Cooperative interactions between the two DNA binding domains of Pax3: helix 2 of the paired domain is in the proximity of the amino terminus of the homeodomain

Identification and function of the Pax gene Bmgsb in the silk gland of Bombyx mori

Paired box (Pax) genes are highly conserved throughout evolution, and the Pax protein is an important transcription factor of embryonic development. The Pax gene Bmgsb is expressed in the silk glands of silkworm, but its biological functions remain unclear. This study aimed to investigate the expression pattern of Bmgsb in the silk gland and explore its functions using RNA interference (RNAi). Here, we identified eight Pax genes in Bombyx mori. Phylogenetic analysis showed that the B. mori Pax genes were highly homologous to the Pax genes in other insects and highly evolutionarily conserved. The tissue expression profile showed that Bmgsb was expressed in the anterior silk gland and anterior part of the middle silk gland (AMSG). RNAi of Bmgsb resulted in defective development of the AMSG, and the larvae were mostly unable to cocoon in the wandering stage. RNA-seq analysis showed that the fibroin genes fib-l, fib-h and p25, cellular heat shock response-related genes and phenol oxidase genes were considerably upregulated upon Bmgsb knockdown. Furthermore, quantitative reverse transcription-PCR results showed that the fibroin genes and ubiquitin proteolytic enzyme-related genes were significantly upregulated in the AMSG after Bmgsb knockdown. This study provides a foundation for future research on the biological functions of B. mori Pax genes. In addition, it demonstrates the important roles of Bmgsb in the transcriptional regulation of fibroin genes and silk gland development.

Case Report: A Novel PAX3 Mutation Associated With Waardenburg Syndrome Type 1

Background: Waardenburg Syndrome Type 1 (WS1) is a rare hereditary disease, which is usually caused by the mutations of PAX3 (paired box 3). Here, we reported a pedigree with WS1, which was caused by a novel mutation in PAX3.

Case Report: In this present report, a 10-year-old boy and his twin sister from a Han Chinese family presented with iris pigmentary abnormality, synophrys, and broad and high nasal root. Their father presented premature whitening of the hair, but no iris pigmentary abnormality. Their aunts presented the same clinical characteristics with the twins and premature graying of hair. However, none of the patients reported hearing loss. The clinical diagnosis of the four patients from this pedigree was WS1. The whole exome sequencing (WES) revealed a novel mutation (c.959-5T>G) in the PAX3 gene, which could be responsible for the observed pathogenic of WS1 in this pedigree. The genetic test confirmed the diagnosis of WS1 in the four patients from the studied pedigree.

Conclusion: This present study demonstrated that genetic test based on WES, an effective alternative to regular clinical examinations, helps diagnose WS1. The newly identified PAX3 gene mutation can expand the understanding of WS1.

Phenotypic diversity and genetic complexity of PAX3-related Waardenburg syndrome

Waardenburg syndrome subtypes 1 and 3 are caused by pathogenic variants in PAX3. We investigated 12 individuals from four unrelated families clinically diagnosed with Waardenburg syndrome type 1/3. Novel pathogenic variants identified in PAX3 included single nucleotide variants (c.166C>T, c.829C>T), a 2-base pair deletion (c.366_367delAA) and a multi-exonic deletion. Two novel variants, c.166C>T and c.829C>T and a previously reported variant, c.256A>T in PAX3 were evaluated for their nuclear localization and ability to activate MITF promoter. The coexistence of two subtypes of Waardenburg syndrome with pathogenic variants in PAX3 and EDNRB was seen in one of the affected individuals. Multiple genetic diagnoses of Waardenburg syndrome type 3 and autosomal recessive deafness 1A was identified in an individual. We also review the phenotypic and genomic spectrum of individuals with PAX3-related Waardenburg syndrome reported in the literature.

The clinical and genetic research of Waardenburg syndrome type I and II in Chinese families

OBJECTIVE

Waardenburg Syndrome (WS) is a neurocristopathy with an autosomal dominant mode of inheritance and highly genetic heterogeneity. To date, mutations of PAX3, SOX10, MITF, EDNRB, EDN3 and SNAI2 have been implicated in the pathogenesis of WS. In this study, we aimed to identify pathogenic genes among WS families and to analyze the pathogenic relationship between genotypes and phenotypes.

METHODS

In this study, all six families studied were from Hubei province, China.WS patients underwent screening for all deafness genes including PAX3, SOX10, MITF, EDNRB, EDN3 and SNAI2 using Massively Parallel Sequencing (MPS) and validation of mutations using Sanger sequencing.

