Visuomotor anomalies in achiasmatic mice expressing a transfer-defective Vax1 mutant

In binocular animals that exhibit stereoscopic visual responses, the axons of retinal ganglion cells (RGCs) connect to brain areas bilaterally by forming a commissure called the optic chiasm (OC). Ventral anterior homeobox 1 (Vax1) contributes to formation of the OC, acting endogenously in optic pathway cells and exogenously in growing RGC axons. Here, we generated Vax1 AA/AA mice expressing the Vax1 AA mutant, which is incapable of intercellular transfer. We found that RGC axons cannot take up Vax1 AA protein from Vax1 AA/AA mouse optic stalk (OS) cells, of which maturation is delayed, and fail to access the midline. Consequently, RGC axons of Vax1 AA/AA mice connect exclusively to ipsilateral brain areas, resulting in the reduced visual acuity and the abnormal oculomotor responses. Together, our study provides physiological evidences for the necessity of intercellular transfer of Vax1 and the importance of the bilateral RGC axon projection in visuomotor responses.