Transport of vesicles facilitated by kinesin and the effects of mutations in nerve transmission in Caenorhabditis elegans Introduction
A nerve cell is made up of three main structures: the soma, the axon and the synapse. When a nerve cell receives a signal, a protein called kinesin travels anterograde along the axon and guides the synaptic vesicles until it reaches the synapse. This triggers the release of the neurotransmitters stored within the vesicles. Once released, the neurotransmitters then bind to receptors of the receiving cell. It would be nearly impossible to have the transportation of vesicles without kinesin to guide it. And without the transportation of these synaptic vesicles to release their neurotransmitters, there would be no movement in the cell at all. This experiment is so important because vesicle transport in neurons helps to identify many neurological disorders. One such example is a research on Drosophila. Since there is only one kinesin light gene in the subject, the mutants in that one chain gene exhibit severe motor neuronal disease (Hirokawa, 2008). The disruption of the anterograde and retrograde transport of membrane vesicles was found to interrupt the function of kinesin in the mutated organisms causing them to be paralyzed (Hirokawa, 2008). This research into the function of kinesin in neurological disorders helps doctors and researchers to better understand the effects of kinesin in mutated organisms. The goal of the experiment was to better understand kinesin facilitated transport of vesicles and to observe the effects of mutations in nerve transmission in Caenorhabditis elegans. C. elegans is a species of nematode that has a simple nervous system and has synaptic vesicles that can be easily tagged with green fluorescent protein (GFP) and viewed under fluorescence microscopy. The experiment was to observe three strains of C. elegans and determine which of the phenotypes observed showed certain mutations and then do a comparison of the phenotypes with images of the GFP tagged synaptic vesicles. The first hypothesis that was stated said the strain with a normal s-shape and high responsiveness would be the wild-type with no mutations. The next hypothesis was that the nonresponsive and contorted C. elegans possessed mutations. The final hypothesis was that the strain with a protein fusion mutation would appear normal under the fluorescence microscopy and the strain with a vesicle transport mutation only the ventral cord would be visible. Results
C. elegans were viewed under a dissecting microscope to observe and distinguish between the phenotypes of the three strains. The movements of C. elegans when prodded and the undisturbed shapes of the strains were recorded (Table 1).Both the NM440 and RK001 showed signs of inhibited movement, however, the NM1233 showed very normal movements. Overall, it seemed that the movement of the C. elegans was correlated with the presence of a visible nerve cord. Table 1. The transport of vesicles in wild-type and mutant C. elegans1 was studied using a dissecting microscope (40x) and a fluorescence microscope (400x).. The movement of synaptic vesicles throughout the nervous system of C. elegans was examined under a fluorescence microscope using a protein tag. Green-fluorescent protein (GFP)2, which had already been fused to a protein located on the membrane of the synaptic vesicles of C. elegans, emitted a green light when illuminated under a fluorescent microscope by ultraviolet light. Strain
| Appearance of GFP
| Almost no movement, twitching
| No visible nerve ring or nerve chords, scattered fluorescent blotches. Contorted body shape.
| Quick, full movements, slithering
| Identifiable nerve ring and nerve chords, snakelike
| Limited, twitching movement
| Identifiable nerve ring and nerve chords, stretched out
| 1 Caenorhabditis elegans is a small worm with a simple nervous system that is similar to the nervous system...
References: Hirokawa N., Sato-Yoshitske R., Kobayashi N., Pfister K.K., George S. Bloom, Scott T. Brady. 1991. Kinesin associates with anterogradely transported membranous organelles in vivo. Cell Biol. 114(2):295- 302
Hirokawa N., Noda Y., 2008. Intracellular transport and kinesin superfamily proteins, KIFS: Structure, Function and Dynamics. Physiol Rev; Jul;88(3):1089-118.Review
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