Pax3 and Pax7 play essential safeguard functions against environmental stress-induced birth defects

Dynamic enhancer landscapes in human craniofacial development

The genetic basis of human facial variation and craniofacial birth defects remains poorly understood. Distant-acting transcriptional enhancers control the fine-tuned spatiotemporal expression of genes during critical stages of craniofacial development. However, a lack of accurate maps of the genomic locations and cell type-resolved activities of craniofacial enhancers prevents their systematic exploration in human genetics studies. Here, we combine histone modification, chromatin accessibility, and gene expression profiling of human craniofacial development with single-cell analyses of the developing mouse face to define the regulatory landscape of facial development at tissue- and single cell-resolution. We provide temporal activity profiles for 14,000 human developmental craniofacial enhancers. We find that 56% of human craniofacial enhancers share chromatin accessibility in the mouse and we provide cell population- and embryonic stage-resolved predictions of their in vivo activity. Taken together, our data provide an expansive resource for genetic and developmental studies of human craniofacial development.

The presence and distribution of various genes in postnatal CLP-affected palatine tissue

BACKGROUND

Worldwide cleft lip with or without a cleft palate (CL/P) is the most common craniofacial birth defect. Apart from changes in facial appearance, additionally affected individuals often suffer from various associated comorbidities requiring complex multidisciplinary treatment with overall high expenses. Understanding the complete pathogenetic mechanisms of CL/P might aid in developing new preventative strategies and therapeutic approaches, help with genetic counselling, and improve quality of life. Many genes have been associated with the development of orofacial clefts; however, the majority require further research. Based on the role of PAX7, PAX9, SHH, SOX3, WNT3A, and WNT9B in orofacial development, the intention was to use chromogenic in situ hybridization to detect the six genes in postnatal CLP-affected palatine tissue and compare their distribution within the tissue samples.

RESULTS

Statistically significant differences in the distribution of PAX7, PAX9, WNT3A, and WNT9B were observed. In total, 19 pairs of moderate to very strong positive correlations were noted.

CONCLUSIONS

Changes in the cleft-affected palatine epithelium primarily seem to be associated with the PAX7 gene; however, PAX9, WNT3A, WNT9B, and SOX3 role seems to be more limited. Whilst connective tissue changes seem to depend on PAX7 only, SHH seems to participate individually and indistinctly. Numerous positive correlations reflect the complicating interactions of the pathways and their components in the orofacial cleft morphopathogenesis.

TFAP2 paralogs regulate midfacial development in part through a conserved ALX genetic pathway

Cranial neural crest development is governed by positional gene regulatory networks (GRNs). Fine-tuning of the GRN components underlies facial shape variation, yet how those networks in the midface are connected and activated remain poorly understood. Here, we show that concerted inactivation of Tfap2a and Tfap2b in the murine neural crest, even during the late migratory phase, results in a midfacial cleft and skeletal abnormalities. Bulk and single-cell RNA-seq profiling reveal that loss of both TFAP2 family members dysregulates numerous midface GRN components involved in midface morphogenesis, patterning and differentiation. Notably, Alx1, Alx3 and Alx4 (ALX) transcript levels are reduced, whereas ChIP-seq analyses suggest TFAP2 family members directly and positively regulate ALX gene expression. Tfap2a, Tfap2b and ALX co-expression in midfacial neural crest cells of both mouse and zebrafish implies conservation of this regulatory axis across vertebrates. Consistent with this notion, tfap2a zebrafish mutants present with abnormal alx3 expression patterns, Tfap2a binds ALX loci and tfap2a-alx3 genetic interactions are observed. Together, these data demonstrate TFAP2 paralogs regulate vertebrate midfacial development in part by activating expression of ALX transcription factor genes.

Biphenotypic Sinonasal Sarcoma with a Novel PAX7::PPARGC1 Fusion: Expanding the Spectrum of Gene Fusions Beyond the PAX3 Gene

Biphenotypic sinonasal sarcoma (BSNS) is a rare low-grade malignancy occurring in the sinonasal tract that is characterized by dual neural and myogenic differentiation. Rearrangements involving the PAX3 gene, usually with MAML3, are a hallmark of this tumor type and their identification are useful for diagnosis. Rarely, a MAML3 rearrangement without associated PAX3 rearrangement has been described. Other gene fusions have not been previously reported. Herein, we report a 22 year-old woman with a BSNS harboring a novel gene fusion involving the PAX7 gene (specifically PAX7::PPARGC1A), which is a paralogue of PAX3. The histologic features of the tumor were typical with two exceptions: a lack of entrapment of surface respiratory mucosa and no hemangiopericytoma-like vasculature. Immunophenotypically, the tumor was notably negative for smooth muscle actin, which is usually positive in BSNS. However, the classic S100 protein-positive, SOX10-negative staining pattern was present. In addition, the tumor was positive for desmin and MyoD1 but negative for myogenin, a pattern that is common among BSNS with variant fusions. Awareness of the possibility of PAX7 gene fusions in BSNS is important as it may aid in the diagnosis of PAX3 fusion negative tumors.

Cell Type- and Tissue-specific Enhancers in Craniofacial Development

The genetic basis of craniofacial birth defects and general variation in human facial shape remains poorly understood. Distant-acting transcriptional enhancers are a major category of non-coding genome function and have been shown to control the fine-tuned spatiotemporal expression of genes during critical stages of craniofacial development1-3. However, a lack of accurate maps of the genomic location and cell type-specific in vivo activities of all craniofacial enhancers prevents their systematic exploration in human genetics studies. Here, we combined histone modification and chromatin accessibility profiling from different stages of human craniofacial development with single-cell analyses of the developing mouse face to create a comprehensive catalogue of the regulatory landscape of facial development at tissue- and single cell-resolution. In total, we identified approximately 14,000 enhancers across seven developmental stages from weeks 4 through 8 of human embryonic face development. We used transgenic mouse reporter assays to determine the in vivo activity patterns of human face enhancers predicted from these data. Across 16 in vivo validated human enhancers, we observed a rich diversity of craniofacial subregions in which these enhancers are active in vivo. To annotate the cell type specificities of human-mouse conserved enhancers, we performed single-cell RNA-seq and single-nucleus ATAC-seq of mouse craniofacial tissues from embryonic days e11.5 to e15.5. By integrating these data across species, we find that the majority (56%) of human craniofacial enhancers are functionally conserved in mice, providing cell type- and embryonic stage-resolved predictions of their in vivo activity profiles. Using retrospective analysis of known craniofacial enhancers in combination with single cell-resolved transgenic reporter assays, we demonstrate the utility of these data for predicting the in vivo cell type specificity of enhancers. Taken together, our data provide an expansive resource for genetic and developmental studies of human craniofacial development.

