Function of retinoic acid receptors during embryonic development

Retinoids, the active metabolites of vitamin A, regulate complex gene networks involved in vertebrate morphogenesis, growth, cellular differentiation and homeostasis. Studies performed in vitro, using either acellular systems or transfected cells, have shown that retinoid actions are mediated through heterodimers between the RAR and RXR nuclear receptors. However, in vitro studies indicate what is possible, but not necessarily what is actually occurring in vivo, because they are performed under non-physiological conditions. Therefore, genetic approaches in the animal have been be used to determine the physiological functions of retinoid receptors. Homologous recombination in embryonic stem cells has been used to generate germline null mutations of the RAR- and RXR-coding genes in the mouse. As reviewed here, the generation of such germline mutations, combined with pharmacological approaches to block the RA signalling pathway, has provided genetic evidence that RAR/RXR heterodimers are indeed the functional units transducing the RA signal during prenatal development. However, due to (i) the complexity in “hormonal” signalling through transduction by the multiple RARs and RXRs, (ii) the functional redundancies (possibly artefactually generated by the mutations) within receptor isotypes belonging to a given family, and (iii) in utero or early postnatal lethality of certain germline null mutations, these genetic studies have failed to reveal all the physiological functions of RARs and RXRs, notably in adults. Spatio-temporally-controlled somatic mutations generated in given cell types/tissues and at chosen times during postnatal life, will be required to reveal all the functions of RAR and RXR throughout the lifetime of the mouse

A comparison of the in vitro effects of 2'fucosyllactose and lactose on the composition and activity of gut microbiota from infants and toddlers

Because of the recognized health benefits of breast milk, it is recommended as the sole nutrition source during the first 6 months of life. Among the bioactive components are human milk oligosaccharides (HMOs) that exert part of their activity via the gut microbiota. Here, we investigated the gut microbiota fermentation of HMO 2'fucosyllactose (2'-FL), using two in vitro models (48 h fecal incubations and the long-term mucosal simulator of the human intestinal microbial ecosystem [M-SHIME(R)]) with fecal samples from 3-month-old breastfed (BF) infants as well as 2-3 year old toddlers. The short-term model allowed the screening of five donors for each group and provided supportive data for the M-SHIME(R) study. A key finding was the strong and immediate increase in the relative abundance of Bifidobacteriaceae following 2'-FL fermentation by both the BF infant and toddler microbiota in the M-SHIME(R). At the metabolic level, while decreasing branched-chain fatty acids, 2'-FL strongly increased acetate production together with increases in the health-related propionate and butyrate whilst gas production only mildly increased. Notably, consistently lower gas production was observed with 2'-FL fermentation as compared to lactose, suggesting that reduced discomfort during the dynamic microbiome establishment in early life may be an advantage along with the bifidogenic effect observed

Retinoid receptors and binding proteins

Skip to Next Section Retinoids, in particular all-trans retinoic acid (T-RA), are essential for normal development and homeostasis of vertebrates. Although many effects of retinoids, particularily with regard to teratogenicity, have been described in the literature, the mechanisms by which these simple signalling molecules work has only recently begun to be elucidated. We now recognize at least two classes of retinoid-binding proteins and two families of retinoid receptors. The ultimate interpretation of the retinoid signal within a given cell is probably the result of a complex series of interactions between these proteins, yet little is understood concerning the role each member of this signalling pathway plays. It is therefore imperative to dissect the molecular mechanisms which transduce the effects of these ligands, both in vivo and in isolated systems. One approach we are employing is gene targeting of retinoic acid receptors (RARs) and cellular retinoid-binding proteins to generate mice in which one or more of these genes has been functionally inactivated

Retinoic Acid Drives Aryl Hydrocarbon Receptor Expression and Is Instrumental to Dioxin-Induced Toxicity during Palate Development

Background: Palate development depends on complex events and is very sensitive to disruption. Accordingly, clefts are the most common congenital malformations worldwide, and a connection is proposed with fetal exposure to toxic factors or environmental contaminants, such as dioxins. There is increasing evidence that dioxin interferes with all-trans-retinoic acid (atRA), a hormone-like signal derived from vitamin A, which plays an essential role during embryonic development. Although similarities have been described between dioxin-induced toxicity and the outcome of altered atRA signaling during palate development, their relationship needs to be clarified

Retinoic acid receptor α as a novel contributor to adrenal cortex structure and function through interactions with Wnt and Vegfa signalling

International audiencePrimary aldosteronism (PA) is the most frequent form of secondary arterial hypertension. Mutations in different genes increase aldosterone production in PA, but additional mechanisms may contribute to increased cell proliferation and aldosterone producing adenoma (APA) development. We performed transcriptome analysis in APA and identified retinoic acid receptor alpha (RARα) signaling as a central molecular network involved in nodule formation. To understand how RARα modulates adrenal structure and function, we explored the adrenal phenotype of male and female Rarα knockout mice. inactivation of Rarα in mice led to significant structural disorganization of the adrenal cortex in both sexes, with increased adrenal cortex size in female mice and increased cell proliferation in males. Abnormalities of vessel architecture and extracellular matrix were due to decreased Vegfa expression and modifications in extracellular matrix components. On the molecular level, Rarα inactivation leads to inhibition of non-canonical Wnt signaling, without affecting the canonical Wnt pathway nor PKA signaling. Our study suggests that Rarα contributes to the maintenance of normal adrenal cortex structure and cell proliferation, by modulating Wnt signaling. Dysregulation of this interaction may contribute to abnormal cell proliferation, creating a propitious environment for the emergence of specific driver mutations in PA. Primary aldosteronism (PA) is the most common and curable form of secondary arterial hypertension, with prevalence estimations of up to 10% of cases in referred hypertensive patients, 4% of patients in primary care 1,2 and 20% of patients with resistant hypertension 3,4. Rapid diagnosis and treatment are important to prevent severe cardiovas-cular consequences of long term aldosterone exposure, which are independent of blood pressure levels and are du

