Philippe Monget

Multihormonal regulation of the human prolactin gene expression from 5000 bp of its upstream sequence

We have cloned DNA sequences extending up to 6000 bp upstream from the first exon of the human prolactin (hPRL) gene. 5000 bp of these upstream sequences were fused to a CAT reporter gene and shown to provide tissue-specific transient expression in rat pituitary GH3 cells. Multihormonal response was found in this transient expression assay, leading to significant 2- to 5-fold induction by addition of 8-chlorophenylthio-cyclic AMP, thyrotropin-releasing hormone, epidermal growth factor, basic fibroblast growth factor, phorbol myristate acetate, a calcium channel agonist (Bay K-8644) and triiodothyronine. A 3-fold inhibition was observed in the presence of the glucocorticoid agonist dexamethasone. The sequence of the hPRL promoter was determined up to coordinate -3470. Computer similarity search between the rat and human sequences showed two highly conserved regions corresponding to the proximal and distal tissue specific enhancers described in both PRL promoters.

The Ovarian Reserve of Primordial Follicles and the Dynamic Reserve of Antral Growing Follicles: What Is the Link?

ABSTRACT The growing follicles develop from a reserve of primordial follicles constituted early in life. From this pre-established reserve, a second ovarian reserve is formed, which consists of gonadotropin-responsive small antral growing follicles and is a dynamic reserve for ovulation. Its size, evaluated by direct antral follicular count or endocrine markers, determines the success of assisted reproductive technologies in humans and embryo production biotechnologies in animals. Strong evidence indicates that these two reserves are functionally related. The size of both reserves appears to be highly variable between individuals of similar age, but the equilibrium size of the dynamic reserve in adults seems to be specific to each individual. The dynamics of both follicular reserves appears to result from the fine tuning of regulations involving two main pathways, the phosphatase and tensin homolog (PTEN)/phosphatidylinositol-3 kinase (PI3K)/3-phosphoinositide-dependent protein kinase-1 (PDPK1)/v-akt murine thymoma viral oncogene homolog 1 (AKT1) and the bone morphogenetic protein (BMP)/anti-Müllerian hormone (AMH)/SMAD signaling pathways. Mutations in genes encoding the ligands, receptors, or signaling effectors of these pathways can accelerate or modulate the exhaustion rate of the ovarian reserves, causing premature ovarian insufficiency (POI) or increase in reproductive longevity, respectively. With female aging, the decline in primordial follicle numbers parallels the decrease in the size of the dynamic reserve of small antral follicles and the deterioration of oocyte quality. Recent progress in our knowledge of signaling pathways and their environmental and hormonal control during adult and fetal life opens new perspectives to improve the management of the ovarian reserves.

The ovarian reserve in mammals: A functional and evolutionary perspective

The constitution and the control of the ovarian reserve is of importance in mammals and women. In particular, the number of primordial follicles at puberty is positively correlated with the number of growing follicles and their response to gonadotropin treatments. The size of this ovarian reserve depends on genes involved in germ cell proliferation and differentiation, sexual differentiation, meiosis, germ cell degeneration, formation of primordial follicles, and on a potential mechanism of self-renewal of germ stem cells. In this review, we present the state of the art of the knowledge of genes and factors involved in all these processes. We first focus on the almost 70 genes identified mainly by mouse invalidation models, then we discuss the most plausible hypothesis concerning the possibility of the existence of germ cell self-renewal by neo-oogenesis in animal species and human, with a special interest for the role of corresponding genes in evolutionary distinct model species. All of the genes pointed out here are candidates susceptible to explain fertility defects such as the premature ovarian failure in human.

Thyrotropin-releasing hormone and epidermal growth factor induce human prolactin expression via identical multiple cis elements

Pituitary GH3 cells were transfected with different deletion mutants of the human prolactin (hPRL) promoter fused to the CAT reporter gene. The proximal region (-250 to -42) was sufficient to confer stimulation by both thyrotropin-releasing hormone (TRH) and epidermal growth factor (EGF). Further deletion analyses demonstrated the importance of the three proximal Pit-1 binding sites in this response. However, Pit-1 binding oligonucleotides confer neither TRH nor EGF induction to a linked neutral promoter, suggesting that other elements might be involved. We have previously shown that sequence A (-115 to -85) is needed together with Pit-1 binding sites for full cyclic AMP response of hPRL-CAT. Mutation of this sequence strongly affects TRH and EGF induction. On the other hand, three copies of sequence A confer both TRH and EGF response to a linked neutral promoter. In conclusion, although TRH and EGF activate mostly different intracellular pathways, they mediate transcriptional induction of the hPRL promoter via identical cis elements.

La néo-ovogenèse dans l’ovaire des vertébrés : une vision expérimentale et évolutive

L’arret de l’ovogenese pendant la vie fœtale ou autour de la naissance chez les mammiferes est un dogme de la biologie de la reproduction chez les mammiferes, dogme qui a ete ebranle par l’equipe de Jonathan Tilly en 2004 et 2005, qui a suggere qu’il existait une neo-ovogenese ovarienne chez la souris adulte. Cette neo-ovogenese aurait pour origine des cellules souches presentes dans l’epithelium de surface ou dans la moelle osseuse. Ces travaux, qui souffrent de nombreuses erreurs d’interpretation histologique, n’ont jamais pu etre repetes. Depuis, il a ete conclu que chez la souris, et par extension chez les mammiferes, il n’y a pas de neo-ovogenese ovarienne chez les adultes. A la suite de ces publications, des travaux recents ont montre qu’in vitro, des cellules souches somatiques, dans des conditions de culture particulieres, peuvent se transformer en cellules ressemblant a des ovocytes, qui expriment des marqueurs ovocytaires, meme si ces derniers sont incapables d’ovuler, d’etre fecondes et d’assurer un developpement embryonnaire. En revanche, un groupe a recemment reussi a faire proliferer des cellules germinales souches pendant plusieurs semaines in vitro, cellules qui se sont revelees capables de recoloniser un ovaire adulte, de donner des ovocytes fecondables puis des nouveau-nes. On peut donc reproduire une neo-ovogenese in vitro, mais pas in vivo, chez les mammiferes adultes. D’un point de vue evolutif, cette neo-ovogenese ovarienne existe chez les poissons et les amphibiens, ce qui permet d’assurer la ponte d’un grand nombre d’ovocytes a chaque saison sexuelle (jusqu’a plusieurs milliers ou millions d’œufs chez certaines especes). Au cours de l’evolution des vertebres terrestres, en particulier des mammiferes, cette fonction a ete perdue. En conclusion, ces resultats recents nourrissent l’espoir de pouvoir maitriser un jour une forme de neo-ovogenese in vitro, et donc de restaurer la fertilite des femmes souffrant de troubles graves de la fecondite.