Disruption of Epidermal Growth Factor Receptor but Not EGF Blocks Follicle Activation in Zebrafish Ovary

Single-cell RNA sequencing revealed the roles of macromolecule epidermal growth factor receptor (EGFR) in the hybrid sterility of hermaphroditic Argopecten scallops

The macromolecule epidermal growth factor receptor (EGFR) is a transmembrane glycoprotein that belongs to the protein kinase superfamily, which plays versatile functions in cell proliferation, development and fertility regulation. Almost all F1 hybrids obtained from the hermaphroditic bay scallops and Peruvian scallops exhibit infertility, and the genetic mechanism remains unclear. In this study, the comprehensive scRNA-seq was first conducted in the gonads of hybrid scallops, deducing the developmental sequence of germ cells and identifying the critical regulators in hybrid sterility: epidermal growth factor receptor. During the development from oogenesis phase germ cells to oocytes, the expression of the EGFR gene gradually decreased in sterile hybrids but increased in fertile hybrids. The significantly lower EGFR expression and ATP content, but higher ROS production rate was detected in the gonad of sterile hybrids than that in fertile hybrids, which might cause slow development of oocytes, stagnation of cell cycle, insufficient energy supply, high level of apoptosis and final sterility. Specific knock-down of EGFR gene led to decreased ATP content, increased ROS production rate, and inhibited oocyte maturation and gonadal development. These findings provide new insights into the roles of EGFR in hybrid infertility of bivalves and the healthy development of scallop breeding.

In-depth analysis of transcriptomes in ovarian cortical follicles from children and adults reveals interfollicular heterogeneity

The ovarian cortical reserve of follicles is vital for fertility. Some medical treatments are toxic to follicles, leading to premature ovarian insufficiency. Ovarian tissue cryopreservation is an established method to preserve fertility in adults and even applied in prepuberty despite unproven efficacy. Here, we analyze transcriptomes of 120 cortical follicles from children and adults for detailed comparison. We discover heterogeneity with two main types of follicles in both age groups: one with expected oocyte-granulosa profiles and another with predicted role in signaling. Transcriptional changes during growth to the secondary stage are similar overall in children and adults, but variations related to extracellular matrix, theca cells, and miRNA profiles are found. Notably, cyclophosphamide dose correlates with interferon signaling in child follicles. Additionally, morphology alone is insufficient for follicle categorization suggesting a need for additional markers. Marker genes for early follicle activation are determined. These findings will help refine follicular classification and fertility preservation techniques across critical ages.

In Search of a Target Gene for a Desirable Phenotype in Aquaculture: Genome Editing of Cyprinidae and Salmonidae Species

Aquaculture supplies the world food market with a significant amount of valuable protein. Highly productive aquaculture fishes can be derived by utilizing genome-editing methods, and the main problem is to choose a target gene to obtain the desirable phenotype. This paper presents a review of the studies of genome editing for genes controlling body development, growth, pigmentation and sex determination in five key aquaculture Salmonidae and Cyprinidae species, such as rainbow trout (Onchorhynchus mykiss), Atlantic salmon (Salmo salar), common carp (Cyprinus carpio), goldfish (Carassius auratus), Gibel carp (Carassius gibelio) and the model fish zebrafish (Danio rerio). Among the genes studied, the most applicable for aquaculture are mstnba, pomc, and acvr2, the knockout of which leads to enhanced muscle growth; runx2b, mutants of which do not form bones in myoseptae; lepr, whose lack of function makes fish fast-growing; fads2, Δ6abc/5Mt, and Δ6bcMt, affecting the composition of fatty acids in fish meat; dnd mettl3, and wnt4a, mutants of which are sterile; and disease-susceptibility genes prmt7, gab3, gcJAM-A, and cxcr3.2. Schemes for obtaining common carp populations consisting of only large females are promising for use in aquaculture. The immobilized and uncolored zebrafish line is of interest for laboratory use.

