NCBI Summary:
The protein encoded by this gene is a member of the epidermal growth factor family. It is an autocrine growth factor as well as a mitogen for astrocytes, Schwann cells and fibroblasts. It is related to epidermal growth factor (EGF) and transforming growth factor alpha (TGF-alpha). The protein interacts with the EGF/TGF-alpha receptor to promote the growth of normal epithelial cells, and it inhibits the growth of certain aggressive carcinoma cell lines. It also functions in mammary gland, oocyte and bone tissue development. This gene is associated with a psoriasis-like skin phenotype, and is also associated with other pathological disorders, including various types of cancers and inflammatory conditions. [provided by RefSeq, Apr 2014]
General function
Ligand, Growth factor
Comment
Cellular localization
Secreted, Plasma membrane
Comment
Ovarian function
Cumulus expansion, Ovulation, Follicle rupture, Steroid metabolism, Luteinization, Oocyte growth, Oocyte maturation, Early embryo development
, Germinal vesicle breakdown
Comment
Human chorionic gonadotropin-induced amphiregulin stimulates aromatase expression in human granulosa-lutein cells: a mechanism for estradiol production in the luteal phase. Fang L et al. (2019) Does amphiregulin (AREG), the most abundant and important epidermal growth factor receptor (EGFR) ligand in the follicular fluid, regulate aromatase expression in human granulosa-lutein (hGL) cells? AREG mediates the hCG-induced up-regulation of aromatase expression and estradiol (E2) production in hGL cells. AREG expression and secretion are rapidly induced by hCG in hGL cells and mediate physiological functions of LH/hCG in the ovary. EGFR protein is expressed in follicles not only in the pre-ovulatory phase but also throughout the luteal phase of the menstrual cycle. After the LH surge, the human corpus luteum secretes high levels of E2, which regulates various luteal cell functions. Aromatase is an enzyme responsible for a key step in the biosynthesis of E2. However, whether AREG regulates aromatase expression and E2 production in hGL cells remains unexplored. This study is an experimental study performed over a 1-year period. In vitro investigations examined the role of AREG in the regulation of aromatase expression and E2 production in primary hGL cells. Primary hGL cells were obtained from women undergoing IVF treatment in an academic research center. Aromatase mRNA and protein levels were examined after exposure of hGL cells to recombinant human AREG, hCG or LH. The EGFR tyrosine kinase inhibitor AG1478, PI3K inhibitor LY294002 and siRNAs targeting EGFR, LH receptor, StAR and AREG were used to verify the specificity of the effects and to investigate the underlying molecular mechanisms. Reverse transcription quantitative real-time PCR (RT-qPCR) and western blot were used to measure the specific mRNA and protein levels, respectively. Follicular fluid and serum were collected from 65 infertile women during IVF treatment. Pearson's correlation analysis was performed to examine the correlation coefficient between two values. Treatment of hGL cells with AREG-stimulated aromatase expression and E2 production. Using pharmacological inhibitors and specific siRNAs, we revealed that AREG-stimulated aromatase expression and E2 production via EGFR-mediated activation of the protein kinase B (AKT) signaling pathway. In addition, inhibition of EGFR activity and AREG knockdown attenuated hCG-induced up-regulation of aromatase expression and E2 production. Importantly, the protein levels of AREG in the follicular fluid were positively correlated with the E2 levels in serum after 2 days of oocyte pick-up and in the follicular fluid of IVF patients. N/A. The in vitro setting of this study is a limitation that may not reflect the real intra-ovarian microenvironment. Clinical data were obtained from a small sample size. Our results provide the first evidence that hCG-induced AREG contributes to aromatase expression and E2 production in the luteal phase of the menstrual cycle. A better understanding of the hormonal regulation of female reproductive function may help to develop new strategies for the treatment of clinical infertility. This work was supported by the National Natural Science Foundation of China for Young Scientists (81601253), the specific fund of clinical medical research of Chinese Medical Association (16020160632) and the Foundation from the First Affiliated Hospital of Zhengzhou University for Young Scientists to Lanlan Fang. This work was also supported by an operating grant from the National Natural Science Foundation of China (81820108016) to Ying-Pu Sun. All authors declare no conflict of interest.//////////////////
