Sox-4 messenger RNA is expressed in the embryonic growth plate and regulated via the parathyroid hormone/parathyroid hormone-related protein receptor in osteoblast-like cells

Inorganic Biomaterials Shape the Transcriptome Profile to Induce Endochondral Differentiation

Minerals play a vital role, working synergistically with enzymes and other cofactors to regulate physiological functions including tissue healing and regeneration. The bioactive characteristics of mineral-based nanomaterials can be harnessed to facilitate in situ tissue regeneration by attracting endogenous progenitor and stem cells and subsequently directing tissue-specific differentiation. Here, cellular responses of human mesenchymal stem/stromal cells to traditional bioactive mineral-based nanomaterials, such as hydroxyapatite, whitlockite, silicon-dioxide, and the emerging synthetic 2D nanosilicates are investigated. Transcriptome sequencing is utilized to probe the cellular response and determine the significantly affected signaling pathways due to exposure to these inorganic nanomaterials. Transcriptome profiles of stem cells treated with nanosilicates reveals a stabilized skeletal progenitor state suggestive of endochondral differentiation. This observation is bolstered by enhanced deposition of matrix mineralization in nanosilicate treated stem cells compared to control or other treatments. Specifically, use of 2D nanosilicates directs osteogenic differentiation of stem cells via activation of bone morphogenetic proteins and hypoxia-inducible factor 1-alpha signaling pathway. This study provides  insight into impact of nanomaterials on cellular gene expression profile and predicts downstream effects of nanomaterial induction of endochondral differentiation.

Growing Pains: The Need for Engineered Platforms to Study Growth Plate Biology

Growth plates, or physis, are highly specialized cartilage tissues responsible for longitudinal bone growth in children and adolescents. Chondrocytes that reside in growth plates are organized into three distinct zones essential for proper function. Modeling key features of growth plates may provide an avenue to develop advanced tissue engineering strategies and perspectives for cartilage and bone regenerative medicine applications and a platform to study processes linked to disease progression. In this review, a brief introduction of the growth plates and their role in skeletal development is first provided. Injuries and diseases of the growth plates as well as physiological and pathological mechanisms associated with remodeling and disease progression are discussed. Growth plate biology, namely, its architecture and extracellular matrix organization, resident cell types, and growth factor signaling are then focused. Next, opportunities and challenges for developing 3D biomaterial models to study aspects of growth plate biology and disease in vitro are discussed. Finally, opportunities for increasingly sophisticated in vitro biomaterial models of the growth plate to study spatiotemporal aspects of growth plate remodeling, to investigate multicellular signaling underlying growth plate biology, and to develop platforms that address key roadblocks to in vivo musculoskeletal tissue engineering applications are described.

Roles and regulation of SOX transcription factors in skeletogenesis

SOX transcription factors participate in the specification, differentiation and activities of many cell types in development and beyond. The 20 mammalian family members are distributed into eight groups based on sequence identity, and while co-expressed same-group proteins often have redundant functions, different-group proteins typically have distinct functions. More than a handful of SOX proteins have pivotal roles in skeletogenesis. Heterozygous mutations in their genes cause human diseases, in which skeletal dysmorphism is a major feature, such as campomelic dysplasia (SOX9), or a minor feature, such as LAMSHF syndrome (SOX5) and Coffin-Siris-like syndromes (SOX4 and SOX11). Loss- and gain-of-function experiments in animal models have revealed that SOX4 and SOX11 (SOXC group) promote skeletal progenitor survival and control skeleton patterning and growth; SOX8 (SOXE group) delays the differentiation of osteoblast progenitors; SOX9 (SOXE group) is essential for chondrocyte fate maintenance and differentiation, and works in cooperation with SOX5 and SOX6 (SOXD group) and other types of transcription factors. These and other SOX proteins have also been proposed, mainly through in vitro experiments, to have key roles in other aspects of skeletogenesis, such as SOX2 in osteoblast stem cell self-renewal. We here review current knowledge of well-established and proposed skeletogenic roles of SOX proteins, their transcriptional and non-transcriptional actions, and their modes of regulation at the gene, RNA and protein levels. We also discuss gaps in knowledge and directions for future research to further decipher mechanisms underlying skeletogenesis in health and diseases and identify treatment options for skeletal malformation and degeneration diseases.

The effect of forced exercise on knee joints in Dio2(-/-) mice: type II iodothyronine deiodinase-deficient mice are less prone to develop OA-like cartilage damage upon excessive mechanical stress

OBJECTIVE

To further explore deiodinase iodothyronine type 2 (DIO2) as a therapeutic target in osteoarthritis (OA) by studying the effects of forced mechanical loading on in vivo joint cartilage tissue homeostasis and the modulating effect herein of Dio2 deficiency.

