Effect of bombyxin-II, an insulin-related peptide of insects, on Bombyx mori hemocyte division in single-cell culture

Abstract

We examined the effect of an insulin-related peptide, bombyxin-II, on the mitotic division of Bombyx mori hemocytes in vitro. Hemocytes isolated from larval hemolymph (day 1 of 4th instar) were cultured singly in MGM-450 medium. Some cultured prohemocytes (11.1%), plasmatocytes (2.6%), granulocytes (8.5%) and spherulocytes (10.8%) underwent mitotic division in the medium. Synthetic bombyxin-II added to the medium together with 10% larval hemolymph notably increased the ratio of dividing granulocytes to 45.5%, while no effect was evident on the other types of hemocytes. Bombyxin-II or hemolymph alone failed to stimulate the division of granulocytes. These results suggest that bombyxin-II acts cooperatively with hemolymph factor(s) to stimulate mitotic division of granulocytes. Bovine pancreas insulin was also active and could substitute for bombyxin.