Decreased projections to LP in <i>Brn3b</i> mutants occur postnatally.

Axonal projections were visualized by AP signals. (A) Schematic diagram of a coronal image showing the brain area (boxed) used for analysis (top) and sagittal images depicting the level (dashed line) where each coronal section was obtained (bottom) at P1-P5 and P8-P13. (B) (Left) Axonal branches in LP were barely detectable at P1/P2 in control and cKO mice (n = 4 mice/group). (Right) Magnified view of the boxed areas. (C) (Left) Axonal branches in LP were clearly noticeable at P4/P5 in control but barely visible in cKO mice (n = 4 mice/group). (Right) Magnified view of the boxed areas showing the LP regions used for analysis. (D) Quantification was presented as a relative difference between the AP-covered LP area in controls and mutants (1.00 ± 0.07 for control, 0.20 ± 0.03 for cKO; n = 4 mice/group). (E) (Left) Axonal branches in LP became abundant at P8/P9 in control and cKO mice, but the LP area covered by AP signals was smaller in cKO (n = 4 mice/group). (Right) Magnified view of the boxed areas. (F) Quantification (1.00 ± 0.07 for control, 0.40 ± 0.04 for cKO). (G) (Left) Axonal innervation in the LP is complete at P12/P13 in control mice, however, clearly decreased in cKO animals (n = 4 mice/group). (Right) Magnified view of the boxed areas. (H) Quantification (1.00 ± 0.09 for control, 0.45 ± 0.03 for cKO); unpaired two-tailed Student’s t test (mean ± SEM; p p = 0.0004 [***] at P8/P9; p = 0.0012 [**] at P12/P13). Scale bars: 250 μm. The data underlying this figure can be found in S1 Data. (TIF)