METHODS

Wild-type and C57BL/6-Dio2(-/-) -mice were subjected to a forced running regime for 1 h per day for 3 weeks. Severity of OA was assessed by histological scoring for cartilage damage and synovitis. Genome-wide gene expression was determined in knee cartilage by microarray analysis (Illumina MouseWG-6 v2). STRING-db analyses were applied to determine enrichment for specific pathways and to visualise protein-protein interactions.

RESULTS

In total, 158 probes representing 147 unique genes showed significantly differential expression with a fold-change ≥1.5 upon forced exercise. Among these are genes known for their association with OA (eg, Mef2c, Egfr, Ctgf, Prg4 and Ctnnb1), supporting the use of forced running as an OA model in mice. Dio2-deficient mice showed significantly less cartilage damage and signs of synovitis. Gene expression response upon exercise between wild-type and knockout mice was significantly different for 29 genes.

CONCLUSIONS

Mice subjected to a running regime have significant increased cartilage damage and synovitis scores. Lack of Dio2 protected against cartilage damage in this model and was reflected in a specific gene expression profile, and either mark a favourable effect in the Dio2 knockout (eg, Gnas) or an unfavourable effect in wild-type cartilage homeostasis (eg, Hmbg2 and Calr). These data further support DIO2 activity as a therapeutic target in OA.

MicroRNA expression profile of dexamethasone-induced human bone marrow-derived mesenchymal stem cells during osteogenic differentiation

MiRNAs have been identified in various plants and animals where they function in post-transcriptional regulation. Although studies revealed that dexamethasone play a pivotal role in the osteogenic differentiation of human bone marrow-derived mesenchymal stem cells (hBMSCs), the identification of specific miRNAs and their regulatory roles in this process remain poorly defined. In this study, microarrays were used to analyze the miRNA expression profile of dexamethasone-induced hBMSCs derived from three donors, and RT-PCRs were used to confirm the microarray results. Nine upregulated miRNAs and seven downregulated miRNAs were identified. The putative target genes of these miRNAs were predicted using bioinformatics analysis. Subsequently, we focused our attention on the functional analysis of an upregulated miRNA, miR-23a. Overexpression of miR-23a inhibited osteogenic differentiation of hBMSCs at the cellular, mRNA, and protein levels. The results of our study provide an experimental basis for further research on miRNAs functions during osteogenic differentiation of dexamethasone-induced hBMSCs.

Pleiotropic function of SRY-related HMG box transcription factor 4 in regulation of tumorigenesis

In addition to their critical roles in embryonic development, cell fate decision, and differentiation, members of Sox (Sry-related high-mobility group box) family of transcription factors including Sox4 have been implicated in various cancers. Multiple studies have revealed an increased expression along with specific oncogenic function of Sox4 in tumors, while others observed a reduced expression of Sox4 in different types of malignancies and suppression of tumor initiation or progression by this protein. More interestingly, the prognostic value of Sox4 is debated due to obvious differences between various reports as well as inconsistencies within specific studies. This review summarizes our current understanding of Sox4 expression pattern and its transcription-dependent, as well as transcription-independent, functions in tumor initiation or progression and its correlation with patient survival. We also discuss the existing discrepancies between different reports and their possible explanations.

The role of SRY-related HMG box transcription factor 4 (SOX4) in tumorigenesis and metastasis: friend or foe?

Development and progression of cancer are mediated by alterations in transcriptional networks, resulting in a disturbed balance between the activity of oncogenes and tumor suppressor genes. Transcription factors have the capacity to regulate global transcriptional profiles, and are consequently often found to be deregulated in their expression and function during tumorigenesis. Sex-determining region Y-related high-mobility-group box transcription factor 4 (SOX4) is a member of the group C subfamily of the SOX transcription factors and has a critical role during embryogenesis, where its expression is widespread and controls the development of numerous tissues. SOX4 expression is elevated in a wide variety of tumors, including leukemia, colorectal cancer, lung cancer and breast cancer, suggesting a fundamental role in the development of these malignancies. In many cancers, deregulated expression of this developmental factor has been correlated with increased cancer cell proliferation, cell survival, inhibition of apoptosis and tumor progression through the induction of an epithelial-to-mesenchymal transition and metastasis. However, in a limited subset of tumors, SOX4 has also been reported to act as a tumor suppressor. These opposing roles suggest that the outcome of SOX4 activation depends on the cellular context and the tumor origin. Indeed, SOX4 expression, transcriptional activity and target gene specificity can be controlled by signaling pathways, including the transforming growth factor-β and the WNT pathway, as well as at the post-translational level through regulation of protein stability and interaction with specific cofactors, such as TCF, syntenin-1 and p53. Here, we provide an overview of our current knowledge concerning the role of SOX4 in tumor development and progression.

