Fig. 7. In the absence of BMPRIB, mouse commissural axons are significantly less responsive to a rat RP explant. (A,A') E11.5 rat RP explants deflect Tag1⁺ commissural axons (green) growing within E10.5 wild-type mouse dorsal spinal cord (d-sc) explants by an average angle of reorientation of 21.8°±2.0 s.e.m. (n=28). (B,B') Commissural axons deficient in BMPRIA (Math1::cre;BmprIa^flox/flox) are reoriented by a rat RP explant, to a similar extent (P>0.4) as BmprIa^flox/flox control littermates, with an average reorientation angle of 20.4°±2.0 s.e.m. (n=18). (C,C') By contrast, BmprIb^-/- commissural axons are significantly less reoriented by a rat RP explant than wild-type littermates (P<1.3x10^-7), with an average angle of reorientation of 9.6°±1.9 s.e.m. (n=19). Note that in the tracings in A', B' and C', only the axons deriving from the mouse d-sc explant are illustrated. (D) Schematic to illustrate the orientation of the E11 rat RP explant and the E10.5 mouse d-sc explant. (E) Histogram of the average angles of reorientation. Scale bar in C: 75 µm for A-C.