Growth factors and female reproduction in vertebrates

Female reproductive efficiency is influenced by the outcomes of various processes, including folliculogenesis, apoptosis, response to gonadotropin signaling, oocyte maturation, and ovulation. The role of hormones in regulating these processes and other reproductive activities has been well established. It is becoming increasingly evident that in addition to well-characterized hormones, growth factors play vital roles in regulating some of these reproductive activities. Growth factors and their receptors are widely distributed in vertebrate ovaries at different stages of ovarian development, indicating their involvement in intraovarian reproductive functions. In the ovary, cell surface receptors allow growth factors to regulate intraovarian reproductive activities. Understanding these actions in the reproductive axis would provide a tool to target growth factors and/or their receptors to yield desirable reproductive outcomes. These include enrichment of in vitro maturation and fertilization culture media, and management of infertility. This review discusses some widely characterized growth factors belonging to the TGF, EGF, IGF, FGF, and BDNF family of peptides and their role in female reproduction in vertebrates, with a focus on mammals.

Genetic and Epigenetic Evidence for Nonestrogenic Disruption of Otolith Development by Bisphenol A in Zebrafish

Bisphenol A (BPA) is a well-known endocrine-disrupting chemical (EDC) that has estrogenic activities. In addition to disrupting reproductive development and function via estrogenic signaling pathways, BPA can also interfere with nonreproductive functions through nonestrogenic pathways; however, the mechanisms underlying such nonestrogenic activities are not well understood. In this study, we demonstrated that BPA could disrupt otolith formation during the early development of zebrafish with long-lasting ethological effects. Using multiple mutants of estrogen receptors, we provided strong genetic evidence that the BPA-induced otolith malformation was independent of estrogen signaling. Transcriptome analysis revealed that two genes related to otolith development, otopetrin 1 (otop1) and starmaker (stm), decreased their expression significantly after BPA exposure. Knockout of both otop1 and stm genes could phenocopy the BPA-induced otolith malformation, while microinjection of their mRNAs could rescue the BPA-induced abnormalities of otolith formation. Further experiments showed that BPA inhibited the expression of otop1 and stm by activating the MEK/ERK-EZH2-H3K27me3 signaling pathway. Taken together, our study provided comprehensive genetic and molecular evidence that BPA induced the otolith malformation through nonestrogenic pathway during zebrafish early development and its activities involved epigenetic control of key genes (e.g., otop1 and stm) participating in otolith formation.

Proteomic analysis of zebrafish folliculogenesis identifies YB-1 (Ybx1/ybx1) as a potential gatekeeping molecule controlling early ovarian folliculogenesis

As in mammals, ovarian folliculogenesis in teleosts also consists of two phases: the primary growth (PG) and secondary growth (SG) phases, which are analogous to the preantral and antral phases respectively in mammals. In this study, we performed a proteomic analysis on zebrafish follicles undergoing the PG-SG transition aiming to identify factors involved in the event. Numerous proteins showed significant changes, and the most prominent one was Y-box binding protein 1 (YB-1; Ybx1/ybx1), a transcription factor and mRNA-binding protein. YB-1 belongs to the Y-box binding protein family, which also includes the gonad-specific YB-2. Interestingly, phylogenetic analysis showed no YB-2 homolog in zebrafish. Although ybx1 mRNA was expressed in various tissues, its protein Ybx1 was primarily produced in the gonads, similar to YB-2 in other species. In the ovary, Ybx1 protein started to appear in early follicles newly emerged from the germ cell cysts, reached the highest level in late PG oocytes, but decreased precipitously when the follicles entered the SG phase. In PG follicles, Ybx1 might function as a key component of the messenger ribonucleoprotein particles (mRNPs) in association with other RNA-binding proteins. Similar to mammalian YB-1, zebrafish Ybx1 also contains functional signals that determine its intracellular localization. In conclusion, Ybx1 may play dual roles of YB-1 and YB-2 in zebrafish. In the ovary, Ybx1 binds mRNAs to stabilize them while preventing their translation. At PG-SG transition, Ybx1 is removed to release the masked mRNAs for translation into functional proteins, leading to follicle activation.

