RT-qPCR measurement of differential gene expression. Quantification of transcript abundance indicates significant up-regulation of COMP (b) and TGFβR3 (e) gene expression in adult articular cartilage relative to neonatal articular cartilage. In contrast, gene expression for COL2A1 (a), P4HA1 (c), and TNC (d) are significantly up-regulated in neonatal articular cartilage relative to adult articular cartilage. Expression of TGFβ1 (f) was not significantly different between neonatal and adult samples. The RT-qPCR data for all six target genes confirm the results of microarray hybridization experiments. Data are presented as box and whisker plots indicating lowest value, first (0.25) quartile, median, third quartile (0.75), and highest value. Mathematical means of expression are indicated below each age group, and mean fold differences for each target gene are also given numerically as "Mean FC" under the abscissa. ** (p < 0.01).