Ostrinia furnacalis integrin β1 may be involved in polymerization of actin to modulate spreading and encapsulation of plasmatocytes

Abstract

Insect hemocytes must change their state from non-adhesive to adhesive when they spread on or encapsulate foreign invaders. Although integrin β has been reported to play an important role in hemocyte spreading and encapsulation in several insects, how it is involved in the encapsulation process is still unclear. Here we report that integrin β1 of Ostrinia furnacalis (Ofint β1) may modulate plasmatocyte spreading by regulating polymerization of F-actin and further affecting formation of capsules. In the Sephadex A-25 bead-injected larvae, hemocytes forming capsules expressed approximately ten times more Ofint β1 than hemocytes that are free in circulation in hemolymph. When the expression of Ofint β1 in hemocytes was inhibited by dsRNA of Ofint β1 (dsINT), polymerization of F-actin in hemocytes, especially in plasmatocytes, was significantly decreased, spreading of plasmatocytes was inhibited, and encapsulation rate of Sephadex beads was also significantly decreased. Furthermore, hemocytes formed individual aggregates on beads in the dsINT injected larvae, while hemocytes formed complete capsules surrounding the beads in the control larvae; and most of the hemocytes on the beads in the dsINT-injected larvae assumed round forms rather than spread forms. Based on these results, we speculate that integrins on cellular membranes may modulate hemocyte spreading by regulating polymerization of F-actin and further affecting encapsulation of foreign objects.