Hormonal symphony: The dynamic duo of IGF and EGF in gonadotropin-induced fish ovarian development and egg maturation

Fish oocyte maturation (FOM) is a critical biological process that occurs before ovulation and is influenced by gonadotropins, particularly luteinizing hormone (LH). The release of LH stimulates the ovarian follicle to produce a maturation-inducing hormone (MIH), specifically 17α, 20β-dihydroxy-4-pregnen-3-one (17α, 20β-DP), which initiates the formation of maturation-promoting factor (MPF) through the activation of cyclin B and cdc2 kinase. Insulin-like growth factor I (IGF-I) significantly regulates ovarian functions, including steroidogenesis, by activating its membrane receptors and the tyrosine kinase pathway. IGF-I influences oocyte maturation directly via the PI3 kinase pathway, independent of steroid hormones. Additionally, epidermal growth factor (EGF) promotes cell growth and differentiation by binding to its receptor (EGFR). It is implicated in mediating human chorionic gonadotropin (hCG)-induced DNA synthesis in ovarian follicles while suppressing apoptosis. The presence of EGF in follicle cells and oocytes, along with its higher expression in oocytes, suggests it may act as a paracrine signal regulating somatic cell activity. Recent studies indicate that the activin system in follicle cells could be a target for EGF activity. The EGFR signaling pathway enhances gonadotropin-induced steroidogenesis and governs the transition of oocyte maturation stages, essential for successful fertilization. This review synthesizes current research on the roles of gonadotropins, IGFs, and EGFs in fish oocyte maturation and ovarian steroid production.

Efficacy of Fat Supplements with Different Unsaturated/Saturated FA Ratios Undergoing First Postpartum Ovulation in Lactating Anovulatory Goats

We investigated whether microalgae or linseed supply during the early postpartum period affects ovarian restimulation and supports the first postpartum ovulation in lactating anovulatory goats. Thirty-eight An-glo-Nubian-crossbred adult goats were allocated into three groups, one with a control diet (n = 12), fed a total mixed ration (TMR) comprising chopped elephant grass and concentrate; an algal diet (n = 13), fed TMR + green microalgae (1% dry matter); and a linseed diet (n = 13), TMR + linseed (12% dry matter). Supplements were furnished from the second to fifth week (time of weaning). Goats were estrus synchronized on day 40 by insertion of an intravaginal CIDR device for 5 days, after which 0.075 mg PGF2α was applied to induce ovulation, and estrus was monitored for 72 h. From the 5th-15th day of ovulation induction, the corpus luteum (CL) area and progesterone rate were monitored. The algal and linseed groups showed lower feed intake (p < 0.001) and higher (p < 0.001) triglyceride levels/follicle numbers, respectively. After estrus induction, no differences were observed in estrus response; however, the linseed group showed more and larger growing follicles (p = 0.016 and p < 0.01), a higher ovulation rate (p < 0.05), a larger CL area (p < 0.05), and higher progesterone levels (p < 0.001). Linseed after delivery stimulates follicular growth before and after ovulation induction, favoring better CL quality during the first ovulation.

Participation of follicular superoxides, inflammatory modulators, and endocrine factors in zebrafish (Danio rerio) ovulation: Cross-talk between PKA and MAPK signaling in Pgr regulation of ovulatory markers

The ovulatory response involves diverse molecular determinants, the interplay between which remains less investigated in fish. This study explores the temporal changes in the follicular microenvironment, regulatory factors, and underlying signaling events during ovulation in female zebrafish subjected to 14L:10D at 28 ± 1 °C in vivo vis-à-vis in hCG-stimulated full-grown (FG) follicles in vitro. Congruent with reduced GSH levels, SOD, and GPx activity, a graded increase in follicular free radicals, Nox4, and p38 MAPK phosphorylation in the morning hour groups (05:00 and 06:30) correlates positively with the ovulatory surge in inflammatory mediators (Tnf-α, Il-1β, Il-6, Nos2, and Cox-2). Further, elevated Pgr expression and its nuclear translocation, congruent with follicular lhcgr, star, and hsd20b2 upregulation in vivo, corroborates well with the transcriptional activation of genes (pla2g4aa, ptgesl, ptger4b, mmp9, adamts9), triggering ovulation in this species. Mechanistically, an elevated ovulatory response in hCG-treated FG follicles in vitro involves the upregulation of inflammatory mediators, pgr and ovulation-associated genes in a manner sensitive to PKA- and MAPK3/1-mediated signaling.

