Atypical Cadherin Fat2 is Involved in Axogenesis of Cerebellar Granule Cells in Zebrafish.

Fat2 is an atypical cadherin with a large extracellular domain containing multiple cadherin repeats. Although members of the Fat family have been implicated in organ development, the role of Fat2 in neural development remains poorly understood. Here, we investigated the function of Fat2 in zebrafish, focusing on its involvement in the development of cerebellar granule cells. Granule cells in the rostromedial cerebellum project their axons, known as parallel fibers, to Purkinje cell dendrites. In contrast, granule cells in the caudolateral cerebellum project their axons to Purkinje cells and further extend them caudally to innervate crest cells, Purkinje-like neurons located in the dorsal hindbrain region called the medio-octaval lateralis. We found that in fat2 mutants, axons of caudolateral cerebellar granule cells projecting to crest cells exhibit abnormal branching and frequently overshoot their targets. These results indicate that Fat2 is required for proper axon formation in at least a subset of cerebellar granule cells.