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

Cover  This striking example of biological pattern formation comes from a protozoan, Echinosphaerium nucleofilum. Shown is a transverse section through one of the numerous axopodia, long slender cell surface projections, that radiate from the small, spherical cell bodies of Heliozoa. For the protozoan, the axopodia play a central role in the feeding process. The axopodia serve to increase the cell surface area available for prey capture. Moreover, upon adhesion of a prey organism, the axopodia shrink and thus convey the food particle to the cell body where it can be engulfed. Lew Tilney and his colleagues showed that each axopodium contains a remarkable array of microtubules. The description of the behavior of the axopodia provided an early example of the importance of microtubule dynamics in biological processes and represented one of the first illustrations of microtubule involvement in the establishment of anisometric cell shape. In addition, the direct visualization of cross-links between the axopodial microtubules presaged the biochemical identification of microtubule-associated proteins. The image of the double-coiled pattern of microtubules within a Heliozoan axopodium represents a timeless illustration of the captivating beauty of biological systems and serves to remind us that many secrets are yet to be revealed. (Reprinted with permission from Tilney, L.G., and Byers, B. [1969]. Studies on the microtubules in Heliozoa. V. Factors controlling the organization of microtubules in the axonemal pattern in Echinosphaerium (Actinosphaerium) nucleofilum. J. Cell Biol. 43, 148-165). Mary Beckerle.