Isolation and expression of hemolin in Bombyx mori

Abstract

Hemolin is a bacteria-induced immune protein found in the lepidopteran insect species. We isolated 1357 bp hemolin cDNA from the mid-gut in the middle of the spinning stage in B. mori, that demonstrated a high degree of similarity with hemolins from 4 species, M. sexta, H. cuena, H. cecropia, and L. dispar. Hemolin mRNA was detected only in a microorganism invasion. The expression was not influenced by the external environment or materials. The developmental profile of the level of hemolin mRNA was determined in the absence of bacterial challenge. Hemolin mRNA was expressed only in the mid-gut, not in hemocytes, fat body, silk glands and gonads. During the development of B. mori, hemolin mRNAs were not detected in the mid-gut until the spinning stage of the last instar larvae, however, dramatically increased beginning the spinning and gradually decreased through the pupal and adult stages. The results of the in situ hybridization were consistent with northern blot analysis. The major transcription site of hemolin is the columnar cells in the mid-gut. It is presumed that the function of hemolin is unique to the physiological process at the post-spinning stage.