Osteoblast-Specific Overexpression of Nucleolar Protein /RIOX1 in Mouse Embryos Leads to Osteoporosis in Adult Mice.

In previous study, we showed that nucleolar protein 66 (NO66) is a chromatin modifier and negatively regulates Osterix activity as well as mesenchymal progenitor differentiation. Genetic ablation of the 66 () gene in cells of the 1-expressing mesenchymal lineage leads to acceleration of osteochondrogenic differentiation and a larger skeleton in adult mice, whereas mesenchyme-specific overexpression of 66 inhibits osteochondrogenesis resulting in dwarfism and osteopenia. However, the impact of NO66 overexpression in cells of the osteoblast lineage remains largely undefined.

Wnt/ß-catenin-mediated p53 suppression is indispensable for osteogenesis of mesenchymal progenitor cells.

The developmental origins of mesenchymal progenitor cells (MPCs) and molecular machineries regulating their fate and differentiation are far from defined owing to their complexity. Osteoblasts and adipocytes are descended from common MPCs. Their fates are collectively determined by an orchestra of pathways in response to physiological and external cues.

Specificity Protein 7 Is Required for Proliferation and Differentiation of Ameloblasts and Odontoblasts.

The Sp7/Osterix transcription factor is essential for bone development. Mutations of the Sp7 gene in humans are associated with craniofacial anomalies and osteogenesis imperfecta. However, the role of Sp7 in embryonic tooth development remains unknown.

Characterization of Mesenchymal-Fibroblast Cells Using the Col1a2 Promoter/Enhancer.

Excessive deposition of extracellular matrix (ECM) is a common hallmark of fibrotic diseases in various organs. Chiefly among this ECM are collagen types I and III, secreted by local fibroblasts, and other mesenchymal cells recruited for repair purposes. In the last two decades, the search for a fibroblast-specific promoter/enhancer has intensified in order to control the regulation of ECM in these cells and limit the scarring of the fibrotic process.

Endothelial-to-Osteoblast Conversion Generates Osteoblastic Metastasis of Prostate Cancer.

Prostate cancer (PCa) bone metastasis is frequently associated with bone-forming lesions, but the source of the osteoblastic lesions remains unclear. We show that the tumor-induced bone derives partly from tumor-associated endothelial cells that have undergone endothelial-to-osteoblast (EC-to-OSB) conversion. The tumor-associated osteoblasts in PCa bone metastasis specimens and patient-derived xenografts (PDXs) were found to co-express endothelial marker Tie-2.

A Novel Regulatory Mechanism of Type II Collagen Expression via a SOX9-dependent Enhancer in Intron 6.

Type II collagen α1 is specific for cartilaginous tissues, and mutations in its gene are associated with skeletal diseases. Its expression has been shown to be dependent on SOX9, a master transcription factor required for chondrogenesis that binds to an enhancer region in intron 1. However, ChIP sequencing revealed that SOX9 does not strongly bind to intron 1, but rather it binds to intron 6 and a site 30 kb upstream of the transcription start site.

SOX9 directly Regulates CTGF/CCN2 Transcription in Growth Plate Chondrocytes and in Nucleus Pulposus Cells of Intervertebral Disc.

Several lines of evidence indicate that connective tissue growth factor (CTGF/CCN2) stimulates chondrocyte proliferation and maturation. Given the fact that SOX9 is essential for several steps of the chondrocyte differentiation pathway, we asked whether Ctgf (Ccn2) is the direct target gene of SOX9. We found that Ctgf mRNA was down-regulated in primary sternal chondrocytes from Sox9(flox/flox) mice infected with Ad-CMV-Cre.

Dual pathways to endochondral osteoblasts: a novel chondrocyte-derived osteoprogenitor cell identified in hypertrophic cartilage.

