Oncogenicity of the developmental transcription factor Sox9

SOX9 [sex-determining region Y (SRY)-box 9 protein], a high mobility group box transcription factor, plays critical roles during embryogenesis and its activity is required for development, differentiation, and lineage commitment in various tissues including the intestinal epithelium. Here, we present functional and clinical data of a broadly important role for SOX9 in tumorigenesis. SOX9 was overexpressed in a wide range of human cancers, where its expression correlated with malignant character and progression. Gain of SOX9 copy number is detected in some primary colorectal cancers. SOX9 exhibited several pro-oncogenic properties, including the ability to promote proliferation, inhibit senescence, and collaborate with other oncogenes in neoplastic transformation. In primary mouse embryo fibroblasts and colorectal cancer cells, SOX9 expression facilitated tumor growth and progression whereas its inactivation reduced tumorigenicity. Mechanistically, we have found that Sox9 directly binds and activates the promoter of the polycomb Bmi1, whose upregulation represses the tumor suppressor Ink4a/Arf locus. In agreement with this, human colorectal cancers showed a positive correlation between expression levels of SOX9 and BMI1 and a negative correlation between SOX9 and ARF in clinical samples. Taken together, our findings provide direct mechanistic evidence of the involvement of SOX9 in neoplastic pathobiology, particularly, in colorectal cancer.

Long-range regulation at the SOX9 locus in development and disease

The involvement of SOX9 in congenital skeletal malformation was demonstrated 15 years ago with the identification of mutations in and around the gene in patients with campomelic dysplasia (CD). Translocations upstream of the coding sequence suggested that altered expression of SOX9 was capable of severely impacting on skeletal development. Subsequent studies in humans and animal models pointed towards a complex regulatory region controlling SOX9 transcription, involving approximately 1 Mb of upstream sequence. Recent data indicate that this regulatory domain may extend substantially further, with identification of several disruptions greater than 1 Mb upstream of SOX9 associated with isolated Pierre Robin sequence (PRS), a craniofacial disorder that is frequently a component of CD. The translocation breakpoints upstream of SOX9 can now be clustered into three groups, with a trend towards less severe skeletal phenotypes as the distance of each cluster from SOX9 increases. In this review we discuss how the identification of novel lesions surrounding SOX9 support the existence of tissue specific enhancers acting over a large distance to regulate expression of the gene during craniofacial development, and we highlight the potential for discovery of additional regulatory elements within the extended SOX9 control region.

SOX9 keeps growth plates and articular cartilage healthy by inhibiting chondrocyte dedifferentiation/osteoblastic redifferentiation

Cartilage is essential throughout vertebrate life. It starts developing in embryos when osteochondroprogenitor cells commit to chondrogenesis, activate a pancartilaginous program to form cartilaginous skeletal primordia, and also embrace a growth-plate program to drive skeletal growth or an articular program to build permanent joint cartilage. Various forms of cartilage malformation and degeneration diseases afflict humans, but underlying mechanisms are still incompletely understood and treatment options suboptimal. The transcription factor SOX9 is required for embryonic chondrogenesis, but its postnatal roles remain unclear, despite evidence that it is down-regulated in osteoarthritis and heterozygously inactivated in campomelic dysplasia, a severe skeletal dysplasia characterized postnatally by small stature and kyphoscoliosis. Using conditional knockout mice and high-throughput sequencing assays, we show here that SOX9 is required postnatally to prevent growth-plate closure and preosteoarthritic deterioration of articular cartilage. Its deficiency prompts growth-plate chondrocytes at all stages to swiftly reach a terminal/dedifferentiated stage marked by expression of chondrocyte-specific (Mgp) and progenitor-specific (Nt5e and Sox4) genes. Up-regulation of osteogenic genes (Runx2, Sp7, and Postn) and overt osteoblastogenesis quickly ensue. SOX9 deficiency does not perturb the articular program, except in load-bearing regions, where it also provokes chondrocyte-to-osteoblast conversion via a progenitor stage. Pathway analyses support roles for SOX9 in controlling TGFβ and BMP signaling activities during this cell lineage transition. Altogether, these findings deepen our current understanding of the cellular and molecular mechanisms that specifically ensure lifelong growth-plate and articular cartilage vigor by identifying osteogenic plasticity of growth-plate and articular chondrocytes and a SOX9-countered chondrocyte dedifferentiation/osteoblast redifferentiation process.

