Synchronized Retrovirus Fusion in Cells Expressing Alternative Receptor Isoforms Releases the Viral Core into Distinct Sub-cellular Compartments
Alternative receptor isoforms direct ASLV entry through distinct pathways that culminate in fusion with early endosomes. Normal entry pathways through TVA800 and TVA950 may converge to early endosomes where mildly acidic pH initiates the viral content release, albeit with different efficiency . In the presence of NH4Cl (gray arrows), the virus bypasses early endosomes and enters intermediate compartments of TVA950 cells and late endosome-like compartments of TVA800 cells. Removal of NH4Cl initiates fusion with the limiting membrane of intermediate endosomes in TVA950 cells. Subsequent dilation of a fusion pore releases the viral core (triangle) into the cytosol. In TVA800 cells, ASLV is trapped within a small intralumenal vesicle, which is enclosed by a larger vesicle surrounded by the limiting membrane of an endosome. Fusion results in the content and core release into a large intralumenal vesicle. The viral core then traverses two membranes via back-fusion of an enlarge vesicle with the limiting membrane of an endosome (dashed arrow). The latter step is likely to be temperature-dependent and independent of ASLV Env.