Novel transcriptional targets of the SRY-HMG box transcription factor SOX4 link its expression to the development of small cell lung cancer

The HMG box transcription factor SOX4 involved in neuronal development is amplified and overexpressed in a subset of lung cancers, suggesting that it may be a driver oncogene. In this study, we sought to develop this hypothesis including by defining targets of SOX4 that may mediate its involvement in lung cancer. Ablating SOX4 expression in SOX4-amplified lung cancer cells revealed a gene expression signature that included genes involved in neuronal development such as PCDHB, MYB, RBP1, and TEAD2. Direct recruitment of SOX4 to gene promoters was associated with their upregulation upon ectopic overexpression of SOX4. We confirmed upregulation of the SOX4 expression signature in a panel of primary lung tumors, validating their specific response by a comparison using embryonic fibroblasts from Sox4-deficient mice. Interestingly, we found that small cell lung cancer (SCLC), a subtype of lung cancer with neuroendocrine characteristics, was generally characterized by high levels of SOX2, SOX4, and SOX11 along with the SOX4-specific gene expression signature identified. Taken together, our findings identify a functional role for SOX genes in SCLC, particularly for SOX4 and several novel targets defined in this study.

Developmental mechanisms in articular cartilage degradation in osteoarthritis

Osteoarthritis is the most common arthritic condition, which involves progressive degeneration of articular cartilage. The most recent accomplishments have significantly advanced our understanding on the mechanisms of the disease development and progression. The most intriguing is the growing evidence indicating that extracellular matrix destruction in osteoarthritic articular cartilage resembles that in the hypertrophic zone of fetal growth plate during endochondral ossification. This suggests common regulatory mechanisms of matrix degradation in OA and in the development and can provide new approaches for the treatment of the disease by targeting reparation of chondrocyte phenotype.

Development of an oligo DNA microarray for the European sea bass and its application to expression profiling of jaw deformity

Background

The European sea bass (Dicentrarchus labrax) is a marine fish of great importance for fisheries and aquaculture. Functional genomics offers the possibility to discover the molecular mechanisms underlying productive traits in farmed fish, and a step towards the application of marker assisted selection methods in this species. To this end, we report here on the development of an oligo DNA microarray for D. labrax.

Results

A database consisting of 19,048 unique transcripts was constructed, of which 12,008 (63%) could be annotated by similarity and 4,692 received a GO functional annotation. Two non-overlapping 60mer probes were designed for each unique transcript and in-situ synthesized on glass slides using Agilent SurePrint™ technology. Probe design was positively completed for 19,035 target clusters; the oligo microarray was then applied to profile gene expression in mandibles and whole-heads of fish affected by prognathism, a skeletal malformation that strongly affects sea bass production. Statistical analysis identified 242 transcripts that are significantly down-regulated in deformed individuals compared to normal fish, with a significant enrichment in genes related to nervous system development and functioning. A set of genes spanning a wide dynamic range in gene expression level were selected for quantitative RT-PCR validation. Fold change correlation between microarray and qPCR data was always significant.

Conclusions

The microarray platform developed for the European sea bass has a high level of flexibility, reliability, and reproducibility. Despite the well known limitations in achieving a proper functional annotation in non-model species, sufficient information was obtained to identify biological processes that are significantly enriched among differentially expressed genes. New insights were obtained on putative mechanisms involved on mandibular prognathism, suggesting that bone/nervous system development might play a role in this phenomenon.

Critical roles for SoxC transcription factors in development and cancer

Sox4, Sox11 and Sox12 constitute the group C of Sry-related HMG box proteins. They are co-expressed in embryonic neuronal progenitors and in mesenchymal cells in many developing organs. More closely related to each other than to any other proteins, they nevertheless bind DNA and activate transcription in vitro with different efficiencies. Sox4-null embryos and Sox11-null newborns die from heart malformations and the latter display widespread defects, while Sox12-null mice are viable and do not show obvious malformations. Sox4 facilitates differentiation of lymphocytes, pancreatic beta cells, osteoblasts and acts in redundancy with Sox11 to promote neuronal differentiation. Sox4 and Sox11 are upregulated in many tumor types in humans, where their roles in cell survival, proliferation, and metastasis remain controversial. Together, these data hint that Sox4 and Sox11 regulate cell differentiation, proliferation and survival in multiple essential processes, and suggest that they may act in redundancy to control many more developmental, physiological and pathological processes than currently known.

PTH and PTHrP signaling in osteoblasts

The striking clinical benefit of PTH in osteoporosis began a new era of skeletal anabolic agents. Several studies have been performed, new studies are emerging out and yet controversies remain on PTH anabolic action in bone. This review focuses on the molecular aspects of PTH and PTHrP signaling in light of old players and recent advances in understanding the control of osteoblast proliferation, differentiation and function.

