Abstract

The mammalian cerebral cortex is patterned into layers of neurons that share characteristic morphologies, physiological properties, and axonal connections. Neurons in the various layers are thought to acquire their lamina-specific identities shortly before the time of their final mitosis in the cortical ventricular zone. In order to investigate the molecular basis of laminar patterning in the CNS, we have performed in situ hybridization studies of the POU homeodomain gene SCIP (also known as Tst-1 or Oct-6), which is expressed in proliferating Schwann cells in the PNS and O2A progenitor cells in the developing CNS. In the CNS of adult rats, SCIP is expressed at high levels in the cerebral cortex, specifically in layer 5 pyramidal neurons that form subcortical axonal connections. SCIP is both temporally and spatially regulated during cortical development. Its initial expression in the intermediate zone and cortical plate is correlated with the early migration and differentiation of layer 5 neurons. SCIP hybridization was not, however, observed within the ventricular zone during the period of neurogenesis. SCIP is also expressed at high levels in the neurons of cortical layer 2/3, during their migration and differentiation within the cortical plate. This expression in the upper layers is apparently downregulated during postnatal periods, with the adult pattern apparent by postnatal day 30 (P30). POU domain genes are thought to play a role in cell lineage and cell fate decisions in several systems; thus, SCIP may serve a function in generating discrete laminar phenotypes in the developing cerebral cortex. In addition, since SCIP is a putative repressor of myelin gene expression, our results suggest that SCIP plays a role in regulating transcription in differentiated CNS neurons as well as in proliferating glial precursors.