Toxicological impacts of nanopolystyrene on zebrafish oocyte with insight into the mechanism of action: An expression-based analysis

Many studies have investigated the negative impacts of microplastics on teleost fishes with very little or no evidence of their mechanism of action. This scenario entreats us to investigate the toxicities of nanopolystyrene in zebrafish oocyte with emphasis on the mechanism of action. In the present study, the cellular levels of mRNA transcripts of different genetic markers (such as: sod, gpx, nrf2, inos, ucp2, and atp6 (redox-sensitive markers); nfkβ, tnfα, il-10, ikβ, gdf9, and bmp15 (immune markers); gadd45, rad51, p53 and bcl2 (DNA damage and apoptotic)) have been quantified by real-time PCR after 6 h of incubation of isolated oocyte with different doses of nanopolystyrene viz. P0 (control i.e. no polystyrene in culture medium), P1 (100 ng/ml), and P2 (400 ng/ml). Results showed that both the treatment concentrations of nanopolystyrene induce oxidative stress with % DPPH = 30.75, 31.61, and 32.43% for P0, P1, and P2, respectively. Increase in oxidative stress in oocytes with increasing doses of nanopolystyrene was also observed in TBARS assay with MDA content 0.12 and 0.21 μM for P1 and P2, respectively as compaired to the control 0.08 μM. This increased oxidative stress can regulate the expression pattern (upregulation/downregulation) of selected genes leading to different toxic effects like - oxidative stress, immunotoxicity, and apoptosis in oocytes, which suggests the impairment of reproductive functions by nanopolystyrene.

Functions of interleukin-6 in ovulation of female climbing perch, Anabas testudineus

In mammals, interleukin 6 (IL-6) has an important function during ovulation, however, the functions of IL-6 in fish have not been elucidated. In the present study, there was quantification of de novo synthesis of ovarian IL-6 and tumor necrosis factor-alpha (TNFα) in control and hCG-treated fish and results were compared with those from an in vitro study where there was evaluation of the regulatory functions of gonadotropins and TNFα of IL-6 secretions. Relatively greater concentrations of ovarian IL-6 at the post-GVBD (post-germinal vesicle breakdown) stage indicates IL-6 modulates ovulatory processes. The hCG-induced increase in relative abundance of IL-6 (in vitro) mRNA transcript and secretion from the ovary were attenuated when there was administration of the inhibitor of TNFα secreting enzyme, TAPI-I, which indicates TNFα modulates IL-6 secretion. Treatments with IL-6 induced a marked increase in ovulation rate in vitro when there was induction of activating matrix metalloproteinase (MMP). Furthermore, treatment with IL-6 resulted in production of prostaglandin as indicated by the IL-6 induced increase in the abundance of ptgs2 mRNA transcript in the ovary of Anabas testudineus. Furthermore, results indicate the source of IL-6 in the ovary is the granulosa cells with secretion of IL-6 being induced by the additions of hCG and TNFα in the medium. There was also an IL-6-induced increase in abundance of receptors (IL-6 Rα and gp130) to which it binds indicating IL-6 autoregulates this population of receptors. Results from this study, for the first time, elucidate the reproductive functions of IL-6 in a teleost fish.

Interleukin-1β and TNF-α systems in ovarian follicles and their roles during follicular development, oocyte maturation and ovulation

Tumour necrosis factor-α (TNF-α) and interleukin-1β (IL-1β) are cytokines that are involved in the development, proliferation and apoptosis of ovarian follicular cells in domestic mammals. The expression of these cytokines in various follicular compartments, depending on the stage of follicle development, demonstrates their involvement in the control of primordial follicle growth up to the preovulatory stage. The mechanism of action of these factors depends on the presence of their receptors that transduce their biological actions. This review shows the expression sites of TNF-α, IL-1β and their receptors in ovarian follicles, and discusses the mechanism of action of these cytokines during follicle development, oocyte maturation and ovulation in domestic animals.