An extensive genetic program occurring during postnatal growth in multiple tissues

Mammalian somatic growth is rapid in early postnatal life but then slows and eventually ceases in multiple tissues. We hypothesized that there exists a postnatal gene expression program that is common to multiple tissues and is responsible for this coordinate growth deceleration. Consistent with this hypothesis, microarray analysis identified more than 1600 genes that were regulated with age (1 vs. 4 wk) coordinately in kidney, lung, and heart of male mice, including many genes that regulate proliferation. As examples, we focused on three growth-promoting genes, Igf2, Mest, and Peg3, that were markedly down-regulated with age. In situ hybridization revealed that expression occurred in organ-specific parenchymal cells and suggested that the decreasing expression with age was due primarily to decreased expression per cell rather than a decreased number of expressing cells. The declining expression of these genes was slowed during hypothyroidism and growth inhibition (induced by propylthiouracil at 0-5 wk of age) in male rats, suggesting that the normal decline in expression is driven by growth rather than by age per se. We conclude that there exists an extensive genetic program occurring during postnatal life. Many of the involved genes are regulated coordinately in multiple organs, including many genes that regulate cell proliferation. At least some of these are themselves apparently regulated by growth, suggesting that, in the embryo, a gene expression pattern is established that allows for rapid somatic growth of multiple tissues, but then, during postnatal life, this growth leads to negative-feedback changes in gene expression that in turn slow and eventually halt somatic growth, thus imposing a fundamental limit on adult body size.

Identification of candidate genes for human pituitary development by EST analysis

Background

The pituitary is a critical neuroendocrine gland that is comprised of five hormone-secreting cell types, which develops in tandem during the embryonic stage. Some essential genes have been identified in the early stage of adenohypophysial development, such as PITX1, FGF8, BMP4 and SF-1. However, it is likely that a large number of signaling molecules and transcription factors essential for determination and terminal differentiation of specific cell types remain unidentified. High-throughput methods such as microarray analysis may facilitate the measurement of gene transcriptional levels, while Expressed sequence tag (EST) sequencing, an efficient method for gene discovery and expression level analysis, may no-redundantly help to understand gene expression patterns during development.

Results

A total of 9,271 ESTs were generated from both fetal and adult pituitaries, and assigned into 961 gene/EST clusters in fetal and 2,747 in adult pituitary by homology analysis. The transcription maps derived from these data indicated that developmentally relevant genes, such as Sox4, ST13 and ZNF185, were dominant in the cDNA library of fetal pituitary, while hormones and hormone-associated genes, such as GH1, GH2, POMC, LHβ, CHGA and CHGB, were dominant in adult pituitary. Furthermore, by using RT-PCR and in situ hybridization, Sox4 was found to be one of the main transcription factors expressed in fetal pituitary for the first time. It was expressed at least at E12.5, but decreased after E17.5. In addition, 40 novel ESTs were identified specifically in this tissue.

Conclusion

The significant changes in gene expression in both tissues suggest a distinct and dynamic switch between embryonic and adult pituitaries. All these data along with Sox4 should be confirmed to further understand the community of multiple signaling pathways that act as a cooperative network that regulates maturation of the pituitary. It was also suggested that EST sequencing is an efficient means of gene discovery.

Global comparative transcriptome analysis of cartilage formation in vivo

Background

During vertebrate embryogenesis the initial stages of bone formation by endochondral ossification involve the aggregation and proliferation of mesenchymal cells into condensations. Continued growth of the condensations and differentiation of the mesenchymal cells into chondrocytes results in the formation of cartilage templates, or anlagen, which prefigure the shape of the future bones. The chondrocytes in the anlagen further differentiate by undergoing a complex sequence of maturation and hypertrophy, and are eventually replaced by mineralized bone. Regulation of the onset of chondrogenesis is incompletely understood, and would be informed by comprehensive analyses of in vivo gene expression.

Results

Tibial and fibular pre-condensed mesenchyme was microdissected from mouse hind limbs at 11.5 dpc, and the corresponding condensations at 12.5 dpc and cartilage anlagen at 13.5 dpc. Total RNA was isolated, and cRNA generated by linear amplification was interrogated using mouse whole genome microarrays. Differential expression was validated by quantitative PCR for Agc1, Bmp8a, Col2a1, Fgfr4, Foxa3, Gdf5, Klf2, Klf4, Lepre1, Ncad, Sox11, and Trpv4. Further, independent validation of the microarray data was achieved by in situ hybridization to analyse the expression of Lepre1, Pcdh8, Sox11, and Trpv4 from 11.5 dpc to 13.5 dpc during mouse hind limb development. We found significant differential expression of 931 genes during these early stages of chondrogenesis. Of these, 380 genes were down-regulated and 551 up-regulated. Our studies characterized the expression pattern of gene families previously associated with chondrogenesis, such as adhesion molecules, secreted signalling molecules, transcription factors, and extracellular matrix components. Gene ontology approaches identified 892 differentially expressed genes not previously identified during the initiation of chondrogenesis. These included several Bmp, Gdf, Wnt, Sox and Fox family members.

Conclusion

These data represent the first global gene expression profiling analysis of chondrogenic tissues during in vivo development. They identify genes for further study on their functional roles in chondrogenesis, and provide a comprehensive and important resource for future studies on cartilage development and disease.

