Cadherin-2 and cadherin-4 in developing, adult and regenerating zebrafish cerebellum.

Cadherins are cell adhesion molecules that regulate development of a variety of tissues and maintenance of adult structures. In this study, we examined expression of two zebrafish classical cadherins, cadherin-2 and cadherin-4, in the cerebellum of developing, normal adult, and regenerating adult zebrafish using in situ hybridization and immunohistochemical methods. Cadherin-2 was widely expressed by the cerebellum of embryonic (24-50-h post fertilization) and larval zebrafish (3-14 days). Cadherin-2 expression became much reduced in the adult cerebellum, but it was greatly up-regulated in the regenerating adult cerebellum. Cadherin-4 was not detected in the embryonic cerebellum, but it was expressed in the Purkinje cells of the larval and adult cerebellum. To gain insight into cadherin-2 role in the formation of the cerebellum, we analyzed embryos injected with a specific cadherin-2 antisense morpholino oligonucleotide (cdh2MO1), and found that the cerebellar development of the cdh2MO1-injected embryos was severely disrupted. This phenotype was confirmed by examining a cadherin-2 mutant, glass onion. Our results suggest that cadherins are crucial for the normal development of the zebrafish cerebellum, and they may also be involved in the regeneration of injured fish cerebellum.