LH-Induced Steroidogenesis in the Mouse Ovary, but Not Testis, Requires Matrix Metalloproteinase 2 and 9-Mediated Cleavage of Upregulated EGF Receptor Ligands. Light A et al. (2015) Oocyte maturation and cumulus cell expansion depend on LH-mediated upregulation of membrane bound EGF-like ligands, including amphiregulin, epiregulin, and betacellulin. These ligands then trans-activate the EGF receptor (EGFR) after release by matrix metalloproteinases (MMPs). However, direct measurement of released EGF-like ligands or MMPs from granulosa cells has not been formally evaluated, nor has direct identification of responsible MMPs. Here we address these issues by analyzing LH-induced steroidogenesis, which is also MMP- and EGFR-dependent, in freshly isolated mouse primary granulosa cells. We demonstrate a correlation between amphiregulin and epiregulin mRNA induction and steroid production in LH-treated granulosa cells as well as in ovaries of hCG-treated mice. In contrast, LH does not alter Mmp1, Mmp2, Mmp3, Mmp8, Mmp9, or Adam17 mRNA expression. We demonstrate that, in primary mouse granulosa cells, LH triggers release of soluble amphiregulin that correlates with steroid production, both of which are blocked by MMP2/9 inhibition, confirming that MMP2/9 likely regulates LH-induced amphiregulin release and downstream processes. Notably, LH does not alter secretion of MMP2/9 from primary granulosa cells, nor does it modulate MMP activity. These findings indicate that, in the ovary, LH dictates EGFR-mediated processes not by regulating MMPs, but instead by increasing EGF-like ligand availability. In contrast, LH stimulation of primary mouse Leydig cells does not induce EGF-like ligand expression or require MMP2/9 for steroidogenesis, confirming marked differences in LH receptor-induced processes in the testes. Our results suggest that MMP inhibition may be a means of attenuating excess ovarian steroid production in diseases like polycystic ovary syndrome.//////////////////
Amphiregulin cooperates with bone morphogenetic protein 15 to increase bovine oocyte developmental competence: effects on gap junction-mediated metabolite supply. Sugimura S 2014 et al.
This study assessed the participation of amphiregulin (AREG) and bone morphogenetic protein 15 (BMP15) during maturation of bovine cumulus oocyte complexes (COCs) on cumulus cell function and their impact on subsequent embryo development. AREG treatment of COCs enhanced blastocyst formation and quality only when in the presence of BMP15. Expression of hyaluronan synthase 2 was enhanced by follicle stimulating hormone (FSH) but not by AREG, which was reflected in the level of cumulus expansion. Although both FSH and AREG stimulated glycolysis, AREG-treated COCs had higher glucose consumption, lactate production and ratio of lactate production to glucose uptake. Autofluorescence levels in oocytes, indicative of NAD(P)H and FAD(++), were increased with combined AREG and BMP15 treatment of COCs. In contrast, these treatments did not alter autoflouresence levels when cumulus cells were removed from oocytes, even in the presence of other COCs, suggesting oocyte-cumulus gap-junctional communication (GJC) is required. FSH contributed to maintaining GJC for an extended period of time. Remarkably, BMP15 was equally effective at maintaining GJC even in the presence of AREG. Hence, AREG stimulation of COC glycolysis and BMP15 preservation of GJC may facilitate efficient transfer of metabolites from cumulus cells to the oocyte thereby enhancing oocyte developmental competence. These results have implications for improving in vitro oocyte maturation systems.
