Cloning and characterization of a novel bicoid-related homeobox transcription factor gene, RIEG, involved in Rieger syndrome

Genetic Mapping of the Absence of Third Molars in EL Mice to Chromosome 3

We noted the absence of all 4 third molars (M3) in Epilepsy-Like disorder (EL) mice, an animal model for the study of epilepsy. This study was conducted to identify the major candidate chromosome and to detect the region that included the candidate gene causing the absence of M3 in EL mice. Linkage analysis was performed on genetic crosses of EL mice and MSM ( Mus musculus molossinus) strain mice, which had a normal complement of teeth. Genome-wide screening by individual genotyping of F2intercross mice identified mouse chromosome 3 as one of the candidate chromosomes. Based on high linkage scores in detailed genotyping of F2intercross and N2backcross mice, the candidate locus for the absence of M3 in EL mice was mapped on the middle of chromosome 3.

Current Perspectives in Cardiac Laterality

The heart is the first organ to break symmetry in the developing embryo and onset of dextral looping is the first indication of this event. Looping is a complex process that progresses concomitantly to cardiac chamber differentiation and ultimately leads to the alignment of the cardiac regions in their final topology. Generation of cardiac asymmetry is crucial to ensuring proper form and consequent functionality of the heart, and therefore it is a highly regulated process. It has long been known that molecular left/right signals originate far before morphological asymmetry and therefore can direct it. The use of several animal models has led to the characterization of a complex regulatory network, which invariably converges on the Tgf-β signaling molecule Nodal and its downstream target, the homeobox transcription factor Pitx2. Here, we review current data on the cellular and molecular bases of cardiac looping and laterality, and discuss the contribution of Nodal and Pitx2 to these processes. A special emphasis will be given to the morphogenetic role of Pitx2 and to its modulation of transcriptional and functional properties, which have also linked laterality to atrial fibrillation.

Expression of CXCL6 and BBS5 that may be glaucoma relevant genes is regulated by PITX2

The transcription factor PITX2 is implicated in glaucoma pathology. In an earlier study we had used microarray analysis to identify genes in the trabecular meshwork (TM) that are affected by knock down of PITX2. Here, those studies were pursued to identify genes that are direct targets of PITX2 and that may be relevant to glaucoma. Initially, bioinformatics tools were used to select among the genes that had been affected by PITX2 knock down those that have PITX2 binding sites and that may be involved in glaucoma related functions. Subsequently, the effect of PITX2 was tested using the dual luciferase assay in four cell cultures including two primary TM cultures co-transfected with vectors containing promoter fragments of six candidate genes upstream of a luciferase gene and a vector that expressed PITX2. Finally, the effect of PITX2 on endogenous expression of two genes was assessed by over expression and knock down of PITX2 in TM cells. Thirty four genes were found to contain PITX2 binding sites in their putative promoter regions, and 16 were found to be associated with TM-specific and/or glaucoma associated functions. Results of dual luciferase assays confirmed that two of six genes tested were directly targeted by PITX2. The two genes were CXCL6 (chemokine (C-X-C motif) ligand 6) and BBS5 (Bardet-Biedl syndrome 5). Over expression and knock down of PITX2 showed that this transcription factor affects endogenous expression of these two genes in TM cells. CXCL6 encodes a pro-inflammatory cytokine, and many studies have suggested that cytokines and other immune system functions are involved in glaucoma pathogenesis. BBS5 is a member of the BBS family of genes that affect ciliary functions, and ciliary bodies in the anterior chamber of the eye produce the aqueous fluid that affects intraocular pressure. Immune related functions and intraocular pressure are both important components of glaucoma pathology. The role of PITX2 in glaucoma may be mediated partly by regulating the expression of CXCL6 and BBS5 and thus affecting immune functions and intraocular pressure.

Novel PITX2 gene mutations in patients with Axenfeld-Rieger syndrome

PURPOSE

Mutations in the bicoid-like transcription factor PITX2 gene often result in Axenfeld-Rieger syndrome (ARS), an autosomal-dominant inherited disorder. We report here the discovery and characterization of novel PITX2 deletions in a small kindred with ARS.

METHODS

Two familial patients (father and son) from a consanguineous family were examined in the present study. Patient DNA samples were screened for PITX2 mutations by DNA sequencing and for copy number variation by SYBR Green quantitative polymerase chain reaction (PCR) analysis.

RESULTS

We report a novel deletion involving the coding region of PITX2 in both patients. The minimum size of the deletion is 1 421 914 bp that spans one upstream regulatory element (CE4), PITX2 and a minimum of 13 neighbouring genes. The maximum size of the deletion is 3 789 983 bp. The proband (son) additionally possesses a novel 2-bp deletion in a non-coding exon of the remaining PITX2 allele predicted to alter correct splicing.

CONCLUSION

Our findings implicate a novel deletion of the PITX2 gene in the pathogenesis of ARS in the affected family. This ARS family presented with an atypical and extremely severe phenotype that resulted in four miscarriages and the death at 10 months of age of a sib of the proband. As the phenotypic manifestations in the proband are more severe than that of the father, we hypothesize that the deletion of the entire PITX2 allele plus a novel 2-bp deletion (observed in the proband) within the remaining PITX2 allele together contributed to the atypical ARS presentation in this family. This is the first study reporting on bi-allelic changes of PITX2 potentially contributing to a more severe ARS phenotype.

DNA Methylation of PITX2 and PANCR Is Prognostic for Overall Survival in Patients with Resected Adenocarcinomas of the Biliary Tract

Biliary tract cancers (BTC) are rare but highly aggressive malignant epithelial tumors. In order to improve the outcome in this lethal disease, novel biomarkers for diagnosis, prognosis, and therapy response prediction are urgently needed. DNA promoter methylation of PITX2 variants (PITX2ab, PITX2c) and intragenic methylation of the PITX2 adjacent non-coding RNA (PANCR) were investigated by methylations-specific qPCR assays in formalin-fixed paraffin-embedded tissue from 80 patients after resection for BTC. Results were correlated with clinicopathologic data and outcome. PITX2 variants and PANCR showed significant hypermethylation in tumor vs. normal adjacent tissue (p < 0.001 and p = 0.015), respectively. In survival analysis, dichotomized DNA methylation of variant PITX2c and PANCR were significantly associated with overall survival (OS). Patients with high tumor methylation levels of PITX2c had a shorter OS compared to patients with low methylation (12 vs. 40 months OS; HR 2.48 [1.38-4.48], p = 0.002). In contrast, PANCR hypermethylation was associated with prolonged survival (25 vs. 19 months OS; HR 0.54 [0.30-0.94], p = 0.015) and qualified as an independent prognostic factor on multivariate analysis. The biomarkers investigated in this study may help to identify BTC subpopulations at risk for worse survival. Further studies are needed to evaluate if PITX2 might be a clinically useful biomarker for an optimized and individualized treatment.

