QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

Cover  The electron microscopic views of cellular organization that were pioneered in the 1940s and 1950s gave cell biologists their first clues about cellular organization. These analyses required strong fixatives to allow tissue to survive in the electron beams, plastic embedding, and heavy metal stains to give sufficient contrast to see cellular organelles. These images helped build the foundations of modern cell biology, but they also gave a rather static, two-dimensional view of cells. Freeze fracture techniques allowed more intimate views of membranes and what are now termed membrane microdomains and rafts. In this method frozen cells were fractured through the center of membranes, and then a replica that could be viewed at high resolution was produced by evaporation platinum at an angle. In a landmark paper entitled "Organization of Acetylcholine Receptors in Quick-Frozen, Deep-etched, and Rotary-replicated Torpedo Postsynaptic Membrane" (J. Cell Biol. 82, 150-173, 1979) J.E. Heuser and S.R. Salpeter described a new technique of viewing tissue that presented membranes and fibers and their interrelationships, both inside and outside the cell, in three dimensions at high magnification. This technique relies on freezing tissue very rapidly (>20,000°C/s) in liquid helium to prevent ice crystal formation, followed by freeze fracture, deep etching, and rotary replication. The platinum/carbon replicas captured the process of exocytosis and showed acetylcholine receptors organized into liquid crystals. The technique also revealed for the first time a cytoskeletal web of cytoplasmic filaments beneath the postsynaptic membrane and the basal lamina above it (right side). These views suggested that the cytoskeleton existed as a discrete structure. In further studies Heuser went on to visualize the processes of receptor-mediated endocytosis in three dimensions. In "Three-Dimensional Visualization of Coated Vesicle Formation in Fibroblasts" (J. Cell Biol. 84, 560-583, 1980) he was able to display with remarkable clarity the stages in the formation of clathrin coats that appear under the plasma membrane during ingestion of low-density lipoproteins (left side). These papers catalyzed a generation of studies by Heuser and others that defined the structural biology of the cytoskeleton in nonmuscle cells and the processes of vesicular transport and endocytosis and changed our image of the cell forever. These figures are reprinted from The Journal of Cell Biology, 1980, 84, p. 560-583 and 1979, 82, p. 150-173 by copyright permission of The Rockefeller University Press.Zena Werb