Control of chondrogenesis by the transcription factor Sox9

Cell-fate determination of pluripotent cells, cell proliferation, differentiation, and maturation, as well as the maintenance of stem cells, are essential cellular events during organogenesis. Previous reports show that some distinct cell-specific transcription factors are the master genes that control cell lineage commitment and the subsequent cell proliferation and differentiation. Some of these transcription factors generate hierarchical regulation of expression and act in concert to fulfill their roles. This review discusses the molecular properties and mechanisms of Sry-related high-mobility-group box (Sox) transcription factor, Sox9, in chondrogenesis.

Hedgehog signaling regulates FOXA2 in esophageal embryogenesis and Barrett's metaplasia

Metaplasia can result when injury reactivates latent developmental signaling pathways that determine cell phenotype. Barrett's esophagus is a squamous-to-columnar epithelial metaplasia caused by reflux esophagitis. Hedgehog (Hh) signaling is active in columnar-lined, embryonic esophagus and inactive in squamous-lined, adult esophagus. We showed previously that Hh signaling is reactivated in Barrett's metaplasia and overexpression of Sonic hedgehog (SHH) in mouse esophageal squamous epithelium leads to a columnar phenotype. Here, our objective was to identify Hh target genes involved in Barrett's pathogenesis. By microarray analysis, we found that the transcription factor Foxa2 is more highly expressed in murine embryonic esophagus compared with postnatal esophagus. Conditional activation of Shh in mouse esophageal epithelium induced FOXA2, while FOXA2 expression was reduced in Shh knockout embryos, establishing Foxa2 as an esophageal Hh target gene. Evaluation of patient samples revealed FOXA2 expression in Barrett's metaplasia, dysplasia, and adenocarcinoma but not in esophageal squamous epithelium or squamous cell carcinoma. In esophageal squamous cell lines, Hh signaling upregulated FOXA2, which induced expression of MUC2, an intestinal mucin found in Barrett's esophagus, and the MUC2-processing protein AGR2. Together, these data indicate that Hh signaling induces expression of genes that determine an intestinal phenotype in esophageal squamous epithelial cells and may contribute to the development of Barrett's metaplasia.

SOX9 regulates ERBB signalling in pancreatic cancer development

OBJECTIVE

The transcription factor SOX9 was recently shown to stimulate ductal gene expression in pancreatic acinar-to-ductal metaplasia and to accelerate development of premalignant lesions preceding pancreatic ductal adenocarcinoma (PDAC). Here, we investigate how SOX9 operates in pancreatic tumourigenesis.

DESIGN

We analysed genomic and transcriptomic data from surgically resected PDAC and extended the expression analysis to xenografts from PDAC samples and to PDAC cell lines. SOX9 expression was manipulated in human cell lines and mouse models developing PDAC.

RESULTS

We found genetic aberrations in the SOX9 gene in about 15% of patient tumours. Most PDAC samples strongly express SOX9 protein, and SOX9 levels are higher in classical PDAC. This tumour subtype is associated with better patient outcome, and cell lines of this subtype respond to therapy targeting epidermal growth factor receptor (EGFR/ERBB1) signalling, a pathway essential for pancreatic tumourigenesis. In human PDAC, high expression of SOX9 correlates with expression of genes belonging to the ERBB pathway. In particular, ERBB2 expression in PDAC cell lines is stimulated by SOX9. Inactivating Sox9 expression in mice confirmed its role in PDAC initiation; it demonstrated that Sox9 stimulates expression of several members of the ERBB pathway and is required for ERBB signalling activity.

CONCLUSIONS

By integrating data from patient samples and mouse models, we found that SOX9 regulates the ERBB pathway throughout pancreatic tumourigenesis. Our work opens perspectives for therapy targeting tumourigenic mechanisms.

