Phenotypic loss of key transcription factors during monolayer expansion. Inner and outer MFCs were expanded from Passage 1 (P1, grey bars) to Passage 3 (P3, white bars) under normal (21%) or low (3%) oxygen tension. mRNA transcript levels of hypoxia-inducible factor 1α (HIF-1α), hypoxia-inducible factor 2α (HIF-2α) and Sry-related HMG box-9 (Sox9) were compared within groups at P1 and P3. Marked dedifferentiation is seen between P1 and P3 for all genes of interest except Sox9. Expression was normalized to levels of the housekeeping gene β-actin using 2-ΔCT method. * = p < 0.05 ** = p < 0.01 represents significant difference between P1 and P3 values within a single group using Student’s two-tailed t-test.