Differential distribution of S100 protein and calretinin in mechanosensory andchemosensory cells of adult zebrafish (Danio rerio)

Calcium-binding proteins play a critical role in vertebrate sensory cells, and some of them have been detected in mechanosensory and chemosensory cells of bony and cartilaginous fishes. In this study immunohistochemistry and Western blot were used to investigate the occurrence and the distribution of S100 protein and calretinin in mechanosensory (neuromasts of the lateral line system; maculae and cristae ampullaris of the inner ear) as well as chemosensory (superficial and oral taste buds; olfactory epithelium) cells in adult zebrafish (Danio rerio). Specific protein bands with an estimated molecular weight of around 10 kDa and 30 kDa were detected by Western blot and were identified with S100 protein and calretinin, respectively. S100 protein and calretinin were observed segregated in mechanosensory and chemosensory cells, and the presence of S100 protein in a cell excluded that of calretinin, and vice versa. As a rule, the mechanosensory cells were S100 protein positive, whereas the chemosensory ones displayed calretinin immunoreactivity. Calretinin was also detected in nerve fibers supplying some of the investigated organs. In the olfactory epithelium, S100 protein immunoreactivity was present in the crypt olfactory sensory neurons, whereas calretinin immunoreactivity was widespread in olfactory sensory neurons and probably other olfactory cells. In this localization the co-expression of S100 protein and calretinin cannot be excluded. These results demonstrate the cell segregation of two specific calcium-binding proteins, and they enable to selectively label these cells by using easily reproducible immunohistochemical techniques associated to well-known antibodies.