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Amphiregulin promotes the maturation of oocytes isolated from the small antral follicles of the rhesus macaque. Peluffo MC et al. BACKGROUNDIn non-primates, the epidermal growth factor (EGF) and EGF-related ligands such as amphiregulin (AREG) serve as critical intermediates between the theca/mural cells and the cumulus-oocyte-complex (COC) following the mid-cycle LH surge. Studies were designed in primates (1) to analyze AREG levels in follicular fluid (follicular fluid) obtained from pre-ovulatory follicles, as well as (2) to assess dose-dependent effects of AREG on oocytes from small antral follicles (SAFs) during culture, including meiotic and cytoplasmic maturation.METHODSControlled ovulation protocols were performed on rhesus monkeys (n = 12) to determine AREG content within the single, naturally selected dominant follicle after an ovulatory stimulus. Using healthy COCs (n = 271) obtained from SAFs during spontaneous cycles (n = 27), in vitro maturation (IVM) was performed in the absence or presence of physiological concentrations of AREG (10 or 100 ng/ml) with or without gonadotrophins (FSH, 75 mIU/ml; LH, 75 mIU/ml). At the end of the culture period, oocyte meiotic maturation was evaluated and ICSI was performed (n = 111), from which fertilization and early embryo development was followed in vitro.RESULTSAREG levels in follicular fluid from pre-ovulatory follicles increased (P< 0.05) following an ovulatory bolus of hCG at 12, 24 and 36 h post-treatment. At 12 h post-hCG, AREG levels in follicular fluid ranged from 4.8 to 121.4 ng/ml. Rhesus macaque COCs incubated with 10 ng/ml AREG in the presence of gonadotrophins displayed an increased percentage of oocytes that progressed to the metaphase II (MII) stage of meiosis (82 versus 56%, P< 0.05) and a decreased percentage of metaphase I (MI) oocytes (2 versus 23%, P< 0.05) relative to controls, respectively. The percentage of either MI or MII oocytes at the end of the culture period was not different between oocytes cultured with 100 ng/ml AREG or in media alone. Fertilization and first cleavage rates obtained by ICSI of all IVM MII oocytes were 93 and 98%, respectively, and did not vary among treatment groups. Of the MII oocytes that fertilized (n = 103), 37 were randomly selected and maintained in culture to assess developmental potential. A total of 13 early blastocysts were obtained, with four embryos developing to expanded blastocysts.CONCLUSIONSThese data indicate that AREG levels increase in rhesus macaque pre-ovulatory follicles after an ovulatory stimulus, and a specific concentration of AREG (10 ng/ml) enhances rhesus macaque oocyte nuclear maturation but not cytoplasmic maturation from SAFs obtained during the natural menstrual cycle. However, owing to the small number of samples in some treatment groups, further studies are now required.
Levels of the epidermal growth factor-like peptide amphiregulin in follicular fluid reflect the mode of triggering ovulation: a comparison between gonadotrophin-releasing hormone agonist and urinary human chorionic gonadotrophin. Humaidan P et al. OBJECTIVE: To detect differences in follicular fluid (FF) levels of amphiregulin (AR), depending on mode of triggering final oocyte maturation. DESIGN: Prospective randomized trial. SETTING: Three IVF units. PATIENT(S): Ninety-six patients undergoing IVF-intracytoplasmic sperm injection. INTERVENTION(S): Ovulation triggered with either urinary hCG or GnRH agonist (GnRH-a). Controls: 15 FF samples from small antral follicles (3-9 mm) and 12 FF samples from natural cycle. MAIN OUTCOME MEASURE(S): Follicular fluid concentration of AR, P(4), E(2), vascular endothelial growth factor, and inhibin B. RESULT(S): Significantly lower levels of AR were found in FF from the GnRH-a group versus the hCG group, 51 ? 3.5 versus 71 ? 6.0 ng/mL. In FF from natural cycles, levels of AR were significantly higher than those of GnRH-a triggering but significantly lower than those of urinary hCG triggering. In small antral follicles only 5 out of 15 follicles contained measurable amounts of AR. When urinary hCG and GnRH-a triggering were compared, FF P(4) was significantly higher after urinary hCG triggering, whereas no difference was seen regarding E(2), vascular endothelial growth factor, and inhibin B. A total of 14% more metaphase II oocytes and 11% more transferable embryos were obtained after GnRH-a triggering. CONCLUSION(S): This study suggests that oocyte competence is linked to granulosa cell AR secretion.
