Retinol-binding protein gene is highly expressed in higher-order association areas of the primate neocortex

The neocortex consists of histochemically, connectionally, and functionally distinguishable areas. Recently, molecular biological techniques have enabled us to find rare types of genes expressed in specific neocortical areas. We previously reported occ1 gene as preferentially expressed in the primary visual cortex (V1), using the differential display method. Here, by differential display, we found selective and strong expression of the serum retinol-binding protein (RBP) gene, in higher-order association areas. In V1, RBP mRNA was expressed only in the superficial part of layer II, but its expression increased, involving deeper layers, along the visual pathway. In visual association areas such as TE, RBP mRNA was strongly expressed in both supra- and infragranular layers. In primary auditory and somatosensory areas, as in V1, RBP expression was low, and restricted to the upper part of the supragranular layers. The laminar pattern of RBP expression is in marked contrast with that of occ1; and in early visual areas where both genes are expressed, these occur in distinct sublayers within the supragranular layers. In neonatal monkeys, the area-specific expression pattern of RBP was less distinct, suggesting that the characteristic expression of RBP in higher-order association areas is mainly established postnatally.