TFAP2 paralogs regulate midfacial development in part through a conserved ALX genetic pathway

Cranial neural crest development is governed by positional gene regulatory networks (GRNs). Fine-tuning of the GRN components underly facial shape variation, yet how those in the midface are connected and activated remain poorly understood. Here, we show that concerted inactivation of Tfap2a and Tfap2b in the murine neural crest even during the late migratory phase results in a midfacial cleft and skeletal abnormalities. Bulk and single-cell RNA-seq profiling reveal that loss of both Tfap2 members dysregulated numerous midface GRN components involved in midface fusion, patterning, and differentiation. Notably, Alx1/3/4 (Alx) transcript levels are reduced, while ChIP-seq analyses suggest TFAP2 directly and positively regulates Alx gene expression. TFAP2 and ALX co-expression in midfacial neural crest cells of both mouse and zebrafish further implies conservation of this regulatory axis across vertebrates. Consistent with this notion, tfap2a mutant zebrafish present abnormal alx3 expression patterns, and the two genes display a genetic interaction in this species. Together, these data demonstrate a critical role for TFAP2 in regulating vertebrate midfacial development in part through ALX transcription factor gene expression.

Integrated Analysis of the Association Between Variants at PAX7 and NSCL/P in the Han Population

OBJECTIVE

Paired box 7 (PAX7) has been considered as a candidate gene for non-syndromic cleft lip with or without palate (NSCL/P). However, there is no research for the XXX, and previous studies concentrated on limited variants. This study aimed to conduct sufficiently dense and powerful scans of variants at PAX7 and explored the roles of variants at PAX7 in NSCL/P among the XXX.

DESIGN

Targeted region sequencing was performed to thoroughly screen variations, followed by a two-phase association analysis. 159 NSCL/P cases and 542 controls were analyzed in phase 1. Then in phase 2, the validation study was performed using 1626 cases and 2255 controls. We also explored the roles of variants at PAX7 gene in NSCL/P subtypes. Additionally, indirect associations were found by calculating LD and haplotypes.

SETTING

The study was conducted in XXX.

PATIENTS, PARTICIPANTS

159 NSCL/P cases and 542 controls were analyzed in phase 1. Then in phase 2, the validation study was performed using 1626 cases and 2255 controls.

INTERVENTIONS

Blood samples were collected.

MAIN OUTCOME MEASURES

To explore the association analysis between variants at PAX7 and NSCL/P in XXX.

RESULTS

The results showed that rs2236810, rs114882979 and rs2236804 were significantly associated with NSCL/P, which were predicted to have regulatory functions. Besides, variants at PAX7 function differently in the NSCL/P subtypes. We also discovered a PAX7 missense variant, NM_001135254 p.A369 V (NM_002584.2:c.1106C > T).

CONCLUSIONS

In summary, we confirmed 3 SNPs at PAX7 were significantly associated with NSCL/P in XXX and identified a missense variant, NM_001135254 p.A369 V (NM_002584.2:c.1106C > T).

Maternal Transmission of the PAX7 Single Nucleotide Polymorphisms among Indian Cleft Trios

Cleft lip and/or cleft palate (CL/P) is one of the most common congenital anomalies of the human face with a complex etiology involving multiple genetic and environmental factors. Several studies have shown the association of the paired box 7 ( PAX7 ) gene with CL/P in different populations worldwide. However, the current literature reveals no reported case-parent trio studies to evaluate the association between the PAX7 gene and the risk of nonsyndromic cleft lip and/or palate (NSCL/P) in the Indian population. Hence, the purpose of this study was to assess the PAX7 gene single nucleotide polymorphisms (SNPs) in the etiology of NSCL/P among the Indian cleft trios. Forty Indian case-parent trios of NSCL/P were included. The cases and their parents' genomic DNA were extracted. The SNPs rs9439714, rs1339062, rs6695765, rs742071, and rs618941of the PAX7 gene were genotyped using the Agena Bio MassARRAY analysis. The allelic transmission disequilibrium test was performed using PLINK software while pair-wise linkage disequilibrium by the Haploview program. The SNP rs9439714 showed evidence of association ( p -value = 0.02, odds ratio = 3) with NSCL/P. Considering the parent-of-origin effects, the SNPs rs9439714 and rs618941 showed an excess maternal transmission of allele C at rs9439714 ( p -value = 0.05) and G allele at rs618941 ( p -value = 0.04). The results of the present study suggested that the SNPs rs9439714 and rs618941 showed an excess maternal transmission of alleles suggestive of the possible role of the PAX7 gene involvement in the etiology of NSCL/P in the Indian population.

The regenerative potential of Pax3/Pax7 on skeletal muscle injury

Background

Skeletal muscle mishaps are the most well-known incidents in society, especially among athletes and the military population. From the various urgency, this accident needs to be cured more quickly. However, the current treatment still has some shortcomings and is less effective. In this case, Paired box 3 and Paired box 7 (Pax3/Pax7) proteins that induce stem cells could potentially be an alternative treatment for skeletal muscle injuries. This paper aimed to analyse the potential treatment of Pax3/Pax7 proteins inducing the stem cell for skeletal muscle injuries.

The main body of the abstract

We did a narrative review by gathering several scientific journals from several leading platforms like PubMed and Scopus. As common accidents, skeletal muscle disease could be due to workplace and non-workplace causes. The highest risk occurs in the athlete and military environment. The treatment of current skeletal muscle injuries is protection, rest, ice, compression, and elevation (PRICE), non-steroidal anti-inflammatory drugs (NSAIDs), and mechanical stimulation. However, it is considered less effective, especially in NSAIDs, inhibiting myogenic cell proliferation. The current finding indicates that the stem cells have markers known as Pax3/Pax7. The role of both markers in muscle injury, Pax3/Pax7, as transcription factors will induce cell division by H3K4 methylation mechanisms and chromatin modifications that stimulate gene activation.

Conclusion

Regulation by Pax3/Pax7 factors that affect stem cells and stem cell proliferation is one of the alternative treatments. This regulation can accelerate the healing of injury victims, especially injuries to the skeletal muscles. Finally, after being compared, Pax3/Pax7 induces stem cells to have the potential to be one of the skeletal muscle injury treatments.

Keywords

Pax3 and Pax7, Pax3/Pax7, Skeletal muscle, Athlete, Stem cells, Cell proliferation, Injuries.