Park JY, et al reported EGF-like Growth Factors as Mediators of LH Action in the Ovulatory Follicle.
Prior to ovulation in mammals, a cascade of events resembling an inflammatory/tissue remodeling process is triggered by luteinizing hormone (LH) in the ovarian follicle. Many LH effects, however, are thought to be indirect because of the restricted expression of its receptor. Here we demonstrate that LH stimulation induces the transient and sequential expression of the epidermal growth factor (EGF) family members amphiregulin, epiregulin, and betacellulin. Incubation of follicles with these growth factors recapitulates the morphological and biochemical events triggered by LH, including cumulus expansion and oocyte maturation. Thus, these EGF-related growth factors are paracrine mediators that propagate the LH signal throughout the follicle.
Expression regulated by
LH
Comment
Altered amphiregulin expression induced by diverse luteinizing hormone receptor reactivity in granulosa cells affects IVF outcomes. Huang Y et al. (2015) The expression of specific genes (LHR, AREG, EREG, EGFR, NPPC and NPR2) involved in peri-ovulatory signalling pathways induced by LH surge in granulosa cells was investigated, and their relationships with IVF outcomes analysed. mRNA levels of the genes of 147 infertile women undergoing IVF and intracytoplasmic sperm injection (ICSI) with embryo transfer were evaluated. Compared with non-pregnant women, amphiregulin (AREG) mRNA levels in mural and cumulus graunulosa cells were significantly higher (P < 0.05) in pregnant women, and were positively correlated with number of oocytes retrieved and good-quality embryos. No significant differences were found between the two groups in the remaining detected genes. To investigate the reason for the differences in AREG expression, mural granulosa cells were cultured and stimulated with human chorionic gonadotrophin (HCG) for 2-24 h. At 4 h after HCG stimulation, AREG and epiregulin mRNA expression peaked, with much greater increases in the pregnant group. The fold-change of AREG expression was positively correlated with number of good-quality embryos. No obvious correlation, however, was found between NPPC/Npr2 expression levels in granulosa cells and IVF outcomes. Altered AREG expression induced by diverse luteinizing hormone receptor reactivity in granulosa cells may provide a useful marker for oocyte developmental competency.//////////////////
The Nuclear Receptor Cofactor Receptor-Interacting Protein 140 Is a Positive Regulator of Amphiregulin Expression and Cumulus Cell-Oocyte Complex Expansion in the Mouse Ovary. Nautiyal J et al. The nuclear receptor cofactor receptor-interacting protein 140 (RIP140) is essential for cumulus cell-oocyte complex (COC) expansion, follicular rupture, and oocyte release during ovulation. The expression of many genes necessary for COC expansion is impaired in the absence of RIP140, but the studies herein document that their expression can be restored and COC expansion rescued by treatment with the epidermal growth factor (EGF)-like factor amphiregulin (AREG) both in vitro and in vivo. We demonstrate by several approaches that RIP140 is required for the expression of the EGF-like factors in granulosa cells, but the dependence of genes involved in cumulus expansion, including Ptgs2 Has2, Tnfaip6, and Ptx3, is indirect because they are induced by AREG. Treatment of granulosa cells with forskolin to mimic the effects of LH increases AREG promoter activity in a RIP140-dependent manner that 1) requires an intact cAMP response element in the proximal promoter region of the Areg gene and 2) involves its actions as a coactivator for cAMP response element-binding protein/c-Jun transcription factors. Although human chorionic gonadotropin and AREG coadministration is sufficient to restore ovulation fully in RIP140 heterozygous mice in vivo, both follicular rupture and ovulation remain impaired in the RIP140 null mice. Thus, we conclude that although the level of RIP140 expression in the ovary is a crucial factor required for the transient expression of EGF-like factors necessary for cumulus expansion, it also plays a role in other signaling pathways that induce follicular rupture.
