Figure 2. Dystroglycan is required for axon tract formation in the forebrain.

(A) L1 immunohistochemistry on P0 brain sections from Dag1^F/+;Sox2^Cre controls (n = 3 animals) labels descending CTAs and ascending TCAs in the internal capsule. In Dag1^F/-;Sox2^Cre (n = 4 animals) (B) and Ispd^L79*/L79* (n = 5 animals) (C) mutants, the internal capsule is highly disorganized, with axons projecting into the upper layers of the cortex (red arrows), forming ectopic bundles in the ventral telencephalon (red asterisks), and abnormal projections extending ventrally (red arrowheads). High magnification insets show L1 +axons in the intermediate zone of the cortex of controls (A’) and ectopic axonal projections into the upper cortical layers in Dag1^F/-;Sox2^Cre (B’) and Ispd^L79*/L79* (C’) mutants. DiI injection in the thalamus of Dag1^F/+;Sox2^Cre controls (n = 4 animals) labels TCAs as they cross the DTB, extend through the ventral telencephalon, across the PSPB, and into the intermediate zone of the cortex. In Dag1^F/-;Sox2^Cre (n = 4 animals) (E) and Ispd^L79*/L79* (n = 4 animals) (F) mutants, TCAs fail to cross the DTB, and instead project ventrally out of the diencephalon. High magnification insets show DiI-labeled TCAs extending into the intermediate zone of the cortex of controls (D’), and a lack of labeled TCAs in the cortex of Dag1^F/-;Sox2^Cre (E’) and Ispd^L79*/L79* (F’) mutants. DiI injection in the cortex of Dag1^F/+;Sox2^Cre controls (n = 3 animals) labels CTAs as they extend across the PSPB, through the ventral telencephalon, and across the DTB into the thalamus. CTAs in Dag1^F/-;Sox2^Cre (n = 4 animals) (H) and Ispd^L79*/L79* (n = 5 animals) (I) mutants fail to cross the PSPB or take abnormal trajectories through the ventral telencephalon. High magnification insets show DiI-labeled CTAs extending into the thalamus in controls (G’), and a lack of labeled CTAs in the thalamus of Dag1^F/-;Sox2^Cre (I’) and Ispd^L79*/L79* (F’) mutants. (J–L) Schematic summarizing CTA (brown) and TCA (blue) axon trajectories in controls (J), Dag1^F/-;Sox2^Cre (K) and Ispd^L79*/L79* (L). Scale bar = 500 μm.

Figure 2—figure supplement 1. Anterior commissure, lateral olfactory tract and corpus callosum phenotypes in Ispd^L79*/L79* mutants.

(A) Dystroglycan is expressed in the basement membrane surrounding the brain at E14.5. Dystroglycan is also expressed in the developing thalamus and in the axons that form the internal capsule (A, A’ inset). (B) Lack of staining in sections from Dag1^βcyto/- mutants verifies the specificity of Dystroglycan staining in the cortex. (C–F) L1 staining was used to label forebrain axon tracts in P0 wildtype (n = 3 animals) (C,E) and Ispd^L79*/L79* mutants (n = 3 animals) (D,F). The corpus callosum (red asterisk) in Ispd^L79*/L79* mutants appears largely normal compared to controls. In contrast, the anterior commissure (red arrows) is thinner and disorganized in Ispd^L79*/L79* mutants (D). The lateral olfactory tract (red arrowheads) extends along the pial surface of the ventrolateral telencephalon in controls (C,E), whereas it appears hyperfasciculated and projects deeper into the piriform cortex as a disorganized bundle in Ispd^L79*/L79* mutants (D,F). Scale bar = 500 μm.