Methylation in promoter regions of PITX2 and RASSF1A genes in association with clinicopathological features in breast cancer patients

Breast cancer is a heterogeneous disease with very different responses to therapy and different length of survival. In many cases, however, the determination of the stage and histopathological characteristics of breast cancer is insufficient to predict prognosis and response to treatment for the vast heterogeneity of the disease. To understand the molecular signature of subtypes of breast cancer, we attempted to identify the methylation status of key tumour suppressor gene Ras association (RalGDS/AF-6) domain family member 1 isoform a (RASSF1A) and a member of the paired-like homeodomain transcription factor family which functions in left-right asymmetry development (PITX2) and to correlate results with known clinicopathological features of breast cancer. Formalin-fixed, paraffin-embedded (FFPE) tissues of breast carcinomas (n = 149) were used for DNA extraction. DNA was modified by bisulphite conversion. Detection of the methylation level of the genes mentioned above was performed by methylation-sensitive high-resolution melting assay (MS-HRM). Based on MS-HRM results for RASSF1A and PITX2, we subdivided the samples into four groups according to methylation level (≤50 % methylated, >50 % methylated, 100 % methylated and completely unmethylated alleles). All degrees of methylation status for both genes underwent analysis of dependence with known clinicopathological features, and we found significant associations. In 134 of 149 (89.9 %) primary breast carcinomas, the RASSF1A promoter was methylated. Total hypermethylation of PITX2 was observed in 60 of 135 (44.4 %) breast cancer cases. RASSF1A hypermethylation had significant association with increased age (p < 0.05), tumour grade (p < 0.0001) and stage (p < 0.0001) in the 100 % methylated group. There was significant association of PITX2 hypermethylation with tumour grade (p < 0.0001) and stage (p < 0.0001). Association between the methylation level of both investigated genes and tumour type was significant for ductal invasive carcinoma cases only (p < 0.0001). This study shows different levels of heterogeneous methylation acquired by MS-HRM assay of the promoter region of RASSF1A and PITX2 and its relationship with clinicopathological features of 149 breast cancer patients. We noticed that immunohistopathological subtypes of breast cancer contain distinct promoter methylation patterns. All these data suggest that hypermethylation of the CpG island promoters of RASSF1A and PITX2 might play an essential role in the very early stages of breast cancer pathogenesis.

Genetic Basis of Nonsyndromic and Syndromic Tooth Agenesis

Human dentition development is a long and complex process which involves a series of reciprocal and sequential interactions between the embryonic stomodeal epithelium and the underlying neural crest-derived mesenchyme. Despite environment disturbances, tooth development is predominantly genetically controlled. To date, more than 200 genes have been identified in tooth development. These genes implied in various signaling pathways such as the bone morphogenetic protein, fibroblast growth factor, sonic hedgehog homolog, ectodysplasin A, wingless-type MMTV integration site family (Wnt), and transform growth factor pathways. Mutations in any of these strictly balanced signaling cascades may cause arrested odontogenesis and/or other dental defects. This article aims to review current knowledge about the genetic mechanisms responsible for selective nonsyndromic tooth agenesis in humans and to present a detailed summary of syndromes with hypodontia as regular features and their causative genes.

Heterozygous Pitx2 Null Mice Accurately Recapitulate the Ocular Features of Axenfeld-Rieger Syndrome and Congenital Glaucoma

Purpose

The purpose of this analysis was to assess the utility of Pitx2+/- mice as a model for the ocular features of Axenfeld-Rieger Syndrome and for congenital glaucoma.

Methods

Eyes of Pitx2+/- and wild-type littermates were examined clinically using optical coherence tomography (OCT) and fundus photography. Intraocular pressures were measured using a TonoLab rebound tonometer. Eyes were examined histologically to assess PITX2 expression, structural integrity, and optic nerve and ganglion cell content.

Results

PITX2 is present postnatally in the corneal endothelium and stroma, iris stroma, trabecular meshwork, and Schlemm's canal. Reduced central corneal thickness, iris defects, and iridicorneal adhesions are all prevalent in Pitx2+/- eyes. Although optic nerve heads appear normal at postnatal day 7, IOP is elevated and optic nerve head cupping is fully penetrant in Pitx2+/- eyes by 3 weeks of age. Neurodegeneration is present in a significant percentage of optic nerves from Pitx2+/- mice by 3 weeks of age, and is fully penetrant by 2 months of age. Pitx2+/- eyes show significant reductions in specifically ganglion cell density in all four quadrants by 2 months of age.

Conclusions

Pitx2+/- mice model the major ocular features of Axenfeld-Rieger Syndrome and will be an important resource for understanding the molecular mechanisms leading to anterior segment dysgenesis and a high prevalence of glaucoma in this disease. In addition, these mice may provide an efficient new model for assessing the molecular events in glaucoma more generally, and for developing and testing new treatment paradigms for this disease.

Mouse Models of Gonadotrope Development

The pituitary gonadotrope is central to reproductive function. Gonadotropes develop in a systematic process dependent on signaling factors secreted from surrounding tissues and those produced within the pituitary gland itself. These signaling pathways are important for stimulating specific transcription factors that ultimately regulate the expression of genes and define gonadotrope identity. Proper gonadotrope development and ultimately gonadotrope function are essential for normal sexual maturation and fertility. Understanding the mechanisms governing differentiation programs of gonadotropes is important to improve treatment and molecular diagnoses for patients with gonadotrope abnormalities. Much of what is known about gonadotrope development has been elucidated from mouse models in which important factors contributing to gonadotrope development and function have been deleted, ectopically expressed, or modified. This chapter will focus on many of these mouse models and their contribution to our current understanding of gonadotrope development.

A Track Record on SHOX: From Basic Research to Complex Models and Therapy

SHOX deficiency is the most frequent genetic growth disorder associated with isolated and syndromic forms of short stature. Caused by mutations in the homeobox gene SHOX, its varied clinical manifestations include isolated short stature, Léri-Weill dyschondrosteosis, and Langer mesomelic dysplasia. In addition, SHOX deficiency contributes to the skeletal features in Turner syndrome. Causative SHOX mutations have allowed downstream pathology to be linked to defined molecular lesions. Expression levels of SHOX are tightly regulated, and almost half of the pathogenic mutations have affected enhancers. Clinical severity of SHOX deficiency varies between genders and ranges from normal stature to profound mesomelic skeletal dysplasia. Treatment options for children with SHOX deficiency are available. Two decades of research support the concept of SHOX as a transcription factor that integrates diverse aspects of bone development, growth plate biology, and apoptosis. Due to its absence in mouse, the animal models of choice have become chicken and zebrafish. These models, therefore, together with micromass cultures and primary cell lines, have been used to address SHOX function. Pathway and network analyses have identified interactors, target genes, and regulators. Here, we summarize recent data and give insight into the critical molecular and cellular functions of SHOX in the etiopathogenesis of short stature and limb development.