EGF-like growth factors: endogenous mediators of the ovulatory response?
Ashkenazi H, et al .
Previous studies showed that EGF and TGFalpha mimic the action of LH on the resumption of oocyte maturation. We tested whether EGF-like agents, such as amphiregulin (AR), epiregulin (ER) and betacellulin (BTC) also mediate the LH stimulation of the ovulatory response in the rat. LH induced transient follicular expression of AR, ER and BTC mRNA reaching a maximum after 3 h incubation. Furthermore, the addition of ER, AR and BTC to the culture medium could mimic some of LH actions. AR and ER fully simulated LH-induced resumption of meiosis in vitro, whereas BTC was less effective. To study the putative involvement of EGF-like factors in mediation of LH signal, the effect of EGFR kinase inhibitor AG1478 was tested. When added with LH, AG1478, but not its inactive analog AG43, reduced EGFR phosphorylation and oocyte maturation compared with follicles treated with LH only. In addition to the inhibition of resumption of meiosis, AG1478 administration into the bursa (3 micro g/bursa) resulted in 51% (P < 0.0005) inhibition of ovulation in the treated ovaries, compared with the untreated contralateral ones, as well as to the vehicle treated ovaries (P < 0.02). LH, as well as ER, induced the expression of genes associated with the ovulatory response like rCOX-2, rHAS-2 and rTSG-6 mRNA, whereas AG1478 inhibited this effect of LH. Release of EGF-like factors from the membrane is dependent on activated metalloproteases. Indeed, Galardin, a broad-spectrum metalloprotease inhibitor, but not a specific matrix metalloprotease 2 and 9 (MMP 2 and 9) inhibitor, suppressed meiotic maturation induced by LH. Conversely, meiotic maturation induced by ER was not affected by Galardin. Thus, supporting the notion that LH releases follicular membrane bound EGF-like agents. In summary, EGF-like factors such as ER, AR and BTC seem to mediate, at least partially, the LH stimulation of oocyte maturation, ovulatory enzyme expression and ovulation.
Regulation of amphiregulin, EGFR-like factor expression by hCG in cultured human granulosa cells. Negishi H et al. Background. It has long been suspected that the epidermal growth factor (EGF) receptor and some of its putative ligands may play an important role in ovarian function. Amphiregulin (AR) is the growth factor with an EGF-like motif, but its potential role in signalling in the ovary is still obscure. AR gene expression and its functional effect were evaluated in human granulosa cells from immature follicles. Method. Granulosa cells from immature follicles with early menstrual phase were cultured with or without 200 mIU/ml of FSH stimulation, following with or without 1 IU/ml of hCG. mRNA levels of AR and luteinising hormone replacement (LHR) were semi-quantified using RT-PCR. Progesterone (P) concentration in the medium was assayed. Results. LHR mRNA was expressed 48 h after FSH stimulation without AR mRNA expression. AR mRNA was expressed 1 h after hCG stimulation, and increased the intensity in 6 h. P biosynthesis was increased by AR in a dose-dependent manner. AR mRNA was elevated by forskolin stimulation without FSH and hCG stimulation before LHR mRNA expression. When cultured with FSH for 15 h, followed by increasing doses of hCG stimulation for 6 h, the AR mRNA levels increased according to hCG concentration up to 1,000 mIU/ml. Conclusion. Occurrence of LHR gene expression following FSH stimulation was necessary for the AR gene expression in vivo, and the AR gene was induced by forskolin without LHR gene expression in vitro. P biosynthesis was stimulated, to some extent, by AR. This result suggests the differentiation effect of AR on granulosa cells. AR might be a mediator of LH signals before ovulation.
