Interactome Screening Identifies the ER Luminal Chaperone Hsp47 as a Regulator of the Unfolded Protein Response Transducer IRE1α.

Maintenance of endoplasmic reticulum (ER) proteostasis is controlled by a dynamic signaling network known as the unfolded protein response (UPR). IRE1α is a major UPR transducer, determining cell fate under ER stress. We used an interactome screening to unveil several regulators of the UPR, highlighting the ER chaperone Hsp47 as the major hit. Cellular and biochemical analysis indicated that Hsp47 instigates IRE1α signaling through a physical interaction. Hsp47 directly binds to the ER luminal domain of IRE1α with high affinity, displacing the negative regulator BiP from the complex to facilitate IRE1α oligomerization. The regulation of IRE1α signaling by Hsp47 is evolutionarily conserved as validated using fly and mouse models of ER stress. Hsp47 deficiency sensitized cells and animals to experimental ER stress, revealing the significance of Hsp47 to global proteostasis maintenance. We conclude that Hsp47 adjusts IRE1α signaling by fine-tuning the threshold to engage an adaptive UPR.

Selective enrichment of founding reproductive microbiomes allows extensive vertical transmission in a fungus-farming termite.

Mutualistic coevolution can be mediated by vertical transmission of symbionts between host generations. Termites host complex gut bacterial communities with evolutionary histories indicative of mixed-mode transmission. Here, we document that vertical transmission of gut bacterial strains is congruent across parent to offspring colonies in four pedigrees of the fungus-farming termite Macrotermes natalensis. We show that 44% of the offspring colony microbiome, including more than 80 bacterial genera and pedigree-specific strains, are consistently inherited. We go on to demonstrate that this is achieved because colony-founding reproductives are selectively enriched with a set of non-random, environmentally sensitive and termite-specific gut microbes from their colonies of origin. These symbionts transfer to offspring colony workers with high fidelity, after which priority effects appear to influence the composition of the establishing microbiome. Termite reproductives thus secure transmission of complex communities of specific, co-evolved microbes that are critical to their offspring colonies. Extensive yet imperfect inheritance implies that the maturing colony benefits from acquiring environmental microbes to complement combinations of termite, fungus and vertically transmitted microbes; a mode of transmission that is emerging as a prevailing strategy for hosts to assemble complex adaptive microbiomes.

More effective transposon regulation in fertile, long-lived termite queens than in sterile workers.

Transposable elements (TEs) are mobile genetic sequences, which can cause the accumulation of genomic damage in the lifetime of an organism. The regulation of TEs, for instance via the piRNA-pathway, is an important mechanism to protect the integrity of genomes, especially in the germ-line where mutations can be transmitted to offspring. In eusocial insects, soma and germ-line are divided among worker and reproductive castes, so one may expect caste-specific differences in TE regulation to exist. To test this, we compared whole-genome levels of repeat element transcription in the fat body of female workers, kings and five different queen stages of the higher termite, Macrotermes natalensis. In this species, queens can live over 20 years, maintaining near maximum reproductive output, while sterile workers only live weeks. We found a strong, positive correlation between TE expression and the expression of neighbouring genes in all castes. However, we found substantially higher TE activity in workers than in reproductives. Furthermore, TE expression did not increase with age in queens, despite a sevenfold increase in overall gene expression, due to a significant upregulation of the piRNA-pathway in 20-year-old queens. Our results suggest a caste- and age-specific regulation of the piRNA-pathway has evolved in higher termites that is analogous to germ-line-specific activity in solitary organisms. In the fat body of these termite queens, an important metabolic tissue for maintaining their extreme longevity and reproductive output, an efficient regulation of TEs likely protects genome integrity, thus further promoting reproductive fitness even at high age.

AXIN deficiency in human and mouse hepatocytes induces hepatocellular carcinoma in the absence of ß-catenin activation.