Role of PAX7 Gene rs766325 and rs4920520 Polymorphisms in the Etiology of Non-syndromic Cleft Lip and Palate: A Genetic Study

Non-syndromic cleft lip and palate (NSCLP) is one of the most common birth defects in humans with an overall prevalence of ∼1 in 700 live births around the world. The etiology of NSCLP is complex involving multiple genes, environmental factors, and gene-to-gene interactions. Several genome-wide associations (GWA) studies have shown the association of the paired box 7 ( PAX7 ) gene in the etiology of cleft lip and palate in different populations worldwide. However, there are no reported studies on the association between the rs766325 and rs4920520 polymorphisms and the risk of developing NSCLP in the Indian population. Hence, the present study aimed to test for the probable association between rs766325 and rs4920520 polymorphisms among NSCLP Indian population using a case-parent trio design. Forty case-parent trios were selected from the cleft lip and palate center based on the inclusion and exclusion criteria. Genomic DNA was isolated from the cases and their parents. The rs766325 and rs4920520 polymorphisms of the PAX7 gene were analyzed for their association using the MassARRAY analysis. The statistical analysis was done using the PLINK software. The rs766325 and rs4920520 polymorphisms were tested for the Hardy–Weinberg equilibrium. None of the polymorphisms showed any statistical significance. Hence, the rs766325 and rs4920520 polymorphisms of the PAX7 gene were found to be not associated with NSCLP in the Indian case-parent trios.

Single-cell transcriptomic signatures and gene regulatory networks modulated by Wls in mammalian midline facial formation and clefts

Formation of highly unique and complex facial structures is controlled by genetic programs that are responsible for the precise coordination of three-dimensional tissue morphogenesis. However, the underlying mechanisms governing these processes remain poorly understood. We combined mouse genetic and genomic approaches to define the mechanisms underlying normal and defective midfacial morphogenesis. Conditional inactivation of the Wnt secretion protein Wls in Pax3-expressing lineage cells disrupted frontonasal primordial patterning, cell survival and directional outgrowth, resulting in altered facial structures, including midfacial hypoplasia and midline facial clefts. Single-cell RNA sequencing revealed unique transcriptomic atlases of mesenchymal subpopulations in the midfacial primordia, which are disrupted in the conditional Wls mutants. Differentially expressed genes and cis-regulatory sequence analyses uncovered that Wls modulates and integrates a core gene regulatory network, consisting of key midfacial regulatory transcription factors (including Msx1, Pax3 and Pax7) and their downstream targets (including Wnt, Shh, Tgfβ and retinoic acid signaling components), in a mesenchymal subpopulation of the medial nasal prominences that is responsible for midline facial formation and fusion. These results reveal fundamental mechanisms underlying mammalian midfacial morphogenesis and related defects at single-cell resolution.

Pax3 Hypomorphs Reveal Hidden Pax7 Functional Genetic Compensation in Utero

Pax3 and Pax7 transcription factors are paralogs within the Pax gene family that that are expressed in early embryos in partially overlapping expression domains and have distinct functions. Significantly, mammalian development is largely unaffected by Pax7 systemic deletion but systemic Pax3 deletion results in defects in neural tube closure, neural crest emigration, cardiac outflow tract septation, muscle hypoplasia and in utero lethality by E14. However, we previously demonstrated that Pax3 hypomorphs expressing only 20% functional Pax3 protein levels exhibit normal neural tube and heart development, but myogenesis is selectively impaired. To determine why only some Pax3-expressing cell lineages are affected and to further titrate Pax3 threshold levels required for neural tube and heart development, we generated hypomorphs containing both a hypomorphic and a null Pax3 allele. This resulted in mutants only expressing 10% functional Pax3 protein with exacerbated neural tube, neural crest and muscle defects, but still a normal heart. To examine why the cardiac neural crest appears resistant to very low Pax3 levels, we examined its paralog Pax7. Significantly, Pax7 expression is both ectopically expressed in Pax3-expressing dorsal neural tube cells and is also upregulated in the Pax3-expressing lineages. To test whether this compensatory Pax7 expression is functional, we deleted Pax7 both systemically and lineage-specifically in hypomorphs expressing only 10% Pax3. Removal of one Pax7 allele resulted in partial outflow tract defects, and complete loss of Pax7 resulted in full penetrance outflow tract defects and in utero lethality. Moreover, combinatorial loss of Pax3 and Pax7 resulted in severe craniofacial defects and a total block of neural crest cell emigration from the neural tube. Pax7^Cre lineage mapping revealed ectopic labeling of Pax3-derived neural crest tissues and within the outflow tract of the heart, experimentally confirming the observation of ectopic activation of Pax7 in 10% Pax3 hypomorphs. Finally, genetic cell ablation of Pax7^Cre-marked cells is sufficient to cause outflow tract defects in hypomorphs expressing only 10% Pax3, confirming that ectopic and induced Pax7 can play an overlapping functional genetic compensational role in both cardiac neural crest lineage and during craniofacial development, which is normally masked by the dominant role of Pax3.

A Novel PAX3 Variant in a Chinese Pedigree with Nonsyndromic Cleft Lip With or Without Palate

Objectives: Nonsyndromic cleft lip with or without palate (NSCL/P) is a common congenital orofacial defect, which is associated with severe disruption of orofacial development. The present study was designed to identify potential underlying gene variants in a Chinese pedigree with NSCL/P, in which the proband and the proband's father were affected. Methods: DNA was extracted from the participants' peripheral venous blood, and whole-exome sequencing was performed on the proband and the proband's parents. Results: After filtering, a paired box gene 3 (PAX3) missense variant (c.92C>G_p.Thr31Ser) was identified, which was verified by Sanger sequencing. This variant, which was not present in 113 unrelated healthy individuals or in a Chinese public database, may affect the transcription inhibition domain of the PAX3 protein. Conservation analysis and in silico predictions suggested that this variant may be evolutionarily conserved and potentially deleterious. In addition, it was reported that mice with PAX3 variants show cleft palates. Thus, the PAX3 missense variant (c.92C>G_p.Thr31Ser) is a candidate causative variant in this family. Conclusions: To the best of our knowledge, the present study is the first to report on a PAX3 variant in a pedigree with NSCL/P. The present study further suggests that PAX3 may be associated with CL/P etiology.

