Movie S2.

Transfer of β-actin–MBS mRNA between donor MEFs. Donor β-actin–MBS MEFs expressing tdMCP–GFP and TagRFP-T-ps were cocultured (with WT MEFs; not shown) for 2.5 h and imaged with a 150× objective, as detailed in Materials and Methods. Cells were imaged at 10-s intervals, 11 z-sections of 0.6 µm each, for 20 min. Exposure time for each wavelength was 300 ms (488-nm laser at 50% power, 561-nm laser at 20% power). Green, GFP; magenta, TagRFP-T. The movie shows maximum projection of each of the 121 frames at 5 fps. (Scale bar: 5 µm.) Note that the donor MBS cell on the right makes two polarized membrane extensions. The first (at the center of the frame) is a mNT that extends out to the acceptor MBS cell on the left (and contains a β-actin–MBS mRNA spot), while the second (at the bottom-left of the frame) is a lamellipodial-like extension. Z-stack analysis reveals that the second extension likely makes contact with the left cell but does not result in a cytoplasmic connection between the two cells.