Mice homozygous for both targeted mutations are viable, fertile, and normal in size. While the donating investigator reports that 10-20% of females homozygous at both loci neglect their litters, no such neglect is reported in the colonies at The Jackson Laboratory (Aug 2009). Double homozygous mice have no endogenous protein expression in inferior colliculus (IC) or superior colliculus (SC), and thus lack the concentration gradient created by the endogenous proteins across the midbrain in wildtype mice. Temporal and nasal retinal axon termination is severely altered: multiple ectopic aborizations in the SC indicate abnormalities in both anteroposterior and dorsoventral topography. Following surgical ablation of portions of the midbrain (including IC and SC), cross-modal innervation by retinal neurons is greater in double homozygous mutants compared to wildtype. Mice heterozygous at both loci are reported to have greater reproductive performance compared to double homozygous mice. Further, double heterozygotes have temporal (but not nasal) retinal axon aborization in the SC with diminished frequency and severity. These ephrin A2/ephrin A5 double mutant mice may be useful in studies of retinocollicular mapping, axon topography, neuron projection, and modality-specific compartmentalization of visual, auditory, and somatosensory thalamic relay pathways.
