed in different tissue-specific patterns. The CYP26A1 gene is regulated by multiple RA response elements. CYP26A1 is essential for embryonic development, whereas CYP26B1 is essential for postnatal survival as well as germ cell development. Enzyme kinetic studies have demonstrated that several CYP proteins are capable of metabolizing at-RA; however, it is likely that CYP26A1 plays a major role in RA clearance. Thus, pharmacological approaches to limiting the activity of CYP26 enzymes may extend the half-life of RA and could be useful clinically in the future.