A Study on Animal Cellular Organization

Cells are comprised of highly organized assemblies of macromolecules, which undergo continuous dynamic rearrangements. Our contributors in this issue of Current Opