Figure 3

Motor neurons migrate to ectopic positions in Npn-2 null mice. (a,b) Dual immunostaining of transverse cryosections (20 μm) of E11.5 wild-type (a) or Npn-2 null (b) littermate mouse embryo spinal cord with antibodies against HB9 (red) or neurofilament (NF; green) reveal numerous HB9-positive ectopic motor neurons located in the marginal zone and ventral nerve root in mutant but not wild-type embryo sections ((b) white arrows). Bar = 150 μm. (c) A quantitative analysis of the distribution of HB9-positive ectopic motor neurons along the rostro-caudal axis of Npn-2 null (triangles) or heterozygous (squares) and wild-type (diamonds) littermate embryos indicates that the number of ectopic motor neurons is normal at forelimb level (red box) but peaks at hind limb level (yellow box). (d) A comparison of pooled and averaged number of HB9-positive ectopic motor neurons in the anterior (forelimb containing half) and the posterior (hindlimb containing half) of the trunk, for E12.5 Npn-2 wild-type, heterozygous and null littermate embryos (n = 4). Consistent with the quantitative analysis shown in (c), there is a significant increase in ectopic motor neurons in the hindlimb region of Npn-2 null mice. **P ≤ 0.01; two-tailed t-test.