Pax 1, a member of a paired box homologous murine gene family, is expressed in segmented structures during development

PAX2 mediated upregulation of ESPL1 contributes to cisplatin resistance in bladder cancer through activating the JAK2/STAT3 pathway

Extra spindle-polar body like 1 (ESPL1) is associated with the development of a variety of cancers, including bladder cancer, and is closely related to chemoresistance. In this study, we aimed to reveal the role of ESPL1 in bladder cancer progression and cisplatin (DDP) resistance. First, ESPL1 was found to be highly expressed in tumor tissues and cells of bladder cancer, and more highly expressed in cisplatin resistant tumor tissues or cells. The binding of PAX2 in ESPL1 promoter region was predicted by Jaspar database and verified by Ch-IP analysis and the luciferase reporter gene assay. Next, cisplatin-resistant T24 cells (T24/DDP) were established and transfected with ESPL1 siRNA (si-ESPL1) or overexpression vector (pcDNA-ESPL1) or co-transfected with PAX2 siRNA (si-PAX2) or overexpression vector (pcDNA-PAX2), and then treated with DDP or AG490, an inhibitor of JAK2. The results showed that silencing ESPL1 significantly reduced T24/DDP cell viability, colony formation and invasion, enhanced sensitivity to DDP, and induced cell apoptosis. Silencing PAX2 decreased ESPL1 expression, enhanced sensitivity to DDP, and induced apoptosis of T24/DDP cells, and inhibited activation of JAK2/STAT3 pathway. Overexpressing ESPL1 reversed the effect of PAX2 silencing on T24/DDP cells, while AG490 counteracted the reversal effect of overexpressing ESPL1. Finally, a xenograft tumor model was established and found that silencing ESPL1 or DDP treatment inhibited tumor growth, while silencing ESPL1 combined with DDP treatment had the best effect. In summary, this study suggested that PAX2-mediated ESPL1 transcriptional activation enhanced cisplatin resistance in bladder cancer by activating JAK2/STAT3 pathway.

The PAX Genes: Roles in Development, Cancer, and Other Diseases

Since their 1986 discovery in Drosophila, Paired box (PAX) genes have been shown to play major roles in the early development of the eye, muscle, skeleton, kidney, and other organs. Consistent with their roles as master regulators of tissue formation, the PAX family members are evolutionarily conserved, regulate large transcriptional networks, and in turn can be regulated by a variety of mechanisms. Losses or mutations in these genes can result in developmental disorders or cancers. The precise mechanisms by which PAX genes control disease pathogenesis are well understood in some cases, but much remains to be explored. A deeper understanding of the biology of these genes, therefore, has the potential to aid in the improvement of disease diagnosis and the development of new treatments.

Building a vertebra: Development of the amniote sclerotome

In embryonic development, the vertebral column arises from the sclerotomal compartment of the somites. The sclerotome is a mesenchymal cell mass which can be subdivided into several subpopulations specified by different regulatory mechanisms and giving rise to different parts of the vertebrae like vertebral body, vertebral arch, ribs, and vertebral joints. This review gives a short overview on the molecular and cellular basis of the formation of sclerotomal subdomains and the morphogenesis of their vertebral derivatives.

An overview of PAX1: Expression, function and regulation in development and diseases

Transcription factors play multifaceted roles in embryonic development and diseases. PAX1, a paired-box transcription factor, has been elucidated to play key roles in multiple tissues during embryonic development by extensive studies. Recently, an emerging role of PAX1 in cancers was clarified. Herein, we summarize the expression and functions of PAX1 in skeletal system and thymus development, as well as cancer biology and outline its cellular and molecular modes of action and the association of PAX1 mutation or dysregulation with human diseases, thus providing insights for the molecular basis of congenital diseases and cancers.

Ectopic expression of T in the paraxial mesoderm disrupts somite maturation in the mouse

T is the founding member of the T-box family of transcription factors; family members are critical for cell fate decisions and tissue morphogenesis throughout the animal kingdom. T is expressed in the primitive streak and notochord with mouse mutant studies revealing its critical role in mesoderm formation in the primitive streak and notochord integrity. We previously demonstrated that misexpression of Tbx6 in the paraxial and lateral plate mesoderm results in embryos resembling Tbx15 and Tbx18 nulls. This, together with results from in vitro transcriptional assays, suggested that ectopically expressed Tbx6 can compete with endogenously expressed Tbx15 and Tbx18 at the binding sites of target genes. Since T-box proteins share a similar DNA binding domain, we hypothesized that misexpressing T in the paraxial and lateral plate mesoderm would also interfere with the endogenous Tbx15 and Tbx18, causing embryonic phenotypes resembling those seen upon Tbx6 expression in the somites and limbs. Interestingly, ectopic T expression led to distinct embryonic phenotypes, specifically, reduced-sized somites in embryos expressing the highest levels of T, which ultimately affects axis length and neural tube morphogenesis. We further demonstrate that ectopic T leads to ectopic expression of Tbx6 and Mesogenin 1, known targets of T. These results suggests that ectopic T expression contributes to the phenotype by activating its own targets rather than via a straight competition with endogenous T-box factors.

The Role of PAX2 in Neurodevelopment and Disease

In developmental biology, transcription factors are involved in regulating the process of neural development, controlling the differentiation of nerve cells, and affecting the normal functioning of neural circuits. Transcription factors regulate the expression of multiple genes at the same time and have become a key gene category that is recognized to be disrupted in neurodevelopmental disorders such as autism spectrum disorders. This paper briefly introduces the expression and role of PAX2 in neurodevelopment and discusses the neurodevelopmental disorders associated with Pax2 mutations and its possible mechanism. Firstly, mutations in the human Pax2 gene are associated with abnormalities in multiple systems which can result in neurodevelopmental disorders such as intellectual disability, epilepsy and autism spectrum disorders. Secondly, the structure of Pax2 gene and PAX2 protein, as well as the function of Pax2 gene in neural development, was discussed. Finally, a diagram of the PAX2 protein regulatory network was made and a possible molecular mechanism of Pax2 mutations leading to neurodevelopmental disorders from the perspectives of developmental process and protein function was proposed.