Conditional deletion of AP-2β in mouse cranial neural crest results in anterior segment dysgenesis and early-onset glaucoma

Anterior segment dysgenesis (ASD) encompasses a group of developmental disorders in which a closed angle phenotype in the anterior chamber of the eye can occur and 50% of patients develop glaucoma. Many ASDs are thought to involve an inappropriate patterning and migration of the periocular mesenchyme (POM), which is derived from cranial neural crest cells (NCCs) and mesoderm. Although, the mechanism of this disruption is not well understood, a number of transcriptional regulatory molecules have previously been implicated in ASDs. Here, we investigate the function of the transcription factor AP-2β, encoded by Tfap2b, which is expressed in NCCs and their derivatives. Wnt1-Cre-mediated conditional deletion of Tfap2b in NCCs resulted in post-natal ocular defects typified by opacity. Histological data revealed that the conditional AP-2β NCC knockout (KO) mutants exhibited dysgenesis of multiple structures in the anterior segment of the eye including defects in the corneal endothelium, corneal stroma, ciliary body and disruption in the iridocorneal angle with adherence of the iris to the cornea. We further show that this phenotype leads to a significant increase in intraocular pressure and a subsequent loss of retinal ganglion cells and optic nerve degeneration, features indicative of glaucoma. Overall, our findings demonstrate that AP-2β is required in the POM for normal development of the anterior segment of the eye and that the AP-2β NCC KO mice might serve as a new and exciting model of ASD and glaucoma that is fully penetrant and with early post-natal onset.

Summary: Tissue-specific deletion of transcription factor AP-2β in the neural-crest-derived periocular mesenchyme generates a novel model of anterior segment dysgenesis and early onset glaucoma in mice.

Mutations in zebrafish pitx2 model congenital malformations in Axenfeld-Rieger syndrome but do not disrupt left-right placement of visceral organs

Pitx2 is a conserved homeodomain transcription factor that has multiple functions during embryonic development. Mutations in human PITX2 cause autosomal dominant Axenfeld-Rieger syndrome (ARS), characterized by congenital eye and tooth malformations. Pitx2(-/-) knockout mouse models recapitulate aspects of ARS, but are embryonic lethal. To date, ARS treatments remain limited to managing individual symptoms due to an incomplete understanding of PITX2 function. In addition to regulating eye and tooth development, Pitx2 is a target of a conserved Nodal (TGFβ) signaling pathway that mediates left-right (LR) asymmetry of visceral organs. Based on its highly conserved asymmetric expression domain, the Nodal-Pitx2 axis has long been considered a common denominator of LR development in vertebrate embryos. However, functions of Pitx2 during asymmetric organ morphogenesis are not well understood. To gain new insight into Pitx2 function we used genome editing to create mutations in the zebrafish pitx2 gene. Mutations in the pitx2 homeodomain caused phenotypes reminiscent of ARS, including aberrant development of the cornea and anterior chamber of the eye and reduced or absent teeth. Intriguingly, LR asymmetric looping of the heart and gut was normal in pitx2 mutants. These results suggest conserved roles for Pitx2 in eye and tooth development and indicate Pitx2 is not required for asymmetric looping of zebrafish visceral organs. This work establishes zebrafish pitx2 mutants as a new animal model for investigating mechanisms underlying congenital malformations in ARS and high-throughput drug screening for ARS therapeutics. Additionally, pitx2 mutants present a unique opportunity to identify new genes involved in vertebrate LR patterning. We show Nodal signaling-independent of Pitx2-controls asymmetric expression of the fatty acid elongase elovl6 in zebrafish, pointing to a potential novel pathway during LR organogenesis.

Pitx2 promotes heart repair by activating the antioxidant response after cardiac injury

Myocardial infarction results in compromised myocardial function and heart failure owing to insufficient cardiomyocyte self-renewal. Unlike many vertebrates, mammalian hearts have only a transient neonatal renewal capacity. Reactivating primitive reparative ability in the mature mammalian heart requires knowledge of the mechanisms that promote early heart repair. By testing an established Hippo-deficient heart regeneration mouse model for factors that promote renewal, here we show that the expression of Pitx2 is induced in injured, Hippo-deficient ventricles. Pitx2-deficient neonatal mouse hearts failed to repair after apex resection, whereas adult mouse cardiomyocytes with Pitx2 gain-of-function efficiently regenerated after myocardial infarction. Genomic analyses indicated that Pitx2 activated genes encoding electron transport chain components and reactive oxygen species scavengers. A subset of Pitx2 target genes was cooperatively regulated with the Hippo pathway effector Yap. Furthermore, Nrf2, a regulator of the antioxidant response, directly regulated the expression and subcellular localization of Pitx2. Pitx2 mutant myocardium had increased levels of reactive oxygen species, while antioxidant supplementation suppressed the Pitx2 loss-of-function phenotype. These findings reveal a genetic pathway activated by tissue damage that is essential for cardiac repair.

PITX2 loss-of-function mutation contributes to tetralogy of Fallot

Congenital heart disease (CHD) is the most prevalent developmental abnormality in humans and is the most common non-infectious cause of infant morbidity and mortality. Increasing evidence demonstrates that genetic defects are involved in the pathogenesis of CHD. However, CHD is genetically heterogeneous, and the genetic determinants underpinning CHD in most patients remain unknown. In this study, the whole coding region of the PITX2 gene (isoform c) was sequenced in 185 unrelated patients with CHD. The available relatives of a mutation carrier and 300 unrelated healthy individuals used as controls were also genotyped for PITX2. The functional characteristics of the mutation were delineated by using a dual-luciferase reporter assay system. As a result, a novel heterozygous PITX2 mutation, p.Q102L, was identified in a patient with tetralogy of Fallot (TOF). Genetic analysis of the index patient's pedigree showed that the mutation co-segregated with TOF. The mutation was absent in 600 reference chromosomes. Biochemical analysis revealed that the Q102L-mutant PITX2 is associated with significantly reduced transcriptional activity compared with its wild-type counterpart. Furthermore, the mutation markedly decreased the synergistic activation between PITX2 and NKX2-5. This study firstly associates PITX2 loss-of-function mutation with increased susceptibility to TOF, providing novel insight into the molecular mechanism of CHD.

PANCR, the PITX2 Adjacent Noncoding RNA, Is Expressed in Human Left Atria and Regulates PITX2c Expression

BACKGROUND

Genome-wide studies reveal that genetic variants at chromosome 4q25 constitute the strongest locus associated with atrial fibrillation, the most frequent arrhythmia. However, the mechanisms underlying this association are unknown. Our goal is to find and characterize left atrial-expressed transcripts in the chromosome 4q25 atrial fibrillation risk locus that may play a role in atrial fibrillation pathogenesis.

METHODS AND RESULTS

RNA sequencing performed on human left/right pairs identified an intergenic long noncoding RNA adjacent to the PITX2 gene, which we have named PANCR (PITX2 adjacent noncoding RNA). In a human tissue screen, PANCR was expressed specifically in the left atria and eye and in no other chambers of the heart. The levels of PANCR and PITX2c RNAs were highly correlated in 233 human left atrial appendage samples. PANCR levels were not associated with either atrial rhythm status or the genotypes of the chromosome 4q25 atrial fibrillation risk variants. Both PANCR and PITX2c RNAs were induced early during differentiation of human embryonic stem cells into cardiomyocytes. Because long noncoding RNAs often control gene expression, we performed siRNA-mediated knockdown of PANCR, and this treatment repressed PITX2c expression and mimicked the effects of PITX2c knockdown on global mRNA and miRNA expression. Cell fractionation studies demonstrate that PANCR is primarily localized in the cytoplasm.

CONCLUSIONS

PANCR and PITX2c are coordinately expressed early during cardiomyocyte differentiation from stem cells. PANCR knockdown decreased PITX2c expression in differentiated cardiomyocytes, altering the transcriptome in a manner similar to PITX2c knockdown.

