Personne :
Santiquet, Nicolas

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Santiquet
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Nicolas
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Faculté de médecine, Université Laval
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ncf11857681
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Résultats de recherche

Voici les éléments 1 - 8 sur 8
  • Publication
    Accès libre
    Régulation des jonctions communicantes chez les complexes ovocyte-cumulus de porc au cours de la maturation in vitro
    (2013) Santiquet, Nicolas; Richard, François; Robert, Claude
    Les jonctions communicantes (JCs) sont particulièrement importantes au sein du follicule ovarien puisque qu’elles vont participer à la régulation de la maturation ovocytaire. Les JCs vont contrôler le flux de molécules tels que l’AMPc et le GMPc qui passent entre les cellules du cumulus et l’ovocyte et qui inhibent la reprise de la méiose. La fermeture de ces canaux, tant in vivo qu’in vitro, va entrainer la reprise de la méiose en empêchant le passage de ces molécules. Dans les études que nous avons réalisées, nous avons tout d’abord développé une méthode d’analyse fonctionnelle des jonctions communicantes (le FRAP : Fluorescence Recovery After Photobleaching) dans la structure tridimensionnelle du complexe ovocyte-cumulus. Cette technique nous a permis de déterminer que les gonadotrophines et le liquide folliculaire présent dans le milieu de maturation pouvaient moduler la dynamique de transfert entre les cellules du cumulus pendant les premières heures de maturation in vitro (MIV). Par la suite, nous avons étudié la régulation des connexines (Cx), qui sont les protéines composant la JC. Nous avons identifié les principales connexines présentes dans le COC porcin, la Cx43, la Cx45 et la Cx60. Nous avons déterminé que les gonadotrophines régulaient l’expression, la dégradation ainsi que la localisation de la connexine 43 (la principale connexine présente dans les cellules du cumulus porcin). Enfin, nous nous sommes intéressés à la régulation de la reprise de la méiose par le peptide natriurétique de type C (CNP). En effet, le CNP a été proposé pour inhiber la reprise de la méiose en se liant à son récepteur NPR-B sur les cellules du cumulus, ce qui stimule la production de GMPc. Il est ensuite transféré dans l’ovocyte, via les JCs, où il va inhiber la reprise de la méiose. Nous avons montré que le CNP et un analogue du GMPc avaient un impact différent sur la dynamique de transfert entre les cellules du cumulus. De plus, le CNP agirait sur un autre récepteur (le récepteur NPR-C) pour promouvoir l’arrêt méiotique. En conclusion, ces résultats ajoutent un niveau de compréhension supplémentaire des mécanismes régulant les JCs et la reprise de la méiose durant la MIV chez le porc.
  • Publication
    Restreint
    Regulation of gap-junctional communication between cumulus cells during in vitro maturation in swine, a gap-FRAP study
    (Society for the Study of Reproduction, 2012-05-30) Santiquet, Nicolas; Richard, François J.; Develle, Yann; Robert, Claude; Laroche, Anthony
    Intercellular gap-junctional communication (GJC) plays an important role in ovarian cell physiology. Closure of GJC has been proposed to be involved in oocyte maturation, particularly in the resumption of meiosis, both in vivo and in vitro, by controlling the flow of meiosis inhibitors, such as cAMP and cGMP. Understanding how GJC dynamics are regulated during in vitro maturation (IVM) could provide a powerful tool for controlling meiotic resumption and oocyte maturation in vitro. Since little is known about the GJC dynamic regulation between cumulus cells, we have developed an assay based on recovery of calcein fluorescence in photobleached cumulus cells, a gap-FRAP assay. The GJC profile has been characterized during the first hours of porcine IVM. We showed that equine chorionic gonadotropin (eCG) and epidermal growth factor (EGF) down-regulated GJC effectiveness between cumulus cells. However, human chorionic gonadotropin was not down-regulating GJC effectiveness. We also showed that the GJC network expanded during this period and that this effect was not regulated by gonadotropins. Porcine follicular fluid present in the maturation medium also had an impact on GJC regulation, increasing GJC network establishment and the effectiveness of calcein transfer rate between cumulus cells. These results show that both eCG and EGF are regulating the decrease in GJC effectiveness after 4.5 h of IVM, while the network extension is gonadotropin independent. Regulation of GJC between cumulus cells would then be specifically regulated during in vitro IVM.
