The Pitx2c N-terminal domain is a critical interaction domain required for asymmetric morphogenesis

Dynamics and recognition of homeodomain containing protein-DNA complex of IRX4

Iroquois Homeobox 4 (IRX4) belongs to a family of homeobox TFs having roles in embryogenesis, cell specification, and organ development. Recently, large scale genome-wide association studies and epigenetic studies have highlighted the role of IRX4 and its associated variants in prostate cancer. No studies have investigated and characterized the structural aspect of the IRX4 homeodomain and its potential to bind to DNA. The current study uses sequence analysis, homology modeling, and molecular dynamics simulations to explore IRX4 homeodomain-DNA recognition mechanisms and the role of somatic mutations affecting these interactions. Using publicly available databases, gene expression of IRX4 was found in different tissues, including prostate, heart, skin, vagina, and the protein expression was found in cancer cell lines (HCT166, HEK293), B cells, ascitic fluid, and brain. Sequence conservation of the homeodomain shed light on the importance of N- and C-terminal residues involved in DNA binding. The specificity of IRX4 homodimer bound to consensus human DNA sequence was confirmed by molecular dynamics simulations, representing the role of conserved amino acids including R145, A194, N195, S190, R198, and R199 in binding to DNA. Additional N-terminal residues like T144 and G143 were also found to have specific interactions highlighting the importance of N-terminus of the homeodomain in DNA recognition. Additionally, the effects of somatic mutations, including the conserved Arginine (R145, R198, and R199) residues on DNA binding elucidated the importance of these residues in stabilizing the protein-DNA complex. Secondary structure and hydrogen bonding analysis showed the roles of specific residues (R145, T191, A194, N195, R198, and R199) in maintaining the homogeneity of the structure and its interaction with DNA. The differences in relative binding free energies of all the mutants shed light on the structural modularity of this protein and the dynamics behind protein-DNA interaction. We also have predicted that the C-terminal sequence of the IRX4 homeodomain could act as a potential cell-penetrating peptide, emphasizing the role these small peptides could play in targeting homeobox TFs.

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.

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.

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.

Prevalence and spectrum of PITX2c mutations associated with congenital heart disease

Congenital heart disease (CHD) is the most common form of birth defect and is the leading noninfectious cause of infant death. A growing body of evidence demonstrates that genetic risk factors are involved in the pathogenesis of CHD. However, CHD is a genetically heterogeneous disease and the genetic defects underlying CHD in an overwhelming majority of patients remain unclear. In this study, the whole coding region and splice junction sites of the PITX2c gene, which encodes variant 3 of paired-like homeodomain transcription factor 2 crucial for normal cardiovascular morphogenesis, were sequenced in 382 unrelated patients with CHD, and 2 novel heterozygous mutations, p.W147X and p.N153D, were identified in 2 unrelated patients with CHD, respectively, including a 1-year-old male patient with double outlet right ventricle in combination with ventricular septal defect and a 4-year-old female patient with ventricular septal defect. The mutations were absent in 400 control chromosomes and were both predicted to be disease-causing by MutationTaster. Multiple alignments of PITX2c proteins across species displayed that the altered amino acids were completely conserved evolutionarily. Functional analysis revealed that the mutated PITX2c proteins were associated with a significantly reduced transactivational activity compared with their wild-type counterpart. These findings provide a novel insight into the molecular mechanisms implicated in CHD, suggesting potential implications for the antenatal prophylaxis and allele-specific treatment of CHD.

A novel PITX2c loss‑of‑function mutation underlies lone atrial fibrillation

Atrial fibrillation (AF) is the most common form of sustained cardiac arrhythmia responsible for substantial morbidity and significantly increased mortality rates. A growing body of evidence documents the important role of genetic defects in the pathogenesis of AF. However, AF is a heterogeneous disease and the genetic determinants for AF in an overwhelming majority of patients remain unknown. In the present study, a cohort of 100 unrelated patients with lone AF and a total of 200 unrelated, ethnically matched healthy individuals used as controls, were recruited. The whole coding exons and splice junctions of the pituitary homeobox 2c (PITX2c) gene, which encodes a paired‑like homeobox transcription factor required for normal cardiovascular morphogenesis, were sequenced in the 100 patients and 200 control subjects. The causative potential of the identified mutation of PITX2c was predicted by MutationTaster and PolyPhen‑2. The functional characteristics of the PITX2c mutation were assayed using a dual‑luciferase reporter assay system. Based on the results, a novel heterozygous PITX2c mutation (p.T97A) was identified in a patient with AF. The missense mutation was absent in the 400 reference chromosomes and was automatically predicted to be disease‑causing. Multiple alignments of PITX2c protein sequences across species revealed that the altered amino acid was completely conserved evolutionarily. Functional analysis demonstrated that the mutant PITX2c protein was associated with significantly decreased transcriptional activity when compared with its wild‑type counterpart. The findings of the present study firstly link the PITX2c loss‑of‑function mutation to lone AF, and provide novel insight into the molecular mechanisms underlying AF, suggesting the potential implications for the early prophylaxis and allele‑specific therapy of this common type of arrhythmia.