PAX7, PAX9 and RYK Expression in Cleft Affected Tissue

Background and Objectives: Cleft lip with or without cleft palate is one of the most common types of congenital malformations. Transcription factors paired box 7 and 9 (PAX7, PAX9) and receptor-like tyrosine kinase (RYK) have been previously associated with the formation of orofacial clefts but their exact possible involvement and interactions in the tissue of specific cleft types remains uncertain. There is a limited number of morphological studies analyzing these specific factors in cleft affected tissue due to ethical aspects and the limited amount of available tissue material. This study analyses the presence of PAX7, PAX9, and RYK immunopositive structures within different cleft affected tissue to assess their possible involvement in cleft morphopathogenesis. Materials and Methods: Cleft affected tissue was collected from non-syndromic orofacial cleft patients during cleft correcting surgery (36 patients with unilateral cleft lip, 13 patients with bilateral cleft lip, 26 patients with isolated cleft palate). Control group oral cavity tissue was obtained from 7 patients without cleft lip and palate. To evaluate the number of immunopositive structures in the cleft affected tissue and the control group, a semiquantitative counting method was used. Non-parametric statistical methods (Kruskal–Wallis H test, Mann–Whitney U test, and Spearman’s rank correlation) were used. Results: Statistically significant differences for the number of PAX7, PAX9, and RYK-positive cells were notified between the controls and the patient groups. Multiple statistically significant correlations between the factors were found in each cleft affected tissue group. Conclusions: PAX7, PAX9, and RYK have a variable involvement and interaction in postnatal morphopathogenesis of orofacial clefts. PAX7 is more associated with the formation of unilateral cleft lip, while PAX9 relates more towards the isolated cleft palate. The stable presence of RYK in all cleft types indicates its possible participation in different facial cleft formations.

Aryl Hydrocarbon Receptor and Its Diverse Ligands and Functions: An Exposome Receptor

The aryl hydrocarbon receptor (AhR) is a transcriptional factor that regulates multiple functions following its activation by a variety of ligands, including xenobiotics, natural products, microbiome metabolites, and endogenous molecules. Because of this diversity, the AhR constitutes an exposome receptor. One of its main functions is to regulate several lines of defense against chemical insults and bacterial infections. Indeed, in addition to its well-established detoxication function, it has several functions at physiological barriers, and it plays a critical role in immunomodulation. The AhR is also involved in the development of several organs and their homeostatic maintenance. Its activity depends on the type of ligand and on the time frame of the receptor activation, which can be either sustained or transient, leading in some cases to opposite modes of regulations as illustrated in the regulation of different cancer pathways. The development of selective modulators and their pharmacological characterization are important areas of research. Expected final online publication date for the Annual Review of Pharmacology and Toxicology, Volume 62 is January 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Orbital Involvement by Biphenotypic Sinonasal Sarcoma With a Literature Review

PURPOSE

To document a case of a biphenotypic sinonasal sarcoma that impinged on the orbit via a tumor-induced mucocele and review the previous literature devoted to this condition.

METHODS

A clinicopathologic case report with detailed histopathologic, immunohistochemical, and radiological studies with tabulations of previously reported cases and immunohistochemical stains for ruling out mimicking lesions.

RESULTS

A biphenotypic sinonasal sarcoma arose from the ethmoid sinus in a middle-aged man. The tumor induced a mucocele that bowed the medial orbital lamina papyracea into the orbit and caused diplopia and mild proptosis. The biopsy's dual positivity for S100 and smooth muscle actin together with positive paired box 3 immunohistochemical staining established the diagnosis of biphenotypic sinonasal sarcoma.

CONCLUSION

Biphenotypic sinonasal sarcoma, which can involve the orbit in 25% of cases, is a rare head and neck malignancy that has only recently been described. Biphenotypic sinonasal sarcoma is a low-grade, locally aggressive, nonmetastasizing sarcoma displaying both neural and muscle differentiation. It is further characterized by rearrangements of the PAX3 gene with multiple fusion partners, most commonly MAML3 (Mastermind like transcriptional coactivator 3). It occurs predominantly in middle-aged women and exclusively in the sinonasal tract. However, it can spread throughout the central facial structures to invade the brain if not detected early. Ophthalmologists should be aware of this new entity to avoid delays in diagnosis and treatment. The previous literature devoted to this condition was reviewed and analyzed for clinical, radiological, histopathological, and immunohistochemical features. In circumstances where molecular testing is not available, paired box 3 immunohistochemical staining can be used as an alternative diagnostic marker. The current case is most unusual because the orbital findings were induced by a mucocele caused by the tumor that obstructed the sinus ostium. This produced diplopia without direct tumor invasion into the orbital fat.

Gene Environment Interactions in the Etiology of Neural Tube Defects

Human structural congenital malformations are the leading cause of infant mortality in the United States. Estimates from the United States Center for Disease Control and Prevention (CDC) determine that close to 3% of all United States newborns present with birth defects; the worldwide estimate approaches 6% of infants presenting with congenital anomalies. The scientific community has recognized for decades that the majority of birth defects have undetermined etiologies, although we propose that environmental agents interacting with inherited susceptibility genes are the major contributing factors. Neural tube defects (NTDs) are among the most prevalent human birth defects and as such, these malformations will be the primary focus of this review. NTDs result from failures in embryonic central nervous system development and are classified by their anatomical locations. Defects in the posterior portion of the neural tube are referred to as meningomyeloceles (spina bifida), while the more anterior defects are differentiated as anencephaly, encephalocele, or iniencephaly. Craniorachischisis involves a failure of the neural folds to elevate and thus disrupt the entire length of the neural tube. Worldwide NTDs have a prevalence of approximately 18.6 per 10,000 live births. It is widely believed that genetic factors are responsible for some 70% of NTDs, while the intrauterine environment tips the balance toward neurulation failure in at risk individuals. Despite aggressive educational campaigns to inform the public about folic acid supplementation and the benefits of providing mandatory folic acid food fortification in the United States, NTDs still affect up to 2,300 United States births annually and some 166,000 spina bifida patients currently live in the United States, more than half of whom are now adults. Within the context of this review, we will consider the role of maternal nutritional status (deficiency states involving B vitamins and one carbon analytes) and the potential modifiers of NTD risk beyond folic acid. There are several well-established human teratogens that contribute to the population burden of NTDs, including: industrial waste and pollutants [e.g., arsenic, pesticides, and polycyclic aromatic hydrocarbons (PAHs)], pharmaceuticals (e.g., anti-epileptic medications), and maternal hyperthermia during the first trimester. Animal models for these teratogens are described with attention focused on valproic acid (VPA; Depakote). Genetic interrogation of model systems involving VPA will be used as a model approach to discerning susceptibility factors that define the gene-environment interactions contributing to the etiology of NTDs.