BACKGROUND & AIMS: The Wnt/ß-catenin pathway is the most frequently deregulated pathway in hepatocellular carcinoma (HCC). Inactivating mutations of the gene encoding AXIN1, a known negative regulator of the Wnt/ß-catenin signaling pathway, are observed in about 10% of HCCs. Whole-genome studies usually place HCC with AXIN1 mutations and CTNNB1 mutations in the group of tumors with Wnt/ß-catenin activated program. However, it has been shown that HCCs with activating CTNNB1 mutations form a group of HCCs, with a different histology, prognosis and genomic signature to those with inactivating biallelic AXIN1 mutations. We aimed to elucidate the relationship between CTNNB1 mutations, AXIN1 mutations and the activation level of the Wnt/ß-catenin program. METHODS: We evaluated two independent human HCC datasets for the expression of a 23-ß-catenin target genes program. We modeled Axin1 loss of function tumorigenesis in two engineered mouse models and performed gene expression profiling. RESULTS: Based on gene expression, we defined three levels of ß-catenin program activation: strong, weak or no activation. While more than 80% CTNNB1-mutated tumors were found in the strong or in the weak activation program, most of the AXIN1-mutated tumors (>70%) were found in the subgroup with no activation. We validated this result by demonstrating that mice with a hepatocyte specific AXIN1 deletion developed HCC in the absence of ß-catenin induction. We defined a 329-gene signature common in human and mouse AXIN1 mutated HCC that is highly enriched in Notch and YAP oncogenic signatures. CONCLUSIONS: AXIN1-mutated HCCs occur independently of the Wnt/ß-catenin pathway and involve Notch and YAP pathways. These pathways constitute potentially interesting targets for the treatment of HCC caused by AXIN1 mutations. LAY SUMMARY: Liver cancer has a poor prognosis. Defining the molecular pathways involved is important for developing new therapeutic approaches. The Wnt/ß-catenin pathway is the most frequently deregulated pathway in hepatocellular carcinoma (HCC). Mutations of AXIN1, a member of this pathway, represent about 10% of HCC mutations. Using both human HCC collections and engineered mouse models of liver cancers with AXIN1 mutation or deletion, we defined a common signature of liver tumors mutated for AXIN1 and demonstrate that these tumors occur independently of the activation of the Wnt/ß-catenin pathway.

Growth factor receptor binding protein 14 inhibition triggers insulin-induced mouse hepatocyte proliferation and is associated with hepatocellular carcinoma.

Metabolic diseases such as obesity and type 2 diabetes are recognized as independent risk factors for hepatocellular carcinoma (HCC). Hyperinsulinemia, a hallmark of these pathologies, is suspected to be involved in HCC development. The molecular adapter growth factor receptor binding protein 14 (Grb14) is an inhibitor of insulin receptor catalytic activity, highly expressed in the liver. To study its involvement in hepatocyte proliferation, we specifically inhibited its liver expression using a short hairpin RNA strategy in mice. Enhanced insulin signaling upon Grb14 inhibition was accompanied by a transient induction of S-phase entrance by quiescent hepatocytes, indicating that Grb14 is a potent repressor of cell division. The proliferation of Grb14-deficient hepatocytes was cell-autonomous as it was also observed in primary cell cultures. Combined Grb14 down-regulation and insulin signaling blockade using pharmacological approaches as well as genetic mouse models demonstrated that Grb14 inhibition-mediated hepatocyte division involved insulin receptor activation and was mediated by the mechanistic target of rapamycin complex 1-S6K pathway and the transcription factor E2F1. In order to determine a potential dysregulation in GRB14 gene expression in human pathophysiology, a collection of 85 human HCCs was investigated. This revealed a highly significant and frequent decrease in GRB14 expression in hepatic tumors when compared to adjacent nontumoral parenchyma, with 60% of the tumors exhibiting a reduced Grb14 mRNA level. CONCLUSION: Our study establishes Grb14 as a physiological repressor of insulin mitogenic action in the liver and further supports that dysregulation of insulin signaling is associated with HCC. (Hepatology 2017;65:1352-1368).

The orphan nuclear receptor COUP-TFII coordinates hypoxia-independent proangiogenic responses in hepatic stellate cells.

