Role of microRNAs in the pathogenesis of Ewing's sarcoma

SummaryEwing's sarcoma family tumors (ESFT) are the second most frequent cancer of bone in adolescents and young adults. ESFT are characterized by a chromosomal translocation that involves the 5' segment of the EWSR1 gene and the 3' segment of an ets transcription factor family member gene. In 85% of cases the chromosomal translocation generates the fusion protein EWSR1-FLI-1. Recent work from our laboratory identified mesenchymal stem cells (MSC) as the putative cell of origin of ESFT and characterized a CD133+ subpopulation of ESFT cells with tumor initating and self-renewal capacity, known as cancer stem cells (CSC). MicroRNAs (miRNAs) are small non-coding RNA that regulate protein expression at the post-transcriptional level by either repressing translation or destabilizing mRNA. MiRNAs participate in several biological processes including cell proliferation and differentiation. We used miRNA expression profile comparison between MSC and ESFT cell lines and CD133+ ESFT cells and CD133" ESFT cells to investigate the role of miRNAs in ESFT pathogenesis. MiRNA expression profile comparison of MSC and ESFT cell lines identified 35 differentially expressed miRNAs. Among these was down-regulation of let-7a which results, in part, by the direct repression of let-7a-l promoter by EWSR1-FLI-1. Overexpression of let-7a in ESFT cells blocked ESFT tumorigenesis through an High-motility group AT-hook2 (HMGA2)-mediated mechanism.MiRNA profiling of CD133+ ESFT and CD 133" ESFT cells revealed a broad repression of miRNAs in CD133+ ESFT mediated by down-regulation of TARBP2, a central regulator of the miRNA maturation pathway. Down-regulation of TARBP2 in ESFT cell lines results in a miRNA expression profile reminescent of that observed in CD133+ ESFT and associated with increased tumorigenicity. Enhancement of TARBP2 activity using the antibiotic enoxacin or overexpression of miRNA-143 or miRNA-145, two targets of TARBP2, impaired ESFT CSC self-renewal and block ESFT tumorigenicity. Moreover in vivo administration of synthetic let- 7a, miRNA-143 or miRNA-145 blocks ESFT tumor growth.Thus, dysregulation of miRNA expression is a key feature in ESFT pathogenesis and restoration of their expressions might be used as a new therapeutic tool.RésuméLe sarcome d'Ewing est la deuxième tumeur osseuse la plus fréquente chez l'enfant et le jeune adolescent. Le sarcome d'Ewing est caractérisé par une translocation chromosomique qui produit une protéine de fusion EWSR1-FLI-1. Des récents travaux ont identifié les cellules mésenchymateuses souches (MSC) comme étant les cellules à l'origine du sarcome d'Ewing ainsi qu'une sous-population de cellules exprimant le marqueur CD 133, dans le sarcome d'Ewing connu comme les cellules cancéreuses souches (CSC). Ces cellules ont la capacité d'initier la croissance tumorale et possèdent des propriétés d'auto-renouvellement. Les microRNAs (miRNAs) sont de petits ARN qui ne codent pas pour des protéines et qui contrôlent l'expression des protéines en bloquant la traduction ou en dégradant l'ARNm. Les miRNAs participent à différents processus biologiques comme la prolifération et la différenciation cellulaires.Le but de ce travail est d'étudier le rôle des miRNAs dans le sarcome d'Ewing. Un profil d'expression de miRNAs entre les MSC et des lignées cellulaires de sarcome d'Ewing a mis en évidence 35 miRNAs différemment exprimés. Parmi ceux-ci, la répression de let-7a est liée à la répression directe du promoteur de let-7a-l par EWSR-FLI-1. La sur-expression de let-7a dans des lignées cellulaires de sarcome d'Ewing inhibe leur croissance tumorale. Cette inhibition de croissance tumorale est régulée par la protéine high-motility group AT-hook2 (HMGA2).Un profil d'expression de miRNAs entre les cellules du sarcome d'Ewing CD133+ et CD133" montre une sous-expression d'un grand nombre de miRNAs dans les cellules CD133+ par rapport aux cellules CD133". Cette différence d'expression de miRNAs est due à la répression du gène TARBP2 qui participe à la maturation des miRNAs. La suppression de TARBP2 dans des cellules d'Ewing induit un profil d'expression de miRNAs similaire aux cellules CD133+ du sarcome d'Ewing et augmente la tumorigenèse des lignées cellulaires. De plus l'utilisation d'enoxacin, une molécule qui augmente l'activité de TARBP2 ou la sur- expression des miRNA143 ou miRNA-145 dans les CSC du sarcome d'Ewing bloque l'auto- renouvellement des cellules et la croissance tumorale. Finalement, l'administration de let-7a, miRNA-143 ou miRNA-145, dans des souris bloque la croissance du sarcome d'Ewing. Ces résultats indiquent que la dysrégulation des miRNAs participe à la pathogenèse du sarcome d'Ewing et que les miRNAs peuvent être utilisés comme des agents thérapeutiques.

