Ectopic Msx2 overexpression inhibits and Msx2 antisense stimulates calvarial osteoblast differentiation

Msx genes delineate a novel molecular map of the developing cerebellar neuroepithelium

In the early cerebellar primordium, there are two progenitor zones, the ventricular zone (VZ) residing atop the IVth ventricle and the rhombic lip (RL) at the lateral edges of the developing cerebellum. These zones give rise to the several cell types that form the GABAergic and glutamatergic populations of the adult cerebellum, respectively. Recently, an understanding of the molecular compartmentation of these zones has emerged. To add to this knowledge base, we report on the Msx genes, a family of three transcription factors, that are expressed downstream of Bone Morphogenetic Protein (BMP) signaling in these zones. Using fluorescent RNA in situ hybridization, we have characterized the Msx (Msh Homeobox) genes and demonstrated that their spatiotemporal pattern segregates specific regions within the progenitor zones. Msx1 and Msx2 are compartmentalized within the rhombic lip (RL), while Msx3 is localized within the ventricular zone (VZ). The relationship of the Msx genes with an early marker of the glutamatergic lineage, Atoh1, was examined in Atoh1-null mice and it was found that the expression of Msx genes persisted. Importantly, the spatial expression of Msx1 and Msx3 altered in response to the elimination of Atoh1. These results point to the Msx genes as novel early markers of cerebellar progenitor zones and more importantly to an updated view of the molecular parcellation of the RL with respect to the canonical marker of the RL, Atoh1.

Creating morphological diversity in reptilian temporal skull region: A review of potential developmental mechanisms

Reptilian skull morphology is highly diverse and broadly categorized into three categories based on the number and position of the temporal fenestrations: anapsid, synapsid, and diapsid. According to recent phylogenetic analysis, temporal fenestrations evolved twice independently in amniotes, once in Synapsida and once in Diapsida. Although functional aspects underlying the evolution of tetrapod temporal fenestrations have been well investigated, few studies have investigated the developmental mechanisms responsible for differences in the pattern of temporal skull region. To determine what these mechanisms might be, we first examined how the five temporal bones develop by comparing embryonic cranial osteogenesis between representative extant reptilian species. The pattern of temporal skull region may depend on differences in temporal bone growth rate and growth direction during ontogeny. Next, we compared the histogenesis patterns and the expression of two key osteogenic genes, Runx2 and Msx2, in the temporal region of the representative reptilian embryos. Our comparative analyses suggest that the embryonic histological condition of the domain where temporal fenestrations would form predicts temporal skull morphology in adults and regulatory modifications of Runx2 and Msx2 expression in osteogenic mesenchymal precursor cells are likely involved in generating morphological diversity in the temporal skull region of reptiles.

Evaluating the Expression of Candidate Homeobox Genes and Their Role in Local-Site Inflammation in Mucosal Tissue Obtained from Children with Non-Syndromic Cleft Lip and Palate

Craniofacial development including palatogenesis is a complex process which requires an orchestrated and spatiotemporal expression of various genes and factors for proper embryogenesis and organogenesis. One such group of genes essential for craniofacial development is the homeobox genes, transcriptional factors that are commonly associated with congenital abnormalities. Amongst these genes, DLX4, HOXB3, and MSX2 have been recently shown to be involved in the etiology of non-syndromic cleft lip and palate. Hence, we investigated the gene and protein expression of these genes in normal and cleft affected mucosal tissue obtained from 22 children, along with analyzing their role in promoting local-site inflammation using NF-κB. Additionally, we investigated the role of PTX3, which plays a critical role in tissue remodeling and wound repair. We found a residual gene and protein expression of DLX4 in cleft mucosa, although no differences in gene expression levels of HOXB3 and MSX2 were noted. However, a significant increase in protein expression for these genes was noted in the cleft mucosa (p < 0.05), indicating increased cellular proliferation. This was coupled with a significant increase in NF-κB protein expression in cleft mucosa (p < 0.05), highlighting the role of these genes in promotion of pro-inflammatory environment. Finally, no differences in gene expression of PTX3 were noted.

Phosphorylation of Msx1 promotes cell proliferation through the Fgf9/18-MAPK signaling pathway during embryonic limb development

Msh homeobox (Msx) is a subclass of homeobox transcriptional regulators that control cell lineage development, including the early stage of vertebrate limb development, although the underlying mechanisms are not clear. Here, we demonstrate that Msx1 promotes the proliferation of myoblasts and mesenchymal stem cells (MSCs) by enhancing mitogen-activated protein kinase (MAPK) signaling. Msx1 directly binds to and upregulates the expression of fibroblast growth factor 9 (Fgf9) and Fgf18. Accordingly, knockdown or antibody neutralization of Fgf9/18 inhibits Msx1-activated extracellular signal-regulated kinase 1/2 (Erk1/2) phosphorylation. Mechanistically, we determined that the phosphorylation of Msx1 at Ser136 is critical for enhancing Fgf9 and Fgf18 expression and cell proliferation, and cyclin-dependent kinase 1 (CDK1) is apparently responsible for Ser136 phosphorylation. Furthermore, mesenchymal deletion of Msx1/2 results in decreased Fgf9 and Fgf18 expression and Erk1/2 phosphorylation, which leads to serious defects in limb development in mice. Collectively, our findings established an important function of the Msx1-Fgf-MAPK signaling axis in promoting cell proliferation, thus providing a new mechanistic insight into limb development.

Effects of Low-Level Er:YAG Laser Irradiation on Proliferation and Calcification of Primary Osteoblast-Like Cells Isolated From Rat Calvaria

Several reports have shown that the photo-bio-modulation of cells by various lasers has favorable biological effects. However, the effects of low-level Er:YAG laser irradiation on osteoblasts remain unclear. The purpose of this study was to evaluate the effects of low-level Er:YAG laser irradiation on proliferation and osteogenic differentiation of primary osteoblast-like cells isolated from the calvariae of 3-5-day-old Wistar rats. Cells were irradiated by Er:YAG laser at energy fluences of 2.2, 3.3, and 4.3 J/cm2, respectively. After irradiation, cell surface temperatures were measured and cell proliferation was evaluated by flow cytometry and CCK-8. Calcification was evaluated by measuring areas of Alizarin red S staining after 7, 14, and 21 days culture in osteoinductive medium. Gene expression in non-irradiated and laser-irradiated cells was evaluated by qPCR at 3, 6, and 12 h, as well as 1, 3, 7, and 14 days after irradiation. Microarray analysis was performed to comprehensively evaluate the gene expression of non-irradiated and irradiated cells at 3.3 J/cm2 at 6 h after irradiation. No pronounced increase of cell surface temperature was induced by irradiation. Irradiation did not affect osteoblast-like cell proliferation. Osteoblast-like cell calcification was significantly increased 7 days after Er:YAG laser irradiation at 3.3 J/cm2. Bglap expression was significantly increased in cells irradiated at 3.3 J/cm2 6 h post-irradiation. Microarray analysis showed that irradiation at 3.3 J/cm2 caused an upregulation of inflammation-related genes and downregulation of Wisp2. Gene set enrichment analysis also clarified enrichment of inflammation-related and Notch signaling gene sets. In conclusion, low-level Er:YAG laser irradiation at 3.3 J/cm2 enhanced calcification of primary osteoblast-like cells via enhanced Bglap expression and enriched Notch signaling.

