Platelets arise as sub-cellular anucleated fragments of megakaryocytes and play a major role in bleeding arrest amongst other functions. They recognize exposed matrix proteins upon vessel injury; and thereafter adhere, activate and aggregate at the site. Given the importance of platelet function in many vital aspects, little is known about the organization and three-dimensional structure of platelet-matrix (focal) adhesions, involved in the critical step of platelet adhesion and spreading. We demonstrate the use of interference reflection microscopy (IRM) and cutting edge cryo-electron tomography (cryo-ET) to elucidate the 3D structure and the morphology of time-dependent spreading of platelet-matrix adhesions, filopodia and lamellipodia on collagen IV and fibrinogen surfaces. Preliminary data suggests a specific organization of the actin cytoskeleton, and early observations of possible adhesion-related particles in filopodial extensions by cryo-ET. Live-platelet imaging by IRM time-lapse movies shows a surface specific mode of spreading, depending on the use of different platelet preparations, platelet-rich plasma (PRP) and purified platelets (PLT).
