The Occurrence and Significance of Sialic Acids in Insects

Abstract

Sialic acids, mainly N-acetylneuraminic acid, have been found during the development of a few insect species. In Drosophila melanogaster and the cicada Philaenus spumarius we detected polysialic acids, using lectins, antibodies, and various methods for the isolation and analysis of the monosaccharide subunits, in areas of neuronal development and in Malpighian tubules, respectively. However, sialic acids were not found in the adult animals of these species. Although the expression of these acidic sugars has unequivocally been demonstrated in vivo, their occurrence in insect cell cultures was, in most cases, not clearly demonstrated. The biosynthesis of sialic acids in cell cultures would be of great biotechnological significance, since the production of recombinant glycoproteins with mammalian type, complex, sialylated N-glycans using the baculovirus expression system would be of great benefit. From the studies dedicated to this problem it appears that the engineering of such glycans may only be possible by the expression of exogenous genes in insect cells. Several genes encoding sialic acid-metabolizing enzymes have therefore been transfected. The work on insect cells shows that sialic acids are not only restricted to the Deuterostomia branch of the animal kingdom but also occur in some Protostomia species, as in insects. This throws new light on the evolution of this acidic sugar.