Calmodulin-dependent kinase 1beta is expressed in the epiphyseal growth plate and regulates proliferation of mouse calvarial osteoblasts in vitro

The Ca(2+)/Calmodulin-dependent protein kinase (CaMK) family is activated in response to elevation of intracellular Ca(2+), and includes CaMK1 (as well as CaMK2 and CaMK4), which exists as different isoforms (alpha, beta, gamma and delta). CaMK1 is present in several cell types and may be involved in various cellular processes, but its role in bone is unknown. In situ hybridization was used to determine the spatial and temporal expression of CaMK1beta during endochondral bone development in mouse embryos and newborn pups. The cellular and subcellular distribution of CaMK1 was assessed by quantitative immunogold electron microscopy (EM). The role of CaMK1beta in mouse calvarial osteoblasts was investigated by using small interfering RNA (siRNA) to silence its expression, while in parallel monitoring cell proliferation and levels of skeletogenic transcripts. cRNA in situ hybridization and EM studies show that CaMK1beta is mainly located in developing long bones and vertebrae (from ED14.5 until day 10 after birth), with highest expression in epiphyseal growth plate hypertrophic chondrocytes. By RT-PCR, we show that CaMK1beta2 (but not beta1) is expressed in mouse hind limbs (in vivo) and mouse calvarial osteoblasts (in vitro), and also in primary human articular chondrocyte cultures. Silencing of CaMK1beta in mouse calvarial osteoblasts by siRNA significantly decreases osteoblast proliferation and c-Fos gene expression (approx. 50%), without affecting skeletogenic markers for more differentiated osteoblasts (i.e. Cbfa1/Runx2, Osterix (Osx), Osteocalcin (Oc), Alkaline phosphatase (Alp) and Osteopontin (Opn)). These results identify CaMK1beta as a novel regulator of osteoblast proliferation, via mechanisms that may at least in part involve c-Fos, thus implicating CaMK1beta in the regulation of bone and cartilage development.

The three SoxC proteins--Sox4, Sox11 and Sox12--exhibit overlapping expression patterns and molecular properties

The group C of Sry-related high-mobility group (HMG) box (Sox) transcription factors has three members in most vertebrates: Sox4, Sox11 and Sox12. Sox4 and Sox11 have key roles in cardiac, neuronal and other major developmental processes, but their molecular roles in many lineages and the roles of Sox12 remain largely unknown. We show here that the three genes are co-expressed at high levels in neuronal and mesenchymal tissues in the developing mouse, and at variable relative levels in many other tissues. The three proteins have conserved remarkable identity through evolution in the HMG box DNA-binding domain and in the C-terminal 33 residues, and we demonstrate that the latter residues constitute their transactivation domain (TAD). Sox11 activates transcription several times more efficiently than Sox4 and up to one order of magnitude more efficiently than Sox12, owing to a more stable α-helical structure of its TAD. This domain and acidic domains interfere with DNA binding, Sox11 being most affected and Sox4 least affected. The proteins are nevertheless capable of competing with one another in reporter gene transactivation. We conclude that the three SoxC proteins have conserved overlapping expression patterns and molecular properties, and might therefore act in concert to fulfill essential roles in vivo.

Osteopenia, decreased bone formation and impaired osteoblast development in Sox4 heterozygous mice

The transcription factor Sox4 is vital for fetal development, as Sox4–/– homozygotes die in utero. Sox4 mRNA is expressed in the early embryonic growth plate and is regulated by parathyroid hormone, but its function in bone modeling/remodeling is unknown. We report that Sox4+/– mice exhibit significantly lower bone mass (by dual-energy X-ray absorptiometry) from an early age, and fail to obtain the peak bone mass of wild-type (WT) animals. Microcomputed tomography (μCT), histomorphometry and biomechanical testing of Sox4+/– bones show reduced trabecular and cortical thickness, growth plate width, ultimate force and stiffness compared with WT. Bone formation rate (BFR) in 3-month-old Sox4+/– mice is 64% lower than in WT. Primary calvarial osteoblasts from Sox4+/– mice demonstrate markedly inhibited proliferation, differentiation and mineralization. In these cultures, osterix (Osx) and osteocalcin (OCN) mRNA expression was reduced, whereas Runx2 mRNA was unaffected. No functional defects were found in osteoclasts. Silencing of Sox4 by siRNA in WT osteoblasts replicated the defects observed in Sox4+/– cells. We demonstrate inhibited formation and altered microarchitecture of bone in Sox4+/– mice versus WT, without apparent defects in bone resorption. Our results implicate the transcription factor Sox4 in regulation of bone formation, by acting upstream of Osx and independent of Runx2.