Development

Mitosis is controlled by multiple kinases that drive cell cycle progression and prevent chromosome mis-segregation. Aurora kinase B interacts with survivin, borealin and incenp to form the chromosomal passenger complex (CPC), which is involved in the regulation of microtubule-kinetochore attachments and cytokinesis. Whereas genetic ablation of survivin, borealin or incenp results in early lethality at the morula stage, we show here that aurora B is dispensable for CPC function during early cell divisions and aurora B-null embryos are normally implanted. This is due to a crucial function of aurora C during these early embryonic cycles. Expression of aurora C decreases during late blastocyst stages resulting in post-implantation defects in aurora B-null embryos. These defects correlate with abundant prometaphase figures and apoptotic cell death of the aurora B-deficient inner cell mass. Conditional deletion of aurora B in somatic cells that do not express aurora C results in chromosomal misalignment and lack of chromosome segregation. Re-expression of wild-type, but not kinase-dead, aurora C rescues this defect, suggesting functional overlap between these two kinases. Finally, aurora B-null cells partially arrest in the presence of nocodazole, suggesting that this kinase is not essential for the spindle assembly checkpoint

Local retinoic acid signaling directs emergence of the extraocular muscle functional unit

Coordinated development of muscles, tendons, and their attachment sites ensures emergence of functional musculoskeletal units that are adapted to diverse anatomical demands among different species. How these different tissues are patterned and functionally assembled during embryogenesis is poorly understood. Here, we investigated the morphogenesis of extraocular muscles (EOMs), an evolutionary conserved cranial muscle group that is crucial for the coordinated movement of the eyeballs and for visual acuity. By means of lineage analysis, we redefined the cellular origins of periocular connective tissues interacting with the EOMs, which do not arise exclusively from neural crest mesenchyme as previously thought. Using 3D imaging approaches, we established an integrative blueprint for the EOM functional unit. By doing so, we identified a developmental time window in which individual EOMs emerge from a unique muscle anlage and establish insertions in the sclera, which sets these muscles apart from classical muscle-to-bone type of insertions. Further, we demonstrate that the eyeballs are a source of diffusible all-trans retinoic acid (ATRA) that allow their targeting by the EOMs in a temporal and dose-dependent manner. Using genetically modified mice and inhibitor treatments, we find that endogenous local variations in the concentration of retinoids contribute to the establishment of tendon condensations and attachment sites that precede the initiation of muscle patterning. Collectively, our results highlight how global and site-specific programs are deployed for the assembly of muscle functional units with precise definition of muscle shapes and topographical wiring of their tendon attachments

Etude de la structure et de la regulation d'un gene androgeno-dependant specifiquement exprime dans la tete de l'epididyme de souris

SIGLEINIST T 76384 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

Etude fonctionnelle de la voie de signalisation de l'acide rétinoïque au cours de la spermatogenèse

L acide rétinoïque (AR) est requis pour de nombreuses fonctions physiologiques parmi lesquelles la reproduction. Il est synthétisé par des rétinaldéhyde déshydrogénases (RALDH1 à 3) et il active la transcription de gènes cible en se liant à ses récepteurs nucléaires RAR (a,b,g). L objet de mon travail de thèse a été d étudier les fonctions de l AR, produit dans les cellules de Sertoli testiculaire, sur la spermatogenèse de la souris. Ainsi, par l étude de l inactivation des gènes des RALDH spécifiquement dans les cellules de Sertoli murines grâce à la mutagenèse somatique, j ai montré que les cellules de Sertoli dirigent la première différenciation des cellules germinales grâce à leur production d AR qui est ensuite dispensable au bon déroulement de la spermatogenèse. L induction de cette première spermatogenèse est possible par l activation sélective de RAR qui est à la base d une pléiade de voies de signalisation. J ai également confirmé le rôle crucial de la voie de signalisation de l AR dans les cellules de Sertoli pour la spermiation, dernière étape du processus de spermatogenèse, et donc pour la fertilité. Enfin, j ai démontré la nécessité in vivo de la signalisation par l AR pour la méiose, qui contrôle l expression de Stra8, un gène essentiel pour la progression méiotique. Cette régulation se fait de manière cellulaire autonome et requiert la fixation d un RAR sur son élément de réponse localisé dans la région promotrice de Stra8.Retinoic acid (RA) is required for many physiological functions including reproduction. It is synthesized by retinaldehyde dehydrogenases (RALDH1 to 3) and activates transcription of target genes by binding to its nuclear receptors (RAR a,b,g ). The purpose of my thesis was to study the functions of RA produced in testicular Sertoli cells in spermatogenesis in the mouse. Thus, by studying the effects of RALDH selective inactivation in murine Sertoli cells by somatic mutagenesis, I showed that Sertoli cells direct the first differentiation of germ cells through their production of RA, which is then dispensable for the proper conduct of spermatogenesis. Induction of the first spermatogenesis is possible by selective activation of RAR , which is at the basis of several signaling pathways. I also confirmed the crucial role of the RA pathway in Sertoli cells for spermiation, the final stage of spermatogenesis, and therefore fertility. Finally, I demonstrated the need of an in vivo RA signaling for meiosis, which controls the expression of Stra8, a gene essential for meiotic progression. This regulation is done cell-autonomously and requires the binding of a RAR on its response element located in the promoter region of Stra8.STRASBOURG-Bib.electronique 063 (674829902) / SudocSudocFranceF