Assembly of the Murine Leukemia Virus Is Directed towards Sites of Cell–Cell Contact
Figure 6
Quantification of MLV assembly events in and outside of the contact zone.
(A) Six representative frames of a 157-frame video when an initiation of de novo virus assembly (blue cross) was detected. See Video S3 and Table S1 for the full analysis. The accumulation of dynamin2 and receptor-CFP was then used to define the contact zone (red line) in each frame. Homogeneous dynamin2 expression and Gag-YFP in the producer cell was used to mark the remaining plasma membrane surface outside the contact zone (white line). (B) Left panel. The analysis described in (A) identified 44 assembly events in the contact zone and eight outside the contact zone. To calculate the overall assembly frequency per surface unit (in square micrometers), the number of assembly events observed in either zone was divided by their average surface area. The resulting fold enhancement of MLV assembly at sites of cell–cell contact over the remaining plasma membrane is presented at the top right (54.5×). The underlying image used to illustrate this time-resolved analysis represents time point 00:19:43 of Video S3. Right panel. An alternative and simplified approach to define the fold enhancement was based on the accumulative merged image of all 157 frames of Video S3. Due to the dynamics of the contact zones, this approach results the definition of a broader contact zone thereby reducing the fold enhancement observed at sites of cell-cell contact (14.7×). For detailed analysis see Table S1. Size bars correspond to 15 µm.