Gene expression analysis of mono-cultured and co-cultured cell pellets after 21 days of culture. Quantitative mRNA gene expression analysis via SYBR Green detection was used to evaluate the expression of a panel of fibrogenic (Collagen I and Versican) and chondrogenic (Aggrecan, Collagen II and SOX9) marker genes as well as the expression of genes characteristic of hypertrophic differentiation of MSCs (Collagen X, MMP-13 and Indian Hedgehog) in pellets from MSCs, MCI/MSCs, MCI, MCO/MSCs, and MCO after 3 weeks of culture in chondrogenic medium (transforming growth factor-beta 1, dexamethasone, and ascorbate). Each data point represents the mean ± standard error of the mean of four donor pairs. One-way analysis of variance with Tukey's multiple comparison post tests: *significance when compared with mono-cultures of meniscus cells - outer meniscus cells (MCO) or inner meniscus cells (MCI) - and MSC pellet controls (P <0.05) or when compared with mono-cultures of MCO versus mono-cultures of MCI; **significance when compared with co-cultures of MCO or MCI and MSC pellet controls (P <0.01); ***significance when compared with MCO or MCI and MSC pellet controls (P <0.0001). No significance (n.s.) (P >0.05). All marker gene expression was presented as relative mRNA level normalized to human β-actin (y-axis); (A) Aggrecan, (B) Collagen I (COL1A2), (C) Collagen II (COL2A1), (D) Collagen × (COL10A1), (E) MMP-13, (F) Indian Hedgehog (IHh), (G) Sox9, and (H) Versican MCI, meniscus cells from inner meniscus region; MCO, meniscus cells from the outer meniscus region; MMP-13, matrix metalloproteinase 13; MSC, mesenchymal stromal cell; SOX9, Sry-related HMG box 9.