A Qualitative Model of the Differentiation Network in Chondrocyte Maturation: A Holistic View of Chondrocyte Hypertrophy

Differentiation of chondrocytes towards hypertrophy is a natural process whose control is essential in endochondral bone formation. It is additionally thought to play a role in several pathophysiological processes, with osteoarthritis being a prominent example. We perform a dynamic analysis of a qualitative mathematical model of the regulatory network that directs this phenotypic switch to investigate the influence of the individual factors holistically. To estimate the stability of a SOX9 positive state (associated with resting/proliferation chondrocytes) versus a RUNX2 positive one (associated with hypertrophy) we employ two measures. The robustness of the state in canalisation (size of the attractor basin) is assessed by a Monte Carlo analysis and the sensitivity to perturbations is assessed by a perturbational analysis of the attractor. Through qualitative predictions, these measures allow for an in silico screening of the effect of the modelled factors on chondrocyte maintenance and hypertrophy. We show how discrepancies between experimental data and the model’s results can be resolved by evaluating the dynamic plausibility of alternative network topologies. The findings are further supported by a literature study of proposed therapeutic targets in the case of osteoarthritis.

Development of the turtle plastron, the order-defining skeletal structure

The dorsal and ventral aspects of the turtle shell, the carapace and the plastron, are developmentally different entities. The carapace contains axial endochondral skeletal elements and exoskeletal dermal bones. The exoskeletal plastron is found in all extant and extinct species of crown turtles found to date and is synaptomorphic of the order Testudines. However, paleontological reconstructed transition forms lack a fully developed carapace and show a progression of bony elements ancestral to the plastron. To understand the evolutionary development of the plastron, it is essential to know how it has formed. Here we studied the molecular development and patterning of plastron bones in a cryptodire turtle Trachemys scripta We show that plastron development begins at developmental stage 15 when osteochondrogenic mesenchyme forms condensates for each plastron bone at the lateral edges of the ventral mesenchyme. These condensations commit to an osteogenic identity and suppress chondrogenesis. Their development overlaps with that of sternal cartilage development in chicks and mice. Thus, we suggest that in turtles, the sternal morphogenesis is prevented in the ventral mesenchyme by the concomitant induction of osteogenesis and the suppression of chondrogenesis. The osteogenic subroutines later direct the growth and patterning of plastron bones in an autonomous manner. The initiation of plastron bone development coincides with that of carapacial ridge formation, suggesting that the development of dorsal and ventral shells are coordinated from the start and that adopting an osteogenesis-inducing and chondrogenesis-suppressing cell fate in the ventral mesenchyme has permitted turtles to develop their order-specific ventral morphology.

Signaling pathways in osteogenesis and osteoclastogenesis: Lessons from cranial sutures and applications to regenerative medicine

One of the simplest models for examining the interplay between bone formation and resorption is the junction between the cranial bones. Although only roughly a quarter of patients diagnosed with craniosynostosis have been linked to known genetic disturbances, the molecular mechanisms elucidated from these studies have provided basic knowledge of bone homeostasis. This work has translated to methods and advances in bone tissue engineering. In this review, we examine the current knowledge of cranial suture biology derived from human craniosynostosis syndromes and discuss its application to regenerative medicine.

Cephalometric assessment of craniofacial dysmorphologies in relation with Msx2 mutations in mouse

OBJECTIVES

To determine the role of Msx2 in craniofacial morphology and growth, we used a mouse model and performed a quantitative morphological characterization of the Msx2 (-/-) and the Msx2 (+/-) phenotype using a 2D cephalometric analysis applied on micrographs.

MATERIALS AND METHODS

Forty-four three-and-a-half-month-old female CD1 mice were divided into the following three groups: Msx2 (+/+) (n = 16), Msx2 (+/-) (n = 16), and Msx2 (-/-) (n = 12). Profile radiographs were scanned. Modified cephalometric analysis was performed to compare the three groups.

RESULTS

Compared with the wild-type mice, the Msx2 (-/-) mutant mice presented an overall craniofacial size decrease and modifications of the shape of the different parts of the craniofacial skeleton, namely the neurocranium, the viscerocranium, the mandible, and the teeth. In particular, dysmorphologies were seen in the cochlear apparatus and the teeth (taurodontism, reduced incisor curvature). Finally contrary to previous published results, we were able to record a specific phenotype of the Msx2 (+/-) mice with this methodology. This Msx2 (+/-) mouse phenotype was not intermediate between the Msx2 (-/-) and the wild-type animals.

CONCLUSION

Msx2 plays an important role in craniofacial morphogenesis and growth because almost all craniofacial structures were affected in the Msx2(-/-) mice including both intramembranous and endochondral bones, the cochlear apparatus, and the teeth. In addition, Msx2 haploinsufficiency involves a specific phenotype with subtle craniofacial structures modifications compared with human mutations.

Skeletal gene expression in the temporal region of the reptilian embryos: implications for the evolution of reptilian skull morphology

Reptiles have achieved highly diverse morphological and physiological traits that allow them to exploit various ecological niches and resources. Morphology of the temporal region of the reptilian skull is highly diverse and historically it has been treated as an important character for classifying reptiles and has helped us understand the ecology and physiology of each species. However, the developmental mechanism that generates diversity of reptilian skull morphology is poorly understood. We reveal a potential developmental basis that generates morphological diversity in the temporal region of the reptilian skull by performing a comparative analysis of gene expression in the embryos of reptile species with different skull morphology. By investigating genes known to regulate early osteoblast development, we find dorsoventrally broadened unique expression of the early osteoblast marker, Runx2, in the temporal region of the head of turtle embryos that do not form temporal fenestrae. We also observe that Msx2 is also uniquely expressed in the mesenchymal cells distributed at the temporal region of the head of turtle embryos. Furthermore, through comparison of gene expression pattern in the embryos of turtle, crocodile, and snake species, we find a possible correlation between the spatial patterns of Runx2 and Msx2 expression in cranial mesenchymal cells and skull morphology of each reptilian lineage. Regulatory modifications of Runx2 and Msx2 expression in osteogenic mesenchymal precursor cells are likely involved in generating morphological diversity in the temporal region of the reptilian skull.

Cranial sutures: a multidisciplinary review

INTRODUCTION

Progress in cranial suture research is shaping our current understanding of the topic; however, emphasis has been placed on individual contributing components rather than the cranial sutural system as a whole. Improving our holistic view helps further guide clinicians who treat cranial sutural abnormalities as well as researchers who study them.

MATERIALS AND METHODS

Information from anatomy, anthropology, surgery, and computed modeling was integrated to provide a perspective to interpret suture formation and variability within the cranial functional and structural system.

RESULTS

Evidence from experimental settings, simulations, and evolution suggest a multifactorial morphogenetic process associated with functions and morphology of the sutures. Despite molecular influences, the biomechanical cranial environment has a main role in both the ontogenetic and phylogenetic suture dynamics.

CONCLUSIONS

Furthering our holistic understanding of the intricate cranial sutural system promises to expand our knowledge and enhance our ability to treat associated anomalies.

MAPK/ERK Signaling Pathway Analysis in Primary Osteoblasts From Patients With Nonsyndromic Sagittal Craniosynostosis

OBJECTIVE

The MAPK/ERK signaling pathway has been implicated in several craniosynostosis syndromes and represents a plausible target for therapeutic management of craniosynostosis. The causes of sagittal nonsyndromic craniosynostosis (sNSC) have not been well understood and the role that MAPK/ERK signaling cascade plays in this condition warrants an investigation. We hypothesized that MAPK-signaling is misregulated in calvarial osteoblasts derived from patients with sNSC.