β1 Integrin regulates convergent extension in mouse notogenesis, ensures notochord integrity and the morphogenesis of vertebrae and intervertebral discs

The notochord drives longitudinal growth of the body axis by convergent extension, a highly conserved developmental process that depends on non-canonical Wnt/planar cell polarity (PCP) signaling. However, the role of cell-matrix interactions mediated by integrins in the development of the notochord is unclear. We developed transgenic Cre mice, in which the β1 integrin gene (Itgb1) is ablated at E8.0 in the notochord only or in the notochord and tail bud. These Itgb1 conditional mutants display misaligned, malformed vertebral bodies, hemi-vertebrae and truncated tails. From early somite stages, the notochord was interrupted and displaced in these mutants. Convergent extension of the notochord was impaired with defective cell movement. Treatment of E7.25 wild-type embryos with anti-β1 integrin blocking antibodies, to target node pit cells, disrupted asymmetric localization of VANGL2. Our study implicates pivotal roles of β1 integrin for the establishment of PCP and convergent extension of the developing notochord, its structural integrity and positioning, thereby ensuring development of the nucleus pulposus and the proper alignment of vertebral bodies and intervertebral discs. Failure of this control may contribute to human congenital spine malformations.

Medial forebrain bundle DBS differentially modulates dopamine release in the nucleus accumbens in a rodent model of depression

BACKGROUND

Medial forebrain bundle (MFB) deep brain stimulation (DBS) has anti-depressant effects clinically and in depression models. Currently, therapeutic mechanisms of MFB DBS or how stimulation parameters acutely impact neurotransmitter release, particularly dopamine, are unknown. Experimentally, MFB DBS has been shown to evoke dopamine response in healthy controls, but not yet in a rodent model of depression.

OBJECTIVE

The study investigated the impact of clinically used stimulation parameters on the dopamine induced response in a validated rodent depression model and in healthy controls.

METHOD

The stimulation-induced dopamine response in Flinders Sensitive Line (FSL, n = 6) rat model of depression was compared with Sprague Dawley (SD, n = 6) rats following MFB DSB, using Fast Scan Cyclic Voltammetry to assess the induced response in the nucleus accumbens. Stimulation parameters were 130 Hz ("clinically" relevant) with pulse widths between 100 and 350 μs.

RESULTS

Linear mixed model analysis showed significant impact in both models following MFB DBS both at 130 and 60 Hz with 100 μs pulse width in inducing dopamine response. Furthermore, at 130 Hz the evoked dopamine responses were different across the groups at the different pulse widths.

CONCLUSION

The differential impact of MFB DBS on the induced dopamine response, including different response patterns at given pulse widths, is suggestive of physiological and anatomical divergence in the MFB in the pathological and healthy state. Studying how varying stimulation parameters affect the physiological outcome will promote a better understanding of the biological substrate of the disease and the possible anti-depressant mechanisms at play in clinical MFB DBS.

Determining Osteogenic Differentiation Efficacy of Pluripotent Stem Cells by Telomerase Activity

Background

Bone tissue engineering based on pluripotent stem cells (PSCs) is a new approach to deal with bone defects. Protocols have been developed to generate osteoblasts from PSCs. However, the low efficiency of this process is still an important issue that needs to be resolved. Many studies have aimed to improve efficiency, but developing accurate methods to determine efficacy is also critical. Studies using pluripotency to estimate efficacy are rare. Telomerase is highly associated with pluripotency.

Methods

We have described a quantitative method to measure telomerase activity, telomeric repeat elongation assay based on quartz crystal microbalance (QCM). To investigate whether this method could be used to determine the efficiency of in vitro osteogenic differentiation based on pluripotency, we measured the pluripotency pattern of cultures through stemness gene expression, proliferation ability and telomerase activity, measured by QCM.

Results

We showed that the pluripotency pattern determined by QCM was similar to the patterns of proliferation ability and gene expression, which showed a slight upregulation at the late stages, within the context of the general downregulation tendency during differentiation. Additionally, a comprehensive gene expression pattern covering nearly every stage of differentiation was identified.

Conclusion

Therefore, this assay may be powerful tools for determining the efficiency of differentiation systems based on pluripotency. In this study, we not only introduce a new method for determining efficiency based on pluripotency, but also provide more information about the characteristics of osteogenic differentiation which help facilitate future development of more efficient protocols.

The role of the notochord in amniote vertebral column segmentation

The vertebral column is segmented, comprising an alternating series of vertebrae and intervertebral discs along the head-tail axis. The vertebrae and outer portion (annulus fibrosus) of the disc are derived from the sclerotome part of the somites, whereas the inner nucleus pulposus of the disc is derived from the notochord. Here we investigate the role of the notochord in vertebral patterning through a series of microsurgical experiments in chick embryos. Ablation of the notochord causes loss of segmentation of vertebral bodies and discs. However, the notochord cannot segment in the absence of the surrounding sclerotome. To test whether the notochord dictates sclerotome segmentation, we grafted an ectopic notochord. We find that the intrinsic segmentation of the sclerotome is dominant over any segmental information the notochord may possess, and no evidence that the chick notochord is intrinsically segmented. We propose that the segmental pattern of vertebral bodies and discs in chick is dictated by the sclerotome, which first signals to the notochord to ensure that the nucleus pulposus develops in register with the somite-derived annulus fibrosus. Later, the notochord is required for maintenance of sclerotome segmentation as the mature vertebral bodies and intervertebral discs form. These results highlight differences in vertebral development between amniotes and teleosts including zebrafish, where the notochord dictates the segmental pattern. The relative importance of the sclerotome and notochord in vertebral patterning has changed significantly during evolution.

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The chick notochord has no intrinsic segmentation.

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Neither notochord or sclerotome can segment normally without the other.

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The notochord attracts sclerotome cells to the midline.

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Vertebral segmentation involves reciprocal signals between notochord and sclerotome.

Developmental dynamics of occipital and cervical somites

Development of somites leading to somite compartments, sclerotome, dermomyotome and myotome, has been intensely investigated. Most knowledge on somite development, including the commonly used somite maturation stages, is based on data from somites at thoracic and lumbar levels. Potential regional differences in somite maturation dynamics have been indicated by a number of studies, but have not yet been comprehensively examined. Here, we present an overview on the developmental dynamics of somites at occipital and cervical levels in the chicken embryo. We show that in these regions, the onset of sclerotomal and myotomal compartment formation is later than at thoracolumbar levels, and is initiated simultaneously in multiple somites, which is in contrast to the serial cranial- to- caudal progression of somite maturation in the trunk. Our data suggest a variant spatiotemporal regulation of somite development in occipitocervical somites.