  • Publication
    Restreint
    New elements in the c-type natriuretic peptide signaling pathway inhibiting swine in vitro oocyte meiotic resumption
    (Academic Press, 2014-07-01) Djender, Nadjib; Papillon-Dion, Émilie; Santiquet, Nicolas; Richard, François J.; Guillemette, Christine
    C-type natriuretic peptide (CNP) and its cognate receptor, natriuretic peptide receptor (NPR) B, have been shown to promote cGMP production in granulosa/cumulus cells. Once transferred to the oocyte through the gap junctions, the cGMP inhibits oocyte meiotic resumption. CNP has been shown to bind another natriuretic receptor, NPR-C. NPR-C is known to interact with and degrade bound CNP, and has been reported to possess signaling functions. Therefore, NPR-C could participate in the control of oocyte maturation during swine in vitro maturation (IVM). Here, we examine the effect of CNP signaling on meiotic resumption, the amount of cGMP and gap junctional communication (GJC) regulation during swine IVM. The results show an inhibitory effect of CNP in inhibiting oocyte meiotic resumption in follicle-stimulating hormone (FSH)-stimulated IVM. We also found that an NPR-C-specific agonist (cANP[4–23]) is likely to play a role in maintaining meiotic arrest during porcine IVM when in the presence of a suboptimal dose of CNP. Moreover, we show that, even if CNP can increase intracellular concentration of cGMP in cumulus-oocyte complexes, cANP(4–23) had no impact on cGMP concentration, suggesting a potential cGMP-independent signaling pathway related to NPR-C activation. These data support a potential involvement of cANP(4–23) through NPR-C in inhibiting oocyte meiotic resumption while in the presence of a suboptimal dose of CNP. The regulation of GJC was not altered by CNP, cANP(4–23), or the combination of CNP and cANP(4–23), supporting their potential contribution in sending signals to the oocytes. These findings offer promising insights in to new elements of the signaling pathways that may be involved in inhibiting resumption of meiosis during FSH-stimulated swine IVM.
  • Publication
    Accès libre
    The dynamics of connexin expression, degradation and localisation are regulated by gonadotropins during the early stages of in vitro maturation of swine oocytes
    (Public Library of Science, 2013-07-04) Santiquet, Nicolas; Richard, François J.; Robert, Claude
    Gap junctional communication (GJC) plays a primordial role in oocyte maturation and meiotic resumption in mammals by directing the transfer of numerous molecules between cumulus cells and the oocyte. Gap junctions are made of connexins (Cx), proteins that regulate GJC in numerous ways. Understanding the dynamic regulation of connexin arrangements during in vitro maturation (IVM) could provide a powerful tool for controlling meiotic resumption and consequently in vitro development of fully competent oocytes. However, physiological events happening during the early hours of IVM may still be elucidated. The present study reports the dynamic regulation of connexin expression, degradation and localization during this stage. Cx43, Cx45 and Cx60 were identified as the main connexins expressed in swine COC. Cx43 and Cx45 transcripts were judged too static to be a regulator of GJC, while Cx43 protein expression was highly responsive to gonadotropins, suggesting that it might be the principal regulator of GJC. In addition, the degradation of Cx43 expressed after 4.5 h of IVM in response to equine chorionic gonadotropin appeared to involve the proteasomal complex. Cx43 localisation appeared to be associated with GJC. Taken together, these results show for the first time that gonadotropins regulate Cx43 protein expression, degradation and localisation in porcine COC during the first several hours of IVM. Regulation of Cx43 may in turn, via GJC, participate in the development of fully competent oocytes.
  • Publication
    Restreint
    Signal transduction pathways in oocyte maturation
    (John Wiley & Sons Inc., 2017-01-01) Khan, Daulat Raheem; Bergeron, Annick; Santiquet, Nicolas; Richard, François J.