According to the general understanding, the chondrocyte lineage terminates with the elimination of late hypertrophic cells by apoptosis in the growth plate. However, recent cell tracking studies have shown that murine hypertrophic chondrocytes can survive beyond "terminal" differentiation and give rise to a progeny of osteoblasts participating in endochondral bone formation. The question how chondrocytes convert into osteoblasts, however, remained open.

Mesenchyme-specific overexpression of nucleolar protein 66 in mice inhibits skeletal growth and bone formation.

Previous studies showed that nucleolar protein 66 (NO66), the Jumonji C-domain-containing histone demethylase for methylated histone H3K4 and H3K36 (H3K36me), negatively regulates osteoblast differentiation in vitro by inhibiting the activity of transcription factor osterix (Osx). However, whether NO66 affects mammalian skeletogenesis in vivo is not yet known. Here, we generated transgenic (TG) mice overexpressing a flag-tagged NO66 transgene driven by the Prx1 (paired related homeobox 1) promoter.

Mesenchymal Deletion of Histone Demethylase NO66 in Mice Promotes Bone Formation.

Our previous studies indicated that the Jumonji C (JmjC)-domain-containing NO66 is a histone demethylase with specificity for methylated histone H3K4 and H3K36. NO66 binds to the transcription factor Osterix (Osx) and inhibits its transcriptional activity in promoter assays. However, the physiological role of NO66 in formation of mammalian bones is unknown.

Chondrocytes transdifferentiate into osteoblasts in endochondral bone during development, postnatal growth and fracture healing in mice.

One of the crucial steps in endochondral bone formation is the replacement of a cartilage matrix produced by chondrocytes with bone trabeculae made by osteoblasts. However, the precise sources of osteoblasts responsible for trabecular bone formation have not been fully defined. To investigate whether cells derived from hypertrophic chondrocytes contribute to the osteoblast pool in trabecular bones, we genetically labeled either hypertrophic chondrocytes by Col10a1-Cre or chondrocytes by tamoxifen-induced Agc1-CreERT2 using EGFP, LacZ or Tomato expression.

Development of the fetal bone marrow niche and regulation of HSC quiescence and homing ability by emerging osteolineage cells.

Hematopoietic stem cells (HSCs) reside within a specialized niche where interactions with vasculature, osteoblasts, and stromal components regulate their self-renewal and differentiation. Little is known about bone marrow niche formation or the role of its cellular components in HSC development; therefore, we established the timing of murine fetal long bone vascularization and ossification relative to the onset of HSC activity. Adult-repopulating HSCs emerged at embryonic day 16.

SOX9 regulates multiple genes in chondrocytes, including genes encoding ECM proteins, ECM modification enzymes, receptors, and transporters.

The transcription factor SOX9 plays an essential role in determining the fate of several cell types and is a master factor in regulation of chondrocyte development. Our aim was to determine which genes in the genome of chondrocytes are either directly or indirectly controlled by SOX9. We used RNA-Seq to identify genes whose expression levels were affected by SOX9 and used SOX9 ChIP-Seq to identify those genes that harbor SOX9-interaction sites.

Specificity protein 7 is not essential for tooth morphogenesis.

Tooth formation is a multifaceted process involving numerous interactions between oral epithelium and neural crest derived ecto-mesenchyme from morphogenesis to cyto-differentiation. The precise molecular regulator that drives the cyto-differentiation and dynamic cross-talk between the two cell types has yet to be fully understood. Runx2 along with its downstream target Sp7 are essential transcription factors for development of the mineralizing cell types.

Sp7 and Runx2 molecular complex synergistically regulate expression of target genes.

Runx2 and Sp7 transcription factors are essential for skeletogenesis. Targeted deletion of either gene results in failure of osteoblast differentiation and bone formation. Loss of bone-matrix gene expression is surprisingly similar in Sp7 and Runx2 null mice.

E6-AP/UBE3A protein acts as a ubiquitin ligase toward SOX9 protein.

