Figure 3

Midline crossing errors in Robo1 / 2 double knockout mice. (A,F,K) TAG-1 immunostained coronal sections of a wild-type (A), heterozygous (F) and homozygous mouse (K); dorsal is to the top. (B,G,L) DiI (1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate) labelled flat mount preparations from a wild-type (B), heterozygous (G) and homozygous mouse (L). Dotted lines represent the approximate border of the floor plate; rostral is to the top. (C-E,H-J,M-O) Fluorescence micrographs of DiI-stained preparations. (D,I,N) Higher magnifications of (C,H,M), respectively. In (C,H,M), weak bright illumination is applied to show the contour of the sections. White arrows in (D,E,I,J,N,O) point to the midline. Note that TAG-1 immunoreactivity is weaker in the midline region of the double knockout mice (arrow in K). In DiI-stained preparations, labelled fibres stall near the midline (arrows in L,N,O). Dorsal is to the top. The bar in (A) is 150 μm and also applies to (F,K); bar in (B) is 400 μm and also applies to (C,G,H,L,M); bar in (D) is 200 μm and also applies to (I,N).