Regulatory mechanism of silkworm hemocyte adhesion to organs

Circulating hemocytes in the body fluid of the silkworm are increased during the larval-larval molting period. We investigated hemocyte adhesion to organs mediating the selectin-selectin ligands during the feeding period and the larval-larval molting period using the lectin staining method, sugar chain digestion test with glycoside hydrolases, and the hemocyte adhesion inhibition test using monosaccharides. The results of these tests suggested that the selectin ligand involved in hemocyte adhesion was the Sialyl Lewis x-type, and the structure was changed from the feeding period to the larval-larval molting period. Beta-galactosidase appears to be an enzyme that eliminates N-acetylgalactosamine and sialylated N-acetylgalactosamine from the terminal of Sialyl Lewis x. Beta-galactosidase activation in skin basement membranes, muscle, fat bodies, midguts, and hemocytes increased markedly during the larval-larval molting period, and at that time, hemocytes were detached from organs. Adding 20-hydroxyecdysone or its analog, tebufenozide to cultured fat bodies increased β-galactosidase activity in these tissues. Therefore, 20-hydroxyecdysone may induce a structural change in Sialyl Lewis x type sugar chains on the cell surface of silkworm's organs by increasing the β-galactosidase activity to detach hemocytes from organs and increase the number of circulating hemocytes during the larval-larval molting period.