sentences:  In addition to its circadian functions, "per" has also been implicated in a variety of other non-circadian processes.The mammalian period 2 gene plays a key role in tumor growth in mice; mice with an mPer2 knockout show a significant increase in tumor development and a significant decrease in apoptosis.This is thought to be caused by mPer2 circadian deregulation of common tumor suppression and cell cycle regulation genes, such as "Cyclin D1", "Cyclin A", "Mdm-2", and "Gadd45α", as well as the transcription factor "c-myc", which is directly controlled by circadian regulators through E box-mediated reactions.