Reproduction

Shelling, Andrew N

doi: 10.1530/rep-09-0567pmid: 20716613

Premature ovarian failure (POF) is a common cause of infertility in women, and is characterised by amenorrhoea, hypo-oestrogenism and elevated gonadotrophin levels in women under the age of 40. Known causes include iatrogenic agents that cause permanent damage to the ovaries, such as chemotherapy, radiation therapy and surgery, autoimmune conditions, X-chromosome abnormalities and autosomal genetic conditions. However, few genes have been identified that can explain a substantial proportion of cases of POF. Most women with POF are deeply upset by the diagnosis, partly due to the unexpected menopausal symptoms, but also due to infertility. Therefore, early detection would provide better opportunity for early intervention, and furthermore, the identification of specific gene defects will help to direct potential targets for future treatment.

Shelling, Andrew N

doi: 10.1530/REP-09-0567pmid: 20716613

Premature ovarian failure (POF) is a common cause of infertility in women, and is characterised by amenorrhoea, hypo-oestrogenismand elevated gonadotrophin levels in women under the age of 40. Known causes include iatrogenic agents that cause permanentdamage to the ovaries, such as chemotherapy, radiation therapy and surgery, autoimmune conditions, X-chromosome abnormalitiesand autosomal genetic conditions. However, few genes have been identified that can explain a substantial proportion of casesof POF. Most women with POF are deeply upset by the diagnosis, partly due to the unexpected menopausal symptoms, but alsodue to infertility. Therefore, early detection would provide better opportunity for early intervention, and furthermore, theidentification of specific gene defects will help to direct potential targets for future treatment.

Egli, Marcel; Leeners, Brigitte; Kruger, Tillmann H C

doi: 10.1530/rep-10-0033pmid: 20733016

Prolactin (PRL) is one of the most versatile hormones in the mammalian body affecting reproductive, sexual, metabolic, immune, and other functions. It is therefore not surprising that the neural control of PRL secretion is complex, involving the coordinated actions of several hypothalamic nuclei. A plethora of experimental data exists on the hypothalamic control of hormone secretion under various physiological stimuli. There have been even mathematical models and computer studies published, which help to understand the complex hypothalamic–pituitary network. Nevertheless, the putative role of PRL for human reproduction still has to be clarified. Here, we review data on the underlying mechanisms controlling PRL secretion using both experimental and mathematical approaches. These investigations primarily focus on rhythmic secretion in rats during early pregnancy or pseudopregnancy, and they point to the important role of oxytocin as a crucial PRL-releasing factor. Recent data on human studies and their theoretical and clinical implications are reviewed as well. In particular, studies demonstrating a sustained PRL surge after sexual climax in males and females are presented, indicating possible implications for both sexual satiation and reproductive functions. Taking these data together, there is evidence for the hypothesis that the PRL surge induced by sexual activity, together with the altered PRL rhythmic pattern, is important for successful initialization of pregnancy not only in rodents but also possibly in humans. However, further investigations are needed to clarify such a role in humans.

Egli, Marcel; Leeners, Brigitte; Kruger, Tillmann H C

doi: 10.1530/REP-10-0033pmid: 20733016

Prolactin (PRL) is one of the most versatile hormones in the mammalian body affecting reproductive, sexual, metabolic, immune,and other functions. It is therefore not surprising that the neural control of PRL secretion is complex, involving the coordinatedactions of several hypothalamic nuclei. A plethora of experimental data exists on the hypothalamic control of hormone secretionunder various physiological stimuli. There have been even mathematical models and computer studies published, which help tounderstand the complex hypothalamic–pituitary network. Nevertheless, the putative role of PRL for human reproduction stillhas to be clarified. Here, we review data on the underlying mechanisms controlling PRL secretion using both experimental andmathematical approaches. These investigations primarily focus on rhythmic secretion in rats during early pregnancy or pseudopregnancy,and they point to the important role of oxytocin as a crucial PRL-releasing factor. Recent data on human studies and theirtheoretical and clinical implications are reviewed as well. In particular, studies demonstrating a sustained PRL surge aftersexual climax in males and females are presented, indicating possible implications for both sexual satiation and reproductivefunctions. Taking these data together, there is evidence for the hypothesis that the PRL surge induced by sexual activity,together with the altered PRL rhythmic pattern, is important for successful initialization of pregnancy not only in rodentsbut also possibly in humans. However, further investigations are needed to clarify such a role in humans.