RESULTS

Clinical evaluation revealed prominent phenotypic variability in Hubei WS patients. Two WS1 families and four WS2 families were diagnosed in six families. Sensorineural hearing loss was the most common, followed by iris pigmentary abnormality. Molecular genetic analysis of the WS genes for six families revealed five novel heterozygous mutations. Two mutations occurred in the PAX3 gene: one nonsense mutation c.667C > T(p.Arg223Ter) and one missense mutation c.220C > T(p.Arg74Cys).One missense mutation c.331T > C (p.Phe111Leu) and one nonsense mutation c.346C > T(p.Gln116Ter) were detected in the SOX10 gene. Two mutations were detected in the MITF gene: one splice site mutation c.859-1G > A and one nonsense mutation c.859G > T(p.Glu287Ter). Among them, the mutations (SOX10 c.331T > C and MITF c.859G > T) were de novo mutations.

CONCLUSION

In this study, six mutations were found to be associated with the phenotype of patients. Our data helped illuminate the phenotypic and genotypic spectrum of WS in Hubei province and could have implications for the genetic counseling of WS in Hubei province.

Transcription Factors That Govern Development and Disease: An Achilles Heel in Cancer

Development requires the careful orchestration of several biological events in order to create any structure and, eventually, to build an entire organism. On the other hand, the fate transformation of terminally differentiated cells is a consequence of erroneous development, and ultimately leads to cancer. In this review, we elaborate how development and cancer share several biological processes, including molecular controls. Transcription factors (TF) are at the helm of both these processes, among many others, and are evolutionarily conserved, ranging from yeast to humans. Here, we discuss four families of TFs that play a pivotal role and have been studied extensively in both embryonic development and cancer-high mobility group box (HMG), GATA, paired box (PAX) and basic helix-loop-helix (bHLH) in the context of their role in development, cancer, and their conservation across several species. Finally, we review TFs as possible therapeutic targets for cancer and reflect on the importance of natural resistance against cancer in certain organisms, yielding knowledge regarding TF function and cancer biology.

Paired box 8 suppresses tumor angiogenesis and metastasis in gastric cancer through repression of FOXM1 via induction of microRNA-612

Background

Paired box 8 (PAX8) has been documented to be downregulated in gastric cancer. However, its biological function in this malignancy is poorly understood.

Methods

In the present work, we investigated the effects of PAX8 overexpression and knockdown on the aggressive phenotype of gastric cancer cells. We further checked the involvement of forkhead box M1 (FOXM1), a ubiquitously expressed oncogene that can facilitate gastric cancer progression, in the action of PAX8.

Results

Ectopic expression of PAX8 blocked the migration and invasion of both AGS and SGC-7901 cells, but had no effect on cell proliferation. Conversely, knockdown of PAX8 enhanced gastric cancer cell migration and invasion. PAX8 overexpression inhibited epithelial-mesenchymal transition (EMT) and pro-angiogenic activity of gastric cancer cells. Mechanistically, PAX8 overexpression downregulated FOXM1 by stimulating microRNA (miR)-612 expression. Ectopic expression of miR-612 recapitulated the effect of PAX8 overexpression on gastric cancer cells, causing an inhibition of migration, invasion, EMT, and angiogenesis. Knockdown of miR-612 or overexpression of FOXM1 significantly reversed the tumor-suppressive activity of PAX8. In vivo studies further demonstrated that PAX8 overexpression restrained tumor angiogenesis and metastasis in nude mice, which was accompanied by increased expression of miR-612 and decreased expression of FOXM1.

Conclusions

PAX8 exerts a tumor-suppressive effect against gastric cancer cells, largely through induction of miR-612 and repression of FOXM1. Therefore, restoration of PAX8 expression may offer therapeutic benefits in the treatment of gastric cancer.

The expression and function of PAX3 in development and disease

The PAX3 gene encodes a member of the PAX family of transcription factors that is characterized by a highly conserved paired box motif. The PAX3 protein is a transcription factor consisting of an N-terminal DNA binding domain (containing a paired box and homeodomain) and a C-terminal transcriptional activation domain. This protein is expressed during development of skeletal muscle, central nervous system and neural crest derivatives, and regulates expression of target genes that impact on proliferation, survival, differentiation and motility in these lineages. Germline mutations of the murine Pax3 and human PAX3 genes cause deficiencies in these developmental lineages and result in the Splotch phenotype and Waardenburg syndrome, respectively. Somatic genetic rearrangements that juxtapose the PAX3 DNA binding domain to the transcriptional activation domain of other transcription factors deregulate PAX3 function and contribute to the pathogenesis of the soft tissue cancers alveolar rhabdomyosarcoma and biphenotypic sinonasal sarcoma. The wild-type PAX3 protein is also expressed in other cancers related to developmental lineages that normally express this protein and exerts phenotypic effects related to its normal developmental role.

