Fig. 5

Robo1 Ig2-5 domains are dispensable for midline repulsion in vivo. a–h Stage 16 embryos stained with anti-HRP (magenta) and anti-FasII (green) antibodies. Lower images show FasII channel alone from the same embryos. FasII-positive axons cross the midline inappropriately in every segment in robo1 null mutants (b, arrow with asterisk). This phenotype is completely rescued by a robo1 genomic rescue transgene expressing full-length Robo1 protein (c) but is not rescued by an equivalent rescue transgene expressing Robo1∆Ig1 (d). Rescue transgenes expressing each of the four additional Ig deletion variants rescue midline crossing as well as, or nearly as well as, full-length Robo1 (e–h). When ectopic crossing is observed in these rescue backgrounds, it is less severe than in robo1 mutants (e, arrow with asterisk). Bar graph shows quantification of ectopic midline crossing in the genotypes shown in (a–h). Error bars indicate standard error. The extent of rescue for each Ig deletion variant (d–h) was compared to robo1 ¹, robo1::robo1 embryos (c) by Student’s t-test, with a Bonferroni correction for multiple comparisons (*p < 0.01 compared to robo1 ¹, robo1::robo1)