METHODS

In order to analyze if the MAPK/ERK pathway is perturbed in sNSC, we established primary calvarial osteoblast cell lines from patients undergoing surgery for correction of this congenital anomaly. Appropriate negative and positive control cell lines were used for comparison, and we examined the levels of phosphorylated ERK by immunoblotting.

RESULTS

Primary osteoblasts from patients with sNSC showed no difference in ERK1/2 phosphorylation with or without FGF2 stimulation as compared with control osteoblasts.

CONCLUSION

Under the described test conditions, we did not observe convincing evidence that MAPK/ERK signaling contributes to the development of sNSC.

Ameloblastin inhibits cranial suture closure by modulating MSX2 expression and proliferation

Deformities of cranial sutures such as craniosynostosis and enlarged parietal foramina greatly impact human development and quality of life. Here we have examined the role of the extracellular matrix protein ameloblastin (Ambn), a recent addition to the family of non-collagenous extracellular bone matrix proteins, in craniofacial bone development and suture formation. Using RT-PCR, western blot and immunohistochemistry, Ambn was localized in mouse calvarial bone and adjacent condensed mesenchyme. Five-fold Ambn overexpression in a K14-driven transgenic mouse model resulted in delayed posterior frontal suture fusion and incomplete suture closure. Moreover, Ambn overexpressor skulls weighed 13.2% less, their interfrontal bones were 35.3% thinner, and the width between frontal bones plus interfrontal suture was 14.3% wider. Ambn overexpressing mice also featured reduced cell proliferation in suture blastemas and in mesenchymal cells from posterior frontal sutures. There was a more than 2-fold reduction of Msx2 in Ambn overexpressing calvariae and suture mesenchymal cells, and this effect was inversely proportionate to the level of Ambn overexpression in different cell lines. The reduction of Msx2 expression as a result of Ambn overexpression was further enhanced in the presence of the MEK/ERK pathway inhibitor O126. Finally, Ambn overexpression significantly reduced Msx2 down-stream target gene expression levels, including osteogenic transcription factors Runx2 and Osx, the bone matrix proteins Ibsp, ColI, Ocn and Opn, and the cell cycle-related gene CcnD1. Together, these data suggest that Ambn plays a crucial role in the regulation of cranial bone growth and suture closure via Msx 2 suppression and proliferation inhibition.

Murine craniofacial development requires Hdac3-mediated repression of Msx gene expression

Craniofacial development is characterized by reciprocal interactions between neural crest cells and neighboring cell populations of ectodermal, endodermal and mesodermal origin. Various genetic pathways play critical roles in coordinating the development of cranial structures by modulating the growth, survival and differentiation of neural crest cells. However, the regulation of these pathways, particularly at the epigenomic level, remains poorly understood. Using murine genetics, we show that neural crest cells exhibit a requirement for the class I histone deacetylase Hdac3 during craniofacial development. Mice in which Hdac3 has been conditionally deleted in neural crest demonstrate fully penetrant craniofacial abnormalities, including microcephaly, cleft secondary palate and dental hypoplasia. Consistent with these abnormalities, we observe dysregulation of cell cycle genes and increased apoptosis in neural crest structures in mutant embryos. Known regulators of cell cycle progression and apoptosis in neural crest, including Msx1, Msx2 and Bmp4, are upregulated in Hdac3-deficient cranial mesenchyme. These results suggest that Hdac3 serves as a critical regulator of craniofacial morphogenesis, in part by repressing core apoptotic pathways in cranial neural crest cells.

Transcriptional regulatory cascades in Runx2-dependent bone development

The development of the musculoskeletal system is a complex process that involves very precise control of bone formation and growth as well as remodeling during postnatal life. Although the understanding of the transcriptional mechanisms of osteogenesis has increased considerably, the molecular regulatory basis, especially the gene regulatory network of osteogenic differentiation, is still poorly understood. This review provides the reader with an overview of the key transcription factors that govern bone formation, highlighting their function and regulation linked to Runt-related transcription factor 2 (Runx2). Runx2 as the master transcription factor of osteoblast differentiation, Twist, Msh homeobox 2 (Msx2), and promyelocytic leukemia zinc-finger protein (PLZF) acting upstream of Runx2, Osterix (Osx) acting downstream of Runx2, and activating transcription factor 4 (ATF4) and zinc-finger protein 521 (ZFP521) acting as cofactors of Runx2 are discussed, and their relevance for tissue engineering is presented. References are provided for more in-depth personal study.

MSX2 in pancreatic tumor development and its clinical application for the diagnosis of pancreatic ductal adenocarcinoma

MSX2, a member of the homeobox genes family, is demonstrated to be the downstream target for ras signaling pathway and is expressed in a variety of carcinoma cells, suggesting its relevance to the development of ductal pancreatic tumors since pancreatic ductal adenocarcinoma (PDAC) and intraductal papillary-mucinous neoplasia (IPMN) harbor frequent K-ras gene mutations. Recent studies revealed the roles of MSX2 in the development of carcinoma of various origins including pancreas. Among gastrointestinal tumors, PDAC is one of the most malignant. PDAC progresses rapidly to develop metastatic lesions, frequently by the time of diagnosis, and these tumors are usually resistant to conventional chemotherapy and radiation therapy. The molecular mechanisms regulating the aggressive behavior of PDAC still remain to be clarified. On the other hand, IPMN of the pancreas is distinct from PDAC because of its intraductal growth in the main pancreatic duct or secondary branches with rare invasion and metastasis to distant organs. However, recent evidence indicated that once IPMN showed stromal invasion, it progresses like PDAC. Therefore, it is important to determin how IPMN progresses to malignant phenotype. In this review, we focus on the involvement of MSX2 in the enhancement of malignant behavior in PDAC and IPMN, and further highlight the clinical approach to differentiate PDAC from chronic pancreatitis by evaluating MSX2 expression level.

PKC signaling inhibits osteogenic differentiation through the regulation of Msx2 function

Protein kinase C (PKC) signaling regulates osteoblast differentiation, but little is known about its downstream effectors. We examined the effect of modulating PKC activity on osteogenic transcription factors and found that the protein level of Msx2 is affected. Msx2 is induced by osteogenic signals such as BMPs and it plays critical roles in bone formation and osteoblast differentiation. Here, we examined the role of PKC signaling in regulating the function of Msx2. We found that the inhibition of PKC signaling enhances osteogenic differentiation in BMP2-stimulated C2C12 cells. Treatment with inhibitors of PKC activity or overexpression of kinase-defective (KD), dominant-negative mutant PKC isoforms strongly reduced the level of Msx2 protein. Several PKC isoforms (α, β, δ, and ζ) interacted with Msx2, and PKCβ phosphorylated Msx2 at Thr135 and Thr141. Msx2 repressed the transcriptional activity of the osteogenic transcription factor Runx2, and this repression was relieved by inhibition of PKC activity or overexpression of the KD mutant PKC isoforms. In addition, PKC prolonged the half-life of Msx2 protein. These results suggest that PKC signaling modulates osteoblast differentiation, at least in part, through the regulation of Msx2.