Small molecule-directed specification of sclerotome-like chondroprogenitors and induction of a somitic chondrogenesis program from embryonic stem cells

Pluripotent embryonic stem cells (ESCs) generate rostral paraxial mesoderm-like progeny in 5-6 days of differentiation induced by Wnt3a and Noggin (Nog). We report that canonical Wnt signaling introduced either by forced expression of activated β-catenin, or the small-molecule inhibitor of Gsk3, CHIR99021, satisfied the need for Wnt3a signaling, and that the small-molecule inhibitor of BMP type I receptors, LDN193189, was able to replace Nog. Mesodermal progeny generated using such small molecules were chondrogenic in vitro, and expressed trunk paraxial mesoderm markers such as Tcf15 and Meox1, and somite markers such as Uncx, but failed to express sclerotome markers such as Pax1. Induction of the osteochondrogenically committed sclerotome from somite requires sonic hedgehog and Nog. Consistently, Pax1 and Bapx1 expression was induced when the isolated paraxial mesodermal progeny were treated with SAG1 (a hedgehog receptor agonist) and LDN193189, then Sox9 expression was induced, leading to cartilaginous nodules and particles in the presence of BMP, indicative of chondrogenesis via sclerotome specification. By contrast, treatment with TGFβ also supported chondrogenesis and stimulated Sox9 expression, but failed to induce the expression of Pax1 and Bapx1. On ectopic transplantation to immunocompromised mice, the cartilage particles developed under either condition became similarly mineralized and formed pieces of bone with marrow. Thus, the use of small molecules led to the effective generation from ESCs of paraxial mesodermal progeny, and to their further differentiation in vitro through sclerotome specification into growth plate-like chondrocytes, a mechanism resembling in vivo somitic chondrogenesis that is not recapitulated with TGFβ.

Endoderm-specific deletion of Tbx1 reveals an FGF-independent role for Tbx1 in pharyngeal apparatus morphogenesis

BACKGROUND

The T-box transcription factor Tbx1, is essential for the normal development of multiple organ systems in the embryo. One of the most striking phenotypes in Tbx1-/- embryos is the failure of the caudal pharyngeal pouches to evaginate from the foregut endoderm. Despite considerable interest in the role of Tbx1 in development, the mechanisms whereby Tbx1 controls caudal pouch formation have remained elusive. In particular, the question as to how Tbx1 expression in the pharyngeal endoderm regulates pharyngeal pouch morphogenesis in the mouse embryo is not known.

RESULTS

To address this question, we produced mouse embryos in which Tbx1 was specifically deleted from the pharyngeal endoderm and, as expected, embryos failed to form caudal pharyngeal pouches. To determine the molecular mechanism, we examined expression of Fgf3 and Fgf8 ligands and downstream effectors. Although Fgf8 expression is greatly reduced in Tbx1-deficient endoderm, FGF signaling levels are unaffected. Furthermore, pouch morphogenesis is only partially perturbed by the loss of both Fgf3 and Fgf8 from the endoderm, indicating that neither are required for pouch formation.

CONCLUSIONS

Tbx1 deletion from the pharyngeal endoderm is sufficient to cause caudal pharyngeal arch segmentation defects by FGF-independent effectors that remain to be identified.

Metameric pattern of intervertebral disc/vertebral body is generated independently of Mesp2/Ripply-mediated rostro-caudal patterning of somites in the mouse embryo

The vertebrae are derived from the sclerotome of somites. Formation of the vertebral body involves a process called resegmentation, by which the caudal half of a sclerotome is combined with the rostral half of the next sclerotome. To elucidate the relationship between resegmentation and rostro-caudal patterning of somite, we used the Uncx4.1-LacZ transgene to characterize the resegmentation process. Our observations suggested that in the thoracic and lumbar vertebrae, the Uncx4.1-expressing caudal sclerotome gave rise to the intervertebral disc (IVD) and rostral portion of the vertebral body (VB). In the cervical vertebrae, the Uncx4.1-expressing caudal sclerotome appeared to contribute to the IVD and both caudal and rostral ends of the VB. This finding suggests that the rostro-caudal gene expression boundary does not necessarily coincide with the resegmentation boundary. This conclusion was supported by analyses of Mesp2 KO and Ripply1/2 double KO embryos lacking rostral and caudal properties, respectively. Resegmentation was not observed in Mesp2 KO embryos, but both the IVD and whole VB were formed from the caudalized sclerotome. Expression analysis of IVD marker genes including Pax1 in the wild-type, Mesp2 KO, and Ripply1/2 DKO embryos also supported the idea that a metameric pattern of IVD/VB is generated independently of Mesp2/Ripply-mediated rostro-caudal patterning of somite. However, in the lumbar region, IVD differentiation appeared to be stimulated by the caudal property and suppressed by the rostral property. Therefore, we propose that rostro-caudal patterning of somites is not a prerequisite for metameric patterning of the IVD and VB, but instead required to stimulate IVD differentiation in the caudal half of the sclerotome.

A hypofunctional PAX1 mutation causes autosomal recessively inherited otofaciocervical syndrome

Otofaciocervical syndrome (OFCS) is an autosomal recessively inherited disorder characterized by facial dysmorphism, external ear anomalies with preauricular pits and hearing impairment, branchial cysts or fistulas, anomalies of the vertebrae and the shoulder girdle, and mild intellectual disability. In a large consanguineous family with OFCS from Turkey, we performed whole-exome sequencing (WES) of a single pooled DNA sample of four affected individuals. Filtering for variants with a percentage of alternate reads ≥ 90 % and a coverage of at least five reads identified only a single novel homozygous variant, c.497G>T, located in PAX1 that co-segregated with the disease in the family. PAX1 encodes a transcription factor with a critical role in pattern formation during embryogenesis in vertebrates. The mutation is predicted to substitute the glycine at position 166 to valine (p.G166V) within the highly conserved paired-box domain of the PAX1 protein. We performed a dual luciferase reporter assay to examine the transactivation of a regulatory sequence in the Nkx3-2 promoter region, which is a direct target of mouse Pax1 transcriptional regulation. We observed a significantly reduced transactivation in HEK293T cells overexpressing Pax1(G157V) in comparison to Pax1(WT) expressing cells, indicating a reduced DNA-binding affinity of the mutant protein. Taken together, our results show that the strategy of pooling DNA is a powerful, cost-effective application for WES in consanguineous families and establish PAX1 as a new disease-causing gene for OFCS and as part of the EYA-DACH-SIX-PAX network, important in early embryogenesis.

