Features of the clear zone of odontoclasts in the Chinook salmon (Oncorhynchus tshawytscha)

This study aims to clarify the features of the clear zone of odontoclasts on shedding teeth of a teleost fish, Chinook salmon, Oncorhynchus tshawytscha (Walbaum), using a light microscope to determine the orientation between a cell body and a resorptive lacuna, followed by transmission electron microscopy. Ultrathin sections of LR White embedded material were incubated in rabbit anti-actin polyclonal antibody and then were incubated with 15 nm gold-conjugated goat anti-rabbit IgG. The clear zones of odontoclasts showed a variable structure with electron-dense structures on sections, but distinct clear zones were not always seen on odontoclasts. In odontoclasts sectioned in the direction perpendicularly to the surface of a resorptive lacuna, some cells showed a wide clear zone, but two types of clear zones were usually observed: a part composed of some cytoplasmic processes and one composed of several complicatedly interwoven processes. Gold particles were localized on the clear zones, especially in electron-dense structures; very few gold particles were detected in ruffled borders. These results show that the clear zone of odontoclasts in Chinook salmon contains actin. Our results suggest that the clear zone of an odontoclast in Chinook salmon is not always a wide annular structure.