The free living soil nematode, Caenorhabditis elegans, offers numerous advantages as a teaching organism, including its small size, ease of maintenance, ready availability, and number of mutant strains. Using C. elegans, we have devised a laboratory exercise using fluorescence microscopy to study endocytosis and phagocytosis in the digestive system.
Instructors prepare the worms prior to class in each of three treatments.
Some worms are fed FITC-conjugated microspheres, which can only be absorbed by phagocytosis. Others are fed RITC-conjugated dextran, which can be absorbed by pinocytosis. The last group of animals is suspended in acridine orange, a fluorochrome that concentrates in acidic organelles. Students examine worms from each treatment, as well as controls, to determine which cellular transport mechanism this nematode uses for food absorption and to relate the mechanism's location to acidic compartments, i.e. lysosomes. Furthermore, the images obtained are aesthetically pleasing and can be spectacularly colorful.