Characterization of pax1, pax9, and uncx sclerotomal genes during Xenopus laevis embryogenesis

BACKGROUND

The axial skeleton develops from the sclerotome, a mesenchymal cell population derived from somites. Sclerotomal cells migrate from somites to the perinotochordal and perineural space where they differentiate into chondrocytes to form cartilage and bone. In anurans, little is known about the way how the sclerotome changes as development proceeds and how these events are regulated at the molecular level. Pax1, Pax9, and Uncx4.1 genes play a central role in the morphogenesis of the axial skeleton in vertebrates, regulating cell proliferation and chondrogenic specification of the sclerotome.

RESULTS

In this work, we cloned and examined through whole-mount in situ hybridization and reverse transcriptase-polymerase chain reaction the expression patterns of pax1, pax9, and uncx transcription factors in the anuran Xenopus laevis.

CONCLUSIONS

We found that these genes are similarly expressed in the sclerotome and in the pharyngeal pouch. A detailed analysis of the location of these transcripts showed that they are expressed in different subdomains of the sclerotomal compartment and differ from that observed in other vertebrates.

Pax1(EGFP): new wildtype and mutant EGFP mouse lines for molecular and fate mapping studies

The Paired box gene 1 (Pax1) transcription factor plays essential roles in the development of axial skeleton, scapula, pelvic girdle, and thymus. Delineating its pleiotropic and molecular roles in the various tissues requires the ability to track and isolate the Pax1-expressing cells for downstream high-throughput experiments such as microarray and RNA-sequencing. With these applications in mind, we have generated two new mouse lines-a Pax1 wildtype (WT) mouse line that co-expresses enhanced green fluorescent protein (EGFP) with functional Pax1, and a Pax1 knockout mouse line which expresses EGFP under the control of Pax1 promoter, using the internal ribosome entry site (IRES) and 2A-peptide multi-cistron concatenating strategies. These mouse lines facilitate the isolation and enrichment of Pax1-specific cells from Pax1-positive and Pax1-null embryos using fluorescence activated cell sorting (FACS). They can be also be used in parallel to investigate the stage- and tissue-specific molecular functions of Pax1.

Mouse as a model for multifactorial inheritance of neural tube defects

Neural tube defects (NTDs) such as spina bifida and anencephaly are some of the most common structural birth defects found in humans. These defects occur due to failures of neurulation, a process where the flat neural plate rolls into a tube. In spite of their prevalence, the causes of NTDs are poorly understood. The multifactorial threshold model best describes the pattern of inheritance of NTDs where multiple undefined gene variants interact with environmental factors to cause an NTD. To date, mouse models have implicated a multitude of genes as required for neurulation, providing a mechanistic understanding of the cellular and molecular pathways that control neurulation. However, the majority of these mouse models exhibit NTDs with a Mendelian pattern of inheritance. Still, many examples of multifactorial inheritance have been demonstrated in mouse models of NTDs. These include null and hypomorphic alleles of neurulation genes that interact in a complex fashion with other genetic mutations or environmental factors to cause NTDs. These models have implicated several genes and pathways for testing as candidates for the genetic basis of NTDs in humans, resulting in identification of putative pathogenic mutations in some patients. Mouse models also provide an experimental paradigm to gain a mechanistic understanding of the environmental factors that influence NTD occurrence, such as folic acid and maternal diabetes, and have led to the discovery of additional preventative nutritional supplements such as inositol. This review provides examples of how multifactorial inheritance of NTDs can be modeled in the mouse.

The specification and maintenance of renal cell types by epigenetic factors

The specification of cell lineages and patterning in the embryo occurs sequentially as specific regions are increasingly restricted in their developmental fates. When and how this occurs is still not entirely clear. Nevertheless, the roles of epigenetic regulatory genes in partitioning the genome into active and inactive domains is evident in a variety of organisms and is highly conserved through evolution. The function of Pax2 in the kidney has been inferred by the phenotypic analysis of loss-of-function mutants in mice, fish and humans. Although Pax2 and the related gene, Pax8, are essential for early intermediate mesoderm specification and are found in the epithelial lineage arising from that mesoderm, how these proteins regulate cell lineage restriction and gene expression patterns has remained obscure. Our recent data, suggests that Pax proteins help establish chromatin domains within cell lineages by providing the locus and tissue specificity for epigenetic imprinting complexes that modify histones. The novel protein PTIP is a key adaptor that links Pax proteins and possibly many other types of DNA binding proteins to a histone H3K4 methyltransferase complex. Given the prevalence of Pax2 expression in kidney development and in kidney disease, we now need to address the effects of epigenetics on renal disease states, on the stability of the terminal epithelial phenotype, and in the aging cell.

The generation of vertebral segmental patterning in the chick embryo

We have carried out a series of experimental manipulations in the chick embryo to assess whether the notochord, neural tube and spinal nerves influence segmental patterning of the vertebral column. Using Pax1 expression in the somite-derived sclerotomes as a marker for segmentation of the developing intervertebral disc, our results exclude such an influence. In contrast to certain teleost species, where the notochord has been shown to generate segmentation of the vertebral bodies (chordacentra), these experiments indicate that segmental patterning of the avian vertebral column arises autonomously in the somite mesoderm. We suggest that in amniotes, the subdivision of each sclerotome into non-miscible anterior and posterior halves plays a critical role in establishing vertebral segmentation, and in maintaining left/right alignment of the developing vertebral elements at the body midline.

Genomic analysis of immune response against Vibrio cholerae hemolysin in Caenorhabditis elegans

Vibrio cholerae cytolysin (VCC) is among the accessory V. cholerae virulence factors that may contribute to disease pathogenesis in humans. VCC, encoded by hlyA gene, belongs to the most common class of bacterial toxins, known as pore-forming toxins (PFTs). V. cholerae infects and kills Caenorhabditis elegans via cholerae toxin independent manner. VCC is required for the lethality, growth retardation and intestinal cell vacuolation during the infection. However, little is known about the host gene expression responses against VCC. To address this question we performed a microarray study in C. elegans exposed to V. cholerae strains with intact and deleted hlyA genes.

