Fig. 5. Chemoattractive and repulsive signalling around the olivary and superficial migrations. Coronal (A,C,D,E,G,I,J) or sagittal (H) sections through the E13.5 caudal hindbrain. (B,F) E11.5 (B) and E12.5 (F) hindbrain explants cultured for 3 and 2 days, respectively, in vitro. (A,B) Netrin-1 midline expression is maintained in E11.5 explants (B) and is similar to its in vivo pattern (A). (E,F) The Dcc netrin receptor is expressed both in vivo (E) and in vitro (F) in the medialmost olivary neurons (arrowheads) and in migrating neurons of the superficial migration (arrows). (C,D,G,H) EphA4 is expressed in the olivary neurons at the end of migration (C) whereas several EphA4 ligands are expressed in the floor plate (D, ephrin B3, ephrin B1 not illustrated) or surround the forming olivary nucleus (G,H, ephrin A5). The inhibitory influence of Sema4C expressing cells (I) could also funnel the olivary migration into its proper pathway. (J) The superficial migration expresses high levels of PACAP transcripts. The arrowheads point to the olivary migration, the arrows to the superficial migration. Asterisks in B, lines of higher netrin expression.