Identification of ventricular-side-enriched molecules regulated in a stage-dependent manner during cerebral cortical development.

Radial glial cells are the main component of the embryonic cortical ventricular zone (VZ), producing deep-layer excitatory neurons in the early stage and upper-layer excitatory neurons in the late stage of development. Previous studies have suggested that the laminar fate of deep-layer neurons might be determined by early-stage-specific secretory or transmembrane molecules (S/TMs) in the VZ. However, the different properties required to produce the different types of neurons in early-stage and late-stage VZ cells are largely unknown. Herein, we investigated the stage-dependent transcriptional profiles of the ventricular side of the mouse cortex, which was manually dissected at embryonic day (E)12, E14 and E16, and identified 3985 'VZ-enriched' genes, regulated stage-dependently, by GeneChip analysis. These molecules were classified into nine types based on stage-dependent regulation patterns. Prediction programs for the S/TMs revealed 659 'VZ-enriched' S/TMs. In situ hybridization and real-time PCR analysis for several of these molecules showed results consistent with the statistical analysis of the GeneChip experiments. Moreover, we identified 17 cell cycle-related early-stage and 'VZ-enriched' molecules. These molecules included not only those involved in cell cycle progression, but also essential molecules for DNA double-strand break repair, such as Rad51 and Rpa1. These results suggest that the early stage-VZ cells, which produce both deep- and upper-layer neurons, and the late-stage VZ cells, which produce only upper-layer neurons, are intrinsically different. The gene lists presented here will be useful for the investigation of stage-dependent changes in VZ cells and their regulatory mechanisms in the developing cortex.