Norris, Rachael P; Freudzon, Marina; Nikolaev, Viacheslav O; Jaffe, Laurinda A

doi: 10.1530/REP-10-0288pmid: 20826538

The meiotic cell cycle in mouse oocytes is arrested in prophase, and then restarted when LH acts on the surrounding granulosacells. The granulosa cells keep meiosis arrested by providing a source of cGMP that diffuses into the oocyte through gap junctions,and LH restarts the cell cycle by closing the junctions and by decreasing granulosa cell cGMP, thus lowering oocyte cGMP.Epidermal growth factor receptor (EGFR) activation is an essential step in triggering LH-induced meiotic resumption, but itsrelationship to the cGMP decrease in the follicle is incompletely understood, and its possible function in causing gap junctionclosure has not been investigated. Here, we use EGFR agonists (epiregulin and amphiregulin) and an EGFR kinase inhibitor (AG1478)to study the function of the EGFR in the signaling pathways leading to the release of oocytes from prophase arrest. Our resultsindicate that the EGFR kinase contributes to LH-induced meiotic resumption in two different ways. First, it is required forgap junction closure. Second, it is required for an essential component of the decrease in follicle cGMP. Our data show thatthe EGFR kinase-dependent component of the cGMP decrease is required for LH-induced meiotic resumption, but they also indicatethat an as yet unidentified pathway accounts for a large part of the cGMP decrease.

Norris, Rachael P; Freudzon, Marina; Nikolaev, Viacheslav O; Jaffe, Laurinda A

doi: 10.1530/rep-10-0288pmid: 20826538

The meiotic cell cycle in mouse oocytes is arrested in prophase, and then restarted when LH acts on the surrounding granulosa cells. The granulosa cells keep meiosis arrested by providing a source of cGMP that diffuses into the oocyte through gap junctions, and LH restarts the cell cycle by closing the junctions and by decreasing granulosa cell cGMP, thus lowering oocyte cGMP. Epidermal growth factor receptor (EGFR) activation is an essential step in triggering LH-induced meiotic resumption, but its relationship to the cGMP decrease in the follicle is incompletely understood, and its possible function in causing gap junction closure has not been investigated. Here, we use EGFR agonists (epiregulin and amphiregulin) and an EGFR kinase inhibitor (AG1478) to study the function of the EGFR in the signaling pathways leading to the release of oocytes from prophase arrest. Our results indicate that the EGFR kinase contributes to LH-induced meiotic resumption in two different ways. First, it is required for gap junction closure. Second, it is required for an essential component of the decrease in follicle cGMP. Our data show that the EGFR kinase-dependent component of the cGMP decrease is required for LH-induced meiotic resumption, but they also indicate that an as yet unidentified pathway accounts for a large part of the cGMP decrease.

Luciano, Alberto M; Lodde, Valentina; Franciosi, Federica; Ceciliani, Fabrizio; Peluso, John J

doi: 10.1530/rep-10-0218pmid: 20739377

Although the mRNA that encodes progesterone receptor membrane component 1 (PGRMC1) is present in mammalian oocytes, nothing is known about either PGRMC1's expression pattern or function in oocytes during maturation, fertilization, and subsequent embryonic development. As PGRMC1 associates with the mitotic spindle in somatic cells, we hypothesized that PGRMC1 is involved in oocyte maturation (meiosis). Western blot analysis confirmed the presence of PGRMC1 in bovine oocytes. This study also shows that PGRMC1 is present at the germinal vesicle (GV)- and MII-stage oocytes and is associated with male and female pronucleus formation of the zygote and is highly expressed in blastocysts. A more detailed examination of PGRMC1 localization using confocal imaging demonstrated that in GV-stage oocytes, PGRMC1 was concentrated throughout the GV but did not localize to the chromatin. With the resumption of meiosis in vitro, PGRMC1 concentrated in the centromeric region of metaphase I chromosomes, while in the anaphase I/telophase I stages the majority of PGRMC1 concentrated between the separating chromosomes. At the metaphase II stage, PGRMC1 re-associated with the centromeric region of the chromosomes. A colocalization study demonstrated that PGRMC1 associated with the phosphorylated form of aurora kinase B, which localizes to the centromeres at metaphase. Finally, PGRMC1 antibody injection significantly lowered the percentage of oocytes that matured and reached the metaphase II stage after 24 h of culture. The majority of the PGRMC1 antibody-injected oocytes arrested in the prometaphase I stage of meiosis. Furthermore, in most of the PGRMC1 antibody-injected oocytes, the chromosomes were disorganized and scattered. Taken together, these data demonstrate that PGRMC1 is expressed in bovine oocytes and its localization changes at specific stages of oocyte maturation. These observations suggest an important role for PGRMC1 in oocyte maturation, which may be specifically related to the mechanism by which chromosomes segregate.

