In sheep, large ovarian antral follicles grow in waves with a periodicity of every 4 to 5 days; each wave is initiated by a peak in serum concentrations of follicle stimulating hormone (FSH). In the present thesis, follicular data and hormone estimations acquired from daily ultrasonography and blood samples, respectively, were used to study mechanisms regulating the number of follicular waves per estrous cycle. Using additional approaches such as implants releasing estradiol-17â and or progesterone, immunization against gonadotropin releasing hormone (GnRH), and injections of GnRH, the role of pulsed luteinizing hormone (LH) secretion and FSH peaks in follicular wave emergence and growth and the dependency of FSH peaks on pulsed GnRH secretion, were studied in sheep. The viability of aged follicles was also addressed.<p> The results of the present studies showed that ewes with three or four waves per cycle had cycles of the same length. The inter-wave interval was longer for the first and the last or ovulatory wave of the cycle in three compared to four wave cycles. The length of the lifespan and regression phase of the largest follicle of a wave declined across the cycle as FSH peak concentration and amplitude decreased. The maximum follicular diameter of the largest follicle growing in the first wave and the last or ovulatory wave of the cycle was greater compared to other waves of the cycle. Treatment of anestrous ewes with estradiol releasing implants alone completely abolished pulsed LH secretion and suppressed follicular wave development; however, FSH secretion was only minimally affected and the pool of small follicles was not affected. When pulsed secretion of LH was restored by frequent injections of GnRH, follicular waves were re-established. Treatment of anestrous ewes with implants releasing estradiol and progesterone, decreased FSH peak amplitude and abolished LH pulses and follicular waves; the size of the pool of small follicles increased. Immunization against GnRH in anestrous ewes abolished pulsatile LH secretion and suppressed follicular wave emergence; however, FSH peaks continued to occur for several weeks. In cyclic ewes, creating an LH pulse frequency typical of the follicular phase, during the luteal phase of the cycle by giving GnRH, increased maximum diameter of the largest follicle in a wave and serum concentrations of estradiol and progesterone. The enhanced growth of follicles in a wave blocked the next expected FSH peak and its associated follicular wave. Decreasing LH pulse frequencies lower than the minimal frequency seen in the luteal phase, by implants releasing progesterone, did not affect the growth of follicular waves.<p> It was previously demonstrated that treatment of non-prolific WWF ewes with Prostaglandin F2á (PGF2á) and medroxy progesterone acetate (MPA) increased the ovulation rate by adding ovulations from the penultimate wave in addition to the final wave of the cycle; however, fertility was not improved. In the last study of my thesis, we collected follicles, with an extended lifespan, from the penultimate wave of the cycle in ewes given the PGF2á and MPA treatment. We compared their quality with follicles from the final wave of the cycle by looking at the expression of markers of follicular development. The results showed that theca cells of follicles from the final wave had significantly higher mRNA expression for vascular endothelial growth factor (VEGF) compared to follicles from the penultimate wave. Granulosa cells of follicles from the final wave had significantly higher mRNA expression for connexion 43 (Cx43) compared to follicles from the penultimate wave. Protein expression for Cx43, proliferating cell nuclear antigen (PCNA) and Factor VIII was greater in follicles from the final compared to the penultimate wave.<p> We concluded from the present studies that: 1) the mechanism that makes a three wave or four wave cycle is unclear; 2) some level of pulsatile LH secretion is required for an FSH peak to trigger emergence of follicular waves in anestrous ewes; 3) progesterone enhances the inhibitory effects of estradiol on FSH secretion in anestrous ewes, suppressing specifically FSH peak amplitude; 4) an endogenous rhythm may exist that drives the peaks in FSH secretion independent of secretory products from the follicles growing in a wave and pulsed GnRH secretion; 5) follicular waves in ewes, when exposed to an LH pulse frequency similar to the follicular phase, during the luteal phase of the cycle, when serum progesterone concentrations are high, can grow and function like ovulatory follicles growing in the follicular phase of the cycle; 6) expression of some markers of vascularization/ angiogenesis, gap-junctional communication and cell proliferation, appeared to be decreased in follicles from the penultimate compared to the final wave of an estrous cycle, when the lifespan of follicles from the penultimate wave was extended such that they were present in the ovary with follicles from the final wave of the cycle.

Depuis plusieurs décennies, la communication intercellulaire par jonctions gap (CIJG) est connue pour être impliquée dans la cancérogenèse. Cette implication semble complexe par le fait que les connexines pourraient augmenter la capacité d’invasion des cellules cancéreuses tout en diminuant leur prolifération. Ceci était particulièrement observé pour la connexine 43 (Cx43) dans le cas de cellules de gliomes. Or, les propriétés d’invasion des gliomes de haut grade, les glioblastomes multiformes (GBM), les rendent difficiles à supprimer par résection chirurgicale et favorisent leur récidive.<br/> Afin de préciser le rôle de la Cx43 dans le contrôle des capacités invasives de cellules de GBM, nous avons utilisé une lignée de cellules de glioblastome humaine U251 exprimant par shRNA des niveaux, en ARNm et protéiques, de Cx43 réduits. Ces clones shRNA des cellules U251 montrent une corrélation entre le niveau d’expression de la Cx43 et le processus d’invasion. Au cours de ce travail, nous avons montré, pour la première fois, que la Cx43 est localisée dans les structures protéolytiques permettant l’invasion, les invadopodes. Nous avons démontré aussi que, par sa localisation, la Cx43 favorise la formation des invadopodes en agissant comme une protéine d’échafaudage qui permet l’interaction de Src de la Cortactine. De plus, l’activité hémicanal de la Cx43, probablement inhibée par le Bisphénol A, possède des effets négatifs sur la cinétique de développement des invadopodes. Une étude du protéome et du sécrétome des cellules U251 et des clones shRNA a permis l’identification des protéines impliquées dans l’invasion et la formation et fonction des invadopodes.<br/> En conclusion, la Cx43 participe au processus invasif des cellules de GBM en favorisant la formation et la fonction des invadopodes. Cette nouvelle fonction de la Cx43 semble être la conséquence de ses propriétés de protéines d’échafaudage et hémicanal, et non de son rôle principalement décrit dans la CIJG. / Since several decades, the gap junction intercellular communication (GJIC) is known to be involved in carcinogenesis. This involvement seems complicated by the fact that connexins could increase cancer cells invasion ability while decreasing their proliferation. This was especially observed for connexin 43 (Cx43) in the case of glioma cells. But high-grade gliomas, glioblastoma multiform (GBM) has invasion properties that make it difficult to remove surgically and promote their recurrence.<br/> To clarify the Cx43 role in the control of GBM cells invasive capacities, we used the GBM U251 cell line expressing Cx43 levels, mRNA and protein, reduced by shRNA strategy. Through this approach, we confirmed that Cx43 expression level is associated with the invasive capacity of GBM cells. Furthermore we have shown, for the first time, that Cx43 is localized in invasive proteolytic structures, the invadopodia. We also show that, by its location, Cx43 promotes invadopodia formation by acting as a scaffolding protein that allows Src and Cortactin interaction. Moreover, Cx43 hemichannel activity, probably inhibited by Bisphenol A, has negative effects on invadopodia kinetics development. A proteome and secretome study of U251 cells and shRNA clones allowed the identification of proteins involved in invasion and invadopodia formation and function.<br/>In conclusion, Cx43 participates in the invasive process of GBM cells by promoting invadopodia formation and function. This new function of Cx43 seems to be the result of its scaffold proteins and hemichannel properties, but not its role described mainly in CIJG.

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