Rescue of bmp15 deficiency in zebrafish by mutation of inha reveals mechanisms of BMP15 regulation of folliculogenesis

As an oocyte-specific growth factor, bone morphogenetic protein 15 (BMP15) plays a critical role in controlling folliculogenesis. However, the mechanism of BMP15 action remains elusive. Using zebrafish as the model, we created a bmp15 mutant using CRISPR/Cas9 and demonstrated that bmp15 deficiency caused a significant delay in follicle activation and puberty onset followed by a complete arrest of follicle development at previtellogenic (PV) stage without yolk accumulation. The mutant females eventually underwent female-to-male sex reversal to become functional males, which was accompanied by a series of changes in secondary sexual characteristics. Interestingly, the blockade of folliculogenesis and sex reversal in bmp15 mutant could be partially rescued by the loss of inhibin (inha-/-). The follicles of double mutant (bmp15-/-;inha-/-) could progress to mid-vitellogenic (MV) stage with yolk accumulation and the fish maintained their femaleness without sex reversal. Transcriptome analysis revealed up-regulation of pathways related to TGF-β signaling and endocytosis in the double mutant follicles. Interestingly, the expression of inhibin/activin βAa subunit (inhbaa) increased significantly in the double mutant ovary. Further knockout of inhbaa in the triple mutant (bmp15-/-;inha-/-;inhbaa-/-) resulted in the loss of yolk granules again. The serum levels of estradiol (E2) and vitellogenin (Vtg) both decreased significantly in bmp15 single mutant females (bmp15-/-), returned to normal in the double mutant (bmp15-/-;inha-/-), but reduced again significantly in the triple mutant (bmp15-/-;inha-/-;inhbaa-/-). E2 treatment could rescue the arrested follicles in bmp15-/-, and fadrozole (a nonsteroidal aromatase inhibitor) treatment blocked yolk accumulation in bmp15-/-;inha-/- fish. The loss of inhbaa also caused a reduction of Vtg receptor-like molecules (e.g., lrp1ab and lrp2a). In summary, the present study provided comprehensive genetic evidence that Bmp15 acts together with the activin-inhibin system in the follicle to control E2 production from the follicle, Vtg biosynthesis in the liver and its uptake by the developing oocytes.

Global expression pattern of genes containing positively selected sites in European anchovy (Engraulis encrasicolus L.) may shed light on teleost reproduction

European anchovy is a multiple-spawning and highly fecundate pelagic fish with high economic and ecological significance. Although fecundity is influenced by nutrition, temperature and weight of spawners, high reproductive capacity is related to molecular processes in the ovary. The ovary is an essential and complex reproductive organ composed of various somatic and germ cells, which interact to facilitate the development of the ovary and functional oocytes. Revealing the ovarian transcriptome profile of highly fecundate fishes provides insights into oocyte production in teleosts. Here we use a comprehensive tissue-specific RNA sequencing which yielded 102.3 billion clean bases to analyze the transcriptional profiles of the ovary compared with other organs (liver, kidney, ovary, testis, fin, cauda and gill) and juvenile tissues of European anchovy. We conducted a comparative transcriptome and positive selection analysis of seven teleost species with varying fecundity rates to identify genes potentially involved in oogenesis and oocyte development. Of the 2,272 single copies of orthologous genes found, up to 535 genes were under positive selection in European anchovy and these genes are associated with a wide spectrum of cellular and molecular functions, with enrichments such as RNA methylation and modification, ribosome biogenesis, DNA repair, cell cycle processing and peptide/amide biosynthesis. Of the 535 positively selected genes, 55 were upregulated, and 45 were downregulated in the ovary, most of which were related to RNA and DNA transferase, developmental transcription factors, protein kinases and replication factors. Overall, our analysis of the transcriptome level in the ovarian tissue of a teleost will provide further insights into molecular processes and deepen our genetic understanding of egg production in highly fecund fish.