KLF4 regulation in intestinal epithelial cell maturation

The Krüppel-like factor 4 (KLF4) transcription factor suppresses tumorigenesis in gastrointestinal epithelium. Thus, its expression is decreased in gastric and colon cancers. Moreover, KLF4 regulates both differentiation and growth that is likely fundamental to its tumor suppressor activity. We dissected the expression of Klf4 in the normal mouse intestinal epithelium along the crypt-villus and cephalo-caudal axes. Klf4 reached its highest level in differentiated cells of the villus, with levels in the duodenum>jejunum>ileum, in inverse relation to the representation of goblet cells in these regions, the lineage previously linked to KLF4. In parallel, in vitro studies using HT29cl.16E and Caco2 colon cancer cell lines clarified that KLF4 increased coincident with differentiation along both the goblet and absorptive cell lineages, respectively, and that KLF4 levels also increased during differentiation induced by the short chain fatty acid butyrate, independently of cell fate. Moreover, we determined that lower levels of KLF4 expression in the proliferative compartment of the intestinal epithelium are regulated by the transcription factors TCF4 and SOX9, an effector and a target, respectively, of beta-catenin/Tcf signaling, and independently of CDX2. Thus, reduced levels of KLF4 tumor suppressor activity in colon tumors may be driven by elevated beta-catenin/Tcf signaling.

Boys, girls and shuttling of SRY and SOX9

In the mammalian embryo, SRY and SOX9 are key Sertoli cell proteins that drive the development of the bipotential gonad into a testes rather than an ovary, leading ultimately to the male phenotype. Clinical SRY and SOX9 mutations causing disorders of sex development (DSD) highlight defective protein-protein interactions between SRY or SOX9, and carrier proteins required for nuclear import (importin-b and calmodulin) and nuclear export (CRM-1). The fine balance between import and export determines the levels of transcriptionally active SRY and SOX9 in the nucleus. Recently, post-translational modifications of SRY and SOX9 have been identified which affect nuclear transport. It is therefore timely that the consequences of sex-reversal mutation upon nuclear transport be reviewed. SRY and SOX9 mutations in DSD have uncovered regulatory sites for sumoylation, ubiquitination, acetylation and phosphorylation, many of which are essential for their transport and sex determining functions.

A zebrafish model for Waardenburg syndrome type IV reveals diverse roles for Sox10 in the otic vesicle

In humans, mutations in the SOX10 gene are a cause of the auditory-pigmentary disorder Waardenburg syndrome type IV (WS4) and related variants. SOX10 encodes an Sry-related HMG box protein essential for the development of the neural crest; deafness in WS4 and other Waardenburg syndromes is usually attributed to loss of neural-crest-derived melanocytes in the stria vascularis of the cochlea. However, SOX10 is strongly expressed in the developing otic vesicle and so direct roles for SOX10 in the otic epithelium might also be important. Here, we examine the otic phenotype of zebrafish sox10 mutants, a model for WS4. As a cochlea is not present in the fish ear, the severe otic phenotype in these mutants cannot be attributed to effects on this tissue. In zebrafish sox10 mutants, we see abnormalities in all otic placodal derivatives. Gene expression studies indicate deregulated expression of several otic genes, including fgf8, in sox10 mutants. Using a combination of mutant and morphant data, we show that the three sox genes belonging to group E (sox9a, sox9b and sox10) provide a link between otic induction pathways and subsequent otic patterning: they act redundantly to maintain sox10 expression throughout otic tissue and to restrict fgf8 expression to anterior macula regions. Single-cell labelling experiments indicate a small and transient neural crest contribution to the zebrafish ear during normal development, but this is unlikely to account for the strong defects seen in the sox10 mutant. We discuss the implication that the deafness in WS4 patients with SOX10 mutations might reflect a haploinsufficiency for SOX10 in the otic epithelium, resulting in patterning and functional abnormalities in the inner ear.