Median facial clefts in Xenopus laevis: roles of retinoic acid signaling and homeobox genes

The upper lip and primary palate form an essential separation between the brain, nasal structures and the oral cavity. Surprisingly little is known about the development of these structures, despite the fact that abnormalities can result in various forms of orofacial clefts. We have uncovered that retinoic acid is a critical regulator of upper lip and primary palate development in Xenopus laevis. Retinoic acid synthesis enzyme, RALDH2, and retinoic acid receptor gamma (RARγ) are expressed in complementary and partially overlapping regions of the orofacial prominences that fate mapping revealed contribute to the upper lip and primary palate. Decreased RALDH2 and RARγ result in a median cleft in the upper lip and primary palate. To further understand how retinoic acid regulates upper lip and palate morphogenesis we searched for genes downregulated in response to RARγ inhibition in orofacial tissue, and uncovered homeobox genes lhx8 and msx2. These genes are both expressed in overlapping domains with RARγ, and together their loss of function also results in a median cleft in the upper lip and primary palate. Inhibition of RARγ and decreased Lhx8/Msx2 function result in decreased cell proliferation and failure of dorsal anterior cartilages to form. These results suggest a model whereby retinoic acid signaling regulates Lhx8 and Msx2, which together direct the tissue growth and differentiation necessary for the upper lip and primary palate morphogenesis. This work has the potential to better understand the complex nature of the upper lip and primary palate development which will lead to important insights into the etiology of human orofacial clefts.

Importance of Sox2 in maintenance of cell proliferation and multipotency of mesenchymal stem cells in low-density culture

OBJECTIVES

This study has aimed to repopulate 'primitive' cells from late-passage mesenchymal stem cells (MSCs) of poor multipotentiality and low cell proliferation rate, by simply altering plating density.

MATERIALS AND METHODS

Effects of low density culture compared t high density culture on late-passage bone marrow (BM)-derived MSCs and pluripotency markers of multipotentiality were investigated. Cell proliferation, gene expression, RNA interference and differentiation potential were assayed.

RESULTS AND CONCLUSIONS

We repopulated 'primitive' cells by replating late-passage MSCs at low density (17 cells/cm(2) ) regardless of donor age. Repopulated MSCs from low-density culture were smaller cells with spindle shaped morphology compared to MSCs from high-density culture. The latter had enhanced colony-forming ability, proliferation rate, and adipogenic and chondrogenic potential. Strong expression of osteogenic-related genes (Cbfa1, Dlx5, alkaline phosphatase and type Ι collagen) in late-passage MSCs was reduced by replating at low density, whereas expression of three pluripotency markers (Sox2, Nanog and Oct-4), Osterix and Msx2 reverted to levels of early-passage MSCs. Knockdown of Sox2 and Msx2 but not Nanog, using RNA interference, showed significant decrease in colony-forming ability. Specifically, knockdown of Sox2 significantly inhibited multipotentiality and cell proliferation. Our data suggest that plating density should be considered to be a critical factor for enrichment of 'primitive' cells from heterogeneous BM and that replicative senescence and multipotentiality of MSCs during in vitro expansion may be predominantly regulated through Sox2.

MSX2 is an oncogenic downstream target of activated WNT signaling in ovarian endometrioid adenocarcinoma

Ovarian endometrioid adenocarcinomas (OEAs) frequently exhibit constitutive activation of canonical WNT signaling, usually as a result of oncogenic mutations that stabilize and dysregulate the β-catenin protein. In previous work, we used microarray-based methods to compare gene expression in OEAs with and without dysregulated β-catenin as a strategy for identifying novel β-catenin/TCF target genes with important roles in ovarian cancer pathogenesis. Among the genes highlighted by the microarray studies was MSX2, which encodes a homeobox transcription factor. We found MSX2 expression was markedly increased in primary human and murine OEAs with dysregulated β-catenin compared with OEAs with intact β-catenin regulation. WNT pathway activation by WNT3a ligand or GSK3β inhibitor treatment potently induced MSX2 and ectopic expression of a dominant negative form of TCF4 inhibited MSX2 expression in ovarian cancer cells. Chromatin immunoprecipitation studies demonstrated that β-catenin/TCF directly regulates MSX2 expression via binding to TCF binding elements in multiple regions of the MSX2 gene. Notably, ectopic MSX2 expression was found to promote neoplastic transformation of the rodent RK3E model epithelial cell line and to enhance the invasiveness of immortalized human ovarian epithelial cells in vitro and ovarian carcinoma cells in vivo. Inhibition of endogenous MSX2 expression in ovarian endometrioid cancer cells carrying a β-catenin mutation using shRNA approaches inhibited neoplastic properties of the cells in vitro and in vivo. Expression of MSX2 in selected ovarian carcinoma cells induced changes suggestive of epithelial-mesenchymal transition (EMT), but based on analysis of ovarian cell lines and primary tumor tissues, effects of MSX2 on EMT appear to be complex and context-dependent. Our findings indicate MSX2 is a direct downstream transcriptional target of β-catenin/TCF and has a key contributing role in the cancer phenotype of OEAs carrying WNT/β-catenin pathway defects.

The diameter of anodic TiO2 nanotubes affects bone formation and correlates with the bone morphogenetic protein-2 expression in vivo

INTRODUCTION

Recently, it has been demonstrated that the nanoscale environment is a critical factor for cellular behaviour. It has been shown that the diameter of TiO2 nanotube layers controls the cellular behaviour of cells involved in the bone-forming process in vitro. Therefore, the aim of the present study was to investigate the effects of the diameter of TiO2 nanotubes on peri-implant bone formation and the expression of bone matrix proteins in vivo.

MATERIALS AND METHODS

Ninety experimental implants with a nanotube diameter ranging from 15 up to 100 nm were placed in the frontal skulls of six domestic pigs, whereas untreated implants served as controls. The bone-implant contact (BIC) as well as the expression of bone morphogenetic protein (BMP)-2, collagen type-I and osteocalcin were histomorphometrically and immunohistochemically analysed after 30 days.

RESULTS

Evaluating the BIC, a significant higher value, could be found for the 50, 70 and 100 nm groups compared with the controls, whereas a correlation with the BMP-2 expression was present. The BMP-2 expression within the 50, 70 and 100 nm groups was statistically different compared with the control group. Significant difference was found for the osteocalcin expression in the 70 nm group. No statistical difference was found evaluating collagen type-I. SEM evaluation of the specimen surfaces revealed that the nanotube coatings do resist shearing forces evoked by implant insertion.

CONCLUSION

The nanotube diameter can be designed to support cellular functions of osteoblasts and osteoclasts in vivo, including differentiation and protein expression and therefore offer a powerful tool for the controlled formation of peri-implant bone around medical implant devices.

Differential expression of MSX2 in nodular hyperplasia, high-grade prostatic intraepithelial neoplasia and prostate adenocarcinoma

One of the common features in advanced prostate cancer is bone metastasis. In this study, we investigated the clinical relevance of a bone factor, MSX2, in predicting the metastatic ability of prostate adenocarcinoma. Evaluation of MSX2 expression was performed using prostate cell lines as well as patient specimens. A sharp decrease in MSX2 was found in primary prostate cancer cells, 22Rv1, when compared with the non-malignant counterparts, followed by a gradual increase in more aggressive prostate cancer cell lines. Interestingly, the MSX2 protein was upregulated and predominantly expressed in the nucleus in aggressive prostate cancer cell line, C4-2b, compared with the less aggressive 22Rv1. Consistent with the in vitro results, MSX2 nuclear expression was significantly higher in nodular hyperplasia when compared with high-grade prostatic intraepithelial neoplasia (PIN), while MSX2 nuclear expression in prostate adenocarcinoma was higher than that in high-grade PIN. Importantly, MSX2 expression was increased significantly in tumors with metastasis compared with those without metastasis. Finally, MSX2 nuclear scores were significantly increased in patients with preoperative serum PSA >20 ng/mL. No correlation between MSX2 nuclear score and Gleason score was found. Taken together, MSX2 may serve as a potential biomarker in predicting primary prostate tumors with higher metastatic capability.

