Extended Data Figure 8. Gene expression in the nemertean Lineus ruber.

(a) None of the nerve cord patterning genes is expressed during gastrulation in L. ruber. In the intracapsular larva, nkx2.1 is expressed in the cephalic imaginal discs (arrowheads), nkx2.2 and nkx6 in an anterior and a posterior domain of the trunk imaginal discs (arrowheads) respectively, and pax6 is detected both in the cephalic and the anterior trunk imaginal discs (arrowheads). pax3/7 is broadly expressed. With metamorphosis, nkx2.1 is detected in the head and proboscis, nkx2.2 is detected in the nerve cords and isolated trunk cells (arrowheads), nkx6 is expressed in the nerve cords (arrowheads), pax6 is observed in the head and nerve cords (arrowheads), and pax3/7 remains broadly expressed. All gastrulae are vegetal views. For larvae and early juveniles, the left column is a dorsoventral view and the right column is a lateral view (anterior to the left). All late juvenile pictures are lateral views, with anterior to the left. (b) Lateral views (anterior to the left) of neuronal markers in juveniles. They are all expressed in the ventral nerve cords (arrowheads), and not in the dorsal neurite bundle. In all panels, the asterisk indicates the position of the mouth opening. bp, blastopore; mo, mouth; pb, proboscis.