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Pituitary development is coordinated by the timely interaction of several signaling pathways and transcription factors. The expression of lhx3 precedes that of transcription factors like tbx19, prop1, gata2 or sf1 and requires earlier expression of others like pitx1 and pitx2 and pathways like sonic hedgehog. The adult pituitary contains SOX2/SOX9 positive pituitary stem cells and progenitors leading to a differentiated pituitary, and in vitro differentiation of embryonic stem cells into mature pituitary cells was shown to recapitulate anterior pituitary development. Conditional inactivation of isl-1 in thyrotrophs induces central hypothyroidism, showing that this LIM domain factor is necessary for thyrotroph function. Large scale genomic techniques identified new pathogenic gene variants in constitutional hypopituitarism, an indirect evidence of their role in pituitary development or function: a variant of GPR161 was identified by whole exome sequencing in GH deficiency; a variant of ARNT2 was associated with constitutional panhypopituitarism, diabetes insipidus and microcephaly. Allelic variations of NFKB2 were associated with pituitary deficiency (mainly ACTH deficiency) and variable immune deficiency (VID), described as DAVID syndrome. IGSF1 alterations were identified in a complex X-linked phenotype with thyrotroph deficiency, macro-orchidism, delayed puberty, transient GH or ACTH deficiency, and low prolactin levels. The first variants of the potassium channel gene KCNQ1 were reported in families with GH deficiency, gingival fibromatosis and arrhythmia. Thanks to new genome wide techniques, more causative genes have been identified over the past 6 years than over the 2 decades following the first identification of the role of pou1f1 in human hypopituitarism. Demonstrating the role of these new genes will require an appropriate cell model that may derive from novel stem cell techniques. Such approaches will help better understand pituitary development and functions.

International audience; In primary cultures of rat pituitary cells and in a pituitary sommatolactotroph cell line (GH4C1), endogenous core-clock- as well as hormone-genes such as prolactin displayed a rhythmic expression pattern, fitted by a sinusoidal equation in which the period value was close to the circadian one. This is consistent with the presence of a functional circadian oscillator in pituitary cells whose importance was ascertained in GH4C1 cell lines stably expressing a dominant negative mutant of BMAL1. In these cells, both endogenous core-clock- and prolactin-genes no more displayed a circadian pattern. Some genes we recently identified as mouse pituitary BMAL1-regulated genes in a DNA-microarray study, lost their circadian pattern in these cells, suggesting that BMAL1 controlled these genes locally in the pituitary. The intra-pituitary circadian oscillator could then play a role in the physiology of the gland that would not be seen anymore as a structure only driven by hypothalamic rhythmic control.

Au cours des deux dernieres decennies, la connaissance des mecanismes regissant l’ontogenese de la glande hypophysaire s’est grandement amelioree. Cependant, notre comprehension des deficits hypophysaire combine multiple (CPHD) d’origine genetique n’a pas suivi la meme evolution. En effet, malgre les avancees technologiques (CGH array, sequencage a haut debit) permettant l’identification de nouvelles mutations chez les patients, nous ne beneficions pas de modele adequat permettant de valider le caractere pathogene des variants alleliques rares identifies. Recemment, en nous inspirant des techniques developpees dans le laboratoire de Y. Sasai pour differencier in vitro des cellules antehypophysaires a partir de cellules souches embryonnaires, nous avons obtenu des cellules somatotropes et corticotropes a partir de cellules souches pluripotentes induites humaines (iPSC). Dans ces cultures tridimensionnelles sous forme d’organoides, nous avons observe une expression sequentielle de genes impliques dans le developpement hypophysaire, similaire a celle observee lors du developpement embryonnaire. Ce nouvel outil devrait s’averer precieux dans l’identification de nouvelles mutations, la validation de leur pathogenicite. Il devrait egalement etre utile pour le criblage pharmacologique, et permettre d’envisager de nouveau traitements bases sur la therapie cellulaire.

International audience; Extracellular regulated kinase (ERK) signalling is believed to play roles in various aspects of circadian clock mechanisms. In this study, we show in rat that the nuclear versus cytoplasmic intracellular distribution of the phosphorylated forms of ERK1/2 (P-ERK1/2) in the central clock, namely the suprachiasmatic nucleus (SCN), is proportionally constant across the light/dark cycle while the spatial distribution and neurochemical phenotype of cells expressing these activated forms are time-regulated according to a daily rhythm and light-regulated. P-ERK1/2 was exclusively found in neuronal elements. At daytime, it was detected throughout the dorsoventral extent of the SCN, partly within neurons synthesizing either arginine-vasopressin or vasoactive intestinal peptide (VIP). At night time, it was segregated in the ventrolateral aspect of the nucleus, within a cluster of cells 45% of which were gastrin-releasing peptide (GRP) neurons with or without co-localization with VIP. After a light pulse at night, expression of P-ERK1/2 increased in GRP neurons but also appeared in a population of neurons that stained for VIP only. These data show that the GRP neurons are closely associated with ERK1/2 activation at night and point to the importance of ERK1/2 signalling not only in intra-SCN transmission of photic information but also in maintenance of neuronal rhythms in the SCN.

La rythmicite circadienne de l’activite de l’adenohypophyse est une composante essentielle de la physiologie de la glande parce que toutes les hormones qu’elle secrete presentent un profil rythmique, pulsatile et/ou circadien. Dans le domaine des rythmes circadiens, il apparait aujourd’hui que les regulations s’exercant au niveau post-transcriptionnel jouent un role preponderant. Dans l’adenohypophyse, nous avons identifie un mecanisme post-transcriptionnel original a la base de la rythmicite d’expression de certains ARNm. Ce mecanisme repose sur la retention nucleaire rythmique d’ARNm par des structures appelees paraspeckles dont l’element structurant est un long ARN non-codant, Neat1 (Nuclear-Enriched-Abundant-Transcript1) egalement connu sous le nom de Men1 (multiple-endocrine-neoplasia1). Nous avons montre que, dans les cellules hypophysaires, tous les composants moleculaires de ces paraspeckles, non seulement Neat1 mais aussi les principaux composants proteiques, presentent un profil d’expression circadienne. Du reste, l’expression de Neat1 est egalement rythmique dans d’autres oscillateurs y compris dans l’horloge circadienne centrale, les noyaux suprachiasmatiques de l’hypothalamus. Nous avons montre que certains ARNm qui sont associes aux differents composants des paraspeckles et dont la rythmicite circadienne est controlee au niveau post-transcriptionnel perdent leur expression circadienne en presence de siRNA dirigees contre Neat1 qui entrainent une destruction des paraspeckles. Le role grandissant que l’on attribue aujourd’hui aux longs ARN non-codants dans la pathogenie de nombreuses maladies et la caracterisation d’un role physiologique joue par un long ARN non-codant dans l’adenohypophyse ouvrent de nouvelles perspectives de strategie possible d’identification de candidats moleculaires participant a l’etiologie de pathologies hypophysaires en particulier de deficits hypophysaires chez l’homme.