Intracortical regionality represented by specific transcription for a novel protein, latexin

The monoclonal antibody (mAb) PC3.1 recognizes a subset of neurons distributed in the infragranular layers of the lateral neocortex of the rat. Immunoaffinity chromatography with mAb PC3.1 showed that this antibody specifically binds a peptide epitope on a 29 kDa protein named latexin. To study the molecular details of the protein, we isolated four independent cDNA clones for latexin from cDNA libraries of the rat cerebral cortex and whole brain using the amino acid sequences of latexin fragments. Analysis of these cDNA clones showed that the predicted primary structure of latexin consists of 223 amino acids, and has no strict homology to any sequences so far known. Western and Northern blots demonstrated that the latexin and its mRNA were expressed predominantly in neural tissues with some expression in non-neural tissues. The gene that encodes latexin in the rat appeared to have homologues in other mammalian species and in the chick. In situ hybridization showed that latexin mRNA is synthesized in a subset of neurons in the lateral but not the dorsal neocortex, and that the distribution profile of these neurons is quite similar to that of neurons expressing latexin. These results indicate that latexin is a novel class of neuronal protein which represents intracortical regionality, and suggest that the regional specification of the neocortex involves selective parcellation of neurons which express a particular gene.