Role of surgery in the management of brain arteriovenous malformations: prospective cohort study.

BACKGROUND AND PURPOSE: Management of brain arteriovenous malformation (bAVM) is controversial. We have analyzed the largest surgical bAVM cohort for outcome. METHODS: Both operated and nonoperated cases were included for analysis. A total of 779 patients with bAVMs were consecutively enrolled between 1989 and 2014. Initial management recommendations were recorded before commencement of treatment. Surgical outcome was prospectively recorded and outcomes assigned at the last follow-up visit using modified Rankin Scale. First, a sensitivity analyses was performed to select a subset of the entire cohort for which the results of surgery could be generalized. Second, from this subset, variables were analyzed for risk of deficit or near miss (intraoperative hemorrhage requiring blood transfusion of ≥2.5 L, hemorrhage in resection bed requiring reoperation, and hemorrhage associated with either digital subtraction angiography or embolization). RESULTS: A total of 7.7% of patients with Spetzler-Ponce classes A and B bAVM had an adverse outcome from surgery leading to a modified Rankin Scale >1. Sensitivity analyses that demonstrated outcome results were not subject to selection bias for Spetzler-Ponce classes A and B bAVMs. Risk factors for adverse outcomes from surgery for these bAVMs include size, presence of deep venous drainage, and eloquent location. Preoperative embolization did not affect the risk of perioperative hemorrhage. CONCLUSIONS: Most of the ruptured and unruptured low and middle-grade bAVMs (Spetzler-Ponce A and B) can be surgically treated with a low risk of permanent morbidity and a high likelihood of preventing future hemorrhage. Our results do not apply to Spetzler-Ponce C bAVMs.

Sex difference and the role of leptin in the association between high-sensitivity C-reactive protein and adiposity in two different populations.

Elevated high-sensitivity C-reactive protein (hs-CRP) concentration is associated with an increased risk of cardiovascular disease but this association seems to be largely mediated via conventional cardiovascular risk factors. In particular, the association between hs-CRP and obesity has been extensively demonstrated and correlations are stronger in women than men. We used fractional polynomials-a method that allows flexible modeling of non linear relations-to investigate the dose/response mathematical relationship between hs-CRP and several indicators of adiposity in Caucasians (Switzerland) and Africans (Seychelles) surveyed in two population-based studies. This relationship was non-linear exhibiting a steeper slope for low levels of hs-CRP and a higher level in women. The observed sex difference in the relationship between hs-CRP and adiposity almost disappeared upon adjustment for leptin, suggesting that these sex differences might be partially mediated, by leptin. All these relationship were similar in Caucasians and Africans. This is the first report on a non-linear relation, stratified by gender, between hs-CRP and adiposity.

