1,720,972 research outputs found
MOLECULAR DETERMINANTS OF MAMMALIAN FERTILITY: ROLE OF PROGESTERONE RECEPTOR MEMBRANE COMPONENT 1 (PGRMC1)
Full text linkReproductive efficiency in dairy cows is decreasing worldwide. The root cause of the declining fertility is probably a combination of a variety of physiological and management factors that have an additive effect on reproductive efficiency. These factors include increasing in milk production and herd size, greater use of confinement housing, labor shortages and higher inbreeding percentages. In addition, the reproductive physiology of dairy cattle has also changed in response to genetic selection for milk production. Compared with traditional dairy cows, modern dairy cows have longer intervals to first ovulation, a higher incidence of anestrus and abnormal luteal phases, lower blood progesterone and IGF-I concentrations, higher incidence of multiple ovulations and twinning rates as well as greater embryonic loss. Declining fertility represents an obstacle in maintaining profitability of dairy farms. It has been estimated that a slight increase in pregnancy rates results in a significant increase in profitability that could make the difference in whether a family farm remains in operation. These findings suggest that defining the factors and mechanisms that contribute to oocyte and embryo quality is essential for improving female fertility. In particular, basic knowledge of which proteins within the oocyte regulate meiosis, oocyte fertilizability and developmental potential would be advantageous.
Starting from these observations, our studies were conducted to test the hypothesis that PGRMC1 is one of the key factors that regulate mammalian oocyte quality and therefore female fertility. Initial indications that PGRMC1 participates in progesterone signaling in the reproductive system come from studies in which PGRMC1 expression was silenced using siRNA in ovarian cells. These experiments demonstrated that Progesterone’s ability to inhibit ovarian cells from undergoing apoptosis in vitro is dependent on PGRMC1, indicating that PGRMC1 plays an essential role in promoting the survival of ovarian cell in vitro. This led us to start our investigations on the function of PGRMC1 in bovine fertility.
Initial experiments were conducted to determine the presence and localization of PGRMC1 in various compartments of the bovine female reproductive organs, during the follicular and luteal phases of the estrous cycle. Importantly, these studies revealed the presence of PGRMC1 in the nucleus of bovine oocytes. Further studies revealed that PGRMC1 is present in both GV- and MII-stage oocyte, is associated with male and female pronuclei in the zygote and is highly expressed in the blastocysts, with typical localization at each of these stages.
Since fertilization and embryonic development are mainly dependent on the completion of oocyte maturation, we focused our attention on PGRMC1’s role during this important step. Our localization as well as our functional data suggest an important role of PGRMC1 in oocyte maturation that may be specifically related to the mechanism by which chromosomes segregate and the first polar body extruded. Moreover, we have started to elucidate the mechanism by which PGRMC1 could act as a regulator of oocyte meiosis. In fact we demonstrated not only that PGRMC1 co-localize with the active form of AURKB, but also that the activities of these two molecules may be somehow related. In fact, inhibition of AURKB causes changes in the localization of PGRMC1 and alterations in the MII chromosomal plate. Furthermore, our data suggest that alteration in the localization of PGRMC1 and AURKB could account in part for the increased aneuploidy and low development competence of oocytes of ovaries isolated from cows with reduced ovarian reserve.
