Fig. 3. Sema3f expression is complementary to Npn2 and required to pattern neural crest migration. Npn2 (A) and Sema3f (B) are expressed in reciprocal patterns at E9.5, most notably in the hindbrain, branchial arches and trunk, where Npn2 is expressed in the anterior-half somite (C) and Sema3f in the posterior-half somite (D). At E9.5, the segmental appearance of migrating trunk neural crest (E) that results from migration exclusively through the anterior-half sclerotome (F) is disrupted in Sema3f mutants (G) because neural crest cells migrate throughout the sclerotome (H). (A-D) In situ hybridization for Npn2 (A,C) or Sema3f (B,D). (E-H) Neural crest was visualized by in situ hybridization for Sox10. (E,G) Anterior is towards the left. (F,H) Longitudinal sections of embryos shown in E and G. i, isthmus; r2, rhombomere 2; r4, rhombomere 4; ov, otic vesicle; a, anterior; p, posterior; dm, dermomyotome; sc, sclerotome; nt, neural tube. Scale bars: 0.1 mm.