Cleft Candidate Genes and Their Products in Human Unilateral Cleft Lip Tissue

Cleft lip and palate are common congenital pathologies that affect the human population worldwide. The formation of cleft lip is associated with multiple genes and their coded proteins, which regulate the development of craniofacial region, but the exact role of these factors is not always clear. The use of morphological studies for evaluation of human cleft-affected tissue has been limited because of insufficiency of available pathological material. The aim of this study was to detect and compare the immunohistochemical expression of cleft candidate gene coded proteins (DLX4, MSX2, HOXB3, SHH, PAX7, SOX3, WNT3A, and FOXE1) in the non-syndromic unilateral cleft lip patient tissue and control group tissue. A semiquantitative counting method was used to evaluate the tissue in biotin-streptavidin-stained slides. Statistically significant differences between the patient and control groups were found for the number of immunoreactive structures for SHH (p = 0.019) and FOXE1 (p = 0.011) in the connective tissue and SOX3 (p = 0.012) in the epithelium. Multiple statistically significant very strong and strong correlations were found between the immunoreactives in cleft-affected tissue. These significant differences and various correlations indicate that multiple morphopathogenetic pathways are possibly involved in unilateral cleft lip pathogenesis. Therefore, we further discuss these possible interactions.

Augmented BMP signaling commits cranial neural crest cells to a chondrogenic fate by suppressing autophagic β-catenin degradation

Cranial neural crest cells (CNCCs) are a population of multipotent stem cells that give rise to craniofacial bone and cartilage during development. Bone morphogenetic protein (BMP) signaling and autophagy have been individually implicated in stem cell homeostasis. Mutations that cause constitutive activation of the BMP type I receptor ACVR1 cause the congenital disorder fibrodysplasia ossificans progressiva (FOP), which is characterized by ectopic cartilage and bone in connective tissues in the trunk and sometimes includes ectopic craniofacial bones. Here, we showed that enhanced BMP signaling through the constitutively activated ACVR1 (ca-ACVR1) in CNCCs in mice induced ectopic cartilage formation in the craniofacial region through an autophagy-dependent mechanism. Enhanced BMP signaling suppressed autophagy by activating mTORC1, thus blocking the autophagic degradation of β-catenin, which, in turn, caused CNCCs to adopt a chondrogenic identity. Transient blockade of mTORC1, reactivation of autophagy, or suppression of Wnt-β-catenin signaling reduced ectopic cartilages in ca-Acvr1 mutants. Our results suggest that BMP signaling and autophagy coordinately regulate β-catenin activity to direct the fate of CNCCs during craniofacial development. These findings may also explain why some patients with FOP develop ectopic bones through endochondral ossification in craniofacial regions.

Pax3 inhibits Neuro-2a cells proliferation and neurite outgrowth

Pax3 and Pax7 are closely related transcription factors that are widely expressed in the developing nervous system and somites. During the normal development in the central nervous system (CNS), Pax3 and Pax7 are mainly expressed in the dorsal part of the neural tube. Further analysis revealed that Pax3 and Pax7 shared redundant functions in the spinal cord development. However, it is still unknown whether Pax3 and Pax7 play a role in neuronal differentiation. In this study, Pax3 and Pax7 genes were overexpressed in Neuro‐2a, the mouse neuroblastoma cell line. CCK‐8 and EdU assay results showed that overexpression of Pax3 inhibited cell viability and proliferation of Neuro‐2a cells, whereas the overexpression of Pax7 had no significant difference on their cell viability and proliferation. Overexpression of Pax3 not only increased the percentage of cells in the S phase and G0/G1 phase, but also decreased that in the G2 phase. Moreover, the total neurite lengths of Neuro‐2a cells were significantly shorter in Pax3 overexpressed group than those in negative control group and showed no significant difference between Pax7 overexpressed group and negative control group. These results suggested that Pax3 not only inhibited the cell viability and proliferation but also affected the cell cycle and the neurite outgrowth of Neuro‐2a cells. RNA sequencing analysis showed up‐regulated genes in Pax3 overexpressed group were involved in cell cycle machinery, which may reveal the potential mechanism of Neuro‐2a cells proliferation.

Cdon mutation and fetal alcohol converge on Nodal signaling in a mouse model of holoprosencephaly

Holoprosencephaly (HPE), a defect in midline patterning of the forebrain and midface, arises ~1 in 250 conceptions. It is associated with predisposing mutations in the Nodal and Hedgehog (HH) pathways, with penetrance and expressivity graded by genetic and environmental modifiers, via poorly understood mechanisms. CDON is a multifunctional co-receptor, including for the HH pathway. In mice, Cdon mutation synergizes with fetal alcohol exposure, producing HPE phenotypes closely resembling those seen in humans. We report here that, unexpectedly, Nodal signaling is a major point of synergistic interaction between Cdon mutation and fetal alcohol. Window-of-sensitivity, genetic, and in vitro findings are consistent with a model whereby brief exposure of Cdon mutant embryos to ethanol during gastrulation transiently and partially inhibits Nodal pathway activity, with consequent effects on midline patterning. These results illuminate mechanisms of gene-environment interaction in a multifactorial model of a common birth defect.

Targeted sequencing reveals the mutational landscape responsible for sorafenib therapy in advanced hepatocellular carcinoma

Rationale: The existence of primary and acquired drug resistance is the main obstacle for the effect of multi-kinase inhibitor sorafenib and regorafenib in advanced hepatocellular carcinoma (HCC). However, plenty of patients did not significantly benefit from sorafenib treatment and little is known about the mechanism of drug resistance. Methods: Laser capture microdissection was used to acquire matched normal liver and tumor tissues on formalin-fixed paraffin-embedded specimens collected before sorafenib therapy from the first surgery of 119 HCC patients. Ultra-deep sequencing (~1000×) targeting whole exons of 440 genes in microdissected specimens and siRNA screen in 7 cell lines were performed to find mutations associated with differential responses to sorafenib. Patient-derived xenograft models were employed to determine the role of TP53 in response to sorafenib. Lentiviruses harboring wild-type and c.G52C-mutant OCT4 were applied to explore the function of OCT4 in resistance to sorafenib. ChIP-PCR assay for analysis of OCT4 transcriptional activity was performed to explore the affinity with the KITLG promoter. Statistical analyses were used to associate levels of p53 and OCT4 with tumor features and patient outcomes. Results: Total 1,050 somatic mutations and 26 significant driver genes were identified. SiRNA screening in 7 HCC cell lines was further performed to identify mutations associated with differential responses to sorafenib. A recurrent nonsynonymous mutation c.G52C in OCT4 (OCT4 ^mut) was strongly associated with good response to sorafenib, whereas the stop-gain mutation in TP53 showed the opposite outcome both in vitro and in vivo. OCT4 ^wt-induced stem cell factor (encoded by KITLG gene, SCF) expression and cross-activation of c-KIT/FLT3-BRAF signals were identified indispensably for sorafenib resistance, which could be reversed by the combination of c-KIT tyrosine kinase inhibitors or neutralizing antibody against SCF. Mechanistically, an OCT4 binding site in upstream of KITLG promoter was identified with a higher affinity to wildtype of OCT4 rather than G52C-mutant form, which is indispensable for OCT4-induced expression of KITLG and sorafenib resistance. Conclusion: Our study reported a novel somatic mutation in OCT4 (c.G52C) responsible for the sorafenib effect, and also shed new light on the treatment of HCC through the combination of specific tyrosine kinase inhibitors according to individual genetic patterns.

