The occ1 gene is preferentially expressed in the primary visual cortex in an activity-dependent manner: a pattern of gene expression related to the cytoarchitectonic area in adult macaque neocortex

Marker molecules to visualize specific subsets of neurons are useful for st udying the functional organization of the neocortex. One approach to identi fy such molecular markers is to examine the differences in molecular proper ties among morphologically and physiologically distinct neuronal cell types . We used differential display to compare mRNA expression in the anatomical ly and functionally distinct areas of the adult macaque neocortex. We found that a gene, designated occ1, was preferentially transcribed in the poster ior region of the neocortex, especially in area 17. Complete sequence analy sis revealed that occ1 encodes a macaque homolog of a secretable protein, T SC-36/follistatin-related protein (FRP). In situ hybridization histochemist ry confirmed the characteristic neocortical expression pattern of occ1 and showed that occ1 transcription is high in layers II, III, IVA and IVC of ar ea 17. In addition, occ1 transcription was observed selectively in cells of the magnocellular layers in the lateral geniculate nucleus (LGN). Dual lab eling immunohistochemistry showed that the occ1-positive neurons in area 17 include both gamma -aminobutyric acid (GABA)-positive aspiny inhibitory ce lls and the alpha -subunit of type II calcium/calmodulin-dependent protein kinase (CaMKII alpha)-positive spiny excitatory cells. With brief periods o f monocular deprivation, the occ1 mRNA level decreased markedly in deprived ocular dominance columns of area 17. From this we conclude that the expres sion of occ1 mRNA is present in a subset of neurons that are preferentially localized in particular laminae of area 17 and consist of various morpholo gical and physiological neuronal types, and, furthermore, occ1 transcriptio n is subject to visually driven activity-dependent regulation.