Developmental expression of Manduca sexta hemolin.

Hemolin is hemolymph protein that is a member of the immunoglobulin superfamily. Its induced expression after bacterial infection suggests that it functions in the immune response. In this paper, we describe the expression of the Manduca sexta hemolin gene at certain developmental stages in the absence of microbial challenge. Hemolin was present at a very low level in hemolymph of naive larvae until the beginning of the wandering stage prior to pupation, when its concentration in hemolymph increased dramatically. At the same time, hemolin could be found in the fluid contained in the midgut lumen. The appearance of hemolin mRNA in fat body and midgut at the beginning of the wandering stage correlated with the presence of hemolin in the hemolymph and midgut lumen. Hemolin was present in hemolymph through the pupal and adult stages. Hemolin was also present in newly deposited eggs, and persisted in eggs throughout embryonic development. A hemolin cDNA isolated from an adult fat body library had the same sequence as those previously obtained from larval libraries. Hemolin purified from hemolymph of bacteria-injected larvae, from hemolymph of naive wandering stage larvae and adult moths, and from midgut fluid of wandering stage larvae had the same apparent mass, which was consistent with the mass predicted from the hemolin cDNA sequence. Hemolin from hemolymph of wandering stage larvae did not contain any detectable carbohydrate, but hemolin from the hemolymph of bacteria-injected larvae and from naive adult moths was associated with carbohydrate, although of different amounts and composition. These results suggest that a single hemolin gene is developmentally regulated and is also induced when insects are exposed to microbial infection. M. sexta hemolin apparently lacks post-translational covalent glycosylation, but instead is associated under some conditions with non-covalently bound carbohydrates. Arch.