BMI1 (Polycomb complex protein BMI-1, PCGF4, RNF51) is a polycomb ring finger protein that modulates p16INK4A and p14ARF/p19 expression and is considered an oncogene. Knockout studies in mice as well as various cancer studies show that it is important for central nervous system development, stem cell renewal and negative regulation of aging in neurons, proper neurological function, skeletal patterning and hematopoiesis. It also functions in DNA repair. It is highly upregulated in mantle cell lymphomas and also overexpressed in breast, colorectal, skin, prostate, ovarian and hematological carcinomas. In a number of cancers including glioblastoma multiforme, inhibition of BMI1 results in reduced proliferation of tumor cells. Loss of BMI1 expression is also thought to play a role in sporadic Alzheimer’s disease pathogenesis. In immunohistochemistry, BMI1 has nuclear positivity in all tissues throughout the body. References: Genes Dev. 19 (12): 1432–7, PMID: 15964994; J. Neurosci. 29 (2): 529–42, PMID: 19144853; Journal of Molecular Medicine. 83 (8): 596–600, PMID: 15976916; The Journal of Neuroscience. 29 (28): 8884–96, PMID: 19605626; Cell Rep. 2018 May 29;23(9):2653-2666; Biochim Biophys Acta. 2008 Nov;1782(11):642-8, PMID: 18817867