Project description:The vertebrate skeleton is mostly composed of three specific cell types: immature chondrocytes (IMM), mature (hypertrophic) chondrocytes (MAT), and osteoblasts (OST). These three cell types are distinct, but they also share the expression of many genes. This overlapping gene expression can be attributed to two transcription factors, SOX9 and RUNX2, which operate near the top of hierarchy of the gene regulatory network (GRN) underlying IMM, MAT, and OST. Sox9 drives IMM differentiation, whereas Runx2 regulates OST differentiation. Importantly, MAT do not form without the function of either Sox9 or Runx2, but little is known about mechanisms of GRN regulation in MAT. During MAT differentiation, the expression of Runx2 increases, and many genes regulated by this transcription such as Spp1, Mef2c, Ibsp, and Alpl are activated. To understand regulatory control of gene expression in mature chondrocytes, ChIP-seq experiments were performed using the mouse chondrogenic cell line ATDC5. These experiments identified in vitro RUNX2 binding sites at different stages of chondrogenesis. RUNX2 appeared to bind in most genes enriched in MAT at both day 3 of differentiation. The ChIP-seq analyses presented here verified the molecular mechanisms predicted here to regulate transcription of the many genomic loci in MAT, proving more insight into regulatory control during cartilage maturation.
Project description:Purpose: To demonstrate Runx2's association with organizing the extracellular matrix in primary chondrocytes. Method: RNA samples were collected from primary chondrocytes of 5-day-old Col2a1-CreERT2;Runx2fl/fl and Runx2fl/fl mice, cultured with or without IL-1beta. Results: Thirty-three genes cultured without IL-1beta and 45 genes with IL-1beta were up- or down-regulated by more than 2-fold in the Runx2 knockout in primary chondrocytes. Conclusions: Genes including collagen fibers were down-regulated in Runx2 cKO primary chondrocytes.
Project description:Purpose: To demonstrate the role of Transcription factor Runx2 in primary chondrocytes with or without IL-1beta. Method: Fragmented DNA samples were collected from primary chondrocytes of 5-day-old Runx2-Biotin-FLAG-tag mice, cultured with or without IL-1beta. Results: More than 20,000 and 10,000 peaks were gained from chondrocytes without and with IL-1beta, resepectively. Conclusions: Runx2 are associated cellular process and extracellular matrics transcription in primary chondrocytes.
Project description:Runx2 and Axin2 regulate skeletal development. We recently determined that Axin2 and Runx2 molecularly interact in differentiating osteoblasts to regulate intramembranous bone formation, but the relationship between these factors in endochondral bone formation was unresolved. To address this, we examined the effects of Axin2 deficiency on the cleidocranial dysplasia (CCD) phenotype of Runx2+/-M-BM- mice, focusing on skeletal defects attributed to improper endochondral bone formation. Axin2 deficiency unexpectedly exacerbated calvarial components of the CCD phenotype in the Runx2+/-M-BM- mice; the endocranial layer of the frontal suture, which develops by endochondral bone formation, failed to mineralize in the Axin2-/-:Runx2+/-mice, resulting in a cartilaginous, fibrotic and larger fontanel than observed in Runx2+/-M-BM- mice. Transcripts associated with cartilage development (e.g., Acan, miR140) were expressed at higher levels, whereas blood vessel morphogenesis transcripts (e.g., Slit2) were suppressed in Axin2-/-:Runx2+/-calvaria. Cartilage maturation was impaired, as primary chondrocytes from double mutant mice demonstrated delayed differentiation and produced less calcified matrix in vitro. The genetic dominance of Runx2 was also reflected during endochondral fracture repair, as both Runx2+/-M-BM- and double mutant Axin2-/-:Runx2+/-M-BM- mice had enlarged fracture calluses at early stages of healing. However, by the end stages of fracture healing, double mutant animals diverged from the Runx2+/-M-BM- mice, showing smaller calluses and increased torsional strength indicative of more rapid end stage bone formation as seen in the Axin2-/-M-BM- mice. Taken together, our data demonstrate a dominant role for Runx2 in chondrocyte maturation, but implicate Axin2 as an important modulator of the terminal stages of endochondral bone formation. 4 mice per genotype X 4 genotypes: wildtype (WT), Runx2+/- (R-Het), Axin2-/- (A-KO), Axin2-/-:Runx2+/- (A-KO:R-Het). Total = 16 samples