Comparative Transcriptome Analysis Reveals the Effect of Aurantiochytrium sp. on Gonadal Development in Zebrafish

Aurantiochytrium sp. has received much attention as a potential resource for mass production of omega-3 fatty acids, which contribute to improved growth and reproduction in aquatic animals. In this study, we evaluated the gonadal index changes in zebrafish supplemented with 1-3% Aurantiochytrium sp. crude extract (TE) and the effects of ex vivo environmental Aurantiochytrium sp. on oocytes. 1% TE group showed significant improvement in the gonadal index, and both in vitro incubation and intraperitoneal injection promoted the maturation of zebrafish oocytes. In contrast, the transcriptome revealed 576 genes that were differentially expressed between the 1% TE group and the control group, including 456 up-regulated genes and 120 down-regulated genes. Kyoto Encyclopedia of Genes and Genomes (KEGG) and Gene Ontology (GO) pathway analysis of differentially expressed genes indicated that Aurantiochytrium sp. potentially affects pathways such as lipid metabolism, immune regulation, and oocyte development in zebrafish. The results of this study enriched the knowledge of Aurantiochytrium sp. in regulating gonadal development in zebrafish and provided a theoretical basis for its application in aquaculture.

Simultaneous Occurrence of Hypospadias and Bilateral Cleft Lip and Jaw in a Crossbred Calf: Clinical, Computer Tomographic, and Genomic Characterization

Congenital abnormalities in animals, including abnormalities of the cleft lip and jaw and hypospadias have been reported in all domesticated species. They are a major concern for breeders due to the increased economic loss they entail. In this article, we described a congenital bilateral cheilognathoschisis (cleft lip and jaw) with campylognathia in association with penile hypospadias and preputial hypoplasia with failure of preputial fusion in a Bos taurus crossbred Piedmontese × Wagyu calf. Clinical examination, computed tomography, and whole genome sequencing were performed to describe and identify a possible cause of the abnormalities. Clinical examination revealed a bilateral cheilognathoschisis of approximately 4 cm in length and 3 cm in width in the widest part, with computer tomography analyses confirming the bilateral absence of the processus nasalis of the incisive bone and the lateral deviation of the processus palatinus towards the left side. Genomic data analyses identified 13 mutations with a high impact on the products of the following overlapped genes: ACVR1, ADGRA2, BHMT2, BMPR1B, CCDC8, CDH1, EGF, F13A1, GSTP1, IRF6, MMP14, MYBPHL, and PHC2 with ADGRA2, EGF, F13A1, GSTP1, and IRF6 having mutations in a homozygous state. The whole genome investigation indicates the involvement of multiple genes in the birth defects observed in this case.

FHL2 deficiency impairs follicular development and fertility by attenuating EGF/EGFR/YAP signaling in ovarian granulosa cells

Female subfertility is an increasing reproductive issue worldwide, which is partially related to abnormal ovarian follicular development. Granulosa cells (GCs), by providing the necessary physical support and microenvironment for follicular development, play critical roles in maintaining female fertility. We previously showed that ectopic expression of four and a half LIM domains 2 (FHL2) promoted ovarian granulosa cell tumor progression. However, its function in follicular development and fertility remains unknown. Here, we confirmed that FHL2 is highly expressed in human and mouse ovaries. FHL2 immunosignals were predominantly expressed in ovarian GCs. A Fhl2 knockout (KO) mouse model was generated to examine its roles in follicular development and fertility. Compared with wildtype, knockout of Fhl2 significantly decreased female litter size and offspring number. Furthermore, Fhl2 deficiency reduced ovarian size and impaired follicular development. RNA-sequencing analysis of GCs isolated from either KO or WT mice revealed that, Fhl2 deletion impaired multiple biological functions and signaling pathways, such as Ovarian Putative Early Atresia Granulosa Cell, ErbB, Hippo/YAP, etc. In vitro studies confirmed that FHL2 silencing suppressed GCs growth and EGF-induced GCs proliferation, while its overexpression promoted GC proliferation and decreased apoptosis. Mechanistic studies indicated that FHL2, via forming complexes with transcriptional factors AP-1 or NF-κB, regulated Egf and Egfr expression, respectively. Besides, FHL2 depletion decreased YAP1 expression, especially the active form of YAP1 (nuclear YAP1) in GCs of growing follicles. EGF, serving as an autocrine/paracrine factor, not only induced FHL2 expression and nuclear accumulation, but also stimulated YAP1 expression and activation. Collectively, our study suggests that FHL2 interacts with EGFR and Hippo/YAP signaling to regulate follicular development and maintain fertility. This study illuminates a novel mechanism for follicular development and a potential therapeutic target to address subfertility.

