Figure 4.
Abnormal dendritic morphology of Tbr2-deficient mitral and tufted cells. A–H, Immunofluorescence labeling of Tbx21 (A, E), PGP9.5 (B, F), Pcdh21 (C, G), and neurofilament-165 kDa (D, H) on OB coronal sections from control (A–D) and Tbr2 conditional knockout (E–H) mice. Dendritic morphology of mitral and tufted cells is abnormal in Tbr2 conditional knockout mice. I, Cumulative plots of the projection angles of mitral cell primary dendrites. Angles between the orientation of primary dendrites (as visualized by immunolabeling of neurofilament) and a line perpendicular to the OB layers were measured at the middle of the EPL (inset) from control (blue) and Tbr2 conditional knock-out (orange) mice (n = 39 mitral cells for each genotype). In contrast to control mice in which most primary dendrites project vertically toward target glomeruli, primary dendrites of Tbr2-deficient mitral cells extend into more random directions. J, Quantitative analysis of the EPL sublayer organization. Thickness of the total EPL, PGP9.5-negative outer EPL, and PGP9.5-positive inner EPL was measured from control and Tbr2-mutant OB sections. The thickness of outer EPL is significantly reduced in Tbr2 conditional knockout mice. Values are mean ± SEM (n = 5), ***p < 0.001 (two-tailed t test). K, L, Representative morphology of individual mitral cells of control (K) and Tbr2 conditional knockout (L) mice. Lucifer yellow was intracellularly injected into single mitral cells in fixed OB coronal slices of P16–P18 mice. Projected images of whole-cell shapes taken by a two-photon microscope are presented. Primary dendrites are indicated with asterisks. M–T, Anatomy of the LOT at different anteroposterior levels. Axons of mitral and tufted cells were visualized by immunofluorescence labeling of calretinin. The gross morphology of the LOT is not apparently affected in Tbr2 conditional knockout mice. AC, anterior commissure; Tu, olfactory tubercle; Pir, piriform cortex; PMCo, posteromedial cortical amygdaloid nucleus. Scale bars: (in G) A–H, K, L, 50 μm; (in T) M–T, 1 mm.