Timelapse microscopy sequence showing transport of a fluorescently-tagged version of the vesicular stomatitis virus envelope glycoprotein (VSV-G) through the secretory pathway. Vesicular stomatitis virus belongs to the family of Rhabdoviridae, the same virus family as Rabies, and can cause a variety of diseases in animals and humans. VSV-G is used by biologists to study the cellâ€™s secretory pathway. Low temperature traps VSV-G in the endoplasmic reticulum (ER), where it is synthesized. The ER can be seen as the faint cyan network in the beginning of the movie, and is soon depleted of VSV-G. Warming up results first in transport to the Golgi apparatus, the large bright green structure on top, and subsequent transport to the cell membrane in large transport vesicles that stop and fuse with the cell membrane. The movie has been recorded with total internal reflection microscopy, which only illuminates the very bottom of the cell and highlights these secretory events that appear as bursts of fluorescence intensity as vesicles fuse with the plasma membrane and labeled VSV-G diffuses into the cell membrane. The length of the movie is approximately 10 minutes. Because of its infectivity, VSV-G has been considered for gene therapy delivery particles.