The arrangement of the Golgi complex beads is not controlled by the cytoskeleton

Golgi complex beads and the transition region

Secretory proteins and membranes move in transfer vesicles from the rough endoplasmic reticulum through the transition region to the outer saccule of the Golgi complex. In both arthropod and vertebrate cells, the GC beads are a characteristic structural component of the transitional region. The beads are particles about half the size of ribosomes arranged equidistantly from one another and the smooth face of the ER. In an active GC, the beads are in rings through which the ER membrane emerges to form transfer vesicles. The beads may be part of the energy-dependent step required for the movement of proteins along eht secretory pathway, since they lose their ring arrangement under conditions that lower cellular ATP. The beads are organizers for Golgi complexes in the sense that they are the first recognizable components of new GCs as they arise from ER. Arthropod GC beads, but not those of vertebrates, can be visualized through their reaction with bismuth in vivo and in fixed tissue. Useful paradigms for traffic between the ER and the GC need to combine structural and biochemical information. Insect fat body, with its readily resolvable bismuth-strained beads and easily fractionated cell components may have particular value for this problem.

Influence of antimicrotubular drugs on the Golgi apparatus of stomach secretory mucoid cells and small intestine absorptive cells

The effects of vinblastine and colchicine on the Golgi apparatus of stomach surface mucoid and absorptive intestinal cells were compared by cytochemical analysis. The two epithelial cells were chosen because of their different specific functions in the formation of secretory granules, the production of lysosomes and the intensity of membrane traffic in the cytoplasm. For the analysis, adult mice were injected with 1 mg/100 g b.w. of vinblastine and 1 mg/100 g b.w. of colchicine. For the demonstration of cis and trans cisternae of the Golgi apparatus, prolonged osmification, thiamine pyrophosphatase and acid phosphatase activity identification were applied. After treatment with vinblastine or colchicine, polarity of stacks in the Golgi apparatus of surface mucoid cells is preserved although the number of cisternae with thiamine pyrophosphatase or acid phosphatase activity decreases. However, the Golgi apparatus of intestinal absorptive cells completely disintegrates and only a few separated cis or trans cisternae can be identified. The main effect seems to be a reduction of vesicles which can be cytochemically identified as parts of the Golgi apparatus and an accumulation of vesicles which probably originate from budding ER. Communication between the ER and the Golgi apparatus seems to be interrupted.

The charge distribution in the rough endoplasmic reticulum/Golgi complex transitional area investigated by microinjection of charged tracers

The distribution of microinjected ferritin, ranging in charge from anionic to highly cationic, has been used to indicate differences in surface charge on the rough endoplasmic reticulum and the Golgi complex of intact cells. Highly cationic ferritins (HCF)(HCF1, pI 7.9-9.1; HCF2, pI 8.5-9.4; and HCF3.pI 9.5-10.1) were mostly bound and caused swelling of the rough endoplasmic reticulum. Cationic ferritin (CF) (pI 7.0-8.0) and anionic ferritin (AF) (pI 4.0-4.4) caused no changes in morphology. The distribution of these ferritins in the cytoplasmic space varied with their charge. Significantly more CF was bound to surfaces than was found in the free cytoplasmic space. Conversely, there was significantly more AF in the free cytoplasmic space than close to surfaces. Therefore, the intracellular surfaces are negatively charged. Comparison of the structures in the secretory pathway showed no differences in ferritin binding to transition vesicles, rough endoplasmic reticulum, Golgi saccules or secretory vesicles. The Golgi complex beads are not distinguished by their charge. It is therefore unlikely that charge differences play a role in regulating membrane-membrane interactions in this region of the secretory pathway.