Bilateral RetinoTectal Connections in Umleitung Mutants

Dorsal views of 5 day old zebrafish in which retinal axons in the left eye were labeled using the fluroescent dyes DiI (red) and DiO (green).  Left image shows the normal projections between the eye and brain, with all retinal axons connecting to the contralateral tectal lobe.  Right image shows abnormal bilateral projections that are sometimes seen in umleitung mutants (ipsilateral projections are more commonly seen).  The umleitung mutations affects a gene called Brother of CDO (BOC) and encodes a cell surface protein that binds Sonic Hedgehog and is needed for cellular responses to Shh signaling.  In this case, retinal axon pathfinding defects seem to be due to defects in Hedgehog-mediated forebrain patterning.  For more information about the umleitung(BOC) mutant see our paper in the journal Development (Bergeron et al 2011).