In conclusion, the present study raise important questions regarding the role of PGRMC1 in the regulation of oocyte maturation and the loss of fertility of dairy cows. Despite the mechanism through which PGRMC1 regulates these processes is still unknown and remains to be deeply investigated, our data indicate that functional alterations of PGRMC1 could impair meiosis and reduce development competence of oocytes. Finally, understanding these mechanisms in cattle could provide insight into how these processes are regulated in other species, including humans
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Oxidative stress may impair oocyte quality in dairy cows of reproductive age with a reduced antral follicle count
No full textIn dairy cattle, oocytes isolated from ovaries with a reduced antral follicle count (AFC) have a low embryonic developmental competence. This may be related to oxidative stress, as indicated by our recent finding that ovaries with reduced AFC show a defective endothelial nitric oxide synthase/nitric oxide system. To further test this hypothesis, we evaluated whether the poor developmental competence of these oocytes was possibly due 1) to an imbalance of the reduced glutathione (GSH) system, because GSH is the major antioxidant compound stored within the oocyte and protects the zygote and early embryos from oxidative damage, and 2) to reduced mitochondrial activity. Ovaries were obtained from the abattoir, and oocytes were collected from ovaries with reduced AFC, with fewer than 10 follicles of 2 to 6 mm in diameter, and aged-matched controls, with more than 10 follicles of 2 to 6 mm in diameter. Oocyte GSH content was evaluated using the 5,5′-dithio-bis(2-nitrobenzoic acid)-GSH reductase recycling micro-GSH assay before and after in vitro maturation (IVM) in the presence or absence of 100 μM cysteamine, a GSH precursor. At the same time the developmental competence after IVF was assessed. Moreover, the mitochondrial activity during IVM was evaluated in additional oocytes from the two ovarian categories by specific MitoTracker dyes (MitoTracker FM Green and MitoTracker Orange CMTMRos, Invitrogen, Carlsbad, CA, USA) and subsequent image analysis (ImageJ software). All data were analysed by ANOVA followed by Fisher’s least significant differences test, and P-values <0.05 were considered significant. Experiments were repeated at least three times. Oocytes isolated from ovaries with a low AFC had a similar GSH content compared with oocytes isolated from control ovaries (n = 65 and 85, respectively; 4.31 ± 0.41 v. 4.51 ± 0.42 pmol oocyte–1). After IVM, oocytes from ovaries with reduced AFC showed a significantly lower GSH content compared with control oocytes (n = 55 and 65, respectively; 4.36 ± 0.31 v. 6.59 ± 0.39 pmol oocyte–1); however, cysteamine supplementation during IVM induced GSH accumulation similar to the control (n = 80 and 85, respectively; 9.88 ± 0.77 v. 10.45 ± 0.88 pmol oocyte–1). It is interesting that the increase in intracellular GSH content significantly improved the developmental competence of oocytes from ovaries with a reduced AFC (n = 196 and 201, respectively; 20.1 ± 2.9% v. 6.2 ± 1.6%), although the blastocyst rate remained lower than the control either with or without cysteamine (n = 218 and 212, respectively; 33.3 ± 3.8% and 34.2 ± 2.4%). Further, immature oocytes from ovaries with a low AFC showed a reduced mitochondrial membrane potential compared with control oocytes (n = 13 and 18, respectively; 1.74 ± 1.19 v. 2.22 ± 1.72, calculated as the ratio between the fluorescence of active and total mitochondria), whereas at the end of IVM, it declined in both categories at a comparable level (n = 17 and 24, respectively; 1.19 ± 0.10 and 1.30 ± 0.06). Our data confirmed the hypothesis that both the GSH imbalance and defective mitochondrial activity contribute to the limited developmental competence of oocytes from ovaries with a reduced AFC
Gap junction-mediated intercellular coupling controls chromatin remodeling during bovine oocyte growth and differentiation through cAMP-dependent mechanism(s)
No full textSynaptophysin and synaptobrevin 2 associate closely with packaging and storage of synaptic vesicles and transmitter release, and both play important roles in the development of rat cochlea. We examined the differential expression of synaptophysin and synaptobrevin 2 in the developing Sprague-Dawley rat cochlea, and investigated the relationship between their expression and auditory development. The expression of synaptophysin and synaptobrevin 2 was not observed in Kolliker's and Corti's organ at postnatal 1 day (P1) and P5, and the top turn of the cochlea at P10. Expression was detected in the outer spiral bundle (OSB), the inner spiral bundle (ISB), and the medial wall of the Deiters' cell of the cochlea at P14, and P28, and in the middle or the basal turn of Corti's organ at P10. Synaptobrevin 2 was expressed in the top of the inner hair cells (IHCs) in Corti's organ of both P14 and P28 rats. All spiral ganglion neurons (SGNs) were stained at all ages examined. The localization of synaptophysin and synaptobrevin 2 in the cochlea was closely associated with the distribution of nerve fibers and neural activity (the docking and release of synaptic vesicles). Synaptophysin and synaptobrevin 2 were expressed in a dynamic manner during the development of rat cochlea. Their expression differences during the development were in favor of the configuration course constructed between nerve endings and target cells. It also played a key role in the formation of the correct coding of auditory information during auditory system development
