Lecture notes for Monday, February 9, 2015The term "Amoeboid Locomotion" refers to more than one phenomenon. The following are some specific examples: 1) The species most often used in introductory biology courses is Amoeba proteus. These have the advantage of crawling faster than other cells and having a very dramatic pattern of cytoplasmic flow. A larger multicellular species, named Chaos carolinenses (often called Pelomyxa) has these same two advantages. It was discovered by UNC's own H. V. Wilson while teaching an undergraduate laboratory, and he named in in honor of this university. Both these species are quite rare, and I have never seen any that weren't ordered from a commercial supply house. 2) Dictyostelium discoideum is the most-studied one of the "Cellular Slime Molds". These are smaller and slower, but have the special advantages of chemotactic aggregation, followed by multicellular locomotion of masses of from hundreds to hundreds of thousands of cells, which then differentiate into three differentiated cell types (bean-shaped spores, cylindrical stalk cells, and another cell type that supports the stalk base. Their "fruiting bodies" consist of a tapering stalk, with a lemon-shaped mass of spores at the top, and have the same proportions over a size range of at least 500. This is even more than Driesch's revolutionary discovery that starfish embryos can "scale" over a sixteen-fold size range. (Incidentally, this most-studied species was discovered by a UNC undergraduate [Kenneth Raper] on some horse dung in Duke Forest) For many years, the leading researcher on slime molds was Lindsay Olive, who was a professor in this department, and kindly provided many different species to use in laboratories of this course. 3) Shelled Amoebae make hollow, rigid, vase-shaped containers, in which they live, as unicellular analogies to hermit crabs. Some species make their shells by sticking very small sand grains together, and other species secrete their shell. This group really do stick out long, stiff pseudopodia which adhere and contract. (which many textbooks say is how tissue culture cells move, but isn't) 4) In several species, the plasma membrane flows forward on the top of each cell, and flows rearward on the bottom, like a "tractor tread". 5) Labyrinthula may surprise you more than any other amoeboid organism. These secrete extracellular layers of lipid, membrane, apparently with some actin and myosin between the foot-ball shaped cells and multiple layers of extracellular membrane. Their cells slide actively, as if pulled by one end. Most species live in the ocean, cause a disease in sea grasses, and can be easily cultured from just about any piece of (still wet) sea grass you find on the beach. The summer before my senior year in college, I had the enormous, good luck to receive an 11 week NSF fellowship for research on Labyrinthula at the U. of Miami Marine Lab on Virginia Key, next to the Seaquarium. If Chris Martin, Sam Meyers, Mark Friedman, Paul, Sandy or any of those nice people happen to find this web site, then please accept my thanks and best wishes. Many days I wonder why I didn't stay down there in the Keys. 6) "Crawling Locomotion of Tissue Cells" Including tissue culture cells, elongating axons and dendrites, wound healing, locomotion of mesenchymal cells during embryonic development, the constant rearrangement of all cells of sponges.
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