Glucose-dependent downregulation of glucagon gene expression mediated by selective interactions between ALX3 and PAX6 in mouse alpha cells

AIMS/HYPOTHESIS

The stimulation of glucagon secretion in response to decreased glucose levels has been studied extensively. In contrast, little is known about the regulation of glucagon gene expression in response to fluctuations in glucose concentration. Paired box 6 (PAX6) is a key transcription factor that regulates the glucagon promoter by binding to the G1 and G3 elements. Here, we investigated the role of the transcription factor aristaless-like homeobox 3 (ALX3) as a glucose-dependent modulator of PAX6 activity in alpha cells.

METHODS

Experiments were performed in wild-type or Alx3-deficient islets and alphaTC1 cells. We used chromatin immunoprecipitations and electrophoretic mobility shift assays for DNA binding, immunoprecipitations and pull-down assays for protein interactions, transfected cells for promoter activity, and small interfering RNA and quantitative RT-PCR for gene expression.

RESULTS

Elevated glucose concentration resulted in stimulated expression of Alx3 and decreased glucagon gene expression in wild-type islets. In ALX3-deficient islets, basal glucagon levels were non-responsive to changes in glucose concentration. In basal conditions ALX3 bound to the glucagon promoter at G3, but not at G1. ALX3 could form heterodimers with PAX6 that were permissive for binding to G3 but not to G1. Thus, increasing the levels of ALX3 in response to glucose resulted in the sequestration of PAX6 by ALX3 for binding to G1, thus reducing glucagon promoter activation and glucagon gene expression.

CONCLUSIONS/INTERPRETATION

Glucose-stimulated expression of ALX3 in alpha cells provides a regulatory mechanism for the downregulation of glucagon gene expression by interfering with PAX6-mediated transactivation on the glucagon G1 promoter element.

PAX genes in childhood oncogenesis: developmental biology gone awry?

Childhood solid tumors often arise from embryonal-like cells, which are distinct from the epithelial cancers observed in adults, and etiologically can be considered as 'developmental patterning gone awry'. Paired-box (PAX) genes encode a family of evolutionarily conserved transcription factors that are important regulators of cell lineage specification, migration and tissue patterning. PAX loss-of-function mutations are well known to cause potent developmental phenotypes in animal models and underlie genetic disease in humans, whereas dysregulation and/or genetic modification of PAX genes have been shown to function as critical triggers for human tumorigenesis. Consequently, exploring PAX-related pathobiology generates insights into both normal developmental biology and key molecular mechanisms that underlie pediatric cancer, which are the topics of this review.

Functional dissection of Pax3 in paraxial mesoderm development and myogenesis

The paired box transcription factor Pax3 is well-known as a major regulator of embryonic myogenesis. Before Pax3 expression becomes restricted to the dermomyotome, this transcription factor is also expressed in the developing somites. The role of Pax3 at this early stage is unclear, in particular because of the scarce frequency of Pax3-positive cells in the early mouse embryo. Inducible gene expression in embryonic stem cells (ESCs) represents an excellent tool to overcome this limitation, since it can provide large quantities of otherwise rare embryonic populations expressing a factor of interest. Here we used engineered mouse ESCs to perform a functional analysis of Pax3 with the aim to identify the molecular determinants involved in the early functions of this transcription factor. We find that Pax3 induction during embryoid body differentiation results in the upregulation of genes expressed in the presomitic and somitic mesoderm. Moreover, we show that paraxial mesoderm induced by transient expression of Pax3 is not irreversibly committed to myogenesis rather requires sustained Pax3 expression. Using a series of deletion mutants of Pax3, which differentially affect its transcriptional activity, we map protein domains necessary for induction of paraxial mesoderm and induction of the myogenic program. The paired, homeo-, and transcriptional activation domains were each required for both processes, however, the paired-c-terminal RED domain showed a paraxial mesoderm-specific activity that was dispensable for myogenesis. These findings demonstrate and provide mechanistic insight into an early role for Pax3 in the generation of paraxial mesoderm.

Pax genes in embryogenesis and oncogenesis

The paired box genes are a family of nine developmental control genes, which in human beings (PAX) and mice (Pax) encode nuclear transcription factors. The temporal and spatial expressions of these highly conserved genes are tightly regulated during foetal development including organogenesis. PAY/Paxgenes are switched off during the terminal differentiation of most structures. Specific mutations within a number of PAX/Pax genes lead to developmental abnormalities in both human beings and mice. Mutation in PAX3 causes Waardenburg syndrome, and craniofacial-deafness-hand syndrome. The Splotch phenotype in mouse exhibits defects in neural crest derivatives such as, pigment cells, sympathetic ganglia and cardiac neural crest-derived structures. The PAX family also plays key roles in several human malignancies. In particular, PAX3 is involved in rhabdomyosarcoma and tumours of neural crest origin, including melanoma and neuroblastoma. This review critically evaluates the roles of PAX/Pax in oncogenesis. It especially highlights recent advances in knowledge of how their genetic alterations directly interfere in the transcriptional networks that regulate cell differentiation, proliferation, migration and survival and may contribute to oncogenesis.