Figure 4

Expression of Sema6A protein at late embryonic stages. (a, a') Staining for the reporter PLAP on sagittal E17.5 sections from Sema6A^+/- mice. (b-q) Immunohistochemistry for Sema6A (red) and, as reference stain to visualize fibres, neurofilament M (green) on sagittal (b-e) (rostral is left) and coronal (f-q) sections of E17.5 (b-h) and P1 (i-q) wild-type mice. At E17.5, PLAP staining shows that Sema6A is expressed by corticospinal tract (CST) neurons (a, a'); arrowheads in a' show CST axons. At the same age, anti-Sema6A staining highlights corticofugal projections that travel through the internal capsule (ic) and cerebral peduncle (cp) (b), as well as CST axons as they pass the pontine nuclei (Pn; arrowheads in (c, d)) (c-h). Sema6A staining on CST axons at the level of the pons is no longer visible at P1 (i-k) (arrowheads in (i, j)) and is also lacking from these axons as the pass the inferior olive (IO). Along the CST trajectory, Sema6A immunoreactivity was detected at lower levels in the Pn (c, f, i) at E17.5 and P1, and at moderate to high levels in the IO at E17.5 (l, o). aAC, anterior arm of the anterior commissure; pAC posterior arm of the anterior commissure. Scale bar in (a, a', b) is 200 μm. Scale bar in (q) is: 100 μm for (c-h); 200 μm for (i-n); 50 μm for (o-q).