The transcriptional-level circadian nature of Per2 has been extensively studied and monitored for various applications in vitro, using reporters expressing truncated murine Per2 promoters in NIH3T3 (mouse fibroblast) [23,24] and U2OS (human bone osteosarcoma) cells [25,26], among others [10,27,28]. The gene discussed is PER2; the disease is bone osteosarcoma.