A role of myosin II in phagocytosis of protist Dictyostelium Discoideum

Fagocitoza je proces pri kojem fagocitne stanice, poput protista Dictyostelium discoideum, internaliziraju čestice veće od 0.5 µm. Te čestice bivaju probavljene tijekom endocitnog prijenosa i izbačene iz stanice procesom egzocitoze. Za odvijanje fagocitoze i egzocitoze nužna je aktivnost aktinskog citoskeleta, a pretpostavlja se i uloga motornog proteina miozina II. U ovom je radu konfokalnom pretražnom mikroskopijom praćena lokalizacija fuzijskih proteina GFP-miozin II i YFP-ABD tijekom fagocitoze u živim Dictyostelium stanicama. Ustanovljeno je da, u stanicama kojima nedostaje miozin II, dolazi do pretežne pojave izbacivanja sadržaja fagosoma iz stanice unutar pet minuta nakon internalizacije, koja je nazvana prijevremena egzocitoza. Uočene su i razlike u trajanju pojedinih faza fagocitoze u ovisnosti o prisustvu miozina II, što upućuje na ulogu miozina II u regulaciji dinamike fagocitoze. Zaključeno je da miozin II nema ključnu ulogu u početnoj fazi fagocitoze, ali njegov nedostatak utječe u velikoj mjeri na efikasnost toga procesa, odosno na njegov krajnji ishod.Phagocytosis is a process used by phagocytic cells, including the protist Dictyostelium discoideum, to internalize particles larger than 0.5 µm. The internalized particles are subsequently digested in the course of endocytic transport, and finally expelled out of the cell by exocytosis. Both phagocytosis and exocytosis depend on activity of the actin cytoskeleton, presumably also on the motor protein myosin II. In this graduate paper, confocal scanning microscopy was used to follow localization of the fusion proteins GFP-myosin II and YFP-ABD during phagocytosis in living Dictyostelium cells. It was discovered that cells lacking a functional myosin II typically expel content of their phagosomes within the first five minutes after internalization, a phenomenon that was termed premature exocytosis. Differences in the duration of several phases of phagocytosis, dependent on the presence or absence of myosin II, were determined, indicating a role of myosin II in the regulation of dynamics of phagocytosis. It was concluded that myosin II does not play a key role in the early phase of phagocytosis, but its absence influences in a major way efficiency of this process and determines its final outcome