Influence of interleukin 1 beta and tumour necrosis factor alpha on the in vitro growth, maturation and mitochondrial distribution of bovine oocytes from small antral follicles

SummaryThis study aimed to investigate the effects of IL1β and TNFα on growth and maturation of oocytes from small follicles (1-3 mm) during in vitro culture. To this end, cumulus-oocyte complexes (COCs) with diameters of ~110 µm were cultured in TCM-199 medium alone or supplemented with IL1β (10 ng/ml), TNFα (10 ng/ml) or both for 48 h. The oocytes were measured at the beginning and at the end of the culture period. COCs were cultured for 20 h in pre-maturation medium and then half of the COCs of each group was destined for in vitro maturation and the remaining COCs were used to evaluate meiotic progression, mitochondrial distribution and the expression of mRNAs for GDF-9, c-Mos, Cyclin-B1 and H1foo. The results showed that COCs cultured with TNFα alone or together with IL1β had higher diameters than those cultured in control medium alone or supplemented with IL1β. Control oocytes isolated from large antral follicles (>5 mm) had heterogeneous distribution of mitochondria. Oocytes isolated from small antral follicles, that had been grown in vitro in TCM-199 alone or supplemented with TNFα had similar heterogeneous mitochondrial distribution before in vitro maturation (IVM). After IVM, mitochondria were heterogeneously distribution when cultured in TCM-199. However, when cultured with TNFα and/or IL1β, mitochondria were homogeneously distributed. Presence of TNFα and/or IL1β in TCM-199 culture medium did not influence the expression of mRNAs for GDF-9, c-Mos, Cyclin-B1 and H1foo. In conclusion, TNFα and a mixture of TNFα and IL1β both stimulated the growth of bovine oocytes during their in vitro culture, but do not influence gene expression in grown oocytes.

Regulation of sex steroid production and mRNAs encoding gonadotropin receptors and steroidogenic proteins by gonadotropins, cyclic AMP and insulin-like growth factor-I in ovarian follicles of rainbow trout (Oncorhynchus mykiss) at two stages of vitellogenesis

At the completion of vitellogenesis, the steroid biosynthetic pathway in teleost ovarian follicles switches from estradiol-17β (E2) to maturational progestin production, associated with decreased follicle stimulating hormone (Fsh) and increased luteinizing hormone (Lh) signaling. This study compared effects of gonadotropins, human insulin-like growth factor-I (IGF1), and cAMP/protein kinase A signaling (forskolin) on E2 production and levels of mRNAs encoding steroidogenic proteins and gonadotropin receptors using midvitellogenic (MV) and late/postvitellogenic (L/PV) ovarian follicles of rainbow trout. Fsh, Lh and forskolin, but not IGF1, increased testosterone and E2 production in MV and L/PV follicles. Fsh increased steroidogenic acute regulatory protein (star; MV), 3β-hydroxysteroid dehydrogenase/Δ(5-4) isomerase (hsd3b; MV) and P450 aromatase (cyp19a1a; MV) transcript levels. Lh increased star mRNA levels (MV, L/PV) but reduced cyp19a1a transcripts in L/PV follicles. At both follicle stages, IGF1 reduced levels of hsd3b transcripts. In MV follicles, IGF1 decreased P450 side-chain cleavage enzyme (cyp11a1) transcripts but increased cyp19a1a transcripts. In MV follicles only, forskolin increased star and hsd3b transcripts. Forskolin reduced MV follicle cyp11a1 transcripts and reduced cyp19a1a transcripts in follicles at both stages. Fsh and Lh reduced fshr transcripts in L/PV follicles. Lh also reduced lhcgr transcripts (L/PV). IGF1 had no effect on gonadotropin receptor transcripts. Forskolin reduced MV follicle fshr transcript levels and reduced lhcgr transcripts in L/PV follicles. These results reveal hormone- and stage-specific transcriptional regulation of steroidogenic protein and gonadotropin receptor genes and suggest that the steroidogenic shift at the completion of vitellogenesis involves loss of stimulatory effects of Fsh and Igfs on cyp19a1a expression and inhibition of cyp19a1a transcription by Lh.

The Function of Fish Cytokines

What is known about the biological activity of fish cytokines is reviewed. Most of the functional studies performed to date have been in teleost fish, and have focused on the induced effects of cytokine recombinant proteins, or have used loss- and gain-of-function experiments in zebrafish. Such studies begin to tell us about the role of these molecules in the regulation of fish immune responses and whether they are similar or divergent to the well-characterised functions of mammalian cytokines. This knowledge will aid our ability to determine and modulate the pathways leading to protective immunity, to improve fish health in aquaculture.

