Quantitative real-time PCR. (a) Topographical variation in proteoglycan 4 (PRG4) expression in sham-operated ('normal') joints as demonstrated by the ratio of mRNA copy numbers from cartilage normally covered (COV) versus cartilage normally uncovered (UNCOV) by menisci; in each case the average value is indicated by the line (n = 6). The dotted horizontal line represents the expected ratio of 1 if there were no difference between regions. (b) PRG4 mRNA copy numbers (means ± SEM) from ovine articular cartilage after lateral meniscectomy (MEN). LTP, lateral tibial plateau; MTP, medial tibial plateau.