Polarity Acquisition in Cortical Neurons Is Driven by Synergistic Action of Sox9-Regulated Wwp1 and Wwp2 E3 Ubiquitin Ligases and Intronic miR-140

The establishment of axon-dendrite polarity is fundamental for radial migration of neurons during cortex development of mammals. We demonstrate that the E3 ubiquitin ligases WW-Containing Proteins 1 and 2 (Wwp1 and Wwp2) are indispensable for proper polarization of developing neurons. We show that knockout of Wwp1 and Wwp2 results in defects in axon-dendrite polarity in pyramidal neurons, and their aberrant laminar cortical distribution. Knockout of miR-140, encoded in Wwp2 intron, engenders phenotypic changes analogous to those upon Wwp1 and Wwp2 deletion. Intriguingly, transcription of the Wwp1 and Wwp2/miR-140 loci in neurons is induced by the transcription factor Sox9. Finally, we provide evidence that miR-140 supervises the establishment of axon-dendrite polarity through repression of Fyn kinase mRNA. Our data delineate a novel regulatory pathway that involves Sox9-[Wwp1/Wwp2/miR-140]-Fyn required for axon specification, acquisition of pyramidal morphology, and proper laminar distribution of cortical neurons.

The role of Sox9 in prostate development

The mammalian prostate arises from the urogenital sinus under the influence of testicular androgens. Few factors have been identified to be important in the early stages of prostate development. Here we review the role of the transcription factor Sox9 in prostate development. Sox9 is a member of the Sox gene family that plays an important role during embryogenesis in the cellular differentiation of various tissues, including testicular Sertoli cells, neural crest cells and chondrocytes. This gene is expressed in the epithelia of all mouse prostatic lobes from the initial stages of their development. Mice with a prostate specific deletion of Sox9 showed a lack of ventral prostate development and abnormal anterior prostate differentiation. In depth analysis of these mutant animals suggested that Sox9 is required for the early differentiation of the prostate bud epithelia, consistent with the function of this factor in other developmental processes. These studies also revealed different phases of prostate bud development. These phases were characterized by being dependent on different molecular pathways and having lobe specific properties. Future studies on the identification of pathways regulated by Sox9 will provide insight into the molecular networks required for prostate epithelia differentiation.

Sox9-haploinsufficiency causes glucose intolerance in mice

The HMG box transcription factor Sox9 plays a critical role in progenitor cell expansion during pancreas organogenesis and is required for proper endocrine cell development in the embryo. Based on in vitro studies it has been suggested that Sox9 controls expression of a network of important developmental regulators, including Tcf2/MODY5, Hnf6, and Foxa2, in pancreatic progenitor cells. Here, we sought to: 1) determine whether Sox9 regulates this transcriptional network in vivo and 2) investigate whether reduced Sox9 gene dosage leads to impaired glucose homeostasis in adult mice. Employing two genetic models of temporally-controlled Sox9 inactivation in pancreatic progenitor cells, we demonstrate that contrary to in vitro findings, Sox9 is not required for Tcf2, Hnf6, or Foxa2 expression in vivo. Moreover, our analysis revealed a novel role for Sox9 in maintaining the expression of Pdx1/MODY4, which is an important transcriptional regulator of beta-cell development. We further show that reduced beta-cell mass in Sox9-haploinsufficient mice leads to glucose intolerance during adulthood. Sox9-haploinsufficient mice displayed 50% reduced beta-cell mass at birth, which recovered partially via a compensatory increase in beta-cell proliferation early postnatally. Endocrine islets from mice with reduced Sox9 gene dosage exhibited normal glucose stimulated insulin secretion. Our findings show Sox9 plays an important role in endocrine development by maintaining Ngn3 and Pdx1 expression. Glucose intolerance in Sox9-haploinsufficient mice suggests that mutations in Sox9 could play a role in diabetes in humans.