Human oocyte maturation is dependent on LH-stimulated accumulation of the epidermal growth factor-like growth factor, amphiregulin. Zamah AM et al. BACKGROUND The LH surge promotes ovulation via activation of multiple signaling networks in the ovarian follicle. Studies in animal models have shown the importance of LH-induced activation of the epidermal growth factor (EGF)signaling network in critical peri-ovulatory events. We investigated the biological significance of regulatory mechanisms mediated by EGF-like growth factors during LH stimulation in humans. METHODS We characterized the EGF signaling network in mature human ovarian follicles using in vivo and in vitro approaches. Amphiregulin (AREG) levels were measured in 119 follicular fluid (FF) samples from IVF/ICSI patients. Biological activity of human FF was assessed using in vitro oocyte maturation, cumulus expansion and cell mitogenic assays. RESULTS AREG is the most abundant EGF-like growth factor accumulating in the FF of mature follicles of hCG-stimulated patients. No AREG was detected before the LH surge or before hCG stimulation of granulosa cells in vitro, demonstrating that the accumulation of AREG requires gonadotrophin stimulation. Epiregulin and betacellulin mRNA were detected in both human mural and cumulus granulosa cells, although at significantly lower levels than AREG. FF from stimulated follicles causes cumulus expansion and oocyte maturation in a reconstitution assay. Immunodepletion of AREG abolishes the ability of FF to stimulate expansion (P < 0.0001) and oocyte maturation (P < 0.05), confirming the biological activity of AREG. Conversely, mitogenic activity of FF remained after depletion of AREG, indicating that other mitogens accumulate in FF. FF from follicles yielding an immature germinal vesicle oocyte or from an oocyte that develops into an aberrant embryo contains lower AREG levels than that from follicles yielding a healthy oocyte (P = 0.008). CONCLUSIONS EGF-like growth factors play a role in critical peri-ovulatory events in humans, and AREG accumulation is a useful marker of gonadotrophin stimulation and oocyte competence.
Ovarian localization
Granulosa, Follicular Fluid
Comment
Amphiregulin is much more abundantly expressed than transforming growth factor-alpha and epidermal growth factor in human follicular fluid obtained from patients undergoing in vitro fertilization-embryo transfer. Inoue Y et al. OBJECTIVE: To identify the most important epidermal growth factor (EGF) receptor ligand in the LH or hCG signal pathway in human ovary. DESIGN: A retrospective clinical study. SETTING: Tertiary university hospital. PATIENT(S): Ninety-eight infertile patients who underwent IVF-embryo transfer. INTERVENTION(S): Sera and follicular fluid were collected at the time of oocyte retrieval. The levels of EGF, transforming growth factor-alpha (TGFalpha), and amphiregulin (AR) were measured in follicular fluid and sera by using ELISA. MAIN OUTCOME MEASURE(S): The relationships between the level of AR and level of hCG, fertilization rate, and embryo quality. RESULT(S): Amphiregulin was abundantly expressed in follicular fluid after hCG stimulation. Although large differences were found between AR and both EGF and TGFalpha in follicular fluid, no significant difference was detected in the levels of the three EGF receptor ligands in sera. The level of AR was inversely correlated with the fertilization rate and hCG level, whereas little significant association was observed between the level of AR and embryo quality. CONCLUSION(S): Amphiregulin was expressed most dominantly among EGF receptor ligands tested and may mediate the hCG signal in human oocyte maturation. Elaborate interaction between AR and hCG may be required for an optimal oocyte maturation.
