The identification of NP25: a novel protein that is differentially expressed by neuronal subpopulations.
A novel gene encoding a 25-kDa neuronal-specific protein, here named 'NP25', has been isolated as a cDNA clone from rat brain. The sequence of the NP25 cDNA reveals a single open reading frame that encodes a primary translation product of 206 amino acids. A search of the protein sequence databank indicates that NP25 is significantly homologous with three recently discovered muscle proteins: SM22 alpha, mp20 and calponin. The gene is specifically and ubiquitously expressed in the rat brain and has conserved sequences among chicken, rat, mouse and human. Rat brain NP25 was identified by Western blot using an antiserum elicited against trpE-NP25 fusion protein. On pH gradient electrophoresis, NP25 was separated into at least two isoforms with similar molecular weights. Immunocytochemistry and in situ hybridization demonstrated that NP25 was differentially expressed by neuronal subpopulations of the rat central nervous system. The highest concentration of NP25 protein was localized in central amygdaloid nuclei and glomeruli in the granule layer of cerebellum. The wide and differential distribution of NP25 in the brain suggests that it may play a particular important role in the function of specific neuronal systems.