Primary glioblastomas express mesenchymal stem-like properties

Glioblastoma is the most common and aggressive primary brain cancer. Recent isolation and characterization of brain tumor-initiating cells supports the concept that transformed neural stem cells may seed glioblastoma. We previously identified a wide array of mesenchymal tissue transcripts overexpressed in a broad set of primary glioblastoma (de novo) tumors but not in secondary glioblastoma (derived from lower-grade) tumors, low-grade astrocytomas, or normal brain tissues. Here, we extend this observation and show that a subset of primary glioblastoma tumors and their derived tumor lines express cellular and molecular markers that are associated with mesenchymal stem cells (MSC) and that glioblastoma cell cultures can be induced to differentiate into multiple mesenchymal lineage-like cell types. These findings suggest either that a subset of primary glioblastomas derive from transformed stem cells containing MSC-like properties and retain partial phenotypic aspects of a MSC nature in tumors or that glioblastomas activate a series of genes that result in mesenchymal properties of the cancer cells to effect sustained tumor growth and malignant progression.

Selection of neural differentiation-specific genes by comparing profiles of random differentiation

Differentiation of embryonic stem cells (ESCs) into neurons requires a high level of transcriptional regulation. To further understand the transcriptional regulation of neural differentiation of ESCs, we used oligonucleotide microarray to examine the gene expressions of the guided differentiation (GD) model for dopaminergic (DA) neurons from mouse ESCs. We also determined the gene expression profiles of the random differentiation (RD) model of mouse ESCs into embryoid bodies. From K-means clustering analysis using the expression patterns of the two models, most of the genes (1,282 of 1,884 genes [68.0%]) overlapped in their expression patterns. Six hundred twenty-two differentially expressed genes (DEGs) from the GD model by random variance F-test were classified by their critical molecular functions in neurogenesis and DNA replication (Gene Ontology analysis). However, 400 genes among GD-DEGs (64.3%) showed a high correlation with RD in Spearman's correlation analysis (Spearman's coefficient p(s) >or= .6). The genes showing marginal correlation (-.4 < p(s) < .6) were present in the early stages of differentiation of both GD and RD, which were non-specific to brain development. Finally, we distinguished 66 GD-specific genes based on p(s) <or= -.4, the molecular functions of which were related mainly to vesicle formation, neurogenesis, and transcription factors. From among these GD-specific genes, we confirmed the expression of Serpini1 and Rab33a in P19 differentiation models and adult brains. From these results, we identified the specific genes required for neural differentiation by comparing gene expressions of GD with RD; these would potentially be the highly specific candidate genes necessary for differentiation of DA neurons.

Comparison of effect of BMP-2, -4, and -6 on in vitro cartilage formation of human adult stem cells from bone marrow stroma

The human adult stem cells from bone marrow stroma referred to as mesenchymal stem cells or marrow stromal cells (MSCs) are of interest because they are easily isolated and expanded and are capable of multipotential differentiation. Here, we examined the ability of recombinant human bone morphogenetic protein (BMP)-2, -4, and -6 to enhance in vitro cartilage formation of MSCs. Human MSCs were isolated from bone marrow taken from normal adult donors. The cells were pelleted and cultured for 21 days in chondrogenic medium containing transforming growth factor beta3 and dexamethasone with or without BMP-2, -4, or -6. All the BMPs tested increased chondrogenic differentiation as assayed by immunohistochemistry and by the size and weight of the cartilage synthesized. However, BMP-2 was the most effective. Microarray analyses of approximately 12,000 genes and reverse transcription-polymerase chain reaction assays established that the critical genes for cartilage synthesis were expressed in the expected time sequence in response to BMP-2. The tissue engineering of autologous cartilage derived from MSCs in vitro for transplantation will be a future alternative for patients with cartilage injuries. To obtain large amounts of cartilage rich in proteoglycans, the use of BMP-2 is recommended, instead of BMP-4 or -6.

Butyrate response factor 1 is regulated by parathyroid hormone and bone morphogenetic protein-2 in osteoblastic cells

Parathyroid hormone (PTH) exerts potent and diverse effects in bone and cartilage through activation of type 1 PTH receptors (PTH1R) capable of coupling to protein kinase A (PKA) and PKC. We have used macroarrays to identify zinc finger protein butyrate response factor-1 (BRF1) as a novel PTH regulated gene in clonal and normal osteoblasts of human and rodent origin. We further demonstrate that in human osteoblast-like OHS cells, biologically active hPTH(1-84) and hPTH(1-34) stimulate BRF1 mRNA expression in a dose- and time-dependent manner, while the amino-terminally truncated hPTH(3-84) which does not activate PTH1R has no effect. Moreover, using specific stimulators or inhibitors of PKA and PKC activity, the PTH-elicited BRF1 mRNA expression is mediated through the PKA signaling pathway. In mouse calvarial osteoblasts, BRF1 mRNA levels are upregulated by PTH(1-84) and reduced in response to bone morphogenetic protein 2 (BMP-2). Hence, our data showing that BRF1 is expressed in osteoblastic cells and regulated by PTH and BMP-2, suggest an important role for BRF1 in osteoblasts within the molecular network of PTH-dependent bone remodeling.

