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Atf4 regulates chondrocyte proliferation and differentiation during endochondral ossification by activating Ihh transcription.

ABSTRACT: Activating transcription factor 4 (Atf4) is a leucine-zipper-containing protein of the cAMP response element-binding protein (CREB) family. Ablation of Atf4 (Atf4(-/-)) in mice leads to severe skeletal defects, including delayed ossification and low bone mass, short stature and short limbs. Atf4 is expressed in proliferative and prehypertrophic growth plate chondrocytes, suggesting an autonomous function of Atf4 in chondrocytes during endochondral ossification. In Atf4(-/-) growth plate, the typical columnar structure of proliferative chondrocytes is disturbed. The proliferative zone is shortened, whereas the hypertrophic zone is transiently expanded. The expression of Indian hedgehog (Ihh) is markedly decreased, whereas the expression of other chondrocyte marker genes, such as type II collagen (Col2a1), PTH/PTHrP receptor (Pth1r) and type X collagen (Col10a1), is normal. Furthermore, forced expression of Atf4 in chondrocytes induces endogenous Ihh mRNA, and Atf4 directly binds to the Ihh promoter and activates its transcription. Supporting these findings, reactivation of Hh signaling pharmacologically in mouse limb explants corrects the Atf4(-/-) chondrocyte proliferation and short limb phenotypes. This study thus identifies Atf4 as a novel transcriptional activator of Ihh in chondrocytes that paces longitudinal bone growth by controlling growth plate chondrocyte proliferation and differentiation.

SUBMITTER: Wang W

PROVIDER: S-EPMC2781050 | biostudies-literature | 2009 Dec

REPOSITORIES: biostudies-literature

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Atf4 regulates chondrocyte proliferation and differentiation during endochondral ossification by activating Ihh transcription.

Wang Weiguang W Lian Na N Li Lingzhen L Moss Heather E HE Wang Weixi W Perrien Daniel S DS Elefteriou Florent F Yang Xiangli X

Development (Cambridge, England) 20091111 24

Activating transcription factor 4 (Atf4) is a leucine-zipper-containing protein of the cAMP response element-binding protein (CREB) family. Ablation of Atf4 (Atf4(-/-)) in mice leads to severe skeletal defects, including delayed ossification and low bone mass, short stature and short limbs. Atf4 is expressed in proliferative and prehypertrophic growth plate chondrocytes, suggesting an autonomous function of Atf4 in chondrocytes during endochondral ossification. In Atf4(-/-) growth plate, the typ ...[more]

PMID: 19906842

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Project description:A variety of cell cultures models and in vivo approaches have been used to study gene expression during chondrocyte differentiation. The extent to which the in vitro models reflect bona fide gene regulation in the growth plate has not been quantified. In addition, studies that evaluate global gene expression changes among different growth plate zones are limited. To address these issues, we completed a microarray screen of three growth plate zones derived from manually segmented embryonic mouse tibiae. Classification of genes differentially expressed between each respective growth plate zone, functional categorization as well as characterization of gene expression patterns, cytogenetic loci, signaling pathways and functional motifs confirmed documented data and pointed to novel aspects of chondrocyte differentiation. Parallel comparisons of the microdissected tibiae data set to our previously completed micromass culture screen further corroborated the suitability of micromass cultures for modeling gene expression in chondrocyte development. The micromass culture system demonstrated striking similarities to the in vivo microdissected tibiae screen; however, the micromass system was unable to accurately distinguish gene expression differences in the hypertrophic and mineralized zones of the growth plate. These studies will allow us to better understand zone-specific gene expression patterns in the growth plate. Ultimately, this work will help define both the genomic context in which genes are expressed in the long bones and the extent to which the micromass culture system is able to recapitulate chondrocyte development in endochondral ossification. Experiment Overall Design: Tibiae from 15.5 day old mouse embryos were isolated and partitioned into three distinct zones. Total RNA was isolated from each segment and the individual segments pooled within a litter. Experiment Overall Design: Samples were hybridized to Affymetrix MOE 430 2.0 mouse chips for analysis. Four independent trials were executed for each zone. Experiment Overall Design: Number of time points: 1 Experiment Overall Design: Number of treatments: 0 Experiment Overall Design: Number of Samples: 4 replicates per zone Experiment Overall Design: Affymetrix chip: MOE 430 2.0 Experiment Overall Design: Tissue or origin: Tibiae Experiment Overall Design: Species E15.5 mice Experiment Overall Design: Samples: Total RNA

Dataset Information

Atf4 regulates chondrocyte proliferation and differentiation during endochondral ossification by activating Ihh transcription.

Publications

Atf4 regulates chondrocyte proliferation and differentiation during endochondral ossification by activating Ihh transcription.

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