“Porterplasm” and the microtrabecular lattice

JCB • VOLUME 170 • NUMBER 6 • 2005 864 " Porterplasm " and the microtrabecular lattice eith Porter was to many the father of biological electron microscopy (EM) and even of cell biology. He helped instigate the founding both of this journal and of the K American Society of Cell Biology, and was a key figure in defining the structures of intact and sectioned cells. The latter stages of Keith Porter's eminent cell biology career began with the installation of a 1-MeV high voltage electron microscope (HVEM) at the Molecular, Cellular, and Developmental Biology department at the University of Colorado, Boulder, in 1972. Porter had high hopes that the HVEM would allow him to pursue a long-term goal of defining the structure of the cytoplasm by looking at whole cell mounts. Although success did come in imaging whole cells, in the end, the ambitious goal of defining the definitive structure of the cytoplasm was not matched by the technology of the day (Heuser, 2002). As early as the mid-1950s, Porter had a strong hunch that there must be some structure to the " optically 'empty' parts of the protoplasm " that gave the cell its " elastic framework " (Porter, 1956). With the HVEM he could study a variety of types of cultured cells without the interference of embedding resins. Under a myriad of conditions, he saw a scaffold, or spongework, that encased all the then-known components of the cell. The scaffold consisted of fine, interconnected fibrils, which Porter named microtrabeculae (trabeculae roughly translates from Latin to tiny beams or girders). The concept of the microtrabecular lattice was first described in 1976 (Wolosewick and Porter, 1976). The lattice backed up the idea that the cytosol was not all liquid, but rather contained a structured, linking framework. Porter also extended the responsibilities of the lattice beyond a mere scaffold, to include directing intra-cellular movements (Byers and Porter, 1977), giving shape and rigidity to cells, and even perhaps possessing information for cellular organization (Porter, 1978). But critics soon voiced concern that the lattice might simply represent a fixation artifact of condensed soluble components of cytosol. Cytoskeletal components had just recently been identified, and many cell biologists still struggled with changing their concept of the cytoplasm from " soup " to " scaffold. " Until the Porter studies, investigators had mostly concentrated on the visible cell structures—membranes, organelles, and filaments—and had ignored …