The Golgi Complex
Figure 1
Recent studies have
analysed the form of the Golgi cisternae using electron microscope tomography.
This technique involves cutting 1 micron thick sections and taking a series of
micrographs through the section using a 1 MeV high voltage EM. The
Golgi stack is comprised of seven cisternae, but only the seventh (trans-most)
cisterna displays clathrin coated budding profiles. Clathrin spikes are clearly
seen on equatorial views of certain buds. When these buds are followed to their
edges through the volume of the tomogram, the distinctive 'cage' of the clathrin
triskelions comes into view.
Specimen from work by Ladinsky M and Howell K. and copied from the. ASCB Image & Video Library. June 2007:VID-22. Available at: http://cellimages.ascb.org
Figure 2
Computer generated model of Golgi stack from tomographic preparation similar to that shown above. The penultimate trans-cisterna (gold) is a tubular reticular cisterna; its tubules are coated at the tip but not with clathrin. The trans-most cisterna (red) is a more solid cisterna; many of its tubules and budding vesicles are clathrin coated.
From work by Marsh BJ, Howell KE, McIntosh JR. Copied from ASCB Image & Video Library. June 2007:VID-21. Available at: http://cellimages.ascb.org
Figure 3
A 3-D model of the three trans-Golgi cisternae and associating ER. The modeled cisternae (in cis-to-trans order) are colored rose, gold and red.. The associating trans-ER is blue-gray. Clathrin-coated budding profiles are indicated by yellow stippling, which are present only on the red cisterna. The penultimate trans-cisterna is extremely reticular.
From work by Ladinsky M and Howell K. ASCB Image & Video Library. June 2007:VID-23. Available at: http://cellimages.ascb.org
Colin Hopkins' contribution to the debate