Many of the VCC regulated genes identified, including C-type lectins, Prion-like (glutamine [Q]/asparagine [N]-rich)-domain containing genes, genes regulated by insulin/IGF-1-mediated signaling (IIS) pathway, were previously reported as mediators of innate immune response against other bacteria in C. elegans. Protective function of the subset of the genes up-regulated by VCC was confirmed using RNAi. By means of a machine learning algorithm called FastMEDUSA, we identified several putative VCC induced immune regulatory transcriptional factors and transcription factor binding motifs. Our results suggest that VCC is a major virulence factor, which induces a wide variety of immune response- related genes during V. cholerae infection in C. elegans.

Transcription factors in parathyroid development: lessons from hypoparathyroid disorders

Parathyroid developmental anomalies, which result in hypoparathyroidism, are common and may occur in one in 4,000 live births. Parathyroids, in man, develop from the endodermal cells of the third and fourth pharyngeal pouches, whereas, in the mouse they develop solely from the endoderm of the third pharyngeal pouches. In addition, neural crest cells that arise from the embryonic mid- and hindbrain also contribute to parathyroid gland development. The molecular signaling pathways that are involved in determining the differentiation of the pharyngeal pouch endoderm into parathyroid cells are being elucidated by studies of patients with hypoparathyroidism and appropriate mouse models. These studies have revealed important roles for a number of transcription factors, which include Tbx1, Gata3, Gcm2, Sox3, Aire1 and members of the homeobox (Hox) and paired box (Pax) families.

The role of Pax6 in forebrain development

Pax6 encodes a highly conserved transcriptional regulator with two DNA-binding motifs, a paired domain and a paired-like homeodomain. Humans carrying PAX6 loss-of-function mutations suffer from abnormal development of the eyes (congenital aniridia) and brain. Small eye mice carrying Pax6 loss-of-function mutations provide a good model for these human conditions. Their analysis has demonstrated the critical importance of this transcription factor in multiple cell types and at several key stages of forebrain development. In the forebrain, Pax6 is critical for the establishment of the pallial-subpallial boundary, which separates dorsal (future cerebral cortex) and ventral (future striatum) telencephalic regions. Levels of Pax6 expression are critically important for cortical progenitor proliferation and its presence in a rostro-lateral(high) to caudo-medial(low) gradient in the cortex is necessary to establish rostro-lateral identities. Furthermore, axon guidance is disrupted in Pax6⁻/⁻ mutants: the majority of thalamocortical axons fail to enter the ventral telencephalon and those that do are unable to innervate their cortical targets. The extent to which the effects of Pax6 later in development are secondary to its effects in early patterning and proliferation remains largely unknown. This is likely to be clarified by future studies on the molecular mechanisms of action of Pax6 and, in particular, the identification of its downstream target genes. Such studies should also help generate an increasingly coherent understanding of how this pleiotropic transcription factor becomes involved in so many facets of neural development.

Chondrocytes derived from mouse embryonic stem cells

Our knowledge of cellular differentiation processes during chondro- and osteogenesis, in particular the complex interaction of differentiation factors, is still limited. We used the model system of embryonic stem (ES) cell differentiation in vitro via cellular aggregates, so called embryoid bodies (EBs), to analyze chondrogenic and osteogenic differentiation. ES cells differentiated into chondrocytes and osteocytes throughout a series of developmental stages resembling cellular differentiation events during skeletal development in vivo. A lineage from pluripotent ES cells via mesenchymal, prechondrogenic cells, chondrocytes and hypertrophicchondrocytes up to osteogenic cells was characterized. Furthermore, we found evidence for another osteogenic lineage, bypassing the chondrogenic stage. Together our results suggest that this in vitro system will be helpful to answer so far unacknowledged questions regarding chondrogenic and osteogenic differentiation. For example, we isolated an as yet unknown cDNA fragment from ES cell-derived chondrocytes, which showed a developmentally regulated expression pattern during EB differentiation. Considering ES cell differentiation as an alternative approach for cellular therapy, we used two different methods to obtain pure chondrocyte cultures from the heterogenous EBs. First, members of the transforming growth factor (TGF)-beta family were applied and found to modulate chondrogenic differentiation but were not effective enough to produce sufficient amounts of chondrocytes. Second, chondrocytes were isolated from EBs by micro-manipulation. These cells initially showed dedifferentiation into fiboblastoid cells in culture, but later redifferentiated into mature chondrocytes. However, a small amount of chondrocytes isolated from EBs transdifferentiated into other mesenchymal cell types, indicating that chondrocytes derived from ES cells posses a distinct differentiation plasticity.

20p11 deletion in a female child with panhypopituitarism, cleft lip and palate, dysmorphic facial features, global developmental delay and seizure disorder

Deletions of 20p are rare with the majority of reported cases involving individuals with 20p12 deletions associated with Alagille syndrome. We report on a child with a de novo mosaic 20p11 deletion who presents with panhypopituitarism; hypoplastic pituitary gland and ectopic posterior pituitary gland on MRI of the brain; cleft lip and palate; kyphosis with anterior beaking of L1 and L2 vertebral bodies; pulmonic stenosis; dysmorphic facial features including flat nasal bridge, hypoplastic premaxilla, hypotelorism, preauricular pit, and cupped ears; seizure disorder; variable muscle tone; and global developmental delay. Array comparative genomic hybridization revealed this deletion to be approximately 5.4 Mb in size, containing 35 genes. Previously, an infant with 20p11.22 deletion who had panhypopituitarism, craniofacial, and genital abnormalities was reported, but the precise parameters of that deletion are unavailable. Several other reported cases of 20p11 deletions also have phenotypic overlap with our case. The similarities in clinical features of these patients suggest that the genes at 20p11 have a critical role in development of midline brain structures.