  • Publication
    Restreint
    Transplanted bone marrow cells do not provide new oocytes but rescue fertility in female mice following treatment with chemotherapeutic agents
    (Mary Ann Liebert, Inc., 2012-04-03) Santiquet, Nicolas; Richard, François J.; Robert, Claude; Vallières, Luc; Sirard, Marc-André; Pothier, François
    It is generally accepted that mammalian females are born with a finite pool of oocytes and that this is the sole source of ovules throughout the reproductive life of the adult. This dogma was shaken in 2003 when researchers showed that the oocyte stock might be renewable in adult mammals. It has been proposed that hematopoietic stem cells might be a source of new oocytes. These discoveries have puzzled many researchers and remain controversial. In our study, we attempted to determine if transplanted bone marrow cells could provide new oocytes in PU.1 mice and in severe combined immunideficiency (SCID) mice after treatment with chemotherapeutic agents. We also examined the possibility that grafted bovine embryonic ovarian cortex might provide an environment favoring such a response. We found no evidence that transplanted bone marrow cells provide new fertilizable oocytes in PU.1 mice, in SCID mice treated with chemotherapeutic agents, or with bovine embryonic ovarian tissue grafts. However, transplanted bone marrow cells have improved the fertility of SCID mice previously treated with chemotherapeutic agents. These data suggest that bone marrow cells cannot provide new oocytes but can positively influence ovarian physiology to improve the fertility of mice previously treated with chemotherapeutic agents.
  • Publication
    Accès libre
    Les cellules de la moelle osseuse à la rescousse de l'ovaire : implication des cellules de la moelle osseuse dans le renouvellement post-natal d'ovocytes chez le mammifère adulte
    (2009) Santiquet, Nicolas; Richard, François
    Chez le mammifère, la production d'ovocytes s'arrête pendant la vie foetale. À la naissance, les femelles possèdent un nombre fini d'ovocytes. Mais ce dogme a été remis en question en 2004 alors que des chercheurs ont montré que chez la souris adulte, la néo-ovogénèse était possible (Johnson et al, 2004). En 2005, ces chercheurs ont démontré que des cellules souches de la moelle osseuse étaient capables de coloniser l'ovaire afin de former de nouveaux ovocytes (Johnson et al, 2005). Dans cet ouvrage nous montrons que la néo-ovogenèse chez des souris adultes de type SCID et PU.1 knockout ne se produit pas. Cependant la transplantation de moelle osseuse restaure la fertilité des souris SCID traitées en chimiothérapie. De plus, en greffant du cortex ovarien bovin foetal sous la capsule rénale de souris SCID, nous avons montré que la néo-ovogénèse semble ne pas se produire chez le bovin.
  • Publication
    Restreint
    Activation of 5′ adenosine monophosphate-activated protein kinase blocks cumulus cell expansion through inhibition of protein synthesis during in vitro maturation in swine
    (Oxford University Press, 2014-08-01) Santiquet, Nicolas; Richard, François J.; Guillemette, Christine; Laforest, Martin; Gilchrist, Robert B.; Sasseville, Maxime
    The serine/threonine kinase 5′ adenosine monophosphate-activated protein kinase (AMPK), a heterotrimeric protein known as a metabolic switch, is involved in oocyte nuclear maturation in mice, cattle, and swine. The present study analyzed AMPK activation in cumulus cell expansion during in vitro maturation (IVM) of porcine cumulus-oocyte complexes (COC). 5-Aminoimidazole-4-carboxamide-1-beta-D-ribofuranoside (AICAR) is a well-known activator of AMPK. It inhibited oocyte meiotic resumption in COC. Moreover, cumulus cell expansion did not occur in the presence of AICAR, demonstrating its marked impact on cumulus cells. Activation of AMPK was supported by AICAR-mediated phosphorylation of alpha AMPK subunits. Furthermore, the presence of AICAR increased glucose uptake, a classical response to activation of this metabolic switch in response to depleted cellular energy levels. Neither nuclear maturation nor cumulus expansion was reversed by glucosamine, an alternative substrate in hyaluronic acid synthesis, through the hexosamine biosynthetic pathway, which ruled out possible depletion of substrates. Both increased gap junction communication and phosphodiesterase activity in COC are dependent on protein synthesis during the initial hours of IVM; however, both were inhibited in the presence of AICAR, which supports the finding that activation of AMPK by AICAR mediated inhibition of protein synthesis. Moreover, this protein synthesis inhibition was equivalent to that of the well-known protein synthesis inhibitor cycloheximide, as observed on cumulus expansion and protein concentration. Finally, the phosphorylation level of selected kinases was investigated. The pattern of raptor phosphorylation is supportive of activation of AMPK-mediated inhibition of protein synthesis. In conclusion, AICAR-mediated AMPK activation in porcine COC inhibited cumulus cell expansion and protein synthesis. These results bring new considerations to the importance of this kinase in ovarian physiology and to the development of new oocyte culture medium.