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Abstract:

Digestion plays a crucial role to valorize the nutrients that are the main source of building blocks and energy to start vitellogenesis. Obligate anautogenous insects, like several species of mosquitoes and flesh flies, need a protein meal in order to produce their first batch of eggs. This protein meal elicits an increase in midgut proteolytic activity that is under neuropeptidergic regulation. Time series of decapitation and rescue experiments of liver fed flies evidenced the need of a peptide factor released by corpora cardiaca (CC) within four hours post protein meal in order to assure complete protein digestion. Q-Exactive quantitative differential peptidomics analysis on CC of sugar fed flies and flies five hours post protein meal respectively, showed a unique consistent decrease in the stored amount of adipokinetic hormone (AKH) ranging between 16 up to 63%. Injection of AKH into liver fed decapitated flies as well as sugar fed intact flies resulted in enhanced midgut proteolytic activity up to the level of intact protein fed flies. The pharmalogicaly induced release of AKH from CC, using injections of metformin, also resulted in increase of midgut proteolitic activity and as such mimics AKH injection. Our finding of AKH affecting enzymatic digestive activity confirms earlier data obtained using firefbugs (Kodrik et al., 2012). The other 7 different low molecular weight neuropeptides found in the CC extract are Yamides, short neuropeptides F, myosuppressin, corazonin, pyrokinin and CAPA. The literature study suggests that almost all of these molecules are in some way related to feeding behavior. However our analysis demonstrated that none of them are involved in the process of digestion in sugar or liver fed flies.