BACKGROUND & AIMS: Hepatic stellate cell (HSC) transdifferentiation into collagen-producing myofibroblasts is a key event in hepatic fibrogenesis, but the transcriptional network that controls the acquisition of the activated phenotype is still poorly understood. In this study, we explored whether the nuclear receptor chicken ovalbumin upstream promoter-transcription factor II (COUP-TFII) is involved in HSC activation and in the multifunctional role of these cells during the response to liver injury. METHODS: COUP-TFII expression was evaluated in normal and cirrhotic livers by immunohistochemistry and Western blot. The role of COUP-TFII in HSC was assessed by gain and loss of function transfection experiments and by generation of mice with COUP-TFII deletion in HSC. Molecular changes were determined by gene expression microarray and RT-qPCR. RESULTS: We showed that COUP-TFII is highly expressed in human fibrotic liver and in mouse models of hepatic injury. COUP-TFII expression rapidly increased upon HSC activation and it was associated with the regulation of genes involved in cell motility, proliferation and angiogenesis. Inactivation of COUP-TFII impairs proliferation and invasiveness in activated HSC and COUP-TFII deletion in mice abrogate HSC activation and angiogenesis. Finally, co-culture experiments with HSC and liver sinusoidal endothelial cells (SEC) showed that COUP-TFII expression in HSC influenced SEC migration and tubulogenesis via a hypoxia-independent and nuclear factor kappaB-dependent mechanism. CONCLUSION: This study elucidates a novel transcriptional pathway in HSC that is involved in the acquisition of the proangiogenic phenotype and regulates the paracrine signals between HSC and SEC during hepatic wound healing. LAY SUMMARY: In this study, we identified an important regulator of HSC pathobiology. We showed that the orphan receptor COUP-TFII is an important player in hepatic neoangiogenesis. COUP-TFII expression in HSC controls the crosstalk between HSC and endothelial cells coordinating vascular remodelling during liver injury. TRANSCRIPT PROFILING: ArrayExpress accession E-MTAB-1795.

Rere controls retinoic acid signalling and somite bilateral symmetry.

One of the most notable features of the vertebrate body plan organization is its bilateral symmetry, evident at the level of vertebrae and skeletal muscles. Here we show that a mutation in Rere (also known as atrophin2) leads to the formation of asymmetrical somites in mouse embryos, similar to embryos deprived of retinoic acid. Furthermore, we also demonstrate that Rere controls retinoic acid signalling, which is required to maintain somite symmetry by interacting with Fgf8 in the left-right signalling pathway. Rere forms a complex with Nr2f2, p300 (also known as Ep300) and a retinoic acid receptor, which is recruited to the retinoic acid regulatory element of retinoic acid targets, such as the Rarb promoter. Furthermore, the knockdown of Nr2f2 and/or Rere decreases retinoic acid signalling, suggesting that this complex is required to promote transcriptional activation of retinoic acid targets. The asymmetrical expression of Nr2f2 in the presomitic mesoderm overlaps with the asymmetry of the retinoic acid signalling response, supporting its implication in the control of somitic symmetry. Misregulation of this mechanism could be involved in symmetry defects of the human spine, such as those observed in patients with scoliosis.

Hypothalamic ventromedial COUP-TFII protects against hypoglycemia-associated autonomic failure.

The nuclear receptor Chicken Ovalbumin Upstream Promoter-Transcription Factor II (COUP-TFII) is an important coordinator of glucose homeostasis through its function in different organs such as the endocrine pancreas, adipose tissue, skeletal muscle, and liver. Recently we have demonstrated that COUP-TFII expression in the hypothalamus is restricted to a subpopulation of neurons expressing the steroidogenic factor 1 transcription factor, known to play a crucial role in glucose homeostasis. To understand the functional significance of COUP-TFII expression in the steroidogenic factor 1 neurons, we generated hypothalamic ventromedial nucleus-specific COUP-TFII KO mice using the cyclization recombination/locus of X-overP1 technology. The heterozygous mutant mice display insulin hypersensitivity and a leaner phenotype associated with increased energy expenditure and similar food intake. These mutant mice also present a defective counterregulation to hypoglycemia with altered glucagon secretion. Moreover, the mutant mice are more likely to develop hypoglycemia-associated autonomic failure in response to recurrent hypoglycemic or glucopenic events. Therefore, COUP-TFII expression levels in the ventromedial nucleus are keys in the ability to resist the onset of hypoglycemia-associated autonomic failure.

The role of chicken ovalbumin upstream promoter transcription factor II in the regulation of hepatic fatty acid oxidation and gluconeogenesis in newborn mice.