Expression of MSX2 predicts malignancy of branch duct intraductal papillary mucinous neoplasm of the pancreas

BACKGROUND

To distinguish malignant from benign branch duct (BD)-intraductal papillary mucinous neoplasm (IPMN) still remains difficult. Recently, we revealed that MSX2 was frequently expressed in pancreatic cancer and its expression was correlated with aggressive behavior of the cancer. The aim of this study was to assess the involvement of MSX2 in IPMN development and whether its expression would differentiate malignant from benign IPMN.

METHODS

Seventeen microdissected lesions and 45 IPMN tissues were used for quantitative real-time reverse-transcription polymerase chain reaction (RT-PCR) and immunohistochemistry, respectively. The role of MSX2 in the pancreatic duct cell was assessed by the induced expression of MSX2 in a normal human pancreatic duct epithelial cell line (HPDE).

RESULTS

Malignant IPMN expressed significantly higher levels of MSX2 mRNA than benign IPMN lesions. MSX2 protein expression was frequently found in borderline and malignant lesions (20/29, 68.9%), while its expression was seen in only one of 16 benign IPMN tissues. Univariate analysis showed that nodules of 6 mm or more and MSX2 expression were significantly correlated with the malignancy of BD-IPMN (P = 0.022 and 0.0026, respectively), and multivariate analysis revealed that only MSX2 expression was identified as an independent factor to predict malignant BD-IPMN. HPDE cells expressing MSX2 showed increased cellular proliferation compared to control cells.

CONCLUSIONS

Based on our results, MSX2 plays a pivotal role in the development of IPMN through growth stimulation of tumor cells, and its expression was identified as an independent predictive factor for malignancy of BD-IPMN.

TWIST family of basic helix-loop-helix transcription factors mediate human mesenchymal stem cell growth and commitment

The TWIST family of basic helix-loop-helix transcription factors, Twist-1 and Dermo-1 are known mediators of mesodermal tissue development and contribute to correct patterning of the skeleton. In this study, we demonstrate that freshly purified human bone marrow-derived mesenchymal stromal/stem cells (MSC) express high levels of Twist-1 and Dermo-1 which are downregulated following ex vivo expansion. Enforced expression of Twist-1 or Dermo-1 in human MSC cultures increased expression of the MSC marker, STRO-1, and the early osteogenic transcription factors, Runx2 and Msx2. Conversely, overexpression of Twist-1 and Dermo-1 was associated with a decrease in the gene expression of osteoblast-associated markers, bone morphogenic protein-2, bone sialoprotein, osteopontin, alkaline phosphatase and osteocalcin. High expressing Twist-1 or Dermo-1 MSC lines exhibited an enhanced proliferative potential of approximately 2.5-fold compared with control MSC populations that were associated with elevated levels of Id-1 and Id-2 gene expression. Functional studies demonstrated that high expressing Twist-1 and Dermo-1 MSC displayed a decreased capacity for osteo/chondrogenic differentiation and an enhanced capacity to undergo adipogenesis. These findings implicate the TWIST gene family members as potential mediators of MSC self-renewal and lineage commitment in postnatal skeletal tissues by exerting their effects on genes involved in the early stages of bone development.

Platelet-poor plasma stimulates the proliferation but inhibits the differentiation of rat osteoblastic cells in vitro

INTRODUCTION

Recent studies have shown that the use of platelet preparations in bone and implant surgery might stimulate bone formation. However, the biological mechanisms are not well understood. Moreover, few studies have attempted to evaluate the effect of platelet-poor plasma (PPP), which is a product of the platelet-rich plasma preparation process.

OBJECTIVE

Thus, this study investigated the behavior of osteoblasts isolated from fetal rat calvaria cultivated in the presence of homologous PPP.

MATERIAL AND METHODS

PPP was obtained by centrifugation of the rat mother's blood and used in replacement of fetal calf serum, which is classically used in primary culture procedures. Proliferation was measured by an MTT assay at 24, 48, and 72 h. Real-time PCR was performed to study the expression of Runx2, Dlx5, and osteocalcin (OC) on days 0 (4 h), 1, 3, 7, and 12.

RESULTS

Alkaline phosphatase (ALP) biochemical activity was evaluated on days 0 (4 h), 1, 3, 7, and 12. Observations by phase-contrast microscopy showed that osteoblasts were able to differentiate until the mineralization of the matrix in the presence of PPP. PPP enhanced the proliferation significantly compared with the control group (P< or =0.001). PCR results showed that Runx2, Dlx5, and OC were expressed by cells in the experimental group at lower levels compared with the control group. Biochemical assay of ALP showed a lower activity in the experimental group compared with the control group (P<0.001).

CONCLUSION

These results suggest that, in the presence of homologous PPP, rat osteoblastic cells are able to maintain their phenotype, with a higher rate of proliferation. However, PPP seems to inhibit osteoblastic differentiation.

BMP2 is essential for post natal osteogenesis but not for recruitment of osteogenic stem cells

The effects of BMP2 on bone marrow stromal cell differentiation and bone formation after bone marrow ablation were determined using C57 BL/6J (B6) mice. Inhibition of BMP2 expression with lentiviral BMP2 shRNA prevented both mineralized nodule formation in vitro and bone formation in vivo, and blocked the expression of Runx2 and osterix, transcriptional determinants of terminal osteogenic differentiation. No effect was observed on the expression of Sox9, a transcription factor, which is the one of the first transcriptional determinant to be expressed in committed chondroprogenitor and osteoprogenitor cells. In vitro studies showed that exogenously added BMP7 rescued the expression of osterix and enhanced the expression of Sox9, but had no effect on the expression of Runx2, while it only partially recovered the development of mineral deposition in the cultures. On the other hand, the exogenous addition of BMP2 rescued both Runx2 and osterix expression, did not enhance the expression of Sox9, but fully recovered the inhibition of mineral deposition in the cultures. Using antibodies against CD146 and Sox9, immunohistological examination of the cell populations found in the medullary space three days after bone marrow ablation, showed qualitatively equal numbers of cells expressing these skeletal progenitor and stem cell markers in control and BMP2 shRNA treated animals. Fluorescence Activated Cell Sorting (FACS) analysis of the cells found with the marrow cavities at three days after marrow ablation using CD146 antibody showed near equal numbers of immunopositive cells in both control and shRNA treated animals. In summary, the differences observed in vitro for BMP2 and BMP7 on osteogenic gene expression and mineralization suggest that they have differing effects on bone cell differentiation. These results further demonstrate that in vivo BMP2 is a central morphogenetic regulator of post natal osteoprogenitor differentiation, but does not affect recruitment of progenitors to the osteoblastic lineage.

