Glial cell derived pathway directs regenerating optic nerve axons toward the CNS midline.

Several RGC intrinsic signaling pathways have been shown to enhance RGC survival and RGC axonal growth after optic nerve injury. Yet an unresolved challenge for regenerating RGC axons is to properly navigate the optic chiasm located at the Central Nervous System midline. Here, we use live-cell imaging in larval zebrafish to show that regrowing RGC axons initiate growth toward the midline and extend along a trajectory similar to their original projection. From a candidate genetic screen, we identify the glycosyltransferase Lh3 to be required during the process of regeneration to direct regrowing RGC axons toward the midline. Moreover, we find that mutants in , a putative Lh3 substrate, display RGC axonal misguidance phenotypes similar to those we observe in mutants, suggesting that may act through during regeneration. Finally, we show that transgenic expression in + presumptive + oligodendrocytes located near the optic chiasm restores directed axonal growth. Combined these data identify and as part of a glial derived molecular pathway critical for guiding regenerating RGC axons towards and across the optic chiasm.