Six2 activity is required for the formation of the mammalian pyloric sphincter

The functional activity of Six2, a member of the so/Six family of homeodomain-containing transcription factors, is required during mammalian kidney organogenesis. We have now determined that Six2 activity is also necessary for the formation of the pyloric sphincter, the functional gate at the stomach-duodenum junction that inhibits duodenogastric reflux. Our data reveal that several genes known to be important for pyloric sphincter formation in the chick (e.g., Bmp4, Bmpr1b, Nkx2.5, Sox9, and Gremlin) also appear to be required for the formation of this structure in mammals. Thus, we propose that Six2 activity regulates this gene network during the genesis of the pyloric sphincter in the mouse.

Interference by adrenaline with chondrogenic differentiation through suppression of gene transactivation mediated by Sox9 family members

In contrast to osteoblasts, little attention has been paid to the functional expression of adrenergic signaling machineries in chondrocytes. Expression of mRNA was for the first time demonstrated for different adrenergic receptor (AdR) subtypes in chondrogenic ATDC5 cells and mouse metatarsals isolated before vascularization in culture, but not for other molecules related to adrenergic signaling. In neonatal mouse tibial sections, beta(2)AdR and alpha(2a)AdR mRNA expression was found in chondrocytes at different developmental stages by in situ hybridization. Exposure to adrenaline significantly suppressed expression of several maturation markers through the cAMP/protein kinase A pathway activated by beta(2)AdR without affecting cellular proliferation in both cultured ATDC5 cells and metatarsals. Adrenaline also significantly inhibited gene transactivation by sry-type HMG box 9 (Sox9) family members essential for chondrogenic differentiation in a manner prevented by the general betaAdR antagonist propranolol, with a concomitant significant decrease in the levels of Sox6 mRNA and corresponding protein, in ATDC5 cells and primary cultured mouse costal chondrocytes. Systemic administration of propranolol significantly promoted the increased expression of mRNA for collagen I and collagen X, but not for collagen II, in callus of fractured femur in mice. These results suggest that adrenaline may interfere with chondrogenic differentiation through downregulation of Sox6 expression for subsequent suppression of gene transactivation mediated by Sox9 family members after activation of beta(2)AdR expressed by chondrocytes.

Therapeutic potential of targeting acinar cell reprogramming in pancreatic cancer

Pancreatic ductal adenocarcinoma (PDAC) is a common pancreatic cancer and the fourth leading cause of cancer death in the United States. Treating this life-threatening disease remains challenging due to the lack of effective prognosis, diagnosis and therapy. Apart from pancreatic duct cells, acinar cells may also be the origin of PDAC. During pancreatitis or combined with activating KRas(G12D) mutation, acinar cells lose their cellular identity and undergo a transdifferentiation process called acinar-to-ductal-metaplasia (ADM), forming duct cells which may then transform into pancreatic intraepithelial neoplasia (PanIN) and eventually PDAC. During ADM, the activation of mitogen-activated protein kinases, Wnt, Notch and phosphatidylinositide 3-kinases/Akt signaling inhibits the transcription of acinar-specific genes, including Mist and amylase, but promotes the expression of ductal genes, such as cytokeratin-19. Inhibition of this transdifferentiation process hinders the development of PanIN and PDAC. In addition, the transdifferentiated cells regain acinar identity, indicating ADM may be a reversible process. This provides a new therapeutic direction in treating PDAC through cancer reprogramming. Many studies have already demonstrated the success of switching PanIN/PDAC back to normal cells through the use of PD325901, the expression of E47, and the knockdown of Dickkopf-3. In this review, we discuss the signaling pathways involved in ADM and the therapeutic potential of targeting reprogramming in order to treat PDAC.

Blastula stage specification of avian neural crest

Cell fate specification defines the earliest steps towards a distinct cell lineage. Neural crest, a multipotent stem cell population, is thought to be specified from the ectoderm, but its varied contributions defy canons of segregation potential and challenges its embryonic origin. Aiming to resolve this conflict, we have assayed the earliest specification of neural crest using blastula stage chick embryos. Specification assays on isolated chick epiblast explants identify an intermediate region specified towards the neural crest cell fate. Furthermore, low density culture suggests that the specification of intermediate cells towards the neural crest lineage is independent of contact mediated induction and Wnt-ligand induced signaling, but is, however, dependent on transcriptional activity of β-catenin. Finally, we have validated the regional identity of the intermediate region towards the neural crest cell fate using fate map studies. Our results suggest a model of neural crest specification within a restricted epiblast region in blastula stage chick embryos.

