Osta, M. | Search bioRxiv

bioRxiv2023

CLIPB4 is a central node in the protease network that regulates humoral immunity in Anopheles gambiae mosquitoes

Insect humoral immune responses are regulated in part by protease cascades, whose components circulate as zymogens in the hemolymph. In mosquitoes, these cascades consist of clip domain serine proteases (cSPs) and/or their non-catalytic homologs (cSPHs), which form a complex network, whose molecular make-up is not fully understood. Using a systems biology approach, based on a co-expression network of gene family members that function in melanization and co-immunoprecipitation using the serine protease inhibitor (SRPN)2, a key negative regulator of the melanization response in mosquitoes, we identify the cSP CLIPB4 from the African malaria mosquito Anopheles gambiae as a central node in this protease network. CLIPB4 is tightly co-expressed with SRPN2 and forms protein complexes with SRPN2 in the hemolymph of immune-challenged female mosquitoes. Genetic and biochemical approaches validate our network analysis and show that CLIPB4 is required for melanization and antibacterial immunity, acting as a prophenoloxidase (proPO)-activating protease, which is inhibited by SRPN2. In addition, we provide novel insight into the structural organization of the cSP network in An. gambiae, by demonstrating that CLIPB4 is able to activate proCLIPB8, a cSP upstream of the proPO-activating protease CLIPB9. These data provide the first evidence that, in mosquitoes, cSPs provide branching points in immune protease networks and deliver positive reinforcement in proPO activation cascades.

immunology↗

bioRxiv2020

Major threats to a migratory raptor vary geographically along the eastern Mediterranean flyway

Millions of large soaring birds migrate from the Palaearctic to Africa every year, and follow distinct flyways around the Mediterranean Sea. While there is conservation concern for many long-distance migratory bird populations, the magnitude and geographic range of threats affecting birds along flyways are poorly known, which complicates efficient mitigation. We used an endangered soaring migrant, the Egyptian Vulture Neophron percnopterus, as an example species to assess important threats in 13 countries along the eastern Mediterranean flyway. We tracked 71 birds using satellite telemetry to quantify mortalities, surveyed 4198 km of powerlines to detect dead birds, conducted 910 interviews to quantify the prevalence of poison use, and assessed the magnitude of direct persecution by surveying markets and hunters. We lost 44 birds (50% in Europe and the Mediterranean Sea, 16% in the Middle East, and 34% in Africa), and mortality causes varied geographically. Inadvertent poisoning resulting from rural stakeholders targeting predators occurred along most of the flyway. On the breeding grounds in eastern Europe, poisoning and collision and electrocution continue to be major threats. Electrocution on small and poorly designed electricity pylons was most severe in Turkey, Ethiopia and Saudi Arabia, while direct persecution to meet market demands for belief-based use of vulture products appears to be the largest threat in Nigeria and Niger. Illegal direct persecution for leisure is a major threat in the Middle East and Egypt. Although our work cannot quantitatively estimate which of the identified threats has the greatest demographic impact on Egyptian Vultures, none of threats are species-specific and are therefore relevant for many other migratory birds. Our assessment highlights the key threats per country that range states need to address to meet their obligations under the Convention of Migratory Species to protect migratory birds.

zoology↗