Temporal and spatial dynamics of scaling-specific features of a gene regulatory network in Drosophila

A widely appreciated aspect of developmental robustness is pattern formation in proportion to size. But how such scaling features emerge dynamically remains poorly understood. Here we generate a data set of the expression profiles of six gap genes in Drosophila melanogaster embryos that differ significantly in size. Expression patterns exhibit size-dependent dynamics both spatially and temporally. We uncover a dynamic emergence of under-scaling in the posterior, accompanied by reduced expression levels of gap genes near the middle of large embryos. Simulation results show that a size-dependent Bicoid gradient input can lead to reduced Krüppel expression that can have long-range and dynamic effects on gap gene expression in the posterior. Thus, for emergence of scaled patterns, the entire embryo may be viewed as a single unified dynamic system where maternally derived size-dependent information interpreted locally can be propagated in space and time as governed by the dynamics of a gene regulatory network.

How pattern formation is regulated relative to the size of an organism is unclear. Here, Wu et al. take data from gap gene expression in flies of different sizes together with simulations, identifying how scaling emerges dynamically and that local patterning influences global gene regulatory networks.

Whole exome sequencing identifies a heterozygous missense variant in the PRDM5 gene in a family with Axenfeld-Rieger syndrome

Axenfeld–Rieger syndrome (ARS) is a disorder affecting the anterior segment of the eye, often leading to secondary glaucoma and several systemic malformations. It is inherited in an autosomal dominant fashion that has been associated with genetic defects in PITX2 and FOXC1. Known genes CYP1b1, PITX2, and FOXC1 were excluded by Sanger sequencing. The purpose of current study is to identify the underlying genetic causes in ARS family by whole exome sequencing (WES). WES was performed for affected proband of family, and variants were prioritized based on in silico analyses. Segregation analysis of candidate variants was performed in family members. A novel heterozygous PRDM5 missense variant (c.877A>G; p.Lys293Glu) was found to segregate with the disease in an autosomal dominant fashion. The novel missense variant was absent from population-matched controls, the Exome Variant Server, and an in-house exome variant database. The Lys293Glu variant is predicted to be pathogenic and affects a lysine residue that is conserved in different species. Variants in the PRDM5 gene were previously identified in anterior segment defects, i.e., autosomal recessive brittle cornea syndrome and keratoconus. The results of this study suggest that genetic variants in PRDM5 can lead to various syndromic and nonsyndromic disorders affecting the anterior segment of the eye.

Chromatin Architecture of the Pitx2 Locus Requires CTCF- and Pitx2-Dependent Asymmetry that Mirrors Embryonic Gut Laterality

Expression of Pitx2 on the left side of the embryo patterns left-right (LR) organs including the dorsal mesentery (DM), whose asymmetric cell behavior directs gut looping. Despite the importance of organ laterality, chromatin-level regulation of Pitx2 remains undefined. Here, we show that genes immediately neighboring Pitx2 in chicken and mouse, including a long noncoding RNA (Pitx2 locus-asymmetric regulated RNA or Playrr), are expressed on the right side and repressed by Pitx2. CRISPR/Cas9 genome editing of Playrr, 3D fluorescent in situ hybridization (FISH), and variations of chromatin conformation capture (3C) demonstrate that mutual antagonism between Pitx2 and Playrr is coordinated by asymmetric chromatin interactions dependent on Pitx2 and CTCF. We demonstrate that transcriptional and morphological asymmetries driving gut looping are mirrored by chromatin architectural asymmetries at the Pitx2 locus. We propose a model whereby Pitx2 auto-regulation directs chromatin topology to coordinate LR transcription of this locus essential for LR organogenesis.

Paired-like Homeodomain Transcription factor 2 expression by breast cancer bone marrow disseminated tumor cells is associated with early recurrent disease development

The presence of disseminated tumor cells (DTCs) in the bone marrow (BM) of breast cancer patients is prognostic for early relapse. In the present study, we analyzed the gene expression profiles from BM cells of breast cancer patients to identify molecular signatures associated with DTCs and their relevance to metastatic outcome. We analyzed BM from 30 patients with stage II/III breast cancer by gene expression profiling and correlated expression with metastatic disease development. A candidate gene, PITX2, was analyzed for expression and phenotype in breast cancer cell lines. PITX2 was knocked down in the MDAMB231 cell lines for gene expression analysis and cell invasiveness. Expression of various signaling pathway molecules was confirmed by RT-PCR. We found that the expression of Paired-like Homeobox Transcription factor-2 (PITX2) is absent in the BM of normal healthy volunteers and, when detected in the BM of breast cancer patients, is significantly correlated with early metastatic disease development (p = 0.0062). Suppression of PITX2 expression significantly reduced invasiveness in MDAMB231 cells. Three genes-NKD1, LEF1, and DKK4-were significantly downregulated in response to PITX2 suppression. Expression of PITX2 in BM of early-stage breast cancer patients is associated with risk for early disease recurrence. Furthermore, PITX2 likely plays a role in the metastatic process through its effect on the expression of genes associated with the Wnt/beta-Catenin signaling pathway.

Glaucoma Genes and Mechanisms

Genetic studies have yielded important genes contributing to both early-onset and adult-onset forms of glaucoma. The proteins encoded by the current collection of glaucoma genes participate in a broad range of cellular processes and biological systems. Approximately half the glaucoma-related genes function in the extracellular matrix, however proteins involved in cytokine signaling, lipid metabolism, membrane biology, regulation of cell division, autophagy, and ocular development also contribute to the disease pathogenesis. While the function of these proteins in health and disease are not completely understood, recent studies are providing insight into underlying disease mechanisms, a critical step toward the development of gene-based therapies. In this review, genes known to cause early-onset glaucoma or contribute to adult-onset glaucoma are organized according to the cell processes or biological systems that are impacted by the function of the disease-related protein product.

Distinct developmental genetic mechanisms underlie convergently evolved tooth gain in sticklebacks

Teeth are a classic model system of organogenesis, as repeated and reciprocal epithelial and mesenchymal interactions pattern placode formation and outgrowth. Less is known about the developmental and genetic bases of tooth formation and replacement in polyphyodonts, which are vertebrates with continual tooth replacement. Here, we leverage natural variation in the threespine stickleback fish Gasterosteus aculeatus to investigate the genetic basis of tooth development and replacement. We find that two derived freshwater stickleback populations have both convergently evolved more ventral pharyngeal teeth through heritable genetic changes. In both populations, evolved tooth gain manifests late in development. Using pulse-chase vital dye labeling to mark newly forming teeth in adult fish, we find that both high-toothed freshwater populations have accelerated tooth replacement rates relative to low-toothed ancestral marine fish. Despite the similar evolved phenotype of more teeth and an accelerated adult replacement rate, the timing of tooth number divergence and the spatial patterns of newly formed adult teeth are different in the two populations, suggesting distinct developmental mechanisms. Using genome-wide linkage mapping in marine-freshwater F2 genetic crosses, we find that the genetic basis of evolved tooth gain in the two freshwater populations is largely distinct. Together, our results support a model whereby increased tooth number and an accelerated tooth replacement rate have evolved convergently in two independently derived freshwater stickleback populations using largely distinct developmental and genetic mechanisms.