PITX2c loss-of-function mutations responsible for congenital atrial septal defects

Congenital heart disease (CHD) is the most common form of developmental anomaly and is the leading non-infectious cause of infant mortality. A growing body of evidence demonstrates that genetic risk factors are involved in the pathogenesis of CHD. However, CHD is a genetically heterogeneous disease and the genetic determinants for CHD in most patients remain unclear. In the present study, the entire coding region and splice junction sites of the PITX2c gene, which encodes a homeobox transcription factor crucial for normal cardiovascular genesis, was sequenced in 150 unrelated patients with various CHDs. The 200 unrelated control individuals were subsequently genotyped. The functional characteristics of the mutations were explored using a dual-luciferase reporter assay system. As a result, two novel heterozygous PITX2c mutations, p.H98Q and p.M119T, were identified in 2 unrelated patients with atrial septal defects, respectively. The variations were absent in 400 control chromosomes and the affected amino acids were completely conserved evolutionarily. The two variants were both predicted to be disease-causing by MutationTaster and PolyPhen-2, and the functional analysis revealed that the PITX2c mutants were consistently associated with significantly reduced transcriptional activity compared with their wild-type counterpart. These findings firstly link PITX2c loss-of-function mutations to atrial septal defects in humans, which provide novel insight into the molecular mechanism responsible for CHD, suggesting potential implications for the early prophylaxis and allele-specific treatment of CHD.

Pleiotropic and isoform-specific functions for Pitx2 in superior colliculus and hypothalamic neuronal development

Transcriptional regulation of gene expression during development is critical for proper neuronal differentiation and migration. Alternative splicing and differential isoform expression have been demonstrated for most mammalian genes, but their specific contributions to gene function are not well understood. In mice, the transcription factor gene Pitx2 is expressed as three different isoforms (PITX2A, PITX2B, and PITX2C) which have unique amino termini and common DNA binding homeodomains and carboxyl termini. The specific roles of these isoforms in neuronal development are not known. Here we report the onset of Pitx2ab and Pitx2c isoform-specific expression by E9.5 in the developing mouse brain. Using isoform-specific Pitx2 deletion mouse strains, we show that collicular neuron migration requires PITX2AB and that collicular GABAergic differentiation and targeting of hypothalamic projections require unique Pitx2 isoform dosage. These results provide insights into Pitx2 dosage and isoform-specific requirements underlying midbrain and hypothalamic development.

A zebrafish model of axenfeld-rieger syndrome reveals that pitx2 regulation by retinoic acid is essential for ocular and craniofacial development

PURPOSE

The homeobox transcription factor PITX2 is a known regulator of mammalian ocular development, and human PITX2 mutations are associated with Axenfeld-Rieger syndrome (ARS). However, the treatment of patients with ARS remains mostly supportive and palliative.

METHODS

The authors used molecular genetic, pharmacologic, and embryologic techniques to study the biology of ARS in a zebrafish model that uses transgenes to mark neural crest and muscle cells in the head.

RESULTS

The authors demonstrated in vivo that pitx2 is a key downstream target of retinoic acid (RA) in craniofacial development, and this pathway is required for coordinating neural crest, mesoderm, and ocular development. pitx2a knockdown using morpholino oligonucleotides disrupts jaw and pharyngeal arch formation and recapitulates ocular characteristics of ARS, including corneal and iris stroma maldevelopment. These phenotypes could be rescued with human PITX2A mRNA, demonstrating the specificity of the knockdown and evolutionary conservation of pitx2a function. Expression of the ARS dominant negative human PITX2A K50E allele also caused ARS-like phenotypes. Similarly, inhibition of RA synthesis in the developing eye (genetic or pharmacologic) disrupted craniofacial and ocular development, and human PITX2A mRNA partially rescued these defects.

CONCLUSIONS

RA regulation of pitx2 is essential for coordinating interactions among neural crest, mesoderm, and developing eye. The marked evolutionary conservation of Pitx2 function in eye and craniofacial development makes zebrafish a potentially powerful model of ARS, amenable to in vivo experimentation and development of potential therapies.

Emerging biomarkers in breast cancer care

Currently, decision-making for breast cancer treatment in the clinical setting is mainly based on clinical data, histomorphological features of the tumor tissue and a few cancer biomarkers such as steroid hormone receptor status (estrogen and progesterone receptors) and oncoprotein HER2 status. Although various therapeutic options were introduced into the clinic in recent decades, with the objective of improving surgery, radiotherapy, biochemotherapy and chemotherapy, varying response of individual patients to certain types of therapy and therapy resistance is still a challenge in breast cancer care. Therefore, since breast cancer treatment should be based on individual features of the patient and her tumor, tailored therapy should be an option by integrating cancer biomarkers to define patients at risk and to reliably predict their course of the disease and/or response to cancer therapy. Recently, candidate-marker approaches and genome-wide transcriptomic and epigenetic screening of different breast cancer tissues and bodily fluids resulted in new promising biomarker panels, allowing breast cancer prognosis, prediction of therapy response and monitoring of therapy efficacy. These biomarkers are now subject of validation in prospective clinical trials.