Mechanisms of primordial follicle activation and new pregnancy opportunity for premature ovarian failure patients

Primordial follicles are the starting point of follicular development and the basic functional unit of female reproduction. Primordial follicles are formed around birth, and most of the primordial follicles then enter a dormant state. Since primordial follicles are limited in number and can't be renewed, dormant primordial follicles cannot be reversed once they enter the growing state. Thus, the orderly occurrence of primordial follicles selective activation directly affects the rate of follicle consumption and thus determines the length of female reproductive lifespan. Studies have found that appropriately inhibiting the activation rate of primordial follicles can effectively slow down the rate of follicle consumption, maintain fertility and delay ovarian aging. Based on the known mechanisms of primordial follicle activation, primordial follicle in vitro activation (IVA) technique has been clinically developed. IVA can help patients with premature ovarian failure, middle-aged infertile women, or infertile women due to gynecological surgery treatment to solve infertility problems. The study of the mechanism of selective activation of primordial follicles can contribute to the development of more efficient and safe IVA techniques. In this paper, recent mechanisms of primordial follicle activation and its clinical application are reviewed.

cAMP signaling in ovarian physiology in teleosts: A review

Ovarian function in teleosts, like in other vertebrates, is regulated by two distinct gonadotropins, follicle-stimulating hormone (FSH) and luteinizing hormone (LH). Gonadotropin effects are mediated by membrane-bound G protein-coupled receptors localized on the surface of follicle cells. Gonadotropin receptor activation results in increased intracellular cAMP, the most important second cellular signaling molecule. FSH stimulation induces the production of 17β-estradiol in the cells of growing follicles to promote vitellogenesis in oocytes. In contrast, in response to LH, fully grown post-vitellogenic follicles gain the ability to synthesize maturation-inducing steroids, which induce meiotic resumption and ovulation. All these events were induced downstream of cAMP. In this review, we summarize studies addressing the role of the cAMP pathway in gonadotropin-induced processes in teleost ovarian follicles. Furthermore, we discuss future problems concerning cAMP signaling in relation to teleost ovarian function and the differences and similarities in the gonadotropin-induced cAMP signaling pathways between mammals and teleosts.

Loss of growth differentiation factor 9 causes an arrest of early folliculogenesis in zebrafish-A novel insight into its action mechanism

Growth differentiation factor 9 (GDF9) was the first oocyte-specific growth factor identified; however, most information about GDF9 functions comes from studies in the mouse model. In this study, we created a mutant for Gdf9 gene (gdf9-/-) in zebrafish using TALEN approach. The loss of Gdf9 caused a complete arrest of follicle development at primary growth (PG) stage. These follicles eventually degenerated, and all mutant females gradually changed to males through sex reversal, which could be prevented by mutation of the male-promoting gene dmrt1. Interestingly, the phenotypes of gdf9-/- could be rescued by simultaneous mutation of inhibin α (inha-/-) but not estradiol treatment, suggesting a potential role for the activin-inhibin system or its signaling pathway in Gdf9 actions. In gdf9-null follicles, the expression of activin βAa (inhbaa), but not βAb (inhbab) and βB (inhbb), decreased dramatically; however, its expression rebounded in the double mutant (gdf9-/-;inha-/-). These results indicate clearly that the activation of PG follicles to enter the secondary growth (SG) requires intrinsic factors from the oocyte, such as Gdf9, which in turn works on the neighboring follicle cells to trigger follicle activation, probably involving activins. In addition, our data also support the view that estrogens are not involved in follicle activation as recently reported.