Compendium of projects in the European nanosafety cluster

This is the third edition of the compendium. It documents the status of important projects on nanomaterial toxicity and exposure monitoring, integrated risk management, research infrstructure and coordination and support activities. The compendium is not intended to be a guidance document for human health and environmental safety management of nanotechnologies, as such guidance documents already exist and are widely available. Neither is the compendium intended to be a medium for the publication of scientific papers and research results, as this task is covered by scientific conferences and the reviewed press. The compendium aims to bring researchers closer together and show them the potential for synergy in their work. It is a means to establish links and communication between them during the actual research phase and well before the publication of their results. It thus focuses on the communication of projects' strategic aims, extensively covers specific work objectives and the methods used in research, and documents human capacities and available laboratory infrastructure. As such, the compendium supports collaboration on common goals and the joint elaboration of future plans, whilst compromising neither the potential for scientific publication, nor intellectual property rights. [Auteurs]

Accurate performance of a rat model of schizophrenia in the water maze depends on visual cue availability and stability: a distortion in cognitive mapping abilities?

Rats were treated postnatally (PND 5-16) with BSO (l-buthionine-(S,R)-sulfoximine) in an animal model of schizophrenia based on transient glutathione deficit. The BSO treated rats were impaired in patrolling a maze or a homing table when adult, yet demonstrated preserved escape learning, place discrimination and reversal in a water maze task [37]. In the present work, BSO rats' performance in the water maze was assessed in conditions controlling for the available visual cues. First, in a completely curtained environment with two salient controlled cues, BSO rats showed little accuracy compared to control rats. Secondly, pre-trained BSO rats were impaired in reaching the familiar spatial position when curtains partially occluded different portions of the room environment in successive sessions. The apparently preserved place learning in a classical water maze task thus appears to require the stability and the richness of visual landmarks from the surrounding environment. In other words, the accuracy of BSO rats in place and reversal learning is impaired in a minimal cue condition or when the visual panorama changes between trials. However, if the panorama remains rich and stable between trials, BSO rats are equally efficient in reaching a familiar position or in learning a new one. This suggests that the BSO accurate performance in the water maze does not satisfy all the criteria for a cognitive map based navigation on the integration of polymodal cues. It supports the general hypothesis of a binding deficit in BSO rats.

Nicotine-induced release of vasopressin in the conscious rat: role of opioid peptides and hemodynamic effects.

Nicotine has been shown to stimulate the release of vasopressin and to cause significant hemodynamic changes. The mechanisms leading to enhanced vasopressin secretion and the vascular consequences of the high plasma vasopressin levels during nicotine infusion have not yet been determined. Therefore, the purposes of the present study were 1) to examine in normal conscious rats the role of opioid peptides in the nicotine-induced increase in plasma vasopressin levels and 2) to assess the role of vasopressin in the hemodynamic effects of nicotine (20 micrograms/min for 15 min) using a specific V1 antagonist of the vascular actions of vasopressin. Plasma vasopressin levels were significantly increased in the nicotine-treated animals (39.5 +/- 10 vs. 3.7 +/- 0.6 pg/ml in the controls, P less than .01). Pretreatment with naloxone, an antagonist of opioids at their receptors, did not reduce the vasopressin levels (47.7 +/- 9 pg/ml). Nicotine also increased mean blood pressure (122.5 +/- 2.5 to 145.2 +/- 3.3 mm Hg, P less than .01) and decreased heart rate (461 +/- 6 to 386 +/- 14.5 beats/min, P less than .05). Administration of the vasopressin V1 antagonist before the nicotine infusion did not affect the systemic hemodynamics or the regional blood flow distribution, as assessed by radiolabeled microspheres. Thus, these results suggest that the nicotine-induced secretion of vasopressin is not mediated by opioid receptors and that the high plasma vasopressin levels do not exert any significant hemodynamic effect on cardiac output or blood flow distribution.

Efficient gene delivery and selective transduction of astrocytes in the mammalian brain using viral vectors.