Transcriptional activity analysis of promoter region of human PAX9 gene under dexamethasone, retinoic acid, and ergocalciferol treatment in MCF-7 and MDPC23

PAX9 gene is a member of the family homeobox of transcription factors and performs important function in development and organogenesis. Mutations in PAX9 coding sequences have been implicated in autosomal dominant oligodontia affecting predominantly permanent molars and second premolars. Previous studies have shown that PAX9 is required for secondary palate development and teratogens have been identified as inducers of a tooth and craniofacial malformations. This work focused on the analysis on the 5'-flanking region of the PAX9 gene studying the influence of retinoic acid, dexamethasone, and vitamin D on the expression of PAX9 by expression constructs that carry the reporter gene luciferase. As results, retinoic acid and dexamethasone showed progressive decrease of PAX9 expression. PAX9-pGL3B1 and PAX9-pGL3B2 promoter was inhibited under the treatment of dexamethasone and ergocalciferol. Retinoic acid and dexamethasone did not alter PAX9-pGL3B3 behavior indicating that sequences present between -1106 and +92 were important for the transcriptional activity of PAX9 promoter. In this study, we characterized the transcriptional activity of specific regions of the PAX9 promoter gene and we demonstrated that retinoic acid and ergocalciferol can modulate the transcriptional activity of PAX9 gene.

Stimulatory actions of lysophosphatidic acid on mouse ATDC5 chondroprogenitor cells

Lysophosphatidic acid (LPA) and sphingosine-1-phosphate (S1P) are bioactive lysophospholipids that affect various cellular processes through G protein-coupled receptors. In our current study, we found by in situ hybridization that E11.5 mouse embryos strongly expressed the LPA receptor subtype LPA(1) in cartilaginous bone primordia and the surrounding mesenchymal cells. However, despite their wide-ranging actions, the roles of lysophospholipids in chondrogenesis remain poorly understood. The mouse clonal cell line ATDC5 undergoes a sequential differentiation of chondroprogenitor cells in vitro. Undifferentiated and differentiated ATDC5 cells express LPA(1) and other lysophospholipid receptors including S1P receptor S1P(1) and S1P(2). Taking advantage of this cell model, we studied the effects of LPA on the activities of chondroprogenitor cells. LPA markedly stimulates both DNA synthesis and the migration of ATDC5 chondroprogenitor cells in culture, whereas S1P suppresses the migration of these cells. Treatment with Ki16425, an LPA(1)- and LPA(3)-specific receptor antagonist, suppressed the fetal bovine serum-stimulated migration of ATDC5 cells by almost 80%. These results indicate that LPA plays an important role in the activation of chondroprogenitor cells.

Embryonic expression of cyclooxygenase-2 causes malformations in axial skeleton

Cyclooxygenases (COXs) have important functions in various physiological and pathological processes. COX-2 expression is highly induced by a variety of stimuli and is observed during certain periods of embryonic development. In this report, the direct effect of COX-2 expression on embryonic development is examined in a novel COX-2 transgenic mouse model that ubiquitously expresses human COX-2 from the early stages of embryonic development. COX-2 transgenic fetuses exhibit severe skeletal malformations and die shortly after birth. Skeletal malformations are localized along the entire vertebral column and rib cage and are linked to defective formation of cartilage anlagen. The cartilage anlagen of axial skeleton fail to properly develop in transgenic embryos because of impaired precartilaginous sclerotomal condensation, which results from the reduction of cell number in the sclerotome. Despite the ubiquitous expression of COX-2, the number of apoptotic cells is highly increased in the sclerotome of transgenic embryos but not in other tissues, suggesting that it is a tissue-specific response. Therefore, the loss of sclerotomal cells due to an increased apoptosis is probably responsible for axial skeletal malformations in transgenic fetuses. In addition, the sclerotomal accumulation of p53 protein is observed in transgenic embryos, suggesting that COX-2 may induce apoptosis via the up-regulation of p53. Our results demonstrate that the aberrant COX-2 signaling during embryonic development is teratogenic and suggest a possible association of COX-2 with fetal malformations of unknown etiology.

Retinoic acid receptors exhibit cell-autonomous functions in cranial neural crest cells

Previous work has emphasized the crucial role of retinoic acid (RA) in the ontogenesis of the vast majority of mesenchymal structures derived from the neural crest cells (NCC), which migrate through, or populate, the frontonasal process and branchial arches. Using somatic mutagenesis in the mouse, we have selectively ablated two or three retinoic acid receptors (i.e., RARalpha/RARbeta, RARalpha/RARgamma and RARalpha/RARbeta/RARgamma) in NCC. By rigorously analyzing these mutant mice, we found that survival and migration of NCC is normal until gestational day 10.5, suggesting that RAR-dependent signaling is not intrinsically required for the early steps of NCC development. However, ablation of Rara and Rarg genes in NCC yields an agenesis of the median portion of the face, demonstrating that RARalpha and RARgamma act cell-autonomously in postmigratory NCC to control the development of structures derived from the frontonasal process. In contrast, ablation of the three Rar genes in NCC leads to less severe defects of the branchial arches derived structures compared with Rar compound null mutants. Therefore, RARs exert a function in the NCC as well as in a separated cell population. This work demonstrates that RARs use distinct mechanisms to pattern cranial NCC.

Transcriptional regulation of thymus organogenesis and thymic epithelial cell differentiation

Transcriptional regulatory networks are the central regulatory mechanisms that control organ identity, patterning, and differentiation. In the case of the thymus, several key transcription factors have been identified that are critical for various aspects of thymus organogenesis and thymic epithelial cell (TEC) differentiation. The thymus forms from the third pharyngeal pouch endoderm during embryogenesis. Organ development progresses from initial thymus cell fate specification, through multiple stages of TEC differentiation and cortical (cTEC) and medullary (mTEC) formation. Transcription factors have been identified for each of these stages: a Hoxa3-dependent cascade at initial fate specification, Foxn1 for early (and later) TEC differentiation, and NF-kappaB for mTEC differentiation. As important as these factors are, their interrelationships are not understood, and many more transcription factors are likely required for complete thymus organogenesis to occur. In this chapter, we review the literature on these known genes, as well as identify gaps in our knowledge for future studies.