Luteinizing hormone induces ovulation via tumor necrosis factor α-dependent increases in prostaglandin F2α in a nonmammalian vertebrate

Ovulation is induced by the preovulatory surge of luteinizing hormone (LH) that acts on the ovary and triggers the rupture of the preovulatory ovarian follicle by stimulating proteolysis and apoptosis in the follicle wall, causing the release of the mature oocyte. The pro-inflammatory cytokine tumor necrosis factor α (TNFα) and prostaglandin (PG) F_2α (PGF_2α) are involved in the control of ovulation but their role mediating the pro-ovulatory actions of LH is not well established. Here we show that Lh induces PGF_2α synthesis through its stimulation of Tnfα production in trout, a primitive teleost fish. Recombinant trout Tnfα (rTnfα) and PGF_2α recapitulate the stimulatory in vitro effects of salmon Lh (sLh) on contraction, proteolysis and loss of cell viability in the preovulatory follicle wall and, finally, ovulation. Furthermore, all pro-ovulatory actions of sLh are blocked by inhibition of Tnfα secretion or PG synthesis and all actions of rTnfα are blocked by PG synthesis inhibitors. Therefore, we provide evidence that the Tnfα–dependent increase in PGF_2α production is necessary for the pro-ovulatory actions of Lh. The results from this study shed light onto the mechanisms underlying the pro-ovulatory actions of LH in vertebrates and may prove important in clinical assessments of female infertility.

IGFs mediate the action of LH on oocyte maturation in zebrafish

LH signaling is required for oocyte maturation in fish and other vertebrates. However, the downstream factors mediating LH signaling are largely unexplored in fish. In this study, we investigated whether IGFs could mediate LH action on oocyte maturation in zebrafish. Our results show that all igfs, including igf1, igf2a, igf2b, and igf3, are dynamically expressed during folliculogenesis, with the expression of igf3 reaching its maximal level in full grown stage follicles. The expression of igfs is regulated by LH through a cAMP pathway in intact follicles as well as in primary cultured follicular cells, with igf3 expression being the most sensitive to human chorionic gonadotropin (hCG) treatment. Moreover, recombinant zebrafish IGF-2a, IGF-2b, and IGF-3 proteins significantly enhanced oocyte maturation via IGF-1 receptors (IGF-1rs), with IGF-3 exhibiting the most potent stimulatory action on oocyte maturation. Furthermore, we have demonstrated that IGF-3 or hCG treatment could stimulate IGF-1rs phosphorylation, and hCG-induced oocyte maturation could be attenuated by IGF-1r inhibitors as well as by an anti-IGF-3 antiserum in vitro and in vivo, indicating that the IGF system especially IGF-3 plays a crucial role in mediating LH action on oocyte maturation. In addition, igf3 expression is significantly attenuated in LH β-subunit (lhb) mutant zebrafish and treatment with recombinant IGF-3 could partially rescue the oocyte maturation defects of the lhb mutants in vitro and in vivo. Collectively, our results clearly demonstrated that IGFs, particularly the gonad-specific IGF-3, act as important mediators of LH action on oocyte maturation in zebrafish.

Transcriptomic profiling of progesterone in the male fathead minnow (Pimephales promelas) testis

P4 is a hormone with diverse functions that include roles in reproduction, growth, and development. The objectives of this study were to examine the effects of P4 on androgen production in the mature teleost testis and to identify molecular signaling cascades regulated by P4 to improve understanding of its role in male reproduction. Fathead minnow (FHM) testis explants were treated in vitro with two concentrations of P4 (10(-8) and 10(-6) M) for 6 and 12 h. P4 significantly increased testosterone (T) production in the FHM testis but did not affect 11-ketotestosterone. Gene network analysis revealed that insulin growth factor (Igf1) and tumor necrosis factor receptor (Tnfr) signaling was significantly depressed with P4 treatment after 12h. There was also a 20% increase in a gene network for follicle-stimulating hormone secretion and an 18% decrease in genes involved in vasopressin signaling. Genes in steroid metabolism (e.g. star, cyp19a, 11bhsd) were not significantly affected by P4 treatments in this study, and it is hypothesized that pre-existing molecular machinery may be more involved in the increased production of T rather than the de novo expression of steroid-related transcripts and receptors. There was a significant decrease in prostaglandin E synthase 3b (cytosolic) (ptges3b) after treatment with P4, suggesting that there is cross talk between P4 and prostaglandin pathways in the reproductive testis. P4 has a role in regulating steroid production in the male testis and may do so by modulating gene networks related to endocrine pathways, such as Igf1, Tnfr, and vasopressin.