Fig. 2. Epidermal ECM provides directional cues to the PND. Epidermally secreted ECM was collected onto polycarbonate carriers, then presented in various orientations to the PND pathway of same-stage hosts (Fig. 1). (A) A control embryo undergoing normal PND migration. The PND migrates just below the somites and its tip is indicated by the arrow. (B) The PND has migrated onto somitic mesoderm – dorsal to its normal migratory pathway – following the introduction of a 90° dorsally rotated ECM-bearing carrier. The PND tip (arrow) has here traveled more than halfway up the sixth somite. (C) A 90° ventral rotation of an ECM-conditioned carrier prior to transplantation has redirected PND migration ventrally. The PND tip (arrow) is located ventral to the normal migration path, on lateral mesoderm. (A-C) Anterior is to the right and dorsal to the top.