Protein-Membrane Interaction Is Essential to Normal Assembly of the Microsporidian Spore Invasion Tube

Changes in the protein-membrane interaction during assembly of the microsporidian spore invasion tubes were followed by electron microscopy, by video imaging with differential interference contrast (DIC), and by the fluorescent probes 4',6-diamidino-2-phenylindole (DAPI) and 9-diethylamino-5H-benzo{alpha}phenoxazine-5-one (Nile red). Microsporidian spore invasion tubes form by the eversion of polar filament protein (PFP) and presumptive extrusion apparatus (EAP) membrane. Both of these components are essential for formation of the invasion tube. The results indicate that the behavior of the EAP membrane is greatly affected by the position and chemical state of the PFP at the eversion area that constitutes the advancing tube terminal assembly site (TAS). Visual evidence indicates that the EAP membrane is the vehicle for PFP and that this membrane also provides the envelope that surrounds the sporoplasm after its passage through the invasion tube.