Astrocytes are now considered as key players in brain information processing because of their newly discovered roles in synapse formation and plasticity, energy metabolism and blood flow regulation. However, our understanding of astrocyte function is still fragmented compared to other brain cell types. A better appreciation of the biology of astrocytes requires the development of tools to generate animal models in which astrocyte-specific proteins and pathways can be manipulated. In addition, it is becoming increasingly evident that astrocytes are also important players in many neurological disorders. Targeted modulation of protein expression in astrocytes would be critical for the development of new therapeutic strategies. Gene transfer is valuable to target a subpopulation of cells and explore their function in experimental models. In particular, viral-mediated gene transfer provides a rapid, highly flexible and cost-effective, in vivo paradigm to study the impact of genes of interest during central nervous system development or in adult animals. We will review the different strategies that led to the recent development of efficient viral vectors that can be successfully used to selectively transduce astrocytes in the mammalian brain.

The role of Pten in the Hematopoietic System and the Hematopoietic Stem Cells

Résumé Identification, localisation et activation des cellules souches hématopoiétiques dormantes in vivo Les cellules souches somatiques sont présentes dans la majorité des tissus régénératifs comme la peau, l'épithélium intestinal et le système hématopoiétique. A partir d'une seule cellule, elles ont les capacités de produire d'autres cellules souches du même type (auto-renouvellement) et d'engendrer un ensemble défini de cellules progénitrices différenciées qui vont maintenir ou réparer leur tissu hôte. Les cellules souches adultes les mieux caractérisées sont les cellules souches hématopoiétiques (HSC), localisées dans la moelle osseuse. Un des buts de mon travail de doctorat était de caractériser plus en profondeur la localisation des HSCs endogènes in vivo. Pour ce faire, la technique "label retaining assay", se basant sur la division peu fréquentes et sur la dormance des cellules souches, a été utilisée. Après un marquage des souris avec du BrdU (analogue à l'ADN) suivi d'une longue période sans BrdU, les cellules ayant incorporés le marquage ("label retaining cells" LCRs) ont pu être identifiées dans la moelle osseuse. Ces cellules LCRs étaient enrichies 300 fois en cellules de phenotype HSC et, en utilisant de la cytofluorométrie, il a pu être montré qu'environ 15% de toutes les HSCs d'une souris restent dormantes durant plusieures semaines. Ces HSCs dormantes à long terme ne sont probablement pas impliquées dans la maintenance de 'hématopoièse. Par contre, on assiste à l'activation rapide de ces HSCs dormantes lors d'une blessure, comme une ablation myéloide. Elles re-entrent alors en cycle cellulaire et sont essentielles pour une génération rapide des cellules progénitrices et matures qui vont remplacer les cellules perdues. De plus, la détection des LCRs, combinée avec l'utilisation du marqueur de HSCs c-kit, peut être utilisée pour la localisation des HSCs dormantes présentes dans la paroi endostéale de la cavité osseuse. De manière surprenante, les LCRs c-kit+ ont surtout étés trouvées isolées en cellule unique, suggérant que le micro-environement spécifique entourant et maintenant les HSCs, appelé niche, pourrait être très réduit et abriter une seule HSC par niche. Rôles complexes du gène supresseur de tumeur Pten dans le système hématopoiétique La phosphatase PTEN disparaît dans certains cancers héréditaires ou sporadiques humains, comme les gliomes, les cancers de l'utérus ou du sein. Pten inhibe la voie de signalisation de la PI3-kinase et joue un rôle clé dans l'apoptose, la croissance, la prolifération et la migration cellulaire. Notre but était d'étudier le rôle de Pten dans les HSC normale et durant la formation de leucémies. Pour ce faire, nous avons généré un modèle murin dans lequel le gène Pten peut être supprimé dans les cellules hématopoiétiques, incluant les HSCs. Ceci a été possible en croissant l'allèle conditionnelle ptenflox soit avec le transgène MxCre inductible par l'interféron α soit avec le transgène Scl-CreERt inductible par le tamoxifen. Ceci permet la conversion de l'allèle ptenflox en l'allèle nul PtenΔ dans les