Effects of Secretoneurin and Gonadotropin-Releasing Hormone Agonist on the Spawning of Captive Greater Amberjack (Seriola dumerili)

The greater amberjack (Seriola dumerili), a pelagic marine species with a global distribution, has considerable worldwide potential as an aquaculture species. However, difficulties have been encountered in inducing spontaneous spawning in cultured fish stocks. In this study, we analysed the key regulatory factors, secretoneurin (SN) and gonadotropin-releasing hormone (GnRH), in greater amberjack. Active peptides of SN and GnRH, SdSNa, and SdGnRH, respectively, were obtained by comparative analysis of homologous proteins from different species. Amino acid substitutions of the SdGnRH decapeptide at position 6 with a dextrorotatory (D) amino acid and at position 10 with an ethylamide group yielded a super-active agonist (SdGnRHa). The injection of SdSNa and SdGnRHa elevated luteinizing hormone, thyroid-stimulating hormone, and oxytocin levels in the sera of sexually mature fish, whereas it reduced the level of follicle-stimulating hormone. Furthermore, in response to the SdSNa and SdGnRHa injections, we detected an increase in the expression of genes associated with oocyte development and spermatogenesis. We established that the greater amberjack cultured along the southern coast of China reached sexual maturity at three years of age, and its reproductive season extended from February to April. Spawning of the cultured greater amberjack was successfully induced with a single injection of SdGnRHa/SdSN/DOM/HCG. Our findings indicate that similar to GnRHa, SNa is a potential stimulator of reproduction that can be used to artificially induce spawning in marine fish.

Role of EGFR expressed on the granulosa cells in the pathogenesis of polycystic ovarian syndrome

Polycystic ovarian syndrome (PCOS) is one of the most common endocrinological disorders affecting between 6 to 20% of reproductive aged women. However, the etiology of PCOS is still unclear. Epidermal growth factor receptor (EGFR) plays a critical role in the growth and development of ovarian follicles. In our previous study, we showed that the expression level of EGFR was significantly higher in the cumulus granulosa cells from women with PCOS than that of normal women, suggesting that EGFR may play a potential role in the pathogenesis of PCOS. The present study further evaluated the association between EGFR and PCOS through both in clinical observation and animal experiments. We firstly validated the differential expression of EGFR in cumulus granulosa cells between PCOS patients and normal subjects by qRT-PCR and immunofluorescence staining. Then we generated a mouse model (n=20) of PCOS by injecting dehydroepiandrosterone (DHEA). The PCOS mice were then injected with an E corpus GFR inhibitor (AG1478) (n=10), which significantly improved the sex hormone levels in the estrous cycle stage, and the serum levels of LH, FSH and testosterone were compared with the PCOS mice without EGFR inhibitor treatment (n=10). Decreasing the expression level of EGFR in the PCOS mice also improved the ovulatory function of their ovaries which was indicated by the multifarious follicle stage in these mice as compared with the PCOS mice without EGFR inhibitor treatment. Also, the number of corpopa lutea were higher in the control group and the EGFR inhibitor treated group than in the PCOS group. The sex hormone levels and reproductive function were not significantly different between the control mice and the PCOS mice treated with the EGFR inhibitor. Our results demonstrated that EGF/EGFR signaling affected the proliferation of cumulus granulosa cells, oocyte maturation and meiosis, and played a potential role in the pathogenesis of PCOS. Therefore, the selective inhibition of EGFR may serve as a novel strategy for the clinical management of PCOS.