Prostate Organogenesis

The prostate is a male exocrine gland that secretes components of the seminal fluid. In men, prostate tumors are one of the most prevalent cancers. Studies on the development of the prostate have given a better understanding of the processes and genes that are important in the formation of this organ and have provided insights into the mechanisms of prostate tumorigenesis. These developmental studies have provided evidence that some of the genes and signaling pathways involved in development are reactivated or deregulated during prostate cancer. The prostate goes through a number of different stages during organogenesis, which include organ specification, epithelial budding, branching morphogenesis, canalization, and cytodifferentiation. During development, these processes are tightly regulated, many of which are controlled by the male hormone androgens. The majority of prostate tumors remain hormone regulated, and antiandrogen therapy is a first-line therapy, highlighting the important link between prostate organogenesis and cancer. In this review, we describe some of the data on genes that have important roles during prostate development that also have strong evidence linking them to prostate cancer.

Signaling Cascades Governing Cdc42-Mediated Chondrogenic Differentiation and Mensenchymal Condensation

Endochondral ossification consists of successive steps of chondrocyte differentiation, including mesenchymal condensation, differentiation of chondrocytes, and hypertrophy followed by mineralization and ossification. Loss-of-function studies have revealed that abnormal growth plate cartilage of the Cdc42 mutant contributes to the defects in endochondral bone formation. Here, we have investigated the roles of Cdc42 in osteogenesis and signaling cascades governing Cdc42-mediated chondrogenic differentiation. Though deletion of Cdc42 in limb mesenchymal progenitors led to severe defects in endochondral ossification, either ablation of Cdc42 in limb preosteoblasts or knockdown of Cdc42 in vitro had no obvious effects on bone formation and osteoblast differentiation. However, in Cdc42 mutant limb buds, loss of Cdc42 in mesenchymal progenitors led to marked inactivation of p38 and Smad1/5, and in micromass cultures, Cdc42 lay on the upstream of p38 to activate Smad1/5 in bone morphogenetic protein-2-induced mesenchymal condensation. Finally, Cdc42 also lay on the upstream of protein kinase B to transactivate Sox9 and subsequently induced the expression of chondrocyte differential marker in transforming growth factor-β1-induced chondrogenesis. Taken together, by using biochemical and genetic approaches, we have demonstrated that Cdc42 is involved not in osteogenesis but in chondrogenesis in which the BMP2/Cdc42/Pak/p38/Smad signaling module promotes mesenchymal condensation and the TGF-β/Cdc42/Pak/Akt/Sox9 signaling module facilitates chondrogenic differentiation.

Differential Expression Levels of Sox9 in Early Neocortical Radial Glial Cells Regulate the Decision between Stem Cell Maintenance and Differentiation

Radial glial progenitor cells (RGCs) in the dorsal telencephalon directly or indirectly produce excitatory projection neurons and macroglia of the neocortex. Recent evidence shows that the pool of RGCs is more heterogeneous than originally thought and that progenitor subpopulations can generate particular neuronal cell types. Using single-cell RNA sequencing, we have studied gene expression patterns of RGCs with different neurogenic behavior at early stages of cortical development. At this early age, some RGCs rapidly produce postmitotic neurons, whereas others self-renew and undergo neurogenic divisions at a later age. We have identified candidate genes that are differentially expressed among these early RGC subpopulations, including the transcription factor Sox9. Using in utero electroporation in embryonic mice of either sex, we demonstrate that elevated Sox9 expression in progenitors affects RGC cell cycle duration and leads to the generation of upper layer cortical neurons. Our data thus reveal molecular differences between progenitor cells with different neurogenic behavior at early stages of corticogenesis and indicates that Sox9 is critical for the maintenance of RGCs to regulate the generation of upper layer neurons.SIGNIFICANCE STATEMENT The existence of heterogeneity in the pool of RGCs and its relationship with the generation of cellular diversity in the cerebral cortex has been an interesting topic of debate for many years. Here we describe the existence of RGCs with reduced neurogenic behavior at early embryonic ages presenting a particular molecular signature. This molecular signature consists of differential expression of some genes including the transcription factor Sox9, which has been found to be a specific regulator of this subpopulation of progenitor cells. Functional experiments perturbing expression levels of Sox9 reveal its instructive role in the regulation of the neurogenic behavior of RGCs and its relationship with the generation of upper layer projection neurons at later ages.

