In Drosophila Hemolymph, Serine Proteases Are the Major Gelatinases and Caseinases

Insect hemolymph transports, exchanges, and eliminates soluble compounds from the hemocoel. These processes play a critical role in many physiological processes, including development and immunity. Since matrix metalloproteases (MMPs) are the major circulating gelatinases in the blood of various species, including mammals, we used gel zymography to analyze gelatinase and caseinase activities in Drosophila larval hemolymph under normal and pathological conditions. Our investigations demonstrate that the major gelatinases and caseinases in Drosophila larval hemolymph are not MMPs but serine proteases (SPs). We identified more than 60 SPs in these proteolytic active bands. While a role in immunity has been suggested for some of these circulating SPs, the physiological functions of most of them remain to be elucidated.