Neural crest derivatives in ocular development: discerning the eye of the storm

Neural crest cells (NCCs) are vertebrate-specific transient, multipotent, migratory stem cells that play a crucial role in many aspects of embryonic development. These cells emerge from the dorsal neural tube and subsequently migrate to different regions of the body, contributing to the formation of diverse cell lineages and structures, including much of the peripheral nervous system, craniofacial skeleton, smooth muscle, skin pigmentation, and multiple ocular and periocular structures. Indeed, abnormalities in neural crest development cause craniofacial defects and ocular anomalies, such as Axenfeld-Rieger syndrome and primary congenital glaucoma. Thus, understanding the molecular regulation of neural crest development is important to enhance our knowledge of the basis for congenital eye diseases, reflecting the contributions of these progenitors to multiple cell lineages. Particularly, understanding the underpinnings of neural crest formation will help to discern the complexities of eye development, as these NCCs are involved in every aspect of this process. In this review, we summarize the role of ocular NCCs in eye development, particularly focusing on congenital eye diseases associated with anterior segment defects and the interplay between three prominent molecules, PITX2, CYP1B1, and retinoic acid, which act in concert to specify a population of neural crest-derived mesenchymal progenitors for migration and differentiation, to give rise to distinct anterior segment tissues. We also describe recent findings implicating this stem cell population in ocular coloboma formation, and introduce recent evidence suggesting the involvement of NCCs in optic fissure closure and vascular development.

PITX2 Loss-of-Function Mutation Contributes to Congenital Endocardial Cushion Defect and Axenfeld-Rieger Syndrome

Congenital heart disease (CHD), the most common type of birth defect, is still the leading non-infectious cause of infant morbidity and mortality in humans. Aggregating evidence demonstrates that genetic defects are involved in the pathogenesis of CHD. However, CHD is genetically heterogeneous and the genetic components underpinning CHD in an overwhelming majority of patients remain unclear. In the present study, the coding exons and flanking introns of the PITX2 gene, which encodes a paired-like homeodomain transcription factor 2essential for cardiovascular morphogenesis as well as maxillary facial development, was sequenced in 196 unrelated patients with CHD and subsequently in the mutation carrier's family members available. As a result, a novel heterozygous PITX2 mutation, p.Q102X for PITX2a, or p.Q148X for PITX2b, or p.Q155X for PITX2c, was identified in a family with endocardial cushion defect (ECD) and Axenfeld-Rieger syndrome (ARS). Genetic analysis of the pedigree showed that the nonsense mutation co-segregated with ECD and ARS transmitted in an autosomal dominant pattern with complete penetrance. The mutation was absent in 800 control chromosomes from an ethnically matched population. Functional analysis by using a dual-luciferase reporter assay system revealed that the mutant PITX2 had no transcriptional activity and that the mutation eliminated synergistic transcriptional activation between PITX2 and NKX2.5, another transcription factor pivotal for cardiogenesis. To our knowledge, this is the first report on the association of PITX2 loss-of-function mutation with increased susceptibility to ECD and ARS. The findings provide novel insight into the molecular mechanisms underpinning ECD and ARS, suggesting the potential implications for the antenatal prophylaxis and personalized treatment of CHD and ARS.

Identification of the GTPase-activating protein DEP domain containing 1B (DEPDC1B) as a transcriptional target of Pitx2

Pitx2 is a bicoid-related homeobox transcription factor implicated in regulating left-right patterning and organogenesis. However, only a limited number of Pitx2 downstream target genes have been identified and characterized. Here we demonstrate that Pitx2 is a transcriptional repressor of DEP domain containing 1B (DEPDC1B). The first intron of the human and mouse DEP domain containing 1B genes contains multiple consensus DNA-binding sites for Pitx2. Chromatin immunoprecipitation assays revealed that Pitx2, along with histone deacetylase 1, was recruited to the first intron of Depdc1b. In contrast, RNAi-mediated depletion of Pitx2 not only enhanced the acetylation of histone H4 in the first intron of Depdc1b, but also increased the protein level of Depdc1b. Luciferase reporter assays also showed that Pitx2 could repress the transcriptional activity mediated by the first intron of human DEPDC1B. The GAP domain of DEPDC1B interacted with nucleotide-bound forms of RAC1 in vitro. In addition, exogenous expression of DEPDC1B suppressed RAC1 activation and interfered with actin polymerization induced by the guanine nucleotide exchange factor TRIO. Moreover, DEPDC1B interacted with various signaling molecules such as U2af2, Erh, and Salm. We propose that Pitx2-mediated repression of Depdc1b expression contributes to the regulation of multiple molecular pathways, such as Rho GTPase signaling.

A comparative examination of odontogenic gene expression in both toothed and toothless amniotes

A well-known tenet of murine tooth development is that BMP4 and FGF8 antagonistically initiate odontogenesis, but whether this tenet is conserved across amniotes is largely unexplored. Moreover, changes in BMP4-signaling have previously been implicated in evolutionary tooth loss in Aves. Here we demonstrate that Bmp4, Msx1, and Msx2 expression is limited proximally in the red-eared slider turtle (Trachemys scripta) mandible at stages equivalent to those at which odontogenesis is initiated in mice, a similar finding to previously reported results in chicks. To address whether the limited domains in the turtle and the chicken indicate an evolutionary molecular parallelism, or whether the domains simply constitute an ancestral phenotype, we assessed gene expression in a toothed reptile (the American alligator, Alligator mississippiensis) and a toothed non-placental mammal (the gray short-tailed opossum, Monodelphis domestica). We demonstrate that the Bmp4 domain is limited proximally in M. domestica and that the Fgf8 domain is limited distally in A. mississippiensis just preceding odontogenesis. Additionally, we show that Msx1 and Msx2 expression patterns in these species differ from those found in mice. Our data suggest that a limited Bmp4 domain does not necessarily correlate with edentulism, and reveal that the initiation of odontogenesis in non-murine amniotes is more complex than previously imagined. Our data also suggest a partially conserved odontogenic program in T. scripta, as indicated by conserved Pitx2, Pax9, and Barx1 expression patterns and by the presence of a Shh-expressing palatal epithelium, which we hypothesize may represent potential dental rudiments based on the Testudinata fossil record.

The interactions of genes, age, and environment in glaucoma pathogenesis

Glaucoma, a progressive degenerative condition that results in the death of retinal ganglion cells, is one of the leading causes of blindness, affecting millions worldwide. The mechanisms underlying glaucoma are not well understood, although years of studies have shown that the largest risk factors are elevated intraocular pressure, age, and genetics. Eleven genes and multiple loci have been identified as contributing factors. These genes act by a number of mechanisms, including mechanical stress, ischemic/oxidative stress, and neurodegeneration. We summarize the recent advances in the understanding of glaucoma and propose a unified hypothesis for glaucoma pathogenesis. Glaucoma does not result from a single pathological mechanism, but rather a combination of pathways that are influenced by genes, age, and environment. In particular, we hypothesize that, in the presence of genetic risk factors, exposure to environment stresses results in an earlier age of onset for glaucoma. This hypothesis is based upon the overlap of the molecular pathways in which glaucoma genes are involved. Because of the interactions between these processes, it is likely that there are common therapies that may be effective for different subtypes of glaucoma.

