Structural evidence for multiple transport mechanisms through the Golgi in the pancreatic beta-cell line, HIT-T15.
Accurate data on the three-dimensional architecture of the Golgi is prerequisite for evaluating the mechanisms of transit through this organelle. Here we detail the structure of the Golgi ribbon within part of an insulin-secreting cell in three dimensions at approximately 6 nm resolution. Rapid freezing, freeze-substitution and electron tomography were employed. The Golgi in this region is composed of seven cisternae. The cis-most element is structurally intermediate between the endoplasmic reticulum (ER)-Golgi intermediate compartment (ERGIC) and the cis-most cisterna characterized in three dimensions at high resolution in a normal rat kidney cell [Ladinsky, Mastronarde, McIntosh, Howell and Staehelin (1999) J. Cell Biol. 144, 1135-1149]. There are three trans-cisternae that demonstrate morphological and functional variation. The membrane surface areas and volumes of these elements decrease from cis to trans. The two trans-most cisternae are dissociated from the stack and are fragmented by tubulation. ER closely adheres to and inserts between individual trans-cisternae. Many of the 2119 small, clathrin-negative vesicles that are in close proximity to the Golgi fill the region where trans-cisternae have moved out of register with the ribbon. These data provide evidence that cisternal progression/maturation, trafficking via membrane tubules and vesicle-mediated transport act in concert in the same region of the Golgi ribbon, and suggest an important role for the ER in regulating membrane dynamics at the trans-Golgi.
Marsh
B J
BJ
Boulder Laboratory for 3-D Fine Structure, Department of Molecular, Cellular and Developmental Biology, University of Colorado, Boulder, CO 80309, USA.
Mastronarde
D N
DN
McIntosh
J R
JR
Howell
K E
KE
D000818:Animals; D001692:Biological Transport; D002458:Cell Fractionation; D002460:Cell Line; D006056:Golgi Apparatus / Q000502:physiology*; D007515:Islets of Langerhans / Q000502:physiology* / Q000648:ultrastructure; D008854:Microscopy, Electron; D008961:Models, Structural; D015398:Signal Transduction / Q000502:physiology*; D021601:trans-Golgi Network / Q000502:physiology / Q000648:ultrastructure