HSCs et les autres types cellulaires hématopoiétiques. Les souris mutantes Pten développent une splénomégalie massive causée par une expansion dramatiques de toutes les cellules myéloides. De manière interessante, alors que le nombre de HSCs dans la moelle osseuse diminue progressivement, le nombre des HSCs dans la rate augmente de manière proportionnelle. Etrangement, les analyses de cycle cellulaire ont montrés que Pten n'avait que peu ou pas d'effet sur la dormance des HSCs ou sur leur autorenouvellement. En revanche, une augmentation massive du niveau de la cytokine de mobilisation G-CSF a été détéctée dans le serum sanguin, suggérant que la suppression de Pten stimulerait la mobilisation et la migration des HSC de la moelle osseuse vers la rate. Finallement, la transplantation de moelle osseuse délétée en Pten dans des souris immuno-déficientes montre que Pten fonctionnerait comme un suppresseur de tumeur dans le système hématopoiétique car son absence entraîne la formation rapide de leucémies lymphocytaires. Summary Identification, localization and activation of dormant hematopoietic stun cells in vivo Somatic stem cells are present in most self-renewing tissues including the skin, the intestinal epithelium and the hematopoietic system. On a single cell basis they have the capacity to produce more stem cells of the same phenotype (self-renewal) and to give rise to a defined set of mature differentiated progeny, responsible for the maintenance or repair of the host tissue. The best characterized adult stem cell is the hematopoietic stem cell (HSC) located in the bone marrow. One goal of my thesis work was to further characterize the location of endogenous HSCs in vivo. To do this, a technique called "label retaining assay» was used which takes advantage of the fact that stem cells (including HSCs) divide very infrequently and can be dormant for months. After labeling mice with the DNA analogue BrdU followed by a long BrdU free "chase", BrdU "label retaining cells" (CRCs) could be identified in the bone marrow. These CRCs were 300-fold enriched for phenotypic HSCs and by using flow cytometry analysis it could be shown that about 15% of all HSCs in the mouse are dormant for many weeks. Our results suggest that these long-term dormant HSCs are unlikely to be involved in homeostatic maintenance. However they are rapidly activated and reenter the cell cycle in response to injury signals such as myeloid ablation. In addition, detection of LRCs in combination with the HSC marker c-Kit could be used to locate engrafted dormant HSCs close to the endosteal lining of the bone marrow cavities. Most surprisingly, c-Kit+LRCs were found predominantly as single cells suggesting that the specific stem cell maintaining microenvironment, called niche, has limited space and may house only single HSCs. Complex roles of the tumor suppressor gene Pten in the hematopoietic system. The phosphatase PTEN is lost in hereditary and sporadic forms of human cancers, including gliomas, endometrial and breast cancers. Pten inhibits the PI3-kina.se pathway and plays a key role in apoptosis, cell growth, proliferation and migration. Our aim was to study the role of Pten in normal HSCs and during leukemia formation. To do this, we generated a mouse model in which the Pten gene can be deleted in hematopoietic cells including HSCs. This was achieved by crossing the conditional ptenflox allele with either the interferona inducible MxCre or the tamoxifen inducible Scl-CreERT transgene. This allowed the conversion of the ptenflox allele into a pterr' null allele in HSCs and other hematopoietic cell types. As a result Pten mutant mice developed massive splenomegaly due to a dramatic expansion of all myeloid cells. Interestingly, while the number of bone marrow HSCs progressively decreased, the number of HSCs in the spleen increased to a similar extent. Unexpectedly, extensive cell cycle analysis showed that Pten had little or no effect on HSC dormancy or HSC self-renewal. Instead, dramatically increased levels of the mobilizing cytokine G-CSF were detected in the blood serum suggesting that loss-of Pten stimulates mobilization and migration of HSC from the BM to the spleen. Finally, transplantation of Pten deficient BM cells into immuno-compromised mice showed that Pten can function as a tumor suppressor in the hematopoietic system and that its absence leads to the rapid formation of T cell leukemia.

