Fig. 3. TAG-1 mediates the tangential migration of MGE neurons along the fibers of the corticofugal system. CP, cortical plate; LGE, lateral ganglionic eminence. The broken line demarcates the ventricle and the edge of the slice. The migration of the MGE cells is examined in cortical slice cultures by placing a crystal of DiI in the LGE (A,B), as well as by using immunohistochemistry against GABA (C-F). Cortical slices were cultured for 2 days in the presence of monoclonal or Fab fragments of polyclonal antibodies against TAG-1 (A,C, respectively) or control antibodies (same isotype, Fab fragments of control antisera, see Materials and Methods) (B,D, respectively). Very few DiI-labeled migrating neurons (A) and GABAergic neurons (C) are detected in the presence of antibodies against TAG-1 in E15 rat (A) or E13.5 mouse (C), when compared with the controls in the cortex of E15 rat (B) or E13.5 mouse (D). A marked decrease in the number of GABAergic neurons in E16 rat slice cultures is observed in the presence of TAG-1-Fc protein (E). No effect is observed when control soluble Fc protein (MUC18) is added in the culture medium (F). Antigen depleted antibodies do not reduce the number or affect the density of GABA-containing neurons in the cortex (G). No differences in the expression pattern of TAG-1 is detected in cortical slices cultured in the presence of antibodies against TAG-1 and incubated with the secondary antibody alone (H). Quantification of the blocking effect of antibodies to TAG-1 (I) or TAG-1-Fc (J) protein on the migration of GABAergic neurons. Densitometry of GABA-expressing cells in slice cultures in the presence of Fab antibodies against TAG-1 (I) and control Fab fragments or TAG-1 Fc protein (J) and control MUC18 Fc protein (see also Materials and Methods). Values represent the ratio of the area where pixel densities were measured to the total area measured (i.e. all of neocortex). Value 1.00 would represent the entire length of the neocortex. Error bars represent the s.d.; *P<0.05, one-factor ANOVA. Values were collected from independent slice cultures (A, n=9; B, n=7) Scale bars: 100 µm in A-H.
