The exons (and intervening small introns) that encode the mature robo2 protein have been replaced with a single exon encoding full length robo3 tagged with Tag:HA. The robo2KO.robo3 allele represents the loss of the robo2 open reading frame at the endogenous robo2 locus, while the robo3robo2.HR.Tag:HA allele represents the mature robo3 protein tagged with Tag:HA that is expressed under the control of the robo2 regulatory sequences in place of robo2.
robo2KO.robo3, robo3robo2.HR.Tag:HA has viable phenotype
The defects in the lateral Fas2-expressing longitudinal axons that are seen in lea mutant embryos are partially rescued in leaKO.robo3 robo3lea.HR.T:Ivir\HA1 double homozygous embryos (13.7% of hemisegments have fused or broken lateral Fas2-positive fascicles), but other aspects characteristic of a lea mutant phenotype are not rescued. Fas2-positive axons extend along or across the midline in 14.8% of segments in leaKO.robo3 robo3lea.HR.T:Ivir\HA1 double homozygous embryos (compared to in 23.7% of segments in lea null mutant embryos).