Oxytocin enhances the inhibitory effects of diazepam in the rat central medial amygdala.

Oxytocin is a neuropeptide that can reduce neophobia and improve social affiliation. In vitro, oxytocin induces a massive release of GABA from neurons in the lateral division of the central amygdala which results in inhibition of a subpopulation of peripherally projecting neurons in the medial division of the central amygdala (CeM). Common anxiolytics, such as diazepam, act as allosteric modulators of GABA(A) receptors. Because oxytocin and diazepam act on GABAergic transmission, it is possible that oxytocin can potentiate the inhibitory effects of diazepam if both exert their pre, - respectively postsynaptic effects on the same inhibitory circuit in the central amygdala. We found that in CeM neurons in which diazepam increased the inhibitory postsynaptic current (IPSC) decay time, TGOT (a specific oxytocin receptor agonist) increased IPSC frequency. Combined application of diazepam and TGOT resulted in generation of IPSCs with increased frequency, decay times as well as amplitudes. While individual saturating concentrations of TGOT and diazepam each decreased spontaneous spiking frequency of CeM neurons to similar extent, co-application of the two was still able to cause a significantly larger decrease. These findings show that oxytocin and diazepam act on different components of the same GABAergic circuit in the central amygdala and that oxytocin can facilitate diazepam effects when used in combination. This raises the possibility that neuropeptides could be clinically used in combination with currently used anxiolytic treatments to improve their therapeutic efficacy.

Respiratory symptoms in preterm infants: burden of disease in the first year of life.

OBJECTIVE: While respiratory symptoms in the first year of life are relatively well described for term infants, data for preterm infants are scarce. We aimed to describe the burden of respiratory disease in a group of preterm infants with and without bronchopulmonary dysplasia (BPD) and to assess the association of respiratory symptoms with perinatal, genetic and environmental risk factors. METHODS: Single centre birth cohort study: prospective recording of perinatal risk factors and retrospective assessment of respiratory symptoms during the first year of life by standardised questionnaires. MAIN OUTCOME MEASURES: Cough and wheeze (common symptoms), re-hospitalisation and need for inhalation therapy (severe outcomes). PATIENTS: 126 preterms (median gestational age 28.7 weeks; 78 with, 48 without BPD) hospitalised at the University Children's Hospital of Bern, Switzerland 1999-2006. RESULTS: Cough occurred in 80%, wheeze in 44%, re-hospitalisation in 25% and long term inhalation therapy in wheezers in 13% of the preterm infants. Using logistic regression, the main risk factor for common symptoms was frequent contact with other children. Severe outcomes were associated with maximal peak inspiratory pressure, arterial cord blood pH, APGAR- and CRIB-Score. CONCLUSIONS: Cough in preterm infants is as common as in term infants, whereas wheeze, inhalation therapy and re-hospitalisations occur more often. Severe outcomes are associated with perinatal risk factors. Preterm infants who did not qualify for BPD according to latest guidelines also showed a significant burden of respiratory disease in the first year of life.

Molecular and isotopic characterization of biomarkers in the Frick Swiss Jura sediments: A palaeoenvironmental reconstruction on the northern Tethys margin

