Transcriptional profiling of growth plate chondrocyte differentiation yields insight into endochondral ossification

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. Keywords: Growth plate microdissection 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. Samples were hybridized to Affymetrix MOE 430 2.0 mouse chips for analysis. Four independent trials were executed for each zone. Number of time points: 1 Number of treatments: 0 Number of Samples: 4 replicates per zone Affymetrix chip: MOE 430 2.0 Tissue or origin: Tibiae Species E15.5 mice Samples: Total RNA