Axial level-specific regulation of neuronal development: lessons from PITX2

Transcriptional regulation of gene expression is vital for proper control of proliferation, migration, differentiation, and survival of developing neurons. Pitx2 encodes a homeodomain transcription factor that is highly expressed in the developing and adult mammalian brain. In humans, mutations in PITX2 result in Rieger syndrome, characterized by defects in the development of the eyes, umbilicus, and teeth and variable abnormalities in the brain, including hydrocephalus and cerebellar hypoplasia. Alternative splicing of Pitx2 in the mouse results in three isoforms, Pitx2a, Pitx2b, and Pitx2c, each of which is expressed symmetrically along the left-right axis of the brain throughout development. Here, we review recent evidence for axial and brain region-specific requirements for Pitx2 during neuronal migration and differentiation, highlighting known isoform contributions.

TBX1 protein interactions and microRNA-96-5p regulation controls cell proliferation during craniofacial and dental development: implications for 22q11.2 deletion syndrome

T-box transcription factor TBX1 is the major candidate gene for 22q11.2 deletion syndrome (22q11.2DS, DiGeorge syndrome/Velo-cardio-facial syndrome), whose phenotypes include craniofacial malformations such as dental defects and cleft palate. In this study, Tbx1 was conditionally deleted or over-expressed in the oral and dental epithelium to establish its role in odontogenesis and craniofacial developmental. Tbx1 lineage tracing experiments demonstrated a specific region of Tbx1-positive cells in the labial cervical loop (LaCL, stem cell niche). We found that Tbx1 conditional knockout (Tbx1(cKO)) mice featured microdontia, which coincides with decreased stem cell proliferation in the LaCL of Tbx1(cKO) mice. In contrast, Tbx1 over-expression increased dental epithelial progenitor cells in the LaCL. Furthermore, microRNA-96 (miR-96) repressed Tbx1 expression and Tbx1 repressed miR-96 expression, suggesting that miR-96 and Tbx1 work in a regulatory loop to maintain the correct levels of Tbx1. Cleft palate was observed in both conditional knockout and over-expression mice, consistent with the craniofacial/tooth defects associated with TBX1 deletion and the gene duplication that leads to 22q11.2DS. The biochemical analyses of TBX1 human mutations demonstrate functional differences in their transcriptional regulation of miR-96 and co-regulation of PITX2 activity. TBX1 interacts with PITX2 to negatively regulate PITX2 transcriptional activity and the TBX1 N-terminus is required for its repressive activity. Overall, our results indicate that Tbx1 regulates the proliferation of dental progenitor cells and craniofacial development through miR-96-5p and PITX2. Together, these data suggest a new molecular mechanism controlling pathogenesis of dental anomalies in human 22q11.2DS.

Combined pituitary hormone deficiency: current and future status

Over the last two decades, the understanding of the mechanisms involved in pituitary ontogenesis has largely increased. Since the first description of POU1F1 human mutations responsible for a well-defined phenotype without extra-pituitary malformation, several other genetic defects of transcription factors have been reported with variable degrees of phenotype-genotype correlations. However, to date, despite the identification of an increased number of genetic causes of isolated or multiple pituitary deficiencies, the etiology of most (80-90 %) congenital cases of hypopituitarism remains unsolved. Identifying new etiologies is of importance as a post-natal diagnosis to better diagnose and treat the patients (delayed pituitary deficiencies, differential diagnosis of a pituitary mass on MRI, etc.), and as a prenatal diagnosis to decrease the risk of early death (undiagnosed corticotroph deficiency for instance). The aim of this review is to summarize the main etiologies and phenotypes of combined pituitary hormone deficiencies, associated or not with extra-pituitary anomalies, and to suggest how the identification of such etiologies could be improved in the near future.

The homeodomain transcription factor PITX2 is required for specifying correct cell fates and establishing angiogenic privilege in the developing cornea

BACKGROUND

Correct specification of cell lineages and establishing angiogenic privilege within the developing cornea are essential for normal vision but the mechanisms controlling these processes are poorly understood.

RESULTS

We show that the homeodomain transcription factor PItX2 is expressed in mesenchymal cells of the developing and mature cornea and use a temporal gene knockout approach to demonstrate that PITX2 is required for corneal morphogenesis and the specification of cell fates within the surface ectoderm and mesenchymal primordia. PITX2 is also required to establish angiogenic privilege in the developing cornea. Further, the expression of Dkk2 and suppression of canonical Wnt signaling activity levels are key mechanisms by which PITX2 specifies ocular surface ectoderm as cornea. In contrast, specifying the underlying mesenchyme to corneal fates and establishing angiogenic privilege in the cornea are less sensitive to DKK2 activity. Finally, the cellular expression patterns of FOXC2, PITX1, and BARX2 in Pitx2 and Dkk2 mutants suggest that these transcription factors may be involved in specifying cell fate and establishing angiogenic privilege within the corneal mesenchyme. However, they are unlikely to play a role in specifying cell fate within the corneal ectoderm.

CONCLUSIONS

Together, these data provide important insights into the mechanisms regulating cornea development.

A novel PITX2 mutation causing iris hypoplasia

Iris hypoplasia (IH) is rare autosomal dominant disorder characterized by a poorly developed iris stroma and malformations of the eyes and umbilicus. This disorder is caused by mutation of the paired-like homeodomain 2 (PITX2) gene. Here, we describe a novel PITX2 mutation (c.205C>T) in an IH family presenting with very mild eye features but with tooth agenesis as the most obvious clinical feature.

Redox regulation by Pitx2 and Pitx3 is critical for fetal myogenesis

During development, major metabolic changes occur as cells become more specialized within a lineage. In the case of skeletal muscle, differentiation is accompanied by a switch from a glycolytic proliferative progenitor state to an oxidative postmitotic differentiated state. Such changes require extensive mitochondrial biogenesis leading to increased reactive oxygen species (ROS) production that needs to be balanced by an antioxidant system. Our analysis of double conditional Pitx2/3 mouse mutants, both in vivo during fetal myogenesis and ex vivo in primary muscle cell cultures, reveals excessive upregulation of ROS levels leading to DNA damage and apoptosis of differentiating cells. This is a consequence of downregulation of Nrf1 and genes for antioxidant enzymes, direct targets of Pitx2/3, leading to decreased expression of antioxidant enzymes, as well as impairment of mitochondrial function. Our analysis identifies Pitx2 and Pitx3 as key regulators of the intracellular redox state preventing DNA damage as cells undergo differentiation.

Novel PITX2c loss-of-function mutations associated with complex congenital heart disease

Congenital heart disease (CHD) is the most common form of birth defect in humans and is the leading non-infectious cause of infant mortality. Emerging evidence strongly suggests that genetic risk factors play an important role in the pathogenesis of CHD. However, CHD is of pronounced genetic heterogeneity, and the genetic defects responsible for CHD in an overwhelming majority of patients remain unclear. In this study, the entire coding region and splice junction sites of the PITX2c gene, which encodes a paired-like homeodomain transcription factor crucial for proper cardiovascular morphogenesis, was sequenced in 170 unrelated neonates with CHD. The available relatives of the mutation carriers and 200 unrelated ethnically matched healthy individuals were genotyped. The disease-causing potential of the PITX2c sequence variations was predicted by MutationTaster and PolyPhen-2. The functional effect of the mutations was characterized using a luciferase reporter assay system. As a result, 2 novel heterozygous PITX2c mutations, p.R91Q and p.T129S, were identified in 2 unrelated newborns with transposition of the great arteries and ventricular septal defect, respectively. A genetic scan of the pedigrees revealed that each mutation co-segregated with CHD transmitted in an autosomal dominant pattern with complete penetrance. The mutations, which altered the amino acids completely conserved evolutionarily, were absent in 400 normal chromosomes and were predicted to be causative. Functional analysis revealed that the PITX2c mutations were both associated with significantly diminished transcriptional activity compared with their wild-type counterpart. This study demonstrates the association between PITX2c loss-of-function mutations and the transposition of the great arteries and ventricular septal defect in humans, providing further insight into the molecular mechanisms responsible for CHD.