Follicle stages
Antral, Preovulatory
Comment
Phenotypes
Mutations
2 mutations
Species: mouse
Mutation name: None
type: null mutation fertility: subfertile Comment: LH-Dependent Activation of the EGF Network is Essential for Ovulation. Hsieh M et al. In the preovulatory ovarian follicle, mammalian oocytes are maintained in prophase meiotic arrest until the luteinizing hormone (LH) surge induces reentry into the first meiotic division. Dramatic changes in the somatic cells surrounding the oocytes and in the follicular wall also are induced by LH and are necessary for ovulation. Here, we provide genetic evidence that LH-dependent transactivation of the EGF receptor (EGFR) is indispensable for oocyte reentry into the meiotic cell cycle, for the synthesis of the extracellular matrix surrounding the oocyte that causes cumulus expansion, and for follicle rupture in vivo. Mice deficient in either of two EGFR ligands, amphiregulin or epiregulin, display delayed or reduced oocyte maturation and cumulus expansion. In compound mutant mice where loss of one EGFR ligand is associated with decreased signaling from a hypomorphic allele of the EGFR, LH no longer signals oocyte meiotic resumption. Moreover, induction of genes involved in cumulus expansion and follicle rupture is compromised in these mice, resulting in impaired ovulation. Thus, these studies demonstrate that LH induction of EGF-like growth factors and EGFR transactivation are essential for the regulation of a critical physiological process such as ovulation, and provide new strategies for manipulation of fertility.
Species: mouse
Mutation name: None
type: null mutation fertility: subfertile Comment: Somatic cells regulate maternal mRNA translation and developmental competence of mouse oocytes. Chen J 2013 et al.
Germ cells divide and differentiate in a unique local microenvironment under the control of somatic cells. Signals released in this niche instruct oocyte reentry into the meiotic cell cycle. Once initiated, the progression through meiosis and the associated programme of maternal messenger RNA translation are thought to be cell autonomous. Here we show that translation of a subset of maternal mRNAs critical for embryo development is under the control of somatic cell inputs. Translation of specific maternal transcripts increases in oocytes cultured in association with somatic cells and is sensitive to EGF-like growth factors that act only on the somatic compartment. In mice deficient in amphiregulin, decreased fecundity and oocyte developmental competence is associated with defective translation of a subset of maternal mRNAs. These somatic cell signals that affect translation require activation of the PI(3)K-AKT-mTOR pathway. Thus, mRNA translation depends on somatic cell cues that are essential to reprogramme the oocyte for embryo development.
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Epiregulin-dependent amphiregulin expression and ERBB2 signaling are involved in luteinizing hormone-induced paracrine signaling pathways in mouse ovary. Kim K et al. Sustained EGF receptor (EGFR) phosphorylation by de novo synthesis of EGFR ligands plays an essential role in mediating luteinizing hormone (LH)-induced ovulation process in the preovulatory follicles (POFs). In the present study, the effect of epiregulin (EREG) on oocyte maturation and ovulation was investigated using Ereg knockout (Ereg(-/-)) mice congenic on a C57BL/6 background. Rate of spontaneous oocyte meiotic resumption of denuded oocytes (DOs) or cumulus cell-oocyte complexes (COCs) in vitro is similar between wild-type and Ereg(-/-) mice. However, gonadotropin-induced meiotic resumption in vivo is attenuated, and the number of COCs with expanded cumulus matrix and superovulated eggs dramatically decrease in Ereg(-/-) mice. Nonetheless, the number of eggs ovulated during normal estrus cycles and litter sizes in Ereg(-/-) mice are comparable to those of wild-type littermates. In contrast to other EGFR ligands, induction of amphiregulin (Areg) mRNA is severely reduced in ovaries collected from Ereg(-/-) mice either after human chorionic gonadotropin (hCG) treatment in immature mice or LH surge in adults. Gonadotropin-induced EGFR and ERBB2 phosphorylation in ovaries is attenuated in immature Ereg(-/-) mice, and MAPK3/1 phosphorylation and prostaglandin synthase 2 (PTGS2) protein levels are reduced. This attenuation, however, is no longer detectable in adult Ereg(-/-) mice after LH surge. This study implicates that EREG mediates signals downstream of Areg mRNA expression and that EGFR-ERBB2 signals contributes to regulation of ovulation process.