Luciano, Alberto M; Lodde, Valentina; Franciosi, Federica; Ceciliani, Fabrizio; Peluso, John J

doi: 10.1530/REP-10-0218pmid: 20739377

Although the mRNA that encodes progesterone receptor membrane component 1 (PGRMC1) is present in mammalian oocytes, nothingis known about either PGRMC1's expression pattern or function in oocytes during maturation, fertilization, and subsequentembryonic development. As PGRMC1 associates with the mitotic spindle in somatic cells, we hypothesized that PGRMC1 is involvedin oocyte maturation (meiosis). Western blot analysis confirmed the presence of PGRMC1 in bovine oocytes. This study alsoshows that PGRMC1 is present at the germinal vesicle (GV)- and MII-stage oocytes and is associated with male and female pronucleusformation of the zygote and is highly expressed in blastocysts. A more detailed examination of PGRMC1 localization using confocalimaging demonstrated that in GV-stage oocytes, PGRMC1 was concentrated throughout the GV but did not localize to the chromatin.With the resumption of meiosis in vitro, PGRMC1 concentrated in the centromeric region of metaphase I chromosomes, while in the anaphase I/telophase I stages themajority of PGRMC1 concentrated between the separating chromosomes. At the metaphase II stage, PGRMC1 re-associated with thecentromeric region of the chromosomes. A colocalization study demonstrated that PGRMC1 associated with the phosphorylatedform of aurora kinase B, which localizes to the centromeres at metaphase. Finally, PGRMC1 antibody injection significantlylowered the percentage of oocytes that matured and reached the metaphase II stage after 24 h of culture. The majority of thePGRMC1 antibody-injected oocytes arrested in the prometaphase I stage of meiosis. Furthermore, in most of the PGRMC1 antibody-injectedoocytes, the chromosomes were disorganized and scattered. Taken together, these data demonstrate that PGRMC1 is expressedin bovine oocytes and its localization changes at specific stages of oocyte maturation. These observations suggest an importantrole for PGRMC1 in oocyte maturation, which may be specifically related to the mechanism by which chromosomes segregate.

Bastián, Yadira; Roa-Espitia, Ana L; Mújica, Adela; Hernández-González, Enrique O

doi: 10.1530/rep-09-0545pmid: 20716611

Research on fertilization in mammalian species has revealed that Ca2+ is an important player in biochemical and physiological events enabling the sperm to penetrate the oocyte. Ca2+ is a signal transducer that particularly mediates capacitation and acrosome reaction (AR). Before becoming fertilization competent, sperm must experience several molecular, biochemical, and physiological changes where Ca2+ plays a pivotal role. Calpain-1 and calpain-2 are Ca2+-dependent proteases widely studied in mammalian sperm; they have been involved in capacitation and AR but little is known about their mechanism. In this work, we establish the association of calpastatin with calpain-1 and the changes undergone by this complex during capacitation in guinea pig sperm. We found that calpain-1 is relocated and translocated from cytoplasm to plasma membrane (PM) during capacitation, where it could cleave spectrin, one of the proteins of the PM-associated cytoskeleton, and facilitates AR. The aforementioned results were dependent on the calpastatin phosphorylation and the presence of extracellular Ca2+. Our findings underline the contribution of the sperm cytoskeleton in the regulation of both capacitation and AR. In addition, our findings also reveal one of the mechanisms by which calpain and calcium exert its function in sperm.

Bastián, Yadira; Roa-Espitia, Ana L; Mújica, Adela; Hernández-González, Enrique O

doi: 10.1530/REP-09-0545pmid: 20716611

Research on fertilization in mammalian species has revealed that Ca2+ is an important player in biochemical and physiological events enabling the sperm to penetrate the oocyte. Ca2+ is a signal transducer that particularly mediates capacitation and acrosome reaction (AR). Before becoming fertilizationcompetent, sperm must experience several molecular, biochemical, and physiological changes where Ca2+ plays a pivotal role. Calpain-1 and calpain-2 are Ca2+-dependent proteases widely studied in mammalian sperm; they have been involved in capacitation and AR but little is knownabout their mechanism. In this work, we establish the association of calpastatin with calpain-1 and the changes undergoneby this complex during capacitation in guinea pig sperm. We found that calpain-1 is relocated and translocated from cytoplasmto plasma membrane (PM) during capacitation, where it could cleave spectrin, one of the proteins of the PM-associated cytoskeleton,and facilitates AR. The aforementioned results were dependent on the calpastatin phosphorylation and the presence of extracellularCa2+. Our findings underline the contribution of the sperm cytoskeleton in the regulation of both capacitation and AR. In addition,our findings also reveal one of the mechanisms by which calpain and calcium exert its function in sperm.