Pacific oyster phagosome LC-MSMS

Phagosomes are task-force organelles of innate immune systems responsible for the recognition, processing, and ultimately destruction of invading microorganisms. Among invertebrate and vertebrate species, evolutionary diversity and continuity abound in the protein machinery executing this coordinately regulated process, though its dynamics and full scope of regulators remain incompletely understood. In order to clarify molecular mechanisms underlying phagocytosis, we studied phagocyte response to beads and Vibrio species, using hemocytes of the Pacific oysters (Crassostrea gigas) as a marine invertebrate model. Phagosomes from different stages of phagocytosis were isolated by density-gradient centrifugation, and more than 400 phagosome-associated proteins were subsequently identified via high-throughput quantitative proteomics. In modeling key networks of phagosomal protein-protein interactions, our results support the essential roles of several processes driving phagosome formation and maturation, including actin cytoskeleton remodeling, and signal transduction by myosin and Rab proteins. In further quantitative proteomic analysis, trends of both upregulation and downregulation of protein expression were observed proteins during phagosome formation and maturation. Notably, the signal transducers CgRhoGDI and CgPI4K were implicated. In addition, six Rab proteins including Rab1, Rab2, Rab7, Rab11, RaB21, and Rab33 were also identified as active regulators or mediators in hemocyte phagocytosis. Our current work illustrates the diversity and dynamic interplay of phagosomal proteins, providing a framework for better understanding host-microbe interactions during phagosome formation and maturation in under-examined invertebrate species.