The role of teratogens in neural crest development

The neural crest (NC), discovered by Wilhelm His 150 years ago, gives rise to a multipotent migratory embryonic cell population that generates a remarkably diverse and important array of cell types during the development of the vertebrate embryo. These cells originate in the neural plate border (NPB), which is the ectoderm between the neural plate and the epidermis. They give rise to the neurons and glia of the peripheral nervous system, melanocytes, chondrocytes, smooth muscle cells, odontoblasts and neuroendocrine cells, among others. Neurocristopathies are a class of congenital diseases resulting from the abnormal induction, specification, migration, differentiation or death of NC cells (NCCs) during embryonic development and have an important medical and societal impact. In general, congenital defects affect an appreciable percentage of newborns worldwide. Some of these defects are caused by teratogens, which are agents that negatively impact the formation of tissues and organs during development. In this review, we will discuss the teratogens linked to the development of many birth defects, with a strong focus on those that specifically affect the development of the NC, thereby producing neurocristopathies. Although increasing attention is being paid to the effect of teratogens on embryonic development in general, there is a strong need to critically evaluate the specific role of these agents in NC development. Therefore, increased understanding of the role of these factors in NC development will contribute to the planning of strategies aimed at the prevention and treatment of human neurocristopathies, whose etiology was previously not considered.

Novel genetic loci affecting facial shape variation in humans

The human face represents a combined set of highly heritable phenotypes, but knowledge on its genetic architecture remains limited, despite the relevance for various fields. A series of genome-wide association studies on 78 facial shape phenotypes quantified from 3-dimensional facial images of 10,115 Europeans identified 24 genetic loci reaching study-wide suggestive association (p < 5 × 10-8), among which 17 were previously unreported. A follow-up multi-ethnic study in additional 7917 individuals confirmed 10 loci including six unreported ones (padjusted < 2.1 × 10-3). A global map of derived polygenic face scores assembled facial features in major continental groups consistent with anthropological knowledge. Analyses of epigenomic datasets from cranial neural crest cells revealed abundant cis-regulatory activities at the face-associated genetic loci. Luciferase reporter assays in neural crest progenitor cells highlighted enhancer activities of several face-associated DNA variants. These results substantially advance our understanding of the genetic basis underlying human facial variation and provide candidates for future in-vivo functional studies.

PAX7 nucleotide variants and the risk of non-syndromic orofacial clefts in the Polish population

OBJECTIVE

The etiology of non-syndromic cleft lip with or without cleft palate (nsCL/P) is multifactorial, heterogeneous, and still not completely understood. The aim of the present study was to examine the associations between common and rare PAX7 nucleotide variants and the risk of this common congenital anomaly in a Polish population.

SUBJECTS AND METHODS

Eight top nsCL/P-associated PAX7 variants identified in our cleft genome-wide association study (GWAS) were selected for replication analysis in an independent group of patients and controls (n = 247 and n = 445, respectively). In addition, mutation screening of the PAX7 protein-coding region was conducted.

RESULTS

Analysis of the pooled data from the GWAS and replication study confirmed that common PAX7 nucleotide variants are significantly associated with the increased risk of nsCL/P. The strongest individual variant was rs1339062 (c.586 + 15617T > C) with a p-value = 2.47E-05 (OR = 1.4, 95%CI: 1.20-1.64). Sequencing analysis identified a novel synonymous PAX7 substitution (c.87G > A, p.Val29Val) in a single patient with nsCLP. This transition located in the early exonic position was predicted to disrupt potential splice enhancer elements.

CONCLUSION

Our study confirmed that PAX7 is a strong candidate gene for nsCL/P. Nucleotide variants of this gene contribute to the etiology of nsCL/P in the homogenous Polish population.

Lineage Tracing Reveals a Subset of Reserve Muscle Stem Cells Capable of Clonal Expansion under Stress

Stem cell heterogeneity is recognized as functionally relevant for tissue homeostasis and repair. The identity, context dependence, and regulation of skeletal muscle satellite cell (SC) subsets remains poorly understood. We identify a minor subset of Pax7⁺ SCs that is indelibly marked by an inducible Mx1-Cre transgene in vivo, is enriched for Pax3 expression, and has reduced ROS (reactive oxygen species) levels. Mx1⁺ SCs possess potent stem cell activity upon transplantation but minimally contribute to endogenous muscle repair, due to their relative low abundance. In contrast, a dramatic clonal expansion of Mx1⁺ SCs allows extensive contribution to muscle repair and niche repopulation upon selective pressure of radiation stress, consistent with reserve stem cell (RSC) properties. Loss of Pax3 in RSCs increased ROS content and diminished survival and stress tolerance. These observations demonstrate that the Pax7⁺ SC pool contains a discrete population of radiotolerant RSCs that undergo clonal expansion under severe stress.

Specification and formation of the neural crest: Perspectives on lineage segregation

The neural crest is a fascinating embryonic population unique to vertebrates that is endowed with remarkable differentiation capacity. Thought to originate from ectodermal tissue, neural crest cells generate neurons and glia of the peripheral nervous system, and melanocytes throughout the body. However, the neural crest also generates many ectomesenchymal derivatives in the cranial region, including cell types considered to be of mesodermal origin such as cartilage, bone, and adipose tissue. These ectomesenchymal derivatives play a critical role in the formation of the vertebrate head, and are thought to be a key attribute at the center of vertebrate evolution and diversity. Further, aberrant neural crest cell development and differentiation is the root cause of many human pathologies, including cancers, rare syndromes, and birth malformations. In this review, we discuss the current findings of neural crest cell ontogeny, and consider tissue, cell, and molecular contributions toward neural crest formation. We further provide current perspectives into the molecular network involved during the segregation of the neural crest lineage.

Six NSCL/P Loci Show Associations With Normal-Range Craniofacial Variation

Objectives: Orofacial clefting is one of the most prevalent craniofacial malformations. Previous research has demonstrated that unaffected relatives of patients with non-syndromic cleft lip with/without cleft palate (NSCL/P) show distinctive facial features, which can be an expression of underlying NSCL/P susceptibility genes. These results support the hypothesis that genes involved in the occurrence of a cleft also play a role in normal craniofacial development. In this study, we investigated the influence of genetic variants associated with NSCL/P on normal-range variation in facial shape.