Wnt signaling inhibits osteogenic differentiation of human mesenchymal stem cells

Human mesenchymal stem cells (hMSCs) from the bone marrow represent a potential source of pluripotent cells for autologous bone tissue engineering. We previously discovered that over activation of the Wnt signal transduction pathway by either lithium or Wnt3A stimulates hMSC proliferation while retaining pluripotency. Release of Wnt3A or lithium from porous calcium phosphate scaffolds, which we use for bone tissue engineering, could provide a mitogenic stimulus to implanted hMSCs. To define the proper release profile, we first assessed the effect of Wnt over activation on osteogenic differentiation of hMSCs. Here, we report that both lithium and Wnt3A strongly inhibit dexamethasone-induced expression of the osteogenic marker alkaline phosphatase (ALP). Moreover, lithium partly inhibited mineralization of hMSCs whereas Wnt3A completely blocked it. Time course analysis during osteogenic differentiation revealed that 4 days of Wnt3A exposure before the onset of mineralization is sufficient to block mineralization completely. Gene expression profiling in Wnt3A and lithium-exposed hMSCs showed that many osteogenic and chondrogenic markers, normally expressed in proliferating hMSCs, are downregulated upon Wnt stimulation. We conclude that Wnt signaling inhibits dexamethasone-induced osteogenesis in hMSCs. In future studies, we will try to limit release of lithium or Wnt3A from calcium phosphate scaffolds to the proliferative phase of osteogenesis.

Conservation of Sox4 gene structure and expression during chicken embryogenesis

While mutations in Sox4, a member of the SRY-like HMG box gene family, have been associated with a variety of human disorders and embryonic defects in the mouse, the structure and developmental expression of Sox4 in the avian embryo has not been described. We have isolated and characterized the chicken Sox4 gene. The chicken Sox4 gene shows a high degree of sequence homology with the mouse and human Sox4 genes, particularly in the HMG-like DNA binding domain and at the carboxy terminus. Furthermore, our in situ hybridization studies document an expression pattern during embryonic development that is very similar to that described for the mouse, particularly with regards to expression in the developing heart. However, abundant expression was also detected in tissues of neural crest origin including pharyngeal arch and craniofacial mesoderm, supporting a potential primary role in neural crest cardiac pathology previously detected in Sox4 mutant mice. Furthermore, a reciprocal pattern of Sox4 and Sox11 expression in the developing neural tube was detected in the chicken compared to that seen in the mouse. These studies suggest that Sox4 plays an important and conserved role in the embryonic development of these structures in the chicken as well as in the mouse and lay the foundation for future studies of the role of Sox4 during critical events of organogenesis.

Phenotype discovery by gene expression profiling: mapping of biological processes linked to BMP-2-mediated osteoblast differentiation

Understanding physiological control of osteoblast differentiation necessitates characterization of the regulatory signals that initiate the events directing a cell to lineage commitment and establishing competency for bone formation. The bone morphogenetic protein, BMP-2, a member of the TGFbeta superfamily, induces osteoblast differentiation and functions through the Smad signal transduction pathway during in vivo bone formation. However, the molecular targets of BMP-mediated gene transcription during the process of osteoblast differentiation have not been comprehensively identified. In the present study, BMP-2 responsive factors involved in the early stages of commitment and differentiation to the osteoblast phenotype were analyzed by microarray gene expression profiling in samples ranging from 1 to 24 h following BMP-2 dependent differentiation of C2C12 premyoblasts into the osteogenic lineage. A total of 1,800 genes were responsive to BMP-2 and expression was modulated from 3- to 14-fold for less than 100 genes during the time course. Approximately 50% of these 100 genes are either up- or downregulated. Major events associated with phenotypic changes towards the osteogenic lineage were identified from hierarchical and functional clustering analyses. BMP-2 immediately responsive genes (1-4 h), which exhibited either transient or sustained expression, reflect activation and repression of non-osseous BMP-2 developmental systems. This initial response was followed by waves of expression of nuclear proteins and developmental regulatory factors including inhibitors of DNA binding, Runx2, C/EBP, Zn finger binding proteins, forkhead, and numerous homeobox proteins (e.g., CDP/cut, paired, distaless, Hox) which are expressed at characterized stages during osteoblast differentiation. A sequential profile of genes mediating changes in cell morphology, cell growth, and basement membrane formation is observed as a secondary transient early response (2-8 h). Commitment to the osteogenic phenotype is recognized by 8 h, reflected by downregulation of most myogenic-related genes and induction of a spectrum of signaling proteins and enzymes facilitating synthesis and assembly of an extracellular skeletal environment. These genes included collagens Type I and VI and the small leucine rich repeat family of proteoglycans (e.g., decorin, biglycan, osteomodulin, fibromodulin, and osteoadherin/osteoglycin) that reached peak expression at 24 h. With extracellular matrix development, the bone phenotype was further established from 16 to 24 h by induction of genes for cell adhesion and communication and enzymes that organize the bone ECM. Our microarray analysis resulted in the discovery of a class of genes, initially described in relation to differentiation of astrocytes and oligodendrocytes that are functionally coupled to signals for cellular extensions. They include nexin, neuropilin, latexin, neuroglian, neuron specific gene 1, and Ulip; suggesting novel roles for these genes in the bone microenvironment. This global analysis identified a multistage molecular and cellular cascade that supports BMP-2-mediated osteoblast differentiation.

