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Loss of Foxc1 and Foxc2 function in chondroprogenitor cells disrupts endochondral ossification.

ABSTRACT: Endochondral ossification forms and grows the majority of the mammalian skeleton and is tightly controlled through gene regulatory networks. The forkhead box transcription factors Foxc1 and Foxc2 have been demonstrated to regulate aspects of osteoblast function in the formation of the skeleton but their roles in chondrocytes to control endochondral ossification are less clear. We demonstrate that Foxc1 expression is directly regulated by SOX9 activity, one of the earliest transcription factors to specify the chondrocyte lineages. Moreover we demonstrate that elevelated expression of Foxc1 promotes chondrocyte differentiation in mouse embryonic stem cells and loss of Foxc1 function inhibits chondrogenesis in vitro. Using chondrocyte-targeted deletion of Foxc1 and Foxc2 in mice, we reveal a role for these factors in chondrocyte differentiation in vivo. Loss of both Foxc1 and Foxc2 caused a general skeletal dysplasia predominantly affecting the vertebral column. The long bones of the limb were smaller and mineralization was reduced and organization of the growth plate was disrupted. In particular, the stacked columnar organization of the proliferative chondrocyte layer was reduced in size and cell proliferation in growth plate chondrocytes was reduced. Differential gene expression analysis indicated disrupted expression patterns in chondrogenesis and ossification genes throughout the entire process of endochondral ossification in Col2-cre;Foxc1Δ/Δ;Foxc2Δ/Δ embryos. Our results suggest that Foxc1 and Foxc2 are required for correct chondrocyte differentiation and function. Loss of both genes results in disorganization of the growth plate, reduced chondrocyte proliferation and delays in chondrocyte hypertrophy that prevents correct ossification of the endochondral skeleton.

ORGANISM(S): Mus musculus

PROVIDER: GSE165951 | GEO | 2021/09/08

REPOSITORIES: GEO

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Project description:Objective: Joint formation begins with the establishment of an interzone within the cartilaginous anlagen of the future skeleton and both Gdf5 and Erg are proposed as regulators of chondrocyte differentiation during and post interzone formation. The aim of this study was to examine the relationship between Gdf5 and Erg expression and downstream effects on chondrocyte gene expression. Design: Erg expression was identified in mouse knee joints at E13.5. Expression and microarray analyses were performed using micromass cultures of murine C3H10T1/2 mesenchymal cells undergoing induced chondrogenesis in the presence of absence of Gdf5 and Erg. Results: At E13.5, Erg expression was found to surround epiphyseal chondrocytes and span the interzone up to the intermediate zone. Erg splice forms were expressed in micromass cultures, and their expression profile was altered by the addition of recombinant Gdf5 depending on the stage of differentiation. Overexpression of Erg-010 resulted in a downregulation of Col2a1 and Col10a1. Microarray analysis following Erg-010 overexpression identified two potential downstream targets, Ube2b and Osr2, which were also differentially regulated by Gdf5. Conclusion: Erg regulation by Gdf5 in mesenchymal cells in vitro is dependent on the stage of chondrogenesis, and its expression in vivo demarcates chondrocytes that are not destined to be consumed by endochondral ossification. Functionally, Erg expression causes downregulation of Col2a1 and Col10a1 expression and this effect is potentially mediated by Osr2, which is a known regulator of chondrocyte differentiation. The identification of Ube2b as a putative downstream target of Erg-010 suggests that it may contribute to the regulation of the ubiquitination pathway and thereby BMP2 signaling, which is essential for normal knee joint development. RNA from overexpression experiments was extracted as described above. Total RNA quality was confirmed using a Bioanalyzer 2100 (Agilent). Labelled targets were generated from total RNA and hybridized to GeneChip Mouse Genome 430 2.0 arrays (Affymatrix) (Genomics Centre, University of Manchester). The raw fluorescence intensity values were normalized using a Robust Multi-array Average approach using dChip (V2005)

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Loss of Foxc1 and Foxc2 function in chondroprogenitor cells disrupts endochondral ossification.

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