Synaptotagmin VII Restricts Fusion Pore Expansion during Lysosomal Exocytosis (original) (raw)
Figure 2
Fate of Membrane Protein during Lysosomal Fusion
Lysosomal membranes in MEFs were labeled by transfecting cells with a vector encoding a CD63–GFP fusion protein, and expression was allowed for 48 h. For simultaneous labeling of lysosomal membrane and lumen, the CD63–GFP transfected cells were labeled with 70 kDa TRITC–dextran as described in Figure 1.
(A) Following ionophore-induced calcium increase in WT MEFs, when the TRITC–dextran was released completely (left), CD63–GFP (right) was delivered to the plasma membrane, but it remained in multiple puncta near the site of fusion rather than diffuse away. The panels are pseudocolor surface plots, with the x and y axis representing the coordinates and the z axis representing the fluorescence intensity of individual pixels.
(B) In the event of partial release of TRITC–dextran (top row), the CD63–GFP (bottom row) did not appear to be delivered to the plasma membrane. The lower panel shows the plot of fluorescent intensity of lumenal and membrane label (within the dotted circle) of the lysosome shown in (B).
(C and D) Analysis of CD63–GFP-labeled lysosomes in WT MEFs (C) and in Syt VII KO MEFs (D) indicates that while CD63–GFP is retained in puncta in the WT MEFs, it diffuses freely in the plasma membrane in the SytVII KO MEFs. The lower panel shows the total and peak intensity plots of CD63–GFP-labeled lysosome in (D).