Identification of genes responsible for osteoblast differentiation from human mesodermal progenitor cells

Single human bone marrow-derived mesodermal progenitor cells (MPCs) differentiate into osteoblasts, chondrocytes, adipocytes, myocytes, and endothelial cells. To identify genes involved in the commitment of MPCs to osteoblasts we examined the expressed gene profile of undifferentiated MPCs and MPCs induced to the osteoblast lineage for 1-7 days by cDNA microarray analysis. As expected, growth factor, hormone, and signaling pathway genes known to be involved in osteogenesis were activated during differentiation. In addition, 41 transcription factors (TFs) were differentially expressed over time, including TFs with known roles in osteoblast differentiation and TFs not known to be involved in osteoblast differentiation. As the latter group of TFs coclustered with osteogenesis-specific TFs, they may play a role in osteoblast differentiation. When we compared the gene expression profile of MPCs induced to differentiate to chondroblasts and osteoblasts, significant differences in the nature and/or timing of gene activation were seen. These studies indicate that in vitro differentiation cultures in which MPCs are induced to one of multiple cell fates should be very useful for defining signals important for lineage-specific differentiation.

Genomic approaches to identifying transcriptional regulators of osteoblast differentiation

Recent microarray studies of mouse and human osteoblast differentiation in vitro have identified novel transcription factors that may be important in the establishment and maintenance of differentiation. These findings help unravel the pattern of gene-expression changes that underly the complex process of bone formation.

In vitro cartilage formation by human adult stem cells from bone marrow stroma defines the sequence of cellular and molecular events during chondrogenesis

One approach to resolving the complexities of chondrogenesis is to examine simplified systems in vitro. We analyzed cartilage differentiation by human adult stem cells from bone marrow stroma. Marrow stromal cells were cultured as micromass pellets for 21 days in serum-free medium containing transforming growth factor (TGF)-beta3, dexamethasone, and bone morphogenetic protein (BMP)-6. Assays for pulse-labeled [3H]DNA and for total DNA indicated that there was little proliferation and a progressive loss of cells in the pellets. There were continuous increases in mRNAs for cartilage matrix (proteoglycans and COL2, -9, -10, and -11), receptors [fibroblast growth factor 2 (FGFR2) and parathyroid hormone-related peptide receptor (PTHrP-R)], and transcription factors (SOX5, -6, and -9) as demonstrated by histochemical and microarray assays. Reverse transcription-PCR assays for 11 mRNAs confirmed the microarray data. SOX4, vascular endothelial growth factor (VEGF), and matrix metalloproteinase 14 (MMP14) increased at day 1 and decreased thereafter, suggesting roles early in chondrogenesis. Also, forkhead, CD10, and MMP13 increased up to day 7 and decreased thereafter, suggesting roles in an intermediate stage of chondrogenesis. In addition, two collagens (COL3A1 and COL16A1), a signaling molecule (WNT11), a homeobox homolog (BAPX1), a receptor (IL-1R1), an IGFs modulator (IGFBP5), and a mettaloproteinase (MMP16) increased progressively up to about day 14, suggesting roles later in chondrogenesis. Our results indicate that the simplicity of the system makes it possible to define in detail the cellular and molecular events during chondrogenesis.

Regulation of chondrocyte terminal differentiation in the postembryonic growth plate: the role of the PTHrP-Indian hedgehog axis

Chondrocyte differentiation during embryonic bone growth is controlled by interactions between PTHrP and Indian hedgehog. We have now determined that the major components of this signaling pathway are present in the postembryonic growth plate. PTHrP was immunolocalized throughout the growth plate, and semiquantitative RT-PCR analysis of maturationally distinct chondrocyte fractions indicated that PTHrP, Indian hedgehog, and the PTH/PTHrP receptor were expressed at similar levels throughout the growth plate. However, patched, the hedgehog receptor, was more highly expressed in proliferating chondrocytes. Although all fractionated cells responded to PTHrP in culture by increasing thymidine incorporation and cAMP production and decreasing alkaline phosphatase activity, the magnitude of response was greatest in the proliferative chondrocytes. Bone morphogenetic proteins are considered likely intermediates in PTHrP signaling. Expression of bone morphogenetic protein-2 and 4--7 was detected within the growth plate, and PTHrP inhibited the expression of bone morphogenetic protein-4 and 6. Although organ culture studies indicated a possible paracrine role for epiphyseal chondrocyte-derived PTHrP in regulating growth plate chondrocyte differentiation, the presence within the postembryonic growth plate of functional components of the PTHrP-Indian hedgehog pathway suggests that local mechanisms intrinsic to the growth plate exist to control the rate of endochondral ossification.