The Boston-type craniosynostosis mutation MSX2 (P148H) results in enhanced susceptibility of MSX2 to ubiquitin-dependent degradation

Boston-type craniosynostosis is caused by a single amino acid substitution, P148H, in the transcription factor MSX2. The increased binding affinity of MSX2 (P148H) to the response element has led many to hypothesize that the substitution is a gain-of-function mutation. However, there have been conflicting reports on the function of MSX2, and by extension, the nature of the P148H mutation remains unclear. In this study, we have examined the molecular mechanism of MSX2 function and the nature of the P148H mutation. During cranial suture closure of rodent, Msx2 expression was detected in the suture space. Overexpression of wild type MSX2 in mesenchymal cells stimulated cell proliferation and cyclin D1 expression, whereas P148H mutant did not. These results indicated that MSX2 is involved in maintaining the suture space by stimulating suture mesenchymal cell proliferation and that P148H is defective in this process. The protein levels of P148H were lower than wild type Msx2 (Msx2-WT), and pulse-chase experiments indicated that the mutant protein has a shorter half-life than the Msx2-WT protein. The ubiquitylation level of P148H was greater than that of Msx2-WT. The degradation of Msx2 was mediated by Praja1, and the P148H mutant was degraded more effectively than WT. The ubiquitylation of Msx2-WT was higher in the presence of Msx2 (P148H), which indicated that P148H functions as a dominant-negative mutant. Collectively, the primary function of MSX2 in suture closure is the induction of cell proliferation and suture maintenance, and the mutation results in an increased susceptibility of both wild type and mutant MSX2 to proteasomal degradation.

Mechanical influences on suture development and patency

In addition to their role in skull growth, sutures are sites of flexibility between the more rigid bones. Depending on the suture, predominant loading during life may be either tensile or compressive. Loads are transmitted across sutures via collagenous fibers and a fluid-rich extracellular matrix and can be quasi-static (growth of neighboring tissues) or intermittent (mastication). The mechanical properties of sutures, while always viscoelastic, are therefore quite different for tensile versus compressive loading. The morphology of individual sutures reflects the nature of local loading, evidently by a process of developmental adaptation. In vivo or ex vivo, sutural cells respond to tensile or cyclic loading by expressing markers of proliferation and differentiation, whereas compressive loading appears to favor osteogenesis. Braincase and facial sutures exhibit similar mechanical behavior and reactions despite their different natural environments.

Transcriptional control of mesenchymal stem cell differentiation

SUMMARY

In recent years, transcriptomics and proteomics have provided us with a great deal of information about the expression profiles of various cell types and how these change under different conditions. Stem cell research is one area where this has had a major impact by providing an insight into events at the molecular level that control stem cell growth and differentiation. This includes mesenchymal stem cell (MSC) biology where knowledge about the mechanisms governing differentiation is vital for the development of future therapeutic strategies. Although there is still much to learn, we are starting to build up a picture of the main events in these differentiation processes. This review will discuss control of MSC differentiation at the transcriptional level. Not all the factors which have been shown to play a role in lineage-specific mesenchymal differentiation can be covered here. Instead, we will focus specifically on the key factors that contribute to the regulation of osteogenesis, adipogenesis, and chondrogenesis.

Ubc9 promotes the stability of Smad4 and the nuclear accumulation of Smad1 in osteoblast-like Saos-2 cells

Bone morphogenetic proteins (BMPs) play important roles in osteoblast differentiation and maturation. In mammals, the BMP-induced receptor-regulated Smads form complexes with Smad4. These complexes translocate and accumulate within the nucleus, where they regulate the transcription of various target genes. However, the function of Smad4 remains unclear. We performed a yeast two-hybrid screen using Smad4 as bait and a cDNA library derived from human bone marrow to identify the proteins interacting with Smad4. Two full-length cDNA clones for Ubc9 were identified, and the potential functions of Ubc9 were investigated. To determine the role of Ubc9 in the BMP signaling pathway, the endogenous transcription of Ubc9 in the human osteoblast cell line Saos-2 was silenced using siRNA. The expression of BMP-induced transcription factors, including Runx2, Dlx5, Msx2, and Osterix, was examined using real-time reverse transcription polymerase chain reaction (qRT-PCR), and the protein expression of Smad4, Smad1, phosphorylated Smad1, and BMP type I receptors was determined by Western blotting. The subcellular localization of Smad1 and Smad4 was observed using immunofluorescence staining after Ubc9 silencing. To determine whether Smad4 is sumoylated in vitro, recombinant Smad4 was purified and sumoylated Smad4 was visualized using Western blotting. The mRNA expression of various transcription factors was markedly inhibited after Ubc9 silencing. The protein levels of Smad4 and phosphorylated Smad1 decreased in a dose-dependent manner according to the amount of siRNA applied. Gene silencing also decreased the nuclear accumulation of Smad1 and Smad4. The sumoylation assay showed that sumoylated Smad4 is present and dependent on Ubc9 in vitro, which was confirmed by pretreatment with Senp2, a SUMO-protease. These results suggest that Ubc9 promotes the stability of sumoylated Smad4. Furthermore, the expression of key transcription factors, phosphorylated Smad1 protein, and the nuclear accumulation of Smad1 and Smad4 are inhibited by Ubc9 silencing. Thus, Ubc9 plays an important role in the up-regulation of the BMP signaling pathway.

Up-regulation of MSX2 enhances the malignant phenotype and is associated with twist 1 expression in human pancreatic cancer cells

MSX2 is thought to be a regulator of organ development and a downstream target of the ras signaling pathway; however, little is known about the role of MSX2 in the development of pancreatic cancers, most of which harbor a K-ras gene mutation. Therefore, we examined whether the presence of MSX2 correlates with the malignant behavior of pancreatic cancer cells. BxPC3 pancreatic cancer cells that stably overexpress MSX2 showed a flattened and scattered morphology accompanied by a change in localization of E-cadherin and beta-catenin from membrane to cytoplasm. Cell proliferation rate, cell migration, and anchorage-independent cell growth were enhanced in MSX2-expressing cells. Injection of MSX2-expressing cells into the pancreas of nude mice resulted in a significant increase in liver metastases and peritoneal disseminations compared with injection of control cells. Microarray analysis revealed a significant induction of Twist 1 expression in cells that express MSX2. When MSX2 was inactivated in pancreatic cancer cells following transfection with an MSX2-specific small interfering RNA, Twist 1 was down-regulated. Immunohistochemistry of human pancreatic carcinoma tissue revealed that MSX2 was frequently expressed in cancer cells, and that increased expression of MSX2 significantly correlated with higher tumor grade, vascular invasion, and Twist 1 expression. These data indicate that MSX2 plays a crucial role in pancreatic cancer development by inducing changes consistent with epithelial to mesenchymal transition through enhanced expression of Twist 1.

Osterix induces osteogenic gene expression but not differentiation in primary human fetal mesenchymal stem cells

The transcription factor osterix (Osx) is a key regulator of osteoblast differentiation and induces bone formation in embryonic but not adult stem cells. We investigated the effect of up-regulating Osx on an intermediate stem cell type, first trimester fetal mesenchymal stem cells (MSCs), which are more expandable than adult MSCs. Human fetal (hf ) MSCs were transduced with a lentiviral vector encoding human Osx. In undifferentiating MSCs cultures, forced expression of Osx stimulated osteopontin and alkaline phosphatase expression. However, Osx did not up-regulate osteocalcin, a late marker of osteoblast differentiation or result in extracellular calcium crystals, indicating that Osx does not directly mediate terminal differentiation in primary hfMSCs. To understand the downstream effects of Osx expression in primary hfMSCs, we next investigated the regulatory relationship between Osx, and the transcription factors Dlx5, Runx2, and Msx2. Osx induced Dlx5 but did not affect Runx2 and Msx2, whereas stealth ribonucleic acid interference of Osx inhibited Dlx5 without affecting expression of Runx2 and Msx2. In conclusion, Osx regulates osteogenic gene expression in hfMSCs but is insufficient to induce terminal osteogenic differentiation.

