Fig. 4

Expression of Robo1 Ig2-5 deletion proteins in robo1 mutant embryos. a–f Stage 16 robo1 mutant embryos carrying indicated robo1 rescue transgenes, stained with anti-HRP (magenta) and anti-HA (green) antibodies. Lower images show HA channel alone from the same embryos. Expression of full-length Robo1 via the robo1 rescue transgene in a robo1 null mutant (a) restores the wild-type structure of the axon scaffold, but expression of Robo1∆Ig1 does not (b; compare to robo1 null mutant shown in Fig. 5b). Each of the Ig2-5 deletion variants restore axon scaffold morphology to a similar extent as full-length Robo1 (c–f). In the absence of endogenous robo1, all of the variants are localized to the longitudinal pathways as in wild-type embryos (arrowheads) and excluded from the anterior and posterior commissures (arrows in a, c-f), with the exception of Robo1∆Ig1 (b, arrows with asterisks). As in wild-type embryos, Robo1∆Ig3 displays elevated expression levels in neuronal cell bodies compared to the other Robo1 variants (d, arrowhead with asterisk)