ZENK is an immediate early gene of the zinc finger family. Its name is an acronym of four gene names of which it is the avian homologue: zif268, EGR-1, NGFI-A and krox24.
ZENK (or its homologues) are expressed in vertebrate cells typically while committing to a more differentiated state or undergoing some sort of plastic change. ZENK is expressed in osteocytes when bone is subject to stress, in endothelial cells after an injury requires remapping of capillaries, in liver and kidney development. It's expressed by lymphocytes during their first (and only the first) exposure to an antigen. It is a (passive) tumor suppressant: inactivation of ZENK has been found to be necessary for tumors to develop.
ZENK (or its homologues) is expressed in neurons, usually rapidly and transiently, after exposure to new stimuli or environments. In rats, after exposure to an "enriched environment", ZENK is expressed in the hypocampus in the same cells where remapping of dendritic trees is observed. In canaries following repeated stimulation by song, ZENK is expressed in some auditory nuclei following a habituation dynamics. RNA expression peaks at 30 min and protein expression at 90 min. There is negligible expression after four hours of repeated stimulation. The habituation is song specific: if a new song is used, the cycle repeats.