Project description:Runx2 and Axin2 regulate skeletal development. We recently determined that Axin2 and Runx2 molecularly interact in differentiating osteoblasts to regulate intramembranous bone formation, but the relationship between these factors in endochondral bone formation was unresolved. To address this, we examined the effects of Axin2 deficiency on the cleidocranial dysplasia (CCD) phenotype of Runx2+/- mice, focusing on skeletal defects attributed to improper endochondral bone formation. Axin2 deficiency unexpectedly exacerbated calvarial components of the CCD phenotype in the Runx2+/- mice; the endocranial layer of the frontal suture, which develops by endochondral bone formation, failed to mineralize in the Axin2-/-:Runx2+/-mice, resulting in a cartilaginous, fibrotic and larger fontanel than observed in Runx2+/- mice. Transcripts associated with cartilage development (e.g., Acan, miR140) were expressed at higher levels, whereas blood vessel morphogenesis transcripts (e.g., Slit2) were suppressed in Axin2-/-:Runx2+/-calvaria. Cartilage maturation was impaired, as primary chondrocytes from double mutant mice demonstrated delayed differentiation and produced less calcified matrix in vitro. The genetic dominance of Runx2 was also reflected during endochondral fracture repair, as both Runx2+/- and double mutant Axin2-/-:Runx2+/- mice had enlarged fracture calluses at early stages of healing. However, by the end stages of fracture healing, double mutant animals diverged from the Runx2+/- mice, showing smaller calluses and increased torsional strength indicative of more rapid end stage bone formation as seen in the Axin2-/- mice. Taken together, our data demonstrate a dominant role for Runx2 in chondrocyte maturation, but implicate Axin2 as an important modulator of the terminal stages of endochondral bone formation.
Project description:The transcriptional regulator Runx2 has essential roles in chondrocytes and osteoblasts, central to the coordinated development of cartilage and bone. However, the regulatory mechanisms underlying Runx2’s roles in skeletal programming are not well understood. Here, we performed an integrative analysis of Runx2–DNA binding and chromatin accessibility in vivo and identified cell type-distinct chromatin accessibility underlying Runx2 roles in osteoblasts and chondrocytes.
Project description:The transcriptional regulator Runx2 has essential roles in chondrocytes and osteoblasts, central to the coordinated development of cartilage and bone. However, the regulatory mechanisms underlying Runx2’s roles in skeletal programming are not well understood. Here, we performed an integrative analysis of Runx2–DNA binding and chromatin accessibility in vivo and identified cell type-distinct chromatin accessibility underlying Runx2 roles in osteoblasts and chondrocytes.
Project description:Runx2 and Axin2 regulate skeletal development. We recently determined that Axin2 and Runx2 molecularly interact in differentiating osteoblasts to regulate intramembranous bone formation, but the relationship between these factors in endochondral bone formation was unresolved. To address this, we examined the effects of Axin2 deficiency on the cleidocranial dysplasia (CCD) phenotype of Runx2+/- mice, focusing on skeletal defects attributed to improper endochondral bone formation. Axin2 deficiency unexpectedly exacerbated calvarial components of the CCD phenotype in the Runx2+/- mice; the endocranial layer of the frontal suture, which develops by endochondral bone formation, failed to mineralize in the Axin2-/-:Runx2+/-mice, resulting in a cartilaginous, fibrotic and larger fontanel than observed in Runx2+/- mice. Transcripts associated with cartilage development (e.g., Acan, miR140) were expressed at higher levels, whereas blood vessel morphogenesis transcripts (e.g., Slit2) were suppressed in Axin2-/-:Runx2+/-calvaria. Cartilage maturation was impaired, as primary chondrocytes from double mutant mice demonstrated delayed differentiation and produced less calcified matrix in vitro. The genetic dominance of Runx2 was also reflected during endochondral fracture repair, as both Runx2+/- and double mutant Axin2-/-:Runx2+/- mice had enlarged fracture calluses at early stages of healing. However, by the end stages of fracture healing, double mutant animals diverged from the Runx2+/- mice, showing smaller calluses and increased torsional strength indicative of more rapid end stage bone formation as seen in the Axin2-/- mice. Taken together, our data demonstrate a dominant role for Runx2 in chondrocyte maturation, but implicate Axin2 as an important modulator of the terminal stages of endochondral bone formation. 4 mice per genotype X 4 genotypes: wildtype (WT), Runx2+/- (R-Het), Axin2-/- (A-KO), Axin2-/-:Runx2+/- (A-KO:R-Het). Total = 16 samples