SOX9 is a transcription factor that acts as a key regulator at various stages of cartilage differentiation. There is ample evidence that intracellular SOX9 protein levels are tightly regulated both by sumoylation and by degradation through the ubiquitin-proteasome pathway. Using a proteomics approach, here we report the identification of a SOX9-binding protein, E6-AP/UBE3A, that may act as a ubiquitin ligase toward Sox9.

Osterix and NO66 histone demethylase control the chromatin of Osterix target genes during osteoblast differentiation.

Commitment of Runx2-expressing precursor osteoblasts to functional osteoblasts and then to osteocytes is triggered by Osterix (Osx), which activates its target genes in those cells during bone formation. It is not yet known whether Osx has a role in remodeling the chromatin architecture of its target genes during the transition from preosteoblast to osteoblast. In testing the hypothesis that Osx is indispensable for active chromatin architecture, we first showed that in Osx-null calvarial cells occupancy of the transcriptional activators, including lysine 4 methyl transferase (Wdr5), c-Myc, and H2A.

Persistent low level of osterix accelerates interleukin-6 production and impairs regeneration after tissue injury.

Osterix (Osx) is an essential transcription factor for osteoblast differentiation and bone formation. Osx knockout show a complete absence of bone formation, whereas Osx conditional knockout in osteoblasts produce an osteopenic phenotype after birth. Here, we questioned whether Osx has a potential role in regulating physiological homeostasis.

Structural insights into histone demethylase NO66 in interaction with osteoblast-specific transcription factor osterix and gene repression.

Osterix (Osx) is an osteoblast-specific transcriptional factor and is required for osteoblast differentiation and bone formation. A JmjC domain-containing protein NO66 was previously found to participate in regulation of Osx transcriptional activity and plays an important role in osteoblast differentiation through interaction with Osx. Here, we report the crystal structure of NO66 forming in a functional tetramer.

Connective tissue growth factor causes EMT-like cell fate changes in vivo and in vitro.

Connective tissue growth factor (CTGF) plays an important role in the pathogenesis of chronic fibrotic diseases. However, the mechanism by which paracrine effects of CTGF control the cell fate of neighboring epithelial cells is not known. In this study, we investigated the paracrine effects of CTGF overexpressed in fibroblasts of Col1a2-CTGF transgenic mice on epithelial cells of skin and lung.

Identification and characterization of microRNAs controlled by the osteoblast-specific transcription factor Osterix.

Osterix (Osx) is an osteoblast-specific transcription factor which is essential for bone formation. MicroRNAs (miRNAs) have been previously shown to be involved in osteogenesis. However, it is unclear whether Osx is involved in the regulation of miRNA expression.

Osterix is required for cranial neural crest-derived craniofacial bone formation.

Osx plays essential roles in regulating osteoblast and chondrocyte differentiation, and bone formation during mouse skeletal development. However, many questions remain regarding the requirement for Osx in different cell lineages. In this study, we asked whether Osx is required for craniofacial bone formation derived from cranial neural crest (CNC) cells.

The postnatal role of Sox9 in cartilage.

Sox9 is an essential transcription factor for the differentiation of the chondrocytic lineage during embryonic development. To test whether Sox9 continues to play a critical role in cartilaginous tissues in the adult mice, we used an inducible, genetic strategy to disrupt the Sox9 gene postnatally in these tissues. The postnatal inactivation of Sox9 led to stunted growth characterized by decreased proliferation, increased cell death, and dedifferentiation of growth plate chondrocytes.

Characterization of Dkk1 gene regulation by the osteoblast-specific transcription factor Osx.

Bone formation is a developmental process involving the differentiation of mesenchymal stem cells to osteoblasts. Osterix (Osx) is an osteoblast-specific transcription factor required for bone formation and osteoblast differentiation. Previous observation that Osx inhibits Wnt signaling pathway provides a novel concept of feedback control mechanisms involved in bone formation.