Methods: A literature review of genome wide association studies (GWAS) investigating the genetic etiology of NSCL/P was performed, resulting in a list of 75 single nucleotide polymorphisms (SNPs) located in 38 genetic loci. Genotype data were available for 65 of these selected SNPs in three datasets with a combined sample size of 7,418 participants of European ancestry, whose 3D facial images were also available. The effect of each SNP was tested using a multivariate canonical correlation analysis (CCA) against 63 hierarchically-constructed facial segments in each of the three datasets and meta-analyzed. This allowed for the investigation of associations between SNPs known to be involved in NSCL/P and normal-range facial shape variations in a global-to-local perspective, without preselecting specific facial shape features or characteristics.

Results: Six NSCL/P SNPs showed significant associations with variation in normal-range facial morphology. rs6740960 showed significant effects in the chin area (p = 3.71 × 10⁻²⁸). This SNP lies in a non-coding area. Another SNP, rs227731 near the NOG gene, showed a significant effect in the philtrum area (p = 1.96 × 10⁻¹⁶). Three SNPs showed significant effects on the shape of the nose. rs742071 (p = 8.71 × 10⁻¹⁴), rs34246903 (p = 6.87 × 10⁻¹²), and rs10512248 (p = 8.4 × 10⁻⁹). Respectively, these SNPs are annotated to PAX7, MSX1, and PTCH1. Finally, rs7590268, an intron variant of THADA, showed an effect in the shape of the supraorbital ridge (p = 3.84 × 10⁻⁷).

Conclusions: This study provides additional evidence NSCL/P-associated genetic variants influence normal-range craniofacial morphology, with significant effects observed for the chin, the nose, the supraorbital ridges and the philtrum area.

Biphenotypic Sinonasal Sarcoma: A Review and Update

Context.—

Biphenotypic sinonasal sarcoma (BSNS) is a rare, slow-growing soft tissue sarcoma of the sinonasal tract, typically presenting with nonspecific obstructive nasal symptoms. Although recurrences are common, no metastases have been reported, and only 1 patient has died of disease thus far. It characteristically demonstrates rearrangements of PAX3 with multiple fusion partners, the most common of which is MAML3.

Objectives.—

To highlight the most important diagnostic features, including morphologic, immunohistochemical, and molecular findings, and to provide comparisons to other entities in the differential diagnosis. We also aim to provide a summary of the clinical features and outcomes in cases reported to date.

Data Sources.—

Recently published literature encompassing BSNS and its synonym, low-grade sinonasal sarcoma with neural and myogenic differentiation.

Conclusions.—

BSNS is a sinonasal tumor that is important to recognize because its biologic behavior differs from most of the entities in the differential diagnosis. The diagnosis can typically be rendered through a combination of morphology, immunohistochemical stains, and ancillary testing for characteristic PAX3 rearrangements.

A novel PAX7 10-bp indel variant modulates promoter activity, gene expression and contributes to different phenotypes of Chinese cattle

Paired box 7 (PAX7) gene regulates the conversion of muscle satellite cells into myogenic cells and participates in multi-step processes in myogenesis. Expression levels of PAX7 are decisive for its regulatory function. Previous reports revealed that PAX7 were responsible for the developmental traits of muscle. The relationship of the PAX7 promoter variants and livestock phenotypic traits has not been fully elucidated. We detected a novel 10-bp insertion/deletion (indel) polymorphism in the bovine PAX7 promoter and revealed that the indel altered the binding of the transcriptional factor ZNF219. Luciferase reporter assay showed that deletion-deletion (Del-Del) genotype of the PAX7 gene showed 2.79-fold higher promoter activity than the insertion-insertion (Ins-Ins) genotype (P < 0.05), and ZNF219 overexpression significantly diminished the luciferase activity in Ins-Ins groups. Moreover, the expression of PAX7 and its down-stream genes were detected in fetal skeletal muscle of cattle with different PAX7 genotypes, where the Del-Del genotype also displayed high expression levels. Statistical association analysis demonstrated that this indel had significant effects on early growth traits in cattle. These findings provide a complete overview of the function of the PAX7 10-bp variant, which may have potential as a genetic marker for marker-assisted selection in improving economically significant traits of cattle.

Pax3 overexpression induces cell aggregation and perturbs commissural axon projection during embryonic spinal cord development

Pax3 is a transcription factor that belongs to the paired box family. In the developing spinal cord it is expressed in the dorsal commissural neurons, which project ascending axons contralaterally to form proper spinal cord-brain circuitry. While it has been shown that Pax3 induces cell aggregation in vitro, little is known about the role of Pax3 in cell aggregation and spinal circuit formation in vivo. We have reported that Pax3 is involved in neuron differentiation and that its overexpression induces ectopic cadherin-7 expression. In this study we report that Pax3 overexpression also induces cell aggregation in vivo. Tissue sections and open book preparations revealed that Pax3 overexpression prevents commissural axons from projecting to the contralateral side of the spinal cord. Cells overexpressing Pax3 aggregated in cell clusters that contained shortened neurites with perturbed axon growth and elongation. Pax3-specific shRNA partially rescued the morphological change induced by Pax3 overexpression in vivo. Our results indicate that the normal expression of Pax3 is necessary for proper axonal pathway finding and commissural axon projection. In conclusion, Pax3 regulates neural circuit formation during embryonic development. J. Comp. Neurol. 525:1618-1632, 2017. © 2016 Wiley Periodicals, Inc.

Comparative transcriptomic analysis reveals the oncogenic fusion protein PAX3-FOXO1 globally alters mRNA and miRNA to enhance myoblast invasion

Rhabdomyosarcoma, one of the most common childhood sarcomas, is comprised of two main subtypes, embryonal and alveolar (ARMS). ARMS, the more aggressive subtype, is primarily characterized by the t(2;13)(p35;p14) chromosomal translocation, which fuses two transcription factors, PAX3 and FOXO1 to generate the oncogenic fusion protein PAX3-FOXO1. Patients with PAX3-FOXO1-postitive tumors have a poor prognosis, in part due to the enhanced local invasive capacity of these cells, which leads to the increased metastatic potential for this tumor. Despite this knowledge, little is known about the role that the oncogenic fusion protein has in this increased invasive potential. In this report we use large-scale comparative transcriptomic analyses in physiologically relevant primary myoblasts to demonstrate that the presence of PAX3-FOXO1 is sufficient to alter the expression of 70 mRNA and 27 miRNA in a manner predicted to promote cellular invasion. In contrast the expression of PAX3 alters 60 mRNA and 23 miRNA in a manner predicted to inhibit invasion. We demonstrate that these alterations in mRNA and miRNA translate into changes in the invasive potential of primary myoblasts with PAX3-FOXO1 increasing invasion nearly 2-fold while PAX3 decreases invasion nearly 4-fold. Taken together, these results allow us to build off of previous reports and develop a more expansive molecular model by which the presence of PAX3-FOXO1 alters global gene regulatory networks to enhance the local invasiveness of cells. Further, the global nature of our observed changes highlights the fact that instead of focusing on a single-gene target, we must develop multi-faceted treatment regimens targeting multiple genes of a single oncogenic phenotype or multiple genes that target different oncogenic phenotypes for tumor progression.

