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Gene expression of the intermediate and outer interzone of murine embryos at 15.5 days of gestation

ABSTRACT: Nascent embryonic joints, interzones, contain a distinct cohort of progenitor cells responsible for the formation of the majority of articular tissues. However, to date the interzone has largely been studied using in situ analysis for candidate genes in the context of the embryo rather than using an unbiased genome wide expression analysis on isolated interzone cells, leaving significant controversy regarding the exact role of the intermediate and outer interzone layers in joint formation. Therefore, in this study, using laser capture microdissection (three biological replicates), we selectively harvested the intermediate and outer interzones of mouse embryos at gestational age 15.5 days, just prior to cavitation, when the differences between the layers should be most profound. Microarray analysis (Agilent Whole Mouse Genome Oligo Microarrays) was performed and the differential gene expression between the intermediate interzone cells and outer interzone cells was examined by performing a 2-sided paired student t-test and pathway analysis. 197 genes were differentially expressed (≥ 2-fold) between the intermediate interzone and the outer interzone with a p-value ≤ 0.01. Of these, 91 genes showed higher expression levels in the intermediate interzone and 106 were expressed higher in the outer interzone. Pathway analysis of differentially expressed genes suggests an important role for inflammatory processes in the interzone layers, especially in the intermediate interzone, and hence in joint and articular cartilage development. The high representation of genes relevant to chondrocyte hypertrophy and endochondral ossification in the outer interzone suggests that it undergoes endochondral ossification.

ORGANISM(S): Mus musculus

PROVIDER: GSE51098 | GEO | 2014/09/22

SECONDARY ACCESSION(S): PRJNA221156

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)

Project description:Articular and growth plate cartilage have comparable structures consisting of three distinct layers of chondrocytes, suggesting similar differentiation programs and therefore similar gene expression profiles. To address this hypothesis and to explore transcriptional changes that occur during the onset of articular and growth plate cartilage divergence, we used microdissection of 10-day-old rat proximal tibial epiphyses, microarray analysis, and bioinformatics to compare gene expression profiles in individual layers of articular and growth plate cartilage. We found that many genes that were spatially upregulated in intermediate/deep zone of articular cartilage were also spatially upregulated in resting zone of growth plate cartilage (overlap greater than expected by chance, P < 0.001). Interestingly, superficial zone of articular cartilage showed an expression profile with similarities to both proliferative and hypertrophic zones of growth plate cartilage (P < 0.001 each). Additionally, significant numbers of known proliferative zone markers (3 out of 6) and hypertrophic zone markers (27 out of 126) were spatially upregulated in superficial zone compared to intermediate/deep zone (more than expected by chance, P < 0.001 each). In conclusion, we provide evidence that intermediate/deep zone of articular cartilage has a gene expression profile more similar to resting zone of growth plate cartilage, whereas superficial zone has a gene expression profile more similar to proliferative and hypertrophic zones. 10-day-old rat proximal tibial epiphyses were manually microdissected into articular cartilage superficial (SZ) and intermediate/deep (IDZ) zones and growth plate cartilage resting zone (RZ) for total RNA extraction and hybridization on Affymetrix microarrays. We used 10-day-old animals because, at this age, the secondary ossification center has recently begun to form and divides the epiphysis into articular cartilage distally and growth plate cartilage more centrally. The 4 SZ samples were taken from animals 5-8, respectively, whereas the 4 IDZ and 4 RZ samples were each taken from animals 1-2, 3-4, 5-6, and 7-8, respectively.

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Gene expression of the intermediate and outer interzone of murine embryos at 15.5 days of gestation

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