Cubic crystal protein inclusions in the neodermis of the pancreatic fluke, Eurytrema pancreaticum, and Eurytrema coelomaticum.

Light microscopy of Eurytrema pancreaticum and Eurytrema coelomaticum collected from cattle in Japan, China, Thailand, and Brazil showed many cubic crystal inclusions in the neodermis (tegument) of all flukes. The crystal inclusions were histochemically positive for protein. Scanning electron microscopy showed many cubic protrusions containing cubic crystal protein inclusions on the surface of the neodermis. Transmission electron microscopy showed that cubic crystal protein inclusions appeared in the perikarya of subtegumental parts, passed through the cytoplasmic bridge, moved into the syncytial neodermal cytoplasm, and then protruded from, and finally separated from, the neodermal cytoplasm. Cubic crystal protein inclusions were hexahedral with each side 2-18 microm long. High-resolution microscopy of ultrathin sections of crystal inclusions showed a lattice fringe at spacings of about 0.52 nm by using a filtering processing. Diffractograms were obtained by Fourier transform of the images. The lattice structure of the crystal protein inclusions was shown by inverse Fourier transform, indicating that the cubic crystal protein inclusions were single crystals. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis estimated the molecular weight of protein in the cubic crystal inclusion as 36.6 kDa. Energy-dispersive X-ray spectroscopy proved that the cubic crystal protein inclusions were composed of protein and sulfur.