Chicken ovalbumin upstream promoter transcription factor II (COUP-TFII) is an orphan nuclear receptor involved in the control of numerous functions in various organs (organogenesis, differentiation, metabolic homeostasis, etc.). The aim of the present work was to characterize the regulation and contribution of COUP-TFII in the control of hepatic fatty acid and glucose metabolisms in newborn mice. Our data show that postnatal increase in COUP-TFII mRNA levels is enhanced by glucagon (via cAMP) and PPARα. To characterize COUP-TFII function in the liver of suckling mice, we used a functional (dominant negative form; COUP-TFII-DN) and a genetic (shRNA) approach. Adenoviral COUP-TFII-DN injection induces a profound hypoglycemia due to the inhibition of gluconeogenesis and fatty acid oxidation secondarily to reduced PEPCK, Gl-6-Pase, CPT I, and mHMG-CoA synthase gene expression. Using the crossover plot technique, we show that gluconeogenesis is inhibited at two different levels: 1) pyruvate carboxylation and 2) trioses phosphate synthesis. This could result from a decreased availability in fatty acid oxidation arising cofactors such as acetyl-CoA and reduced equivalents. Similar results are observed using the shRNA approach. Indeed, when fatty acid oxidation is rescued in response to Wy-14643-induced PPARα target genes (CPT I and mHMG-CoA synthase), blood glucose is normalized in COUP-TFII-DN mice. In conclusion, this work demonstrates that postnatal increase in hepatic COUP-TFII gene expression is involved in the regulation of liver fatty acid oxidation, which in turn sustains an active hepatic gluconeogenesis that is essential to maintain an appropriate blood glucose level required for newborn mice survival.

Complex regulatory role of DNA methylation in caste- and age-specific expression of a termite.

The reproductive castes of eusocial insects are often characterized by extreme lifespans and reproductive output, indicating an absence of the fecundity/longevity trade-off. The role of DNA methylation in the regulation of caste- and age-specific gene expression in eusocial insects is controversial. While some studies find a clear link to caste formation in honeybees and ants, others find no correlation when replication is increased across independent colonies. Although recent studies have identified transcription patterns involved in the maintenance of high reproduction throughout the long lives of queens, the role of DNA methylation in the regulation of these genes is unknown. We carried out a comparative analysis of DNA methylation in the regulation of caste-specific transcription and its importance for the regulation of fertility and longevity in queens of the higher termite Macrotermes natalensis. We found evidence for significant, well-regulated changes in DNA methylation in mature compared to young queens, especially in several genes related to ageing and fecundity in mature queens. We also found a strong link between methylation and caste-specific alternative splicing. This study reveals a complex regulatory role of fat body DNA methylation both in the division of labour in termites, and during the reproductive maturation of queens.

Lifespan prolonging mechanisms and insulin upregulation without fat accumulation in long-lived reproductives of a higher termite.

Kings and queens of eusocial termites can live for decades, while queens sustain a nearly maximal fertility. To investigate the molecular mechanisms underlying their long lifespan, we carried out transcriptomics, lipidomics and metabolomics in Macrotermes natalensis on sterile short-lived workers, long-lived kings and five stages spanning twenty years of adult queen maturation. Reproductives share gene expression differences from workers in agreement with a reduction of several aging-related processes, involving upregulation of DNA damage repair and mitochondrial functions. Anti-oxidant gene expression is downregulated, while peroxidability of membranes in queens decreases. Against expectations, we observed an upregulated gene expression in fat bodies of reproductives of several components of the IIS pathway, including an insulin-like peptide, Ilp9. This pattern does not lead to deleterious fat storage in physogastric queens, while simple sugars dominate in their hemolymph and large amounts of resources are allocated towards oogenesis. Our findings support the notion that all processes causing aging need to be addressed simultaneously in order to prevent it.

Apc tumor suppressor gene is the "zonation-keeper" of mouse liver.

The molecular mechanisms by which liver genes are differentially expressed along a portocentral axis, allowing for metabolic zonation, are poorly understood. We provide here compelling evidence that the Wnt/beta-catenin pathway plays a key role in liver zonation. First, we show the complementary localization of activated beta-catenin in the perivenous area and the negative regulator Apc in periportal hepatocytes. We then analyzed the immediate consequences of either a liver-inducible Apc disruption or a blockade of Wnt signaling after infection with an adenovirus encoding Dkk1, and we show that Wnt/beta-catenin signaling inversely controls the perivenous and periportal genetic programs. Finally, we show that genes involved in the periportal urea cycle and the perivenous glutamine synthesis systems are critical targets of beta-catenin signaling, and that perturbations to ammonia metabolism are likely responsible for the death of mice with liver-targeted Apc loss. From our results, we propose that Apc is the liver "zonation-keeper" gene.

Lkb1 suppresses amino acid-driven gluconeogenesis in the liver.

