Cellular and subcellular localization of necdin in fetal and adult mouse brain

Necdin is a 325-amino-acid residue protein encoded by a cDNA clone isolated from neurally differentiated embryonal carcinoma cells. Ectopic expression of necdin induces growth arrest of proliferative cells. Necdin binds to major transcription factors E2F1 and p53, suggesting that necdin exerts its functions through the interactions with these cell-cycle-regulating factors. However, information about precise localization of endogenous necdin protein is currently lacking. A rabbit polyclonal antibody was raised against a bacterially expressed recombinant protein of necdin (amino acids 83-325). Immunoblot analysis revealed that necdin protein was expressed almost exclusively in the brain of adult mice. A relative molecular mass of endogenous necdin was estimated at approximately 43,000. In developing mouse brain, necdin was most abundant during fetal and neonatal periods. Necdin was highly enriched in the cytoplasm of hypothalamic neurons in fetal and adult mice. The subcellular fractionation analysis revealed that necdin was concentrated in the cytosol fraction of brain cells. These results suggest that endogenous necdin protein is localized predominantly in the cytoplasm of differentiated neurons and moves into the nucleus under specific conditions.