Fig. 1. TAG-1 is expressed by the developing corticofugal fibers. (A,B) Immunohistochemistry for TAG-1 in coronal sections of E12.5 (A) or E14.5 (B) mouse cortex. (A) Labeled cells in the PP project to the ventral telencephalon in the region of the IC. (B) Labeled axons are oriented tangentially in the MZ and IZ, and radially in the CP. (C) In situ hybridization for TAG-1 mRNA in coronal sections of E14.5 mouse cortex. The signal is detected predominantly in the IZ and MZ. (D) Western blot analysis of total lysates of E14.5 mouse spinal cord (control, lane 1) and cortex (lane 2) reveals a single band of 135 kDa, as expected of the TAG-1 antigen (arrowhead). The molecular weight standards shown (lane 3) are 111 and 83 kDa (arrows). (E) DiI crystal placement into the dorsal cerebral cortex of E14.5 mouse, labels corticofugal fibers descending via the IZ into the IC. (F-K) Immunohistochemistry for TAG-1 in coronal sections of E14.5 mouse cortex, after placement of DiI in the cortex of the whole brain, reveals numerous DiI- labeled corticofugal fibers that are immunopositive for TAG-1. DiI labeling (red, G,J) and immunohistochemistry for TAG-1 (green, F,I) in the IZ and CP of E14.5 cortical slices (F,G), as well as in the area of the IC (I,J). (H,K) Superimposed images of F,G and I,J, respectively. Arrows in H indicate DiI-labeled-TAG-1-immunopositive corticofugal fibers, radially oriented in the CP, cortical plate. IC, internal capsule; IZ, intermediate zone; MZ, marginal zone; PP, preplate. Scale bars: 100 µm in A,E,I-K; 50 µm in B,F-H; 60 µm in C.