Oocytes isolated from dairy cows with reduced ovarian reserve have a high frequency of aneuploidy and alterations in the localization of progesterone receptor membrane component 1 and aurora kinase B
No full textOocytes isolated from cows of reproductive age with reduced antral follicle counts (AFC) have a diminished capacity of embryonic development, which may be related to alterations in the mechanism that directs the proper segregation of chromosomes. Because we demonstrated that progesterone receptor membrane component 1 (PGRMC1) is involved in chromosome congression and metaphase II (MII) plate formation, the present study was designed to determine 1) if the decrease in oocyte developmental competence observed in dairy cows with a reduced AFC is due to a higher incidence of aneuploidy and 2) whether alterations in PGRMC1 contributes to the incidence of aneuploidy. Oocytes from ovaries with reduced AFC and age-matched controls were matured in vitro and the occurrence of aneuploidy determined as well as the mRNA level and localization of PGRMC1. Although oocytes from ovaries with reduced AFC were capable of undergoing meiosis in vitro, these oocytes showed a 3-fold increase in aneuploidy compared to oocytes isolated from control ovaries (P < 0.05). Although Pgrmc1 mRNA levels were not altered, PGRMC1 and aurora kinase B (AURKB) failed to localize to precise focal points on MII chromosomes of oocytes from ovaries with reduced AFC. Furthermore, when oocytes of control ovaries were cultured with an inhibitor of AURKB activity, their MII plate was disrupted and PGRMC1 was not properly localized to the chromosomes. These results suggest that alterations in PGRMC1 and/or AURKB localization account in part for the increased aneuploidy and low development competence of oocytes from ovaries with reduced AFC
Effect of low doses of FSH and P4 on cystogenesis-induced mice as a polycystic ovary syndrome model
No full textBackground: Polycystic ovary syndrome (PCOS) is the most common endocrine disorder in women of reproductive age, characterised by chronic hyperandrogenic anovulation and dys- regulation of reproductive hormones together with metabolic abnormalities. The aetiology of PCOS is still uncertain and cur- rent therapeutical treatments are moderately effective. Hence, appropriate animal models that mimic many or all PCOS traits can facilitate research, leading to improve understand- ing of the pathogenesis of PCOS and the potential for innovative approaches for its therapy. Several reports indi- cate that hyperandrogenisation can be induced in mice by dehyidroepiandrosterone (DHEA). DHEA-treated mice develop cysts and exhibit many of the salient features of human PCOS.
Aim: To study the effect of a highly diluted and dynamised form of FSH and P4 on a DHEA-PCOS murine model. The morphology of antral follicle population and E2 and P4 serum concentrations were evaluated.
Methods: Thirty-six female-prepubertal Balb/c mice were either injected for 20 consecutive days with DHEA (6 mg kg–1 body weight) dissolved in 0.1 ml sesame oil (DHEA group) or injected with DHEA and treated by oral administration with low dose of an activated solution of P4 plus FSH in saline solution (0.44 pg day–1 and 0.44 fg day–1 respectively, LD group). The solution was activated by shaking. A third group received only sesame oil (control group). Mice were then sacrificed, blood was collected for hormone analysis (enzyme-linked immunosor- bent assay (ELISA)) and ovaries were fixed for morphological studies.
Results and conclusion: Histological examination revealed an increase in the total number of antral follicles >300 m in diameter in both DHEA and LD groups compared with con- trols (p 0.05). Finally, DHEA treatment increased both E2 and P4 serum levels compared with controls (p < 0.05). Nevertheless, LD administration decreased serum E2 to a level similar to controls.
Conclusion: Our preliminary results indicate that low and activated doses of FSH and P4 are able to decrease the follicular alterations induced in DHEA-treated mice. This could represent a novel approach in reducing the severity of PCOS syndrome and its endocrine and reproductive complications
Large-scale chromatin morpho-functional changes during mammalian oocyte growth and differentiation
Full text linkMammalian oocyte development is characterized by impressive changes in chromatin structure and function within the germinal vesicle (GV). These changes are crucial to confer the oocyte with meiotic and developmental competencies. In cow, oocytes collected from early and middle antral follicles present four patterns of chromatin configuration, from GV0 to GV3, and its progressive condensation has been related to the achievement of developmental potential. During oogenesis, follicular cells are essential for the acquisition of meiotic and developmental competencies and communicate with the oocyte by paracrine and gap junction mediated mechanisms. We recently analyzed the role of gap junction communications (GJC) on chromatin remodeling process during the specific phase of folliculogenesis that coincides with the transcriptional silencing and sequential acquisition of meiotic and developmental capabilities. Our studies demonstrated that GJC between germinal and somatic compartments plays a fundamental role in the regulation of chromatin remodeling and transcription activities during the final oocyte differentiation, throughout cAMP dependent mechanism(s)
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