Excessive glucose production by the liver is a key factor in the hyperglycemia observed in type 2 diabetes mellitus (T2DM). Here, we highlight a novel role of liver kinase B1 (Lkb1) in this regulation. We show that mice with a hepatocyte-specific deletion of Lkb1 have higher levels of hepatic amino acid catabolism, driving gluconeogenesis. This effect is observed during both fasting and the postprandial period, identifying Lkb1 as a critical suppressor of postprandial hepatic gluconeogenesis. Hepatic Lkb1 deletion is associated with major changes in whole-body metabolism, leading to a lower lean body mass and, in the longer term, sarcopenia and cachexia, as a consequence of the diversion of amino acids to liver metabolism at the expense of muscle. Using genetic, proteomic and pharmacological approaches, we identify the aminotransferases and specifically Agxt as effectors of the suppressor function of Lkb1 in amino acid-driven gluconeogenesis.

The adapter protein ZIP binds Grb14 and regulates its inhibitory action on insulin signaling by recruiting protein kinase Czeta.

Grb14 is a member of the Grb7 family of adapters and acts as a negative regulator of insulin-mediated signaling. Here we found that the protein kinase Czeta (PKCzeta) interacting protein, ZIP, interacted with Grb14. Coimmunoprecipitation experiments demonstrated that ZIP bound to both Grb14 and PKCzeta, thereby acting as a link in the assembly of a PKCzeta-ZIP-Grb14 heterotrimeric complex. Mapping studies indicated that ZIP interacted through its ZZ zinc finger domain with the phosphorylated insulin receptor interacting region (PIR) of Grb14. PKCzeta phosphorylated Grb14 under in vitro conditions and in CHO-IR cells as demonstrated by in vivo labeling experiments. Furthermore, Grb14 phosphorylation was increased under insulin stimulation, suggesting that the PKCzeta-ZIP-Grb14 complex is involved in insulin signaling. The PIR of Grb14, which also interacts with the catalytic domain of the insulin receptor (IR) and inhibits its activity, was preferentially phosphorylated by PKCzeta. Interestingly, the phosphorylation of Grb14 by PKCzeta increased its inhibitory effect on IR tyrosine kinase activity in vitro. The role of ZIP and Grb14 in insulin signaling was further investigated in vivo in Xenopus laevis oocytes. In this model, ZIP potentiated the inhibitory action of Grb14 on insulin-induced oocyte maturation. Importantly, this effect required the recruitment of PKCzeta and the phosphorylation of Grb14, providing in vivo evidences for a regulation of Grb14-inhibitory action by ZIP and PKCzeta. Together, these results suggest that Grb14, ZIP, and PKCzeta participate in a new feedback pathway of insulin signaling.

Essential role of chicken ovalbumin upstream promoter-transcription factor II in insulin secretion and insulin sensitivity revealed by conditional gene knockout.

Chicken ovalbumin upstream promoter-transcription factor II (COUP-TFII) has been implicated in the control of blood glucose by its potent effect on expression and signaling of various nuclear receptors. To understand the role of COUP-TFII in glucose homeostasis, conditional COUP-TFII-deficient mice were generated and crossed with mice expressing Cre under the control of rat insulin II gene promoter, resulting in deletion of COUP-TFII in pancreatic beta-cells. Homozygous mutants died before birth for yet undetermined reasons. Heterozygous mice appeared healthy at birth and showed normal growth and fertility. When challenged intraperitoneally, the animals had glucose intolerance associated with reduced glucose-stimulated insulin secretion. Moreover, these heterozygous mice presented a mild increase in fasting and random-fed circulating insulin levels. In accordance, islets isolated from these animals exhibited higher insulin secretion in low glucose conditions and markedly decreased glucose-stimulated insulin secretion. Their pancreata presented normal microscopic architecture and insulin content up to 16 weeks of study. Altered insulin secretion was associated with peripheral insulin resistance in whole animals. It can be concluded that COUP-TFII is a new, important regulator of glucose homeostasis and insulin sensitivity.

The role of the glucose-sensing transcription factor carbohydrate-responsive element-binding protein pathway in termite queen fertility.

Termites are among the few animals that themselves can digest the most abundant organic polymer, cellulose, into glucose. In mice and Drosophila, glucose can activate genes via the transcription factor carbohydrate-responsive element-binding protein (ChREBP) to induce glucose utilization and de novo lipogenesis. Here, we identify a termite orthologue of ChREBP and its downstream lipogenic targets, including acetyl-CoA carboxylase and fatty acid synthase. We show that all of these genes, including ChREBP, are upregulated in mature queens compared with kings, sterile workers and soldiers in eight different termite species. ChREBP is expressed in several tissues, including ovaries and fat bodies, and increases in expression in totipotent workers during their differentiation into neotenic mature queens. We further show that ChREBP is regulated by a carbohydrate diet in termite queens. Suppression of the lipogenic pathway by a pharmacological agent in queens elicits the same behavioural alterations in sterile workers as observed in queenless colonies, supporting that the ChREBP pathway partakes in the biosynthesis of semiochemicals that convey the signal of the presence of a fertile queen. Our results highlight ChREBP as a likely key factor for the regulation and signalling of queen fertility.

