smu mutations disrupt formation of forebrain axon tracts and commissures. (A,B) An optic chiasm (arrow) was formed in wildtype (A) but not smu mutant (B) embryos. In smu mutants (D), anterior commissure axons (arrows) projected into hypothalamus (h), optic chiasm was absent and supra-optic tract axons (S) extended toward the ventral midline (compare with wild type in C). (E-H) Expression of netrin1 is altered in smu mutant embryos. In smu mutant embryos (F) netrin1 expression is upregulated in the midline of the neural tube at the level of the post optic commissure (E,F; arrows) and near the presumptive zona limitans intrathalamica (E,F; arrowheads). The netrin1 expression domain close to the presumptive exit point of ganglion cell axons from the retina (G, arrow) is absent in smu mutants (H, arrow). Ac, anterior commissure; h, hypothalamus; Oc, optic chiasm; P, post-optic commissure; S, supra-optic tract; T, telencephalon; Tp, tract of the post-optic commissure. (A,B) Ventral views, dorsal towards the top, DMGRASP label, 36 h. (C-F) Side views, dorsal towards the top, anterior towards the left, 48 h; (C,D) acetylated tubulin label. (G,H) Dorsal views, anterior towards left. Scale bar: 100 μm in A,B; 22.5 μm in C,D; 85 μm in E-H.
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