The presence of N-acetylneuraminic acid in Malpighian tubules of larvae ofthe cicada Philaenus spumarius

Sialic acid-containing glycoconjugates are generally considered to be uniqu e to the deuterostomes, a lineage of the animal kingdom which includes anim als from the echinoderms up to the vertebrates. There are, however, two iso lated reports of sialic acid occurring in the insect species Drosophila mel anogaster and Galleria mellonella. Since insects are classified as protosto mes, these findings call previous assumption on the phylogenetic distributi on and thus on the evolution of sialic acids into question. Here, we report the occurrence of N-acetylneuraminic acid (Neu5Ac) in larvae of the cicada Philaenus spumarius. Cytochemical analysis of larval sections with lectins from Sambucus nigra and Limax flavus suggested the presence of sialic acid s in the concrement vacuoles of the Malpighian tubules. The monoclonal anti body MAb 735, which is specific for polysialic acid, labelled the same stru ctures. A chemical analysis performed by HPLC of fluorescent derivatives of sialic acids and by GLC-MS provided sound evidence for the presence of Neu 5Ac in the Philaenus spumarius larvae. These data suggest that in this cica da Neu5Ac occurs in alpha 2,8-linked polysialic acid structures and in alph a 2,6-linkages. The results provide further evidence for the existence of s ialic acids in insects and in linkages known to occur in glycoconjugates of deuterostomate origin.