Sox9 directs divergent epigenomic states in brain tumor subtypes

Epigenetic dysregulation is a universal feature of cancer that results in altered patterns of gene expression that drive malignancy. Brain tumors exhibit subtype-specific epigenetic alterations; however, the molecular mechanisms responsible for these diverse epigenetic states remain unclear. Here, we show that the developmental transcription factor Sox9 differentially regulates epigenomic states in high-grade glioma (HGG) and ependymoma (EPN). Using our autochthonous mouse models, we found that Sox9 suppresses HGG growth and expands associated H3K27ac states, while promoting ZFTA-RELA (ZRFUS) EPN growth and diminishing H3K27ac states. These contrasting roles for Sox9 correspond with protein interactions with histone deacetylating complexes in HGG and an association with the ZRFUS oncofusion in EPN. Mechanistic studies revealed extensive Sox9 and ZRFUS promoter co-occupancy, indicating functional synergy in promoting EPN tumorigenesis. Together, our studies demonstrate how epigenomic states are differentially regulated in distinct subtypes of brain tumors, while revealing divergent roles for Sox9 in HGG and EPN tumorigenesis.

[Transcriptional regulation in chondrogenesis by Sox9]

To identify a group of transcription factors required for chondrogenesis, several researchers tried to detect a chondrocyte-specific enhancer element of Col2a1 gene. Benoit de Crombrugghe's group finally found out 48bp in the first intron of Col2a1 gene as a chondrocyte-specific enhancer element, and moreover they also concluded that binding of homodimer of Sox9 and homo-or heterodimer of Sox5÷Sox6 to this element is indispensable for Col2a1 transcription in chodrocytes. Furthermore, mouse genetic approaches revealed that Sox9, Sox5 and Sox6 are required for chondrogenesis, leading to conclusion that these Sox transcription factors are master regulators in chondrogenesis. Recent studies showed that p300÷CBP, Trap230 (med12) , Wwp2, and Med25 are components of transcriptional machinery of Sox9 in chondrogenesis.

[Bone and calcium update; bone research update. Molecular mechanisms regulating chondrocyte differentiation and hypertrophy]

Chondrocyte differentiation process is composed of multiple steps. During the process, hypertrophy of chondrocyte is controlled by various factors including Indian hedgehog (Ihh) and parathyroid hormone related peptide (PTHrP) . PTHrP signals regulate HDAC4-MEF2C axis in chondrocyte. Recently, several co-factors have been found to interact with Sox9. Function of chondrocyte-specific microRNA has been determined. Several types of Cre transgenic mice are available to express Cre at various steps during chondrocyte differentiation. Using these mice, gene functions at specific steps of chondrocyte differentiation are analyzed by generating conditional knockout mice and conditional transgenic mice. It may be possible in future to induce chondrocytes from skin fibroblasts of patients with genetic cartilage diseases by using iPS cell technology, and to analyze molecular mechanism that control differentiation of human chondrocytes.

[Novel small compound in combination with cell-sheet technology for articular cartilage regeneration]

Aiming at regeneration of articular cartilage, we have established stable lines of mouse chondrogenic ATDC5 cells expressing green fluorescent protein under the control of type II collagen promoter fused with four repeats of a SOX9 enhancer (COL2A1-GFP) , as a monitoring system for chondrogenic differentiation. A screening of natural and synthetic compound libraries using the system identified some novel compounds. Combined with cell-sheet technology, a novel small compound was applied to the treatment of full-thickness knee cartilage defects in murine and canine models.