Biphenotypic sinonasal sarcoma: an expanded immunoprofile including consistent nuclear β-catenin positivity and absence of SOX10 expression

Biphenotypic sinonasal sarcoma (BSNS) is a recently recognized low-grade sarcoma that exhibits both neural and myogenic differentiation. This unique dual phenotype stems from recurrent rearrangements in PAX3, a transcription factor that promotes commitment along both lineages. While identification of PAX3 rearrangements by fluorescence in situ hybridization (FISH) can confirm a BSNS diagnosis, this assay is not widely available. This study evaluates whether an expanded immunohistochemical panel can facilitate recognition of BSNS without molecular analysis. Eleven cases of BSNS were identified from the surgical pathology archives of two academic medical centers. In 8 cases, the diagnosis was confirmed by FISH using custom probes for PAX3. In 3 cases, FISH failed but histologic and immunophenotypic findings were diagnostic for BSNS. All 11 BSNS (100%) were at least focally positive for S100 as well as calponin and/or smooth muscle actin. In addition, 10 (91%) of 11 expressed nuclear β-catenin, 8 (80%) of 10 expressed factor XIIIa, 4 (36%) of 11 expressed desmin, and 3 (30%) of 10 expressed myogenin. All 11 tumors were negative for SOX10. While no single marker resolves immunohistochemical overlap between BSNS and its histologic mimickers such as nerve sheath tumors, an extended immunohistochemical panel that includes β-catenin and SOX10 helps to support the diagnosis of BSNS without the need for gene rearrangement studies.

Gene-Environment Interactions and the Etiology of Birth Defects

It is thought that most structural birth defects are caused by a complex combination of genetic and environmental factors that interact to interfere with morphogenetic processes. It is important not only to identify individual genetic and environmental risk factors for particular defects but also to identify which environmental factors interact specifically with which genetic variants that predispose to the same defect. Genomic and epidemiological studies are critical to this end. Development and analysis of model systems will also be essential for this goal, as well as for understanding the mechanisms that underlie specific gene-environment interactions.

New insights into craniofacial malformations

Development of the human skull and face is a highly orchestrated and complex three-dimensional morphogenetic process, involving hundreds of genes controlling the coordinated patterning, proliferation and differentiation of tissues having multiple embryological origins. Craniofacial malformations that occur because of abnormal development (including cleft lip and/or palate, craniosynostosis and facial dysostoses), comprise over one-third of all congenital birth defects. High-throughput sequencing has recently led to the identification of many new causative disease genes and functional studies have clarified their mechanisms of action. We present recent findings in craniofacial genetics and discuss how this information together with developmental studies in animal models is helping to increase understanding of normal craniofacial development.

Transcription Factors in Craniofacial Development: From Receptor Signaling to Transcriptional and Epigenetic Regulation

Craniofacial morphogenesis is driven by spatial-temporal terrains of gene expression, which give rise to stereotypical pattern formation. Transcription factors are key cellular components that control these gene expressions. They are information hubs that integrate inputs from extracellular factors and environmental cues, direct epigenetic modifications, and define transcriptional status. These activities allow transcription factors to confer specificity and potency to transcription regulation during development.

PAX transcription factors in neural crest development

The nine vertebrate PAX transcription factors (PAX1-PAX9) play essential roles during early development and organogenesis. Pax genes were identified in vertebrates using their homology with the Drosophila melanogaster paired gene DNA-binding domain. PAX1-9 functions are largely conserved throughout vertebrate evolution, in particular during central nervous system and neural crest development. The neural crest is a vertebrate invention, which gives rise to numerous derivatives during organogenesis, including neurons and glia of the peripheral nervous system, craniofacial skeleton and mesenchyme, the heart outflow tract, endocrine and pigment cells. Human and mouse spontaneous mutations as well as experimental analyses have evidenced the critical and diverse functions of PAX factors during neural crest development. Recent studies have highlighted the role of PAX3 and PAX7 in neural crest induction. Additionally, several PAX proteins - PAX1, 3, 7, 9 - regulate cell proliferation, migration and determination in multiple neural crest-derived lineages, such as cardiac, sensory, and enteric neural crest, pigment cells, glia, craniofacial skeleton and teeth, or in organs developing in close relationship with the neural crest such as the thymus and parathyroids. The diverse PAX molecular functions during neural crest formation rely on fine-tuned modulations of their transcriptional transactivation properties. These modulations are generated by multiple means, such as different roles for the various isoforms (formed by alternative splicing), or posttranslational modifications which alter protein-DNA binding, or carefully orchestrated protein-protein interactions with various co-factors which control PAX proteins activity. Understanding these regulations is the key to decipher the versatile roles of PAX transcription factors in neural crest development, differentiation and disease.

Pax3 and Pax7 interact reciprocally and regulate the expression of cadherin-7 through inducing neuron differentiation in the developing chicken spinal cord

Pax3 and Pax7 are closely related transcription factors that are widely expressed in the developing nervous system and somites. In the CNS, both genes are expressed in the dorsal part of the neural tube during development. Pax3 and Pax7 are involved in the sonic hedgehog (Shh) signaling pathway and are inhibited by Shh overexpression. The present study confirms in vivo that Pax3 overexpression represses the expression of Pax7, whereas Pax7 overexpression endogenously enhances and ectopically induces the expression of Pax3 in the developing chicken spinal cord. Overexpression of Pax3 and Pax7 represses the endogenous expression of cadherin-7, a member of the cadherin family of morphogenetic genes, and induces its ectopic expression. The present study also shows that overexpression of Pax3 and Pax7 changes the fate and morphology of cells in the neuroepithelial layer and induces the expression of postmitotic neuronal markers. We show that both Pax3 and Pax7 promote the differentiation of neural progenitor cells into neurons. Furthermore, the downregulation of Pax3 and Pax7 with specific shRNAs results in apoptosis in the developing spinal cord. Collectively, these results suggest that the transcription factors Pax3 and Pax7 play important roles in regulating morphogenesis and cell differentiation in the developing spinal cord.