Differential axial requirements for lunatic fringe and Hes7 transcription during mouse somitogenesis

Vertebrate segmentation is regulated by the “segmentation clock”, which drives cyclic expression of several genes in the caudal presomitic mesoderm (PSM). One such gene is Lunatic fringe (Lfng), which encodes a modifier of Notch signalling, and which is also expressed in a stripe at the cranial end of the PSM, adjacent to the newly forming somite border. We have investigated the functional requirements for these modes of Lfng expression during somitogenesis by generating mice in which Lfng is expressed in the cranial stripe but strongly reduced in the caudal PSM, and find that requirements for Lfng activity alter during axial growth. Formation of cervical, thoracic and lumbar somites/vertebrae, but not sacral and adjacent tail somites/vertebrae, depends on caudal, cyclic Lfng expression. Indeed, the sacral region segments normally in the complete absence of Lfng and shows a reduced requirement for another oscillating gene, Hes7, indicating that the architecture of the clock alters as segmentation progresses. We present evidence that Lfng controls dorsal-ventral axis specification in the tail, and also suggest that Lfng controls the expression or activity of a long-range signal that regulates axial extension.

BMP inhibition stimulates WNT-dependent generation of chondrogenic mesoderm from embryonic stem cells

WNT and bone morphogenetic protein (BMP) signaling are known to stimulate hemogenesis from pluripotent embryonic stem (ES) cells. However, osteochondrogenic mesoderm was generated effectively when BMP signaling is kept to a low level, while WNT signaling was strongly activated. When mesoderm specification from ES cells was exogenous factor dependent, WNT3a addition supported the generation of cardiomyogenic cells expressing lateral plate/extraembryonic mesoderm genes, and this process involved endogenous BMP activities. Exogenous BMP4 showed a similar effect that depended on endogenous WNT activities. However, neither factor induced robust chondrogenic activity. In support, ES cell differentiation in the presence of either WNT3a or BMP4 was associated with elevated levels of both Bmp and Wnt mRNAs, which appeared to provide sufficient levels of active BMPs and WNTs to promote the nonchondrogenic mesoderm specification. The osteochondrogenic mesoderm expressed PDGFRalpha, which also expressed genes that mark somite and rostral presomitic mesoderm. A strong WNT signaling was required for generating the mesodermal progeny, while approximately 50- to 100-fold lower concentration of WNT3a was sufficient for specifying axial mes(end)oderm. Thus, depending on the dose and cofactor (BMP), WNT signaling stimulates the generation of different biological activities and specification of different types of mesodermal progeny from ES cells.

Sox9 directly promotes Bapx1 gene expression to repress Runx2 in chondrocytes

The transcription factor, Sry-related High Mobility Group (HMG) box containing gene 9 (Sox9), plays a critical role in cartilage development by initiating chondrogenesis and preventing the subsequent maturation process called chondrocyte hypertrophy. This suppression mechanism by Sox9 on late-stage chondrogenesis partially results from the inhibition of Runt-related transcription factor 2 (Runx2), the main activator of hypertrophic chondrocyte differentiation. However, the precise mechanism by which Sox9 regulates late chondrogenesis is poorly understood. In the present study, the transcriptional repressor vertebrate homolog of Drosophila bagpipe (Bapx1) was found to be a direct target of Sox9 for repression of Runx2 expression in chondrocytes. We identified a critical Sox9 responsive region in the Bapx1 promoter via a luciferase reporter assay. Analysis by chromatin immunoprecipitation and electrophoretic mobility shift assays indicated that Sox9 physically bound to this region of the Bapx1 promoter. Consistent with the notion that Bapx1 and Sox9 act as negative regulators of chondrocyte hypertrophy by regulating Runx2 expression, transient knockdown of Sox9 or Bapx1 expression by shRNA in chondrocytes increased Runx2 expression, as well as expression of the late chondrogenesis marker, Col10a1. Furthermore, while over-expression of Sox9 decreased Runx2 and Col10a1 expressions, simultaneous transient knockdown of Bapx1 diminished that Sox9 over-expressing effect. Our findings reveal that the molecular pathway modulated by Bapx1 links two major regulators in chondrogenesis, Sox9 and Runx2, to coordinate skeletal formation.

Modeling neural tube defects in the mouse

Neural tube defects (NTDs) are among the most common structural birth defects observed in humans. Mouse models provide an excellent experimental system to study the underlying causes of NTDs. These models not only allow for identification of the genes required for neurulation, they provide tractable systems for uncovering the developmental, pathological and molecular mechanisms underlying NTDs. In addition, mouse models are essential for elucidating the mechanisms of gene-environment and gene-gene interactions that contribute to the multifactorial inheritance of NTDs. In some cases these studies have led to development of approaches to prevent NTDs and provide an understanding of the underlying molecular mechanism of these therapies prevent NTDs.

Pbx1/Pbx2 govern axial skeletal development by controlling Polycomb and Hox in mesoderm and Pax1/Pax9 in sclerotome

The post-cranial axial skeleton consists of a metameric series of vertebral bodies and intervertebral discs, as well as adjoining ribs and sternum. Patterning of individual vertebrae and distinct regions of the vertebral column is accomplished by Polycomb and Hox proteins in the paraxial mesoderm, while their subsequent morphogenesis depends partially on Pax1/Pax9 in the sclerotome. In this study, we uncover that Pbx1/Pbx2 are co-expressed during successive stages of vertebral and rib development. Next, by exploiting a Pbx1/Pbx2 loss-of-function mouse, we show that decreasing Pbx2 dosage in the absence of Pbx1 affects axial development more severely than single loss of Pbx1. Pbx1/Pbx2 mutants exhibit a homogeneous vertebral column, with loss of vertebral identity, rudimentary ribs, and rostral hindlimb shifts. Of note, these axial defects do not arise from perturbed notochord function, as cellular proliferation, apoptosis, and expression of regulators of notochord signaling are normal in Pbx1/Pbx2 mutants. While the observed defects are consistent with loss of Pbx activity as a Hox-cofactor in the mesoderm, we additionally establish that axial skeletal patterning and hindlimb positioning are governed by Pbx1/Pbx2 through their genetic control of Polycomb and Hox expression and spatial distribution in the mesoderm, as well as of Pax1/Pax9 in the sclerotome.

Molecular basis for skeletal variation: insights from developmental genetic studies in mice

Skeletal variations are common in humans, and potentially are caused by genetic as well as environmental factors. We here review molecular principles in skeletal development to develop a knowledge base of possible alterations that could explain variations in skeletal element number, shape or size. Environmental agents that induce variations, such as teratogens, likely interact with the molecular pathways that regulate skeletal development.

