Giardia spp.: Distribution of contractile proteins in the attachment organelle

Giardia spp. trophozoites isolated from rat small intestine were examined by light microscopy, electron microscopy, SDS-gel electrophoresis, and immunocytochemistry. In SDS-gels of protein extracts of isolated Giardia spp. trophozoites protein bands corresponding to myosin, α-actinin, and actin were identified by comigration with avian myofibril proteins and molecular weight standards. Actin was specifically identified in SDS-gels by immunoautoradiography. Immunostaining for actin, α-actinin, myosin, and tropomyosin in trophozoites was demonstrated in the periphery of the ventral disc in an area corresponding to the lateral crest. Electron-dense fibrillar was observed in the lateral crest of the ventral disc by electron microscopy. Immunostaining for actin and α-actinin was also observed in the area of the median body, a microtubular organelle, and in electron-dense fibrillar material associated with the intracellular axonemes of the posterior-lateral flagella. The localization of these contractile proteins in the ventral disc suggests that they may play an important role in the mechanism of trophozoite attachment.