Exploratory genotype-phenotype correlations of facial form and asymmetry in unaffected relatives of children with non-syndromic cleft lip and/or palate

Family relatives of children with nonsyndromic cleft lip with or without cleft palate (NSCL/P) who presumably carry a genetic risk yet do not manifest overt oral clefts, often present with distinct facial morphology of unknown genetic etiology. This study investigates distinct facial morphology among unaffected relatives and examines whether candidate genes previously associated with overt NSCL/P and left-right body patterning are correlated with such facial morphology. Cases were unaffected relatives of individuals with NSCL/P (n = 188) and controls (n = 194) were individuals without family history of NSCL/P. Cases and controls were genotyped for 20 SNPs across 13 candidate genes for NSCL/P (PAX7, ABCA4-ARHGAP29, IRF6, MSX1, PITX2, 8q24, FOXE1, TGFB3 and MAFB) and left-right body patterning (LEFTY1, LEFTY2, ISL1 and SNAI1). Facial shape and asymmetry phenotypes were obtained via principal component analyses and Procrustes analysis of variance from 32 coordinate landmarks, digitized on 3D facial images. Case-control comparisons of phenotypes obtained were performed via multivariate regression adjusting for age and gender. Phenotypes that differed significantly (P < 0.05) between cases and controls were regressed on the SNPs one at a time. Cases had significantly (P < 0.05) more profile concavity with upper face retrusion, upturned noses with obtuse nasolabial angles, more protrusive chins, increased lower facial heights, thinner and more retrusive lips and more protrusive foreheads. Furthermore, cases showed significantly more directional asymmetry compared to controls. Several of these phenotypes were significantly associated with genetic variants (P < 0.05). Facial height and width were associated with SNAI1. Midface antero-posterior (AP) projection was associated with LEFTY1. The AP position of the chin was related to SNAI1, IRF6, MSX1 and MAFB. The AP position of the forehead and the width of the mouth were associated with ABCA4-ARHGAP29 and MAFB. Lastly, facial asymmetry was related to LEFTY1, LEFTY2 and SNAI1. This study demonstrates that, genes underlying lip and palate formation and left-right patterning also contribute to facial features characteristic of the NSCL/P spectrum.

Tbx1 is required autonomously for cell survival and fate in the pharyngeal core mesoderm to form the muscles of mastication

Velo-cardio-facial/DiGeorge syndrome, also known as 22q11.2 deletion syndrome, is a congenital anomaly disorder characterized by craniofacial anomalies including velo-pharyngeal insufficiency, facial muscle hypotonia and feeding difficulties, in part due to hypoplasia of the branchiomeric muscles. Inactivation of both alleles of mouse Tbx1, encoding a T-box transcription factor, deleted on chromosome 22q11.2, results in reduction or loss of branchiomeric muscles. To identify downstream pathways, we performed gene profiling of microdissected pharyngeal arch one (PA1) from Tbx1(+/+) and Tbx1(-/-) embryos at stages E9.5 (somites 20-25) and E10.5 (somites 30-35). Basic helix-loop-helix (bHLH) transcription factors were reduced, while secondary heart field genes were increased in expression early and were replaced by an increase in expression of cellular stress response genes later, suggesting a change in gene expression patterns or cell populations. Lineage tracing studies using Mesp1(Cre) and T-Cre drivers showed that core mesoderm cells within PA1 were present at E9.5 but were greatly reduced by E10.5 in Tbx1(-/-) embryos. Using Tbx1(Cre) knock-in mice, we found that cells are lost due to apoptosis, consistent with increase in expression of cellular stress response genes at E10.5. To determine whether Tbx1 is required autonomously in the core mesoderm, we used Mesp1(Cre) and T-Cre mesodermal drivers in combination with inactivate Tbx1 and found reduction or loss of branchiomeric muscles from PA1. These mechanistic studies inform us that Tbx1 is required upstream of key myogenic genes needed for core mesoderm cell survival and fate, between E9.5 and E10.5, resulting in formation of the branchiomeric muscles.

Pitx2c ensures habenular asymmetry by restricting parapineal cell number

Left-right (L/R) asymmetries in the brain are thought to underlie lateralised cognitive functions. Understanding how neuroanatomical asymmetries are established has been achieved through the study of the zebrafish epithalamus. Morphological symmetry in the epithalamus is broken by leftward migration of the parapineal, which is required for the subsequent elaboration of left habenular identity; the habenular nuclei flank the midline and show L/R asymmetries in marker expression and connectivity. The Nodal target pitx2c is expressed in the left epithalamus, but nothing is known about its role during the establishment of asymmetry in the brain. We show that abrogating Pitx2c function leads to the right habenula adopting aspects of left character, and to an increase in parapineal cell numbers. Parapineal ablation in Pitx2c loss of function results in right habenular isomerism, indicating that the parapineal is required for the left character detected in the right habenula in this context. Partial parapineal ablation in the absence of Pitx2c, however, reduces the number of parapineal cells to wild-type levels and restores habenular asymmetry. We provide evidence suggesting that antagonism between Nodal and Pitx2c activities sets an upper limit on parapineal cell numbers. We conclude that restricting parapineal cell number is crucial for the correct elaboration of epithalamic asymmetry.

Pitx2c is reactivated in the failing myocardium and stimulates myf5 expression in cultured cardiomyocytes

BACKGROUND

Pitx2 (paired-like homeodomain 2 transcription factor) is crucial for heart development, but its role in heart failure (HF) remains uncertain. The present study lays the groundwork implicating Pitx2 signalling in different modalities of HF.

METHODOLOGY/PRINCIPAL FINDINGS

A variety of molecular, cell-based, biochemical, and immunochemical assays were used to evaluate: (1) Pitx2c expression in the porcine model of diastolic HF (DHF) and in patients with systolic HF (SHF) due to dilated and ischemic cardiomyopathy, and (2) molecular consequences of Pitx2c expression manipulation in cardiomyocytes in vitro. In pigs, the expression of Pitx2c, physiologically downregulated in the postnatal heart, is significantly re-activated in left ventricular (LV) failing myocardium which, in turn, is associated with increased expression of a restrictive set of Pitx2 target genes. Among these, Myf5 was identified as the top upregulated gene. In vitro, forced expression of Pitx2c in cardiomyocytes, but not in skeletal myoblasts, activates Myf5 in dose-dependent manner. In addition, we demonstrate that the level of Pitx2c is upregulated in the LV-myocardium of SHF patients.

