Figure 1

CR is dynamically expressed in layer 5 of the barrel cortex during the first postnatal weeks. At birth, no CR staining can be observed in the deeper layer of the cortex (A). Beginning at P3, CR is detected in the deeper layer of the barrel cortex (B). This CR expression gradually increases and forms a clear row-like zone at P4 (C). The expression level of CR peaks at P8 (D). The intensity of the row-like zone of CR staining decreases at P15 (E). By P30, the CR-positive row-like zone can no longer be detected in the deep layer of the cortex, and the only signal comes from CR-positive interneurons dispersed throughout the cortex (F). Birth-dating analysis indicates that abundant CR-positive neurons at P8 are found to be positive for BrdU administered at E13.5 (G, H, I, arrows). Few BrdU- and CR-positive neurons were observed when BrdU was injected at E12.5 (J), E14.5 (K) and E15.5 (L), which corresponds to the time points at which L6, L4 and L2/3 neurons, respectively, are born. Scale bar: 100?m.