Conditional hepatocarcinogenesis in mice expressing SV 40 early sequences.

We closely mimicked the in vivo setting in which sporadic hepatocarcinoma occurs by establishing a transgenic mouse model carrying regulatable SV40 early sequences under the control of the regulatory sequences of the human antithrombin III gene that confer hepatic expression. In this system, floxed dormant oncogenic sequences became functional after excision due to adenoviral expression of Cre recombinase or the stable transgenic expression in liver of a tamoxifen-inducible Cre. Hepatic oncogene expression was switched on by both methods, leading to the development of hepatocellular carcinoma. This model could be useful for investigating the key steps of the preneoplastic process, to identify suitable targets for the testing of new therapies.

Expression of COUP-TFII in metabolic tissues during development.

In mammals, the COUP-TF-family consisting of two structurally related proteins, COUP-TFI and COUP-TFII belongs to the orphan member of the steroid/thyroid hormone receptor superfamily. In an attempt to gain insights into the role of COUP-TFII, we examined developmental expression pattern of the mouse COUP-TFII focusing our studies on endoderm-derived tissues, pancreas and liver in particular. Independent lines of transgenic mice expressing Escherichia coli beta-galactosidase driven by the COUP-TFII promoter were generated. Embryonic expression of the beta-gal protein at day 9 of gestation was detected in the notochord, the ventral neural tube and, interestingly, in the gut endoderm, a site where COUP-TFII has not been detected previously. Between 9.5 and 11.5 dpc, beta-gal expression pattern that was established earlier persisted and sections revealed a staining of the common atrial chamber of the heart. At 15.5 dpc, beta-gal activity was found in all endoderm-derived tissues. We found that COUP-TFII mRNA and protein were present in fetal and adult hepatocytes. Finally, COUP-TFII expression was detected in pancreas, as judged by co-expression of the beta-gal in some of the glucagon and PDX1 positive-cells at 12.5 dpc and co-expression with insulin positive-cells at 15.5 dpc. In adult pancreas, COUP-TFII protein was present in the endocrine islet cells.

COUP-TFII controls mouse pancreatic ß-cell mass through GLP-1-ß-catenin signaling pathways.

BACKGROUND: The control of the functional pancreatic ß-cell mass serves the key homeostatic function of releasing the right amount of insulin to keep blood sugar in the normal range. It is not fully understood though how ß-cell mass is determined. METHODOLOGY/PRINCIPAL FINDINGS: Conditional chicken ovalbumin upstream promoter transcription factor II (COUP-TFII)-deficient mice were generated and crossed with mice expressing Cre under the control of pancreatic duodenal homeobox 1 (pdx1) gene promoter. Ablation of COUP-TFII in pancreas resulted in glucose intolerance. Beta-cell number was reduced at 1 day and 3 weeks postnatal. Together with a reduced number of insulin-containing cells in the ductal epithelium and normal ß-cell proliferation and apoptosis, this suggests decreased ß-cell differentiation in the neonatal period. By testing islets isolated from these mice and cultured ß-cells with loss and gain of COUP-TFII function, we found that COUP-TFII induces the expression of the ß-catenin gene and its target genes such as cyclin D1 and axin 2. Moreover, induction of these genes by glucagon-like peptide 1 (GLP-1) via ß-catenin was impaired in absence of COUP-TFII. The expression of two other target genes of GLP-1 signaling, GLP-1R and PDX-1 was significantly lower in mutant islets compared to control islets, possibly contributing to reduced ß-cell mass. Finally, we demonstrated that COUP-TFII expression was activated by the Wnt signaling-associated transcription factor TCF7L2 (T-cell factor 7-like 2) in human islets and rat ß-cells providing a feedback loop. CONCLUSIONS/SIGNIFICANCE: Our findings show that COUP-TFII is a novel component of the GLP-1 signaling cascade that increases ß-cell number during the neonatal period. COUP-TFII is required for GLP-1 activation of the ß-catenin-dependent pathway and its expression is under the control of TCF7L2.