CONCLUSIONS/SIGNIFICANCE

The results provide previously unrecognized evidence that Pitx2c is similarly reactivated in postnatal/adult heart at distinct HF phenotypes and suggest that Pitx2c is involved, directly or indirectly, in the regulation of Myf5 expression in cardiomyocytes.

Ectodermal Wnt signaling regulates abdominal myogenesis during ventral body wall development

Defects of the ventral body wall are prevalent birth anomalies marked by deficiencies in body wall closure, hypoplasia of the abdominal musculature and multiple malformations across a gamut of organs. However, the mechanisms underlying ventral body wall defects remain elusive. Here, we investigated the role of Wnt signaling in ventral body wall development by inactivating Wls or β-catenin in murine abdominal ectoderm. The loss of Wls in the ventral epithelium, which blocks the secretion of Wnt proteins, resulted in dysgenesis of ventral musculature and genito-urinary tract during embryonic development. Molecular analyses revealed that the dermis and myogenic differentiation in the underlying mesenchymal progenitor cells was perturbed by the loss of ectodermal Wls. The activity of the Wnt-Pitx2 axis was impaired in the ventral mesenchyme of the mutant body wall, which partially accounted for the defects in ventral musculature formation. In contrast, epithelial depletion of β-catenin or Wnt5a did not resemble the body wall defects in the ectodermal Wls mutant. These findings indicate that ectodermal Wnt signaling instructs the underlying mesodermal specification and abdominal musculature formation during ventral body wall development, adding evidence to the theory that ectoderm-mesenchyme signaling is a potential unifying mechanism for the origin of ventral body wall defects.

Novel and recurrent PITX3 mutations in Belgian families with autosomal dominant congenital cataract and anterior segment dysgenesis have similar phenotypic and functional characteristics

Background

Congenital cataracts are clinically and genetically heterogeneous with more than 45 known loci and 38 identified genes. They can occur as isolated defects or in association with anterior segment developmental anomalies. One of the disease genes for congenital cataract with or without anterior segment dysgenesis (ASD) is PITX3, encoding a transcription factor with a crucial role in lens and anterior segment development. Only five unique PITX3 mutations have been described, of which the 17-bp duplication c.640_656dup, p.(Gly220Profs*95), is the most common one and the only one known to cause cataract with ASD. The aim of this study was to perform a genetic study of the PITX3 gene in five probands with autosomal dominant congenital cataract (ADCC) and ASD, to compare their clinical presentations to previously reported PITX3-associated phenotypes and to functionally evaluate the PITX3 mutations found.

Methods

Sanger sequencing of the coding region and targeted exons of PITX3 was performed in probands and family members respectively. Transactivation, DNA-binding and subcellular localization assays were performed for the PITX3 mutations found. Ophthalmological examinations included visual acuity measurement, slit-lamp biomicroscopy, tonometry and fundoscopy.

Results

In four Belgian families with ADCC and ASD the recurrent 17-bp duplication c.640_656dup, p.(Gly220Profs*95), was found in a heterozygous state. A novel PITX3 mutation c.573del, p.(Ser192Alafs*117), was identified in heterozygous state in a Belgo-Romanian family with a similar phenotype. Functional assays showed that this novel mutation retains its nuclear localization but results in decreased DNA-binding and transactivation activity, similar to the recurrent duplication.

Conclusions

Our study identified a second PITX3 mutation leading to congenital cataract with ASD. The similarity in phenotypic expression was substantiated by our in vitro functional studies which demonstrated comparable molecular consequences for the novel p.(Ser192Alafs*117) and the recurrent p.(Gly220Profs*95) mutations.

Homeobox transcription factor Pitx2: The rise of an asymmetry gene in cardiogenesis and arrhythmogenesis

The homeobox transcription factor Pitx2 displays a highly specific expression pattern during embryogenesis. Gain and loss of function experiments have unraveled its pivotal role in left-right signaling. Conditional deletion in mice has demonstrated a complex and intricate role for Pitx2 in distinct aspects of cardiac development and more recently a link to atrial fibrillation has been proposed based on genome-wide association studies. In this review we will revise the role of Pitx2 in the developing heart, starting from the early events of left-right determination followed by its role in cardiac morphogenesis and ending with its role in cardiac arrhythmogenesis.

PITX2C loss-of-function mutations responsible for idiopathic atrial fibrillation

OBJECTIVE

This study aimed to identify novel PITX2c mutations responsible for idiopathic atrial fibrillation.

METHODS

A cohort of 210 unrelated patients with idiopathic atrial fibrillation and 200 unrelated, ethnically matched healthy individuals used as controls were recruited. The whole coding exons and splice junctions of the PITX2c gene, which encodes a paired-like homeobox transcription factor required for normal cardiovascular morphogenesis, were sequenced in 210 patients and 200 control subjects. The causative potentials of the identified mutations were automatically predicted by MutationTaster and PolyPhen-2. The functional characteristics of the PITX2c mutations were explored using a dual-luciferase reporter assay system.

RESULTS

Two novel heterozygous PITX2c mutations (p.Q105L and p.R122C) were identified in 2 of the 210 unrelated patients with idiopathic atrial fibrillation. These missense mutations were absent in the 400 control chromosomes and were both predicted to be pathogenic. Multiple alignments of PITX2c protein sequences across various species showed that the altered amino acids were highly evolutionarily conserved. A functional analysis demonstrated that the mutant PITX2c proteins were both associated with significantly reduced transcriptional activity compared with their wild-type counterparts.

CONCLUSION

The findings of this study associate PITX2c loss-of-function mutations with atrial fibrillation, supporting the hypothesis that dysfunctional PITX2c confers enhanced susceptibility to atrial fibrillation and suggesting potential implications for early prophylaxis and allele-specific therapy for this common arrhythmia.

A model for the molecular underpinnings of tooth defects in Axenfeld-Rieger syndrome

Patients with Axenfeld-Rieger Syndrome (ARS) present various dental abnormalities, including hypodontia, and enamel hypoplasia. ARS is genetically associated with mutations in the PITX2 gene, which encodes one of the earliest transcription factors to initiate tooth development. Thus, Pitx2 has long been considered as an upstream regulator of the transcriptional hierarchy in early tooth development. However, because Pitx2 is also a major regulator of later stages of tooth development, especially during amelogenesis, it is unclear how mutant forms cause ARS dental anomalies. In this report, we outline the transcriptional mechanism that is defective in ARS. We demonstrate that during normal tooth development Pitx2 activates Amelogenin (Amel) expression, whose product is required for enamel formation, and that this regulation is perturbed by missense PITX2 mutations found in ARS patients. We further show that Pitx2-mediated Amel activation is controlled by chromatin-associated factor Hmgn2, and that Hmgn2 prevents Pitx2 from efficiently binding to and activating the Amel promoter. Consistent with a physiological significance to this interaction, we show that K14-Hmgn2 transgenic mice display a severe loss of Amel expression on the labial side of the lower incisors, as well as enamel hypoplasia-consistent with the human ARS phenotype. Collectively, these findings define transcriptional mechanisms involved in normal tooth development and shed light on the molecular underpinnings of the enamel defect observed in ARS patients who carry PITX2 mutations. Moreover, our findings validate the etiology of the enamel defect in a novel mouse model of ARS.