Developmental expression of Manduca sexta hemolin

Hemolin is hemolymph protein that is a member of the immunoglobulin superfa mily. Its induced expression after bacterial infection suggests that it fun ctions in the immune response. In this paper, we describe the expression of the Manduca sexta hemolin gene at certain developmental stages in the abse nce of microbial challenge. Hemolin was present at a very low level in hemo lymph of naive larvae until the beginning of the wandering stage prior to p upation, when its concentration in hemolymph increased dramatically. At the same time, hemolin could be found in the fluid contained in the midgut lum en. 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 hemol ymph and midgut lumen. Hemolin was present in hemolymph through the pupal a nd adult stages. Hemolin was also present in newly deposited eggs, and pers isted in eggs throughout embryonic development. A hemolin cDNA isolated fro m an adult fat body library had the same sequence as those previously obtai ned from larval libraries. Hemolin purified from hemolymph of bacteria-inje cted larvae, from hemolymph of naive wandering stage larvae and adult moths , and from midgut fluid of wandering stage larvae had the same apparent mas s, which was consistent with the mass predicted from the hemolin cDNA seque nce. Hemolin from hemolymph of wandering stage larvae did not contain any d etectable carbohydrate, but hemolin from the hemolymph of bacteria-injected larvae and from naive adult moths was associated with carbohydrate, althou gh of different amounts and composition. These results suggest that a singl e hemolin gene is developmentally regulated and is also induced when insect s are exposed to microbial infection, M. sexta hemolin apparently lacks pos t-translational covalent glycosylation, but instead is associated under som e conditions with non-covalently bound carbohydrates. Arch. Insect Biochem. Physiol. 42:198-212, 1999. (C) 1999 Wiley-Liss, Inc.