Molecular and stable carbon isotope compositions of source-specific hydrocarbons have been used to reconstruct palaeoenvironmental conditions during deposition of the Middle Hettangian to Upper Sinemurian sediments on the northern epicontinental Tethys margin, Frick Swiss Jura. Increasing algal, cyanobacterial and phytoplanktonic (i.e., dinoflagellate) contributions associated with the C-13-enrichment of cyanobacteria derivatives (i.e., hopanes and monomethylalkanes) suggest enhanced primary productivity upsection. This is related to the C-13-enrichment of dissolved CO2 in the upper layers and the progressive increase of depth and oxygenation of the water column. In the Middle Hettangian shallow-water environments (lagoon), the occurrence of green sulfur bacteria (Chlorobiaceae) derivatives indicates that the lower part of the water column was strictly anoxic and rich in H2S. Since these bacteria require very low light intensity to grow, these euxinic conditions may be extended up to the photic zone, allowing for anaerobic photosynthesis. Light penetration depth is most likely reduced by high productivity and/or turbidity in the photic zone. In these sediments, C-13-depleted hopanoids (-39.5 parts per thousand) are most likely associated with phototrophic purple sulfur bacteria utilizing isotopically light organic carbon at the base of the aerobic zone. These purple sulfur bacteria may have consumed the H2S used by Chlorobiaceae in the deeper layers and thus, sustained the algae and cyanobacteria productivity in the upper layers. The C-13-depleted carbonate (-13.3 parts per thousand) may be partially related to the anaerobic oxidation of the organic matter during bacterial sulfate-reduction. (c) 2006 Elsevier Ltd. All rights reserved.

Female- and male-specific signals of quality in the barn owl

Most bird studies of female signalling have been confined to species in which females display a male-ornament in a vestigial form. However, a great deal of benefit may be gained from considering phenotypic traits that are specific to females. This is because (1) sex-specific traits may signal sex-specific qualities and (2) females may develop a male-ornament not because they are selected to do so, but because fathers transmit to daughters the underlying genes for its expression (genetic correlation between the sexes). We investigated these two propositions in the barn owl Tyto alba, a species in which male plumage is lighter in colour and less marked with black spots than that of females. Firstly, we present published evidence that female plumage spottiness reflects parasite resistance ability. We also show that male plumage coloration is correlated with reproductive success, male feeding rate and heart mass. Secondly, cross-fostering experiments demonstrate that plumage coloration and spottiness are genetically correlated between the sexes. This implies that if a given trait value is selected in one sex, the other sex will indirectly evolve towards a similar value. This prediction is supported by the observation that female plumage coloration and spottiness resembled that of males, in comparisons at the level of Tyto alba alba populations, Tyto alba subspecies and Tyto species. Our results therefore support the hypothesis that sex-specific traits signal sex-specific qualities and that a gene for a sex-specific trait can be expressed in the other sex as the consequence of a genetic correlation between the sexes.

Selective disruption of Tcf7l2 in the pancreatic β cell impairs secretory function and lowers β cell mass.

Type 2 diabetes (T2D) is characterized by β cell dysfunction and loss. Single nucleotide polymorphisms in the T-cell factor 7-like 2 (TCF7L2) gene, associated with T2D by genome-wide association studies, lead to impaired β cell function. While deletion of the homologous murine Tcf7l2 gene throughout the developing pancreas leads to impaired glucose tolerance, deletion in the β cell in adult mice reportedly has more modest effects. To inactivate Tcf7l2 highly selectively in β cells from the earliest expression of the Ins1 gene (∼E11.5) we have therefore used a Cre recombinase introduced at the Ins1 locus. Tcfl2(fl/fl)::Ins1Cre mice display impaired oral and intraperitoneal glucose tolerance by 8 and 16 weeks, respectively, and defective responses to the GLP-1 analogue liraglutide at 8 weeks. Tcfl2(fl/fl)::Ins1Cre islets displayed defective glucose- and GLP-1-stimulated insulin secretion and the expression of both the Ins2 (∼20%) and Glp1r (∼40%) genes were significantly reduced. Glucose- and GLP-1-induced intracellular free Ca(2+) increases, and connectivity between individual β cells, were both lowered by Tcf7l2 deletion in islets from mice maintained on a high (60%) fat diet. Finally, analysis by optical projection tomography revealed ∼30% decrease in β cell mass in pancreata from Tcfl2(fl/fl)::Ins1Cre mice. These data demonstrate that Tcf7l2 plays a cell autonomous role in the control of β cell function and mass, serving as an important regulator of gene expression and islet cell coordination. The possible relevance of these findings for the action of TCF7L2 polymorphisms associated with Type 2 diabetes in man is discussed.