BMP4 and PTHrP interact to stimulate ductal outgrowth during embryonic mammary development and to inhibit hair follicle induction

The mammary glands develop initially as buds arising from the ventral embryonic epidermis. Recent work has shed light on signaling pathways leading to the patterning and formation of the mammary placodes and buds in mouse embryos. Relatively little is known of the signaling pathways that initiate branching morphogenesis and the formation of the ducts from the embryonic buds. Previous studies have shown that parathyroid hormone-related protein (PTHrP; also known as parathyroid hormone-like peptide, Pthlh) is produced by mammary epithelial cells and acts on surrounding mesenchymal cells to promote their differentiation into a mammary-specific dense mesenchyme. As a result of PTHrP signaling, the mammary mesenchyme supports mammary epithelial cell fate, initiates ductal development and patterns the overlying nipple sheath. In this report, we demonstrate that PTHrP acts, in part, by sensitizing mesenchymal cells to BMP signaling. PTHrP upregulates BMP receptor 1A expression in the mammary mesenchyme, enabling it to respond to BMP4, which is expressed within mesenchymal cells underlying the ventral epidermis during mammary bud formation. We demonstrate that BMP signaling is important for outgrowth of normal mammary buds and that BMP4 can rescue outgrowth of PTHrP(-/-) mammary buds. In addition, the combination of PTHrP and BMP signaling is responsible for upregulating Msx2 gene expression within the mammary mesenchyme, and disruption of the Msx2 gene rescues the induction of hair follicles on the ventral surface of mice overexpressing PTHrP in keratinocytes (K14-PTHrP). Our data suggest that PTHrP signaling sensitizes the mammary mesenchyme to the actions of BMP4, triggering outgrowth of the mammary buds and inducing MSX2 expression, which, in turn, leads to lateral inhibition of hair follicle formation within the developing nipple sheath.

Dlx5 drives Runx2 expression and osteogenic differentiation in developing cranial suture mesenchyme

Craniofacial bones derive from cephalic neural crest, by endochondral or intramembranous ossification. Here, we address the role of the homeobox transcription factor Dlx5 during the initial steps of calvaria membranous differentiation and we show that Dlx5 elicits Runx2 induction and full osteoblast differentiation in embryonic suture mesenchyme grown "in vitro". First, we compare Dlx5 expression to bone-related gene expression in the developing skull and mandibular bones. We classify genes into three groups related to consecutive steps of ossification. Secondly, we study Dlx5 activity in osteoblast precursors, by transfecting Dlx5 into skull mesenchyme dissected prior to the onset of either Dlx5 and Runx2 expression or osteogenesis. We find that Dlx5 does not modify the proliferation rate or the expression of suture markers in the immature calvaria cells. Rather, Dlx5 initiates a complete osteogenic differentiation in these early primary cells, by triggering Runx2, osteopontin, alkaline phosphatase, and other gene expression according to the sequential temporal sequence observed during skull osteogenesis "in vivo". Thirdly, we show that BMP signaling activates Dlx5, Runx2, and alkaline phosphatase in those primary cultures and that a dominant-negative Dlx factor interferes with the ability of the BMP pathway to activate Runx2 expression. Together, these data suggest a pivotal role of Dlx5 and related Dlx factors in the onset of differentiation of chick calvaria osteoblasts.

Advances in Runx2 regulation and its isoforms

During the last 10 years, we have witnessed major progress in skeleton biology. Runx2 is an accepted transcription factor essential for osteoblast development from mesenchymal stem cells and maturation into osteocytes and organize crucial events during bone formation. Alternations in Runx2 expression levels are associated with skeletal diseases. In vitro and in vivo studies have reported that multiple integrated complex path ways (such as Wnt/LRP5/beta-catenin, BMP/Smads, 1, 25-(OH)2-vitaminD3/VDR/VDRE pathway, etc.) and several regulatory proteins (such as Msx2, Dlx5, Twists, etc.) play critical roles in modulating Runx2 gene expression, activity, and the subsequent bone formation. These findings provide novel insights through controlling osteoblast differentiation to treat osteoporosis or other bone diseases with altered bone mass by stimulating Runx2 expression. Further studies have shown that expression of RUNX2 is initiated from two promoters, the distal P1 promoter and the proximal P2 promoter. The alternative use of promoters gives rise to the genesis of two major protein isoforms with distinct amino termini, named as Runx2-TypeI and Runx2-TypeII. Here, we also review a complex spatio-temporal pattern of two major isoforms expressions and their possible function differences in skeleton development.

Networks and hubs for the transcriptional control of osteoblastogenesis

We present an overview of the concepts of tissue-specific transcriptional control mechanisms essential for development of the bone cell phenotype. BMP2 induced transcription factors constitute a network of activities and molecular switches for bone development and osteoblast differentiation. Among these regulators are Runx2 (Cbfa1/AML3), the principal osteogenic master gene for bone formation, as well as homeodomain proteins and osterix. Runx2 has multiple regulatory activities, including activation or repression of gene expression, and integration of biological signals from developmental cues, such as BMP/TGFbeta, Wnt and Src signaling pathways. Runx2 provides a new paradigm for transcriptional control by functioning as a principal scaffolding protein in nuclear microenvironments to control gene expression in response to physiologic signals (growth factors, cytokines and hormones). The protein serves as a hub for the coordination of activities essential for the expansion and differentiation of osteogenic lineage cells through the formation of co-regulatory protein complexes organized in subnuclear domains. Mechanisms by which Runx2 supports commitment to osteogenesis and determines cell fate involve its retention on mitotic chromosomes. Disruption of a unique protein module, the subnuclear targeting signal of Runx2, has profound effects on osteoblast differentiation and metastasis of cancer cells in the bone microenvironment. Runx2 target genes include regulators of cell growth control, components of the bone extracellular matrix, angiogenesis, and signaling proteins for development of the osteoblast phenotype and bone turnover. The specificity of Runx2 regulatory activities provides a basis for novel therapeutic strategies to correct bone disorders.

Gene therapy in orthopaedics

Impressive advances in our knowledge of the molecular genetic basis of skeletal disorders and fracture healing have led to the development of novel therapeutics based on ectopic expression of one or more genes in patient cells that can influence repair or regenerative processes in bone. Gene therapy is an attractive new approach to the treatment of bone disorders. Orthopaedics has become one of the most promising areas of research into gene therapy. This is because many potential orthopaedic targets for gene therapy, unlike traditional targets such as cancer and severe genetic disorders, neither present difficult delivery problems nor require prolonged periods of gene expression. Gene therapy offers new possibilities for the clinical management of orthopaedic conditions that are difficult to treat by traditional surgical or medical means. Impaired bone healing, need for extensive bone formation, cartilage repair and metabolic bone diseases are all conditions where alterations of the signalling peptides involved may provide cure or improvement. In orthopaedic oncology, gene therapy may achieve induction of tumour necrosis and increased tumour sensitivity to chemotherapy. An increasing amount of evidence indicates that gene transfer can aid the repair of articular cartilage, menisci, intervertebral disks, ligaments and tendons. These developments have the potential to transform many areas of musculoskeletal care, leading to treatments that are less invasive, more effective and less expensive than existing modalities.