Development of the skeletal system

The analysis of the development of the skeletal system has been greatly facilitated by the availability of a large number of mouse mutants with skeletal defects. Whereas for many of these mutants a description of the main phenotypic abnormalities is known, molecular insight into the ontogeny of the skeletal system is limited. One of the few skeletal mutants for which the molecular basis is known is undulated. These mice have a defect in the differentiation of the sclerotome and Pax-1, a mouse paired-box containing gene, has been identified as a candidate gene for this mutation. A molecular analysis of three independent undulated alleles revealed that in each case the Pax-1 gene is affected. One of the alleles could be classified as a null allele, in which the Pax-1 gene is deleted. A phenotypic analysis shows that Pax-1 is required for proper differentiation of intervertebral discs and vertebral bodies.

Derivation of a mouse model for conditional inactivation of Pax9

Pax9 is required for the formation of a variety of organs during mouse development. The function of Pax9 at postnatal stages is unknown since homozygosity of the null allele (Pax9(lacZ)) causes neonatal lethality. Recently, we have generated a hypomorphic Pax9 allele, Pax9(neo), which contains a removable neomycin resistance cassette (neo) and loxP sites flanking the first two exons of Pax9. Here we show that FLP-mediated in vivo excision of neo generates phenotypically normal Pax9(flox) mice. Crossing Pax9(flox) mice to PGK-Cre mice leads to efficient recombination of loxP sites and neonatal lethality in the resulting Pax9(del/del) offspring. Inactivation of Pax9 using Wnt1-Cre mice causes cleft secondary palate and tooth agenesis and reveals that the Pax9 expressing mesenchymal cells of the nose, palate, and teeth are derived from neural crest cells. The conditional Pax9 allele will be a valuable tool to study Pax9 function in specific tissues of adult mice.

Compartmentalised expression of Delta-like 1 in epithelial somites is required for the formation of intervertebral joints

Background

Expression of the mouse Delta-like 1 (Dll1) gene in the presomitic mesoderm and in the caudal halves of somites of the developing embryo is required for the formation of epithelial somites and for the maintenance of caudal somite identity, respectively. The rostro-caudal polarity of somites is initiated early on within the presomitic mesoderm in nascent somites. Here we have investigated the requirement of restricted Dll1 expression in caudal somite compartments for the maintenance of rostro-caudal somite polarity and the morphogenesis of the axial skeleton. We did this by overexpressing a functional copy of the Dll1 gene throughout the paraxial mesoderm, in particular in anterior somite compartments, during somitogenesis in transgenic mice.

Results

Epithelial somites were generated normally and appeared histologically normal in embryos of two independent Dll1 over-expressing transgenic lines. Gene expression analyses of rostro-caudal marker genes suggested that over-expression of Dll1 without restriction to caudal compartments was not sufficient to confer caudal identity to rostral somite halves in transgenic embryos. Nevertheless, Dll1 over-expression caused dysmorphologies of the axial skeleton, in particular, in morphological structures that derive from the articular joint forming compartment of vertebrae. Accordingly, transgenic animals exhibited missing or reduced intervertebral discs, rostral and caudal articular processes as well as costal heads of ribs. In addition, the midline of the vertebral column did not develop normally. Transgenic mice had open neural arches and split vertebral bodies with ectopic pseudo-growth plates. Endochondral bone formation and ossification in the developing vertebrae were delayed.

Conclusion

The mice overexpressing Dll1 exhibit skeletal dysmorphologies that are also evident in several mutant mice with defects in somite compartmentalisation. The Dll1 transgenic mice demonstrate that vertebral dysmorphologies such as bony fusions of vertebrae and midline vertebral defects can occur without apparent changes in somitic rostro-caudal marker gene expression. Also, we demonstrate that the over-expression of the Dll1 gene in rostral epithelial somites is not sufficient to confer caudal identity to rostral compartments. Our data suggest that the restricted Dll1 expression in caudal epithelial somites may be particularly required for the proper development of the intervertebral joint forming compartment.

Functional analysis of Nkx2.1 and Pax9 for calcitonin gene transcription

Nkx2.1 (TTF-1), a homeodomain-containing transcription factor essential for specific gene expression in thyroid follicular cells, exists also in the thyroidal C cells that secrete calcitonin (CT). In this report, we examined the effect of Nkx2.1 on the CT gene transcription. Luciferase reporter assay using the 2kbp promoter sequence of rat CT/CGRP gene revealed that Nkx2.1 induced a significant increase in the promoter transcription. Furthermore, we detected Pax1 and/or Pax9 gene expression in mammalian medullary thyroid carcinoma cell lines, rat rMTC and human TT cells, and in mammalian thyroid glands by RT-PCR. The Pax9 mRNA, expressed in the TT cells and rat thyroid, was then isolated by cDNA cloning. Sequence analysis showed that both rat and human Pax9 proteins contained characteristic domains: i.e. the paired domain and octapeptide motif. Alternative transcripts encoding Pax9 isoforms were not identified in the rat thyroid or TT cells. Dual luciferase assay indicated that Pax9 did not increase transcription from the CT/CGRP promoter. Pax9 also showed no cooperative effects when it was co-transfected with Nkx2.1. The results suggest that CT gene expression could be directly activated by Nkx2.1, whereas Pax9 is not involved in transcription from the 2kbp CT promoter.

Zic2 and Zic3 synergistically control neurulation and segmentation of paraxial mesoderm in mouse embryo

Zic family zinc-finger proteins play various roles in animal development. In mice, five Zic genes (Zic1-5) have been reported. Despite the partly overlapping expression profiles of these genes, mouse mutants for each Zic show distinct phenotypes. To uncover possible redundant roles, we characterized Zic2/Zic3 compound mutant mice. Zic2 and Zic3 are both expressed in presomitic mesoderm, forming and newly generated somites with differential spatiotemporal accentuation. Mice heterozygous for the hypomorphic Zic2 allele together with null Zic3 allele generally showed severe malformations of the axial skeleton, including asymmetric or rostro-caudally bridged vertebrae, and reduction of the number of caudal vertebral bones, that are not obvious in single mutants. These defects were preceded by perturbed somitic marker expression, and reduced paraxial mesoderm progenitors in the primitive streak. These results suggest that Zic2 and Zic3 cooperatively control the segmentation of paraxial mesoderm at multiple stages. In addition to the segmentation abnormality, the compound mutant also showed neural tube defects that ran the entire rostro-caudal extent (craniorachischisis), suggesting that neurulation is another developmental process where Zic2 and Zic3 have redundant functions.