Project description:Craniofacial and jaw bones have unique physiological specificities when compared to axial and appendicular bones. However, the molecular profile of the jaw osteoblast (OB) remains incomplete. The purpose of this study was to decipher the bone site-specific profile of transcription factors (TF) expressed in jaw osteoblasts in vivo. We accomplished this by performing RNA-seq analysis on flow-sorted osteoblasts isolated from jaw and tibial bones of 9-day-old (P9) transgenic Col1a1*2,3-GFP mice. This study demonstrated the feasibility of a new method to isolate pure OB populations and map their gene expression signature in the context of OB physiological environment, avoiding in vitro culture and its associated biases. Our results provided insights into the site-specific developmental pathways governing OB and identify new major OB regulators of bone physiology.
Project description:Craniofacial and jaw bones have unique physiological specificities when compared to axial and appendicular bones. However, the molecular profile of the jaw osteoblast (OB) remains incomplete. The present study aimed to decipher the bone site-specific profiles of transcription factors (TFs) expressed in OBs in vivo. Using RNA sequencing analysis, we mapped the transcriptome of confirmed OBs from 2 different skeletal sites: mandible (Md) and tibia (Tb). The OB transcriptome contains 709 TF genes: 608 are similarly expressed in Md-OB and Tb-OB, referred to as "OB-core"; 54 TF genes are upregulated in Md-OB, referred to as "Md-set"; and 18 TF genes are upregulated in Tb-OB, referred to as "Tb-set." Notably, the expression of 29 additional TF genes depends on their RNA transcript variants. TF genes with no previously known role in OBs and bone were identified. Bioinformatics analysis combined with review of genetic disease databases and a comprehensive literature search showed a significant contribution of anatomical origin to the OB signatures. Md-set and Tb-set are enriched with site-specific TF genes associated with development and morphogenesis (neural crest vs. mesoderm), and this developmental imprint persists during growth and homeostasis. Jaw and tibia site-specific OB signatures are associated with craniofacial and appendicular skeletal disorders as well as neurocristopathies, dental disorders, and digit malformations. The present study demonstrates the feasibility of a new method to isolate pure OB populations and map their gene expression signature in the context of OB physiological environment, avoiding in vitro culture and its associated biases. Our results provide insights into the site-specific developmental pathways governing OBs and identify new major OB regulators of bone physiology. We also established the importance of the OB transcriptome as a prognostic tool for human rare bone diseases to explore the hidden pathophysiology of craniofacial malformations, among the most prevalent congenital defects in humans.
Project description:Development of the vertebrate jaw apparatus depends on highly conserved signaling pathways. Patterning of the lower jaw is driven by Endothelin receptor type A (Ednra) and secreted ligand Endothelin 1 (Edn1). The Ednra signaling pathway establishes the identity of lower jaw progenitors by regulating expression of numerous patterning genes, but the intracellular signaling mechanisms linking receptor activation to gene regulation remains poorly understood. As a first step towards addressing this question, we examined the function of the Gq/11 family of Gα subunits in zebrafish using pharmacological and genetic ablation of Gq/11 activity and transgenic induction of a constitutively active Gq protein in edn1-/- embryos. Loss of Gq/11 activity fully recapitulated the edn1-/- phenotype, with genes encoding for G11 being most essential. Furthermore, inducing Gq activity in edn1-/- embryos not only restored Ednra-dependent jaw structures and gene expression signatures but also caused homeosis of the upper jaw structures into a lower jaw-like structure. These results indicate that Gq/11 is necessary and sufficient to mediate the lower jaw patterning mechanism for Ednra.
Project description:Analysis of gene expression in activation-tagged jaw-d mutant plants. Total RNA was extracted from the aerial parts of two weeks old jaw-d and control plants. Keywords: other
Project description:The jaws are complementary in form and function but develop asymmetrically, as the lower but not upper jaw bone forms around a prominent cartilage template. How such differences in skeletal composition are patterned is unclear. Here, we identify four Nuclear receptor 2f genes, nr2f1a, nr2f1b, nr2f2, and nr2f5, as enriched in zebrafish upper jaw precursors. Whereas loss of Nr2f genes results in expansion of upper jaw cartilage to resemble that of the lower jaw, Nr2f5 misexpression inhibits lower jaw cartilage formation. Genome-wide analyses show that Nr2f genes prevent expansion of lower jaw-associated gene expression into the upper jaw territory. Further, restriction of Nr2f expression by Endothelin1 signaling is critical for lower jaw development, as reducing Nr2f dosage fully restores lower jaw development in edn1 mutants. We propose that Nr2f genes drive jaw asymmetry by limiting early cartilage differentiation in the upper jaw to preserve more precursors for later osteogenesis.
Project description:Analysis of gene expression in activation-tagged jaw-d mutant plants. Total RNA was extracted from the aerial parts of two weeks old jaw-d and control plants.
Project description:Exposure to environmental contaminants can disrupt normal development of the early vertebrate skeleton. 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) impairs craniofacial skeletal development across many vertebrate species and its effects are especially prominent in early life stages of fish. TCDD activates the aryl hydrocarbon receptor (AHR), a transcription factor that mediates most if not all TCDD responses. We investigated the transcriptional response in the developing zebrafish jaw following TCDD exposure using DNA microarrays. Zebrafish larvae were exposed to TCDD at 96 h postfertilization (hpf) and jaw cartilage tissue was harvested for microarray analysis at 1, 2, 4 and 12 h postexposure (hpe). Numerous chondrogenic transcripts were misregulated by TCDD in the jaw. Comparison of transcripts altered by TCDD in jaw with transcripts altered in embryonic heart showed that the transcriptional responses in the jaw and the heart were strikingly different. Sox9b, a critical chondrogenic transcription factor, was the most significantly reduced transcript in the jaw. We hypothesized that the TCDD reduction of sox9b expression plays an integral role in affecting formation of the embryonic jaw. Morpholino knock down of sox9b expression demonstrated that partial reduction of sox9b expression alone was sufficient to produce a TCDD-like jaw phenotype. Heterozygous sox9b deletion mutant embryos were sensitized to TCDD. Lastly, embryos injected with sox9b mRNA and then exposed to TCDD blocked TCDD-induced jaw toxicity in approximately 14% of sox9b-injected embryos. These results suggest that reduced sox9b expression in TCDD-exposed zebrafish embryos contributes to jaw malformation. Keywords: Time course
Project description:9-day-old jaw-D;pTCP4::mTCP4:GR treated with Cycloheximide (CHX, control) and the combination of Cycloheximide and Dexamethasone (CHX DEX, treated).
Project description:Craniofacial development involves regulation of a compendium of transcription factors, signaling molecules and epigenetic regulators. Histone deacetylases (HDACs) are involved in the regulation of cell proliferation, differentiation and homeostasis across a wide range of tissues, such as brain, cardiovascular system, muscular system, and skeletal system. However, functional role of Hdac4 during craniofacial development is still unclear. In this study, we investigated the effects of Hdac4 knockout in craniofacial skeletal development by conditionally disrupting the Hdac4 gene in cranial neural crest cells (CNCCs) using Cre-mediated recombination. Mice deficient in Hdac4 in CNCCs-derived osteoblasts demonstrated a dramatic decrease in bone formation in frontal bone. In vitro pre-osteoblasts (MC3T3-E1 cells) lacking Hdac4 exhibited reduced proliferation activity in association with dysregulation of cell cycle-related genes. These findings suggest that Hdac4 acts partially as a regulator of craniofacial skeletal development by positively regulating proliferation of CNCCs-derived osteoblasts.