Autoregulatory mechanism of Runx2 through the expression of transcription factors and bone matrix proteins in multipotential mesenchymal cell line, ROB-C26

Runx2 is essential for osteoblast differentiation and gene expression of bone matrix proteins, however, little is known about the mechanism regulating its activity. In this study, the role of Runx2 on gene expression of transcription factors, AJ18, Msx2, and Dlx5, was examined in vitro. It is known that AJ18 and Msx2 act as repressors to inhibit activity of Runx2, whereas Dlx5 promotes its activity. An expression vector inserted Runx2 cDNA was transiently overexpressed in a rat multipotential mesenchymal cell line, ROB-C26 (C26). Real time reverse transcription-PCR analysis showed that, in exogenous Runx2-overexpressing C26 cells (C26-Rx), AJ18 expression increased 1.8-fold, Msx2 expression increased 3.0-fold, and Dlx5 expression increased 2.7-fold compared to the cells transfected with vector alone (C26-Co). Luciferase assay also showed that, in C26-Rx, AJ18 promoter activity increased 2.1-fold compared to C26-Co. Furthermore, gene expression of alkaline phosphatase (ALP) and bone matrix proteins including type I collagen (Col1), osteocalcin (OC), osteopontin (OPN), and matrix Gla protein (MGP) was examined. In C26-Rx, MGP expression increased 1.8-fold, and OPN expression increased 1.4-fold compared to C26-Co. However, no significant difference in Col1, ALP, and OC expressions was detected between C26-Rx and C26-Co. These results suggest that the existence of autoregulatory feed back loops, which inhibit Runx2 activity through the interaction of AJ18, Dlx5, and Msx2 cooperating with that of MGP and OPN, interferes with the differentiation of C26 cells toward mature osteoblasts.

Critical molecular switches involved in BMP-2-induced osteogenic differentiation of mesenchymal cells

Bone morphogenetic protein (BMP)-2 strongly induces bone formation. Introduction of the protein in muscle tissue results in ectopic bone formation. Similarly, BMP-2 treatment also stimulates the in vitro transdifferentiation of myogenic cells to osteogenic cells. The establishment of an in vitro model system has enabled the investigation of intracellular events including BMP receptor activation, BMP-2-induced R-Smad activation, and kinase activation, and the role of osteogenic transcription factors, such as Runx2, Osx, Dlx5, and Msx2. Many reviews have addressed events downstream of BMP-receptor binding but few deal with molecular cascades involved in BMP-2-induced osteogenesis. We focus on critical molecular switches, especially transcription factors, and several kinase pathways involved in osteogenic differentiation.

Ventral abdominal wall dysmorphogenesis of Msx1/Msx2 double-mutant mice

Msx1 and Msx2 genes encode the homeodomain transcription factors. Several gene knockout mice and expression studies suggest that they possess functionally redundant roles in embryogenesis. In this study, we revealed that Msx1 and Msx2 were expressed during ventral body wall formation in an overlapping manner. Msx1/Msx2 double-mutant mice displayed embryonic abdominal wall defects with disorganized muscle layers and connective tissues. These findings indicate that Msx1 and Msx2 play roles in concert during embryonic ventral abdominal wall formation.

The pathophysiology of HOX genes and their role in cancer

The HOM-C clustered prototype homeobox genes of Drosophila, and their counterparts, the HOX genes in humans, are highly conserved at the genomic level. These master regulators of development continue to be expressed throughout adulthood in various tissues and organs. The physiological and patho-physiological functions of this network of genes are being avidly pursued within the scientific community, but defined roles for them remain elusive. The order of expression of HOX genes within a cluster is co-ordinated during development, so that the 3' genes are expressed more anteriorly and earlier than the 5' genes. Mutations in HOXA13 and HOXD13 are associated with disorders of limb formation such as hand-foot-genital syndrome (HFGS), synpolydactyly (SPD), and brachydactyly. Haematopoietic progenitors express HOX genes in a pattern characteristic of the lineage and stage of differentiation of the cells. In leukaemia, dysregulated HOX gene expression can occur due to chromosomal translocations involving upstream regulators such as the MLL gene, or the fusion of a HOX gene to another gene such as the nucleoporin, NUP98. Recent investigations of HOX gene expression in leukaemia are providing important insights into disease classification and prediction of clinical outcome. Whereas the oncogenic potential of certain HOX genes in leukaemia has already been defined, their role in other neoplasms is currently being studied. Progress has been hampered by the experimental approach used in many studies in which the expression of small subsets of HOX genes was analysed, and complicated by the functional redundancy implicit in the HOX gene system. Attempts to elucidate the function of HOX genes in malignant transformation will be enhanced by a better understanding of their upstream regulators and downstream target genes.

FGF-2 Acts through an ERK1/2 Intracellular Pathway to Affect Osteoblast Differentiation

An abundance of genetic and experimental data have suggested that fibroblast growth factor (FGF) signaling plays a central role in physiological and pathological cranial suture fusion. Although alterations in the differentiation and proliferation of sutural osteoblasts may be a key mediator of this process, the mechanisms by which FGF signaling regulates osteoblast differentiation remain incompletely understood. In the current study, the authors show that recombinant human FGF-2 alters osteoblastic expression of bone morphogenetic protein-2 and Msx-2 in vitro to favor cellular differentiation and osteoinduction. The ERK1/2 intracellular signaling cascade was shown to be necessary for recombinant human FGF-2-mediated bone morphogenetic protein-2 transcriptional changes. Furthermore, the cellular production of an intermediate transcriptional modifier was found to be necessary for the recombinant human FGF-2-mediated gene expression changes in bone morphogenetic protein-2 and Msx-2. Together, these findings offer new insight into the mechanisms by which FGF-2 modulates osteoblast biology.

Effects of bone morphogenetic protein-2 and transforming growth factor beta1 on gene expression of transcription factors, AJ18 and Runx2 in cultured osteoblastic cells

Osteoblast differentiation is controlled by multiple transcription factors, Runx2, AJ18, Osterix, Dlx5 and Msx2. The mechanisms of regulation of AJ18 mRNA expression by the transforming growth factor beta (TGF-beta) superfamily remain poorly understood. However, it is known that BMP-2 induces differentiation of C26 cells into more mature osteoblastic cells. The present study, using Northern blot and real-time reverse transcription polymerase chain reaction analyses, investigated the effects of bone morphogenetic protein-2 (BMP-2) and TGF-beta1 on mRNA expression of AJ18 and Runx2 in a clonal osteoblast precursor cell line ROB-C26 (C26) cultured for 3, 6 or 9 days in the presence or absence of BMP-2. Although mRNA expression of Osterix and bone sialoprotein (BSP) was undetectable in the C26 culture, BMP-2 induced Osterix expression on days 3-9, but not BSP expression. BMP-2 also stimulated significantly Dlx5 expression on days 3-9, Msx2 and matrix Gla protein expressions on days 3 and 6, Runx2, alkaline phosphatase and osteocalcin expressions on days 6 and 9 in the culture. Furthermore, BMP-2 increased significantly Smad5 mRNA in the culture on day 3, indicating BMP-2 involvement in the regulation of Smad5 mRNA expression. In contrast, the inhibitory effects of BMP-2 on AJ18 mRNA expression were significant on days 3-9, indicating that a decrease in AJ18 mRNA expression is essential for the increased osteoblastic differentiation. Furthermore, TGF-beta1 (0, 0.1, 1.0 and 5.0 ng/ml) treatment of C26 cells cultured for 6 days in the presence or absence of BMP-2 for 24h stimulated mRNA levels of AJ18 and Runx2, maximal stimulation occurring principally at 1.0 ng/ml. These observations indicate that the expression of AJ18 and Runx2 mRNAs in C26 cells is under the control of BMP-2 and TGF-beta1, which exert different effects on AJ18 mRNA expression, but are potent stimulators of Runx2 mRNA expression during osteoblast differentiation.