Expression of autophagy 8 (Atg8) and its role in the midgut and other organs of the greater wax moth, Galleria mellonella, during metamorphic remodelling and under starvation

A 345 base pair cDNA encoding autophagy 8 (Atg8) of Galleria mellonella (GmAtg8) was cloned and sequenced. The deduced protein was estimated to be 118 amino acids long. Structural comparison and phylogenetic analysis showed that GmAtg8 belong to the Atg8 family of ubiquitin-like proteins. It is predicted to contain four beta-sheets and four a-helices. It also contains a highly conserved glycine residue at the C-terminal, as well as highly conserved Phe77 and Ph79 at a recognition cleavage site of Atg4 and Tyr49, and Leu50 at a site for activation of the lipidated form of Atg8 by Atg7 and Atg3. The developmental expression profile demonstrated that GmAtg8 transcript and its protein products are expressed in such organs as the midgut, ovary, Malpighian tubules, fat body and silk gland. In the midgut and silk gland, GmAtg8 transcript and its protein products increased during metamorphosis and under starvation, but decreased after re-feeding. Expression of autophagy seems to precede apoptosis in the midgut transformation from larva to pupa and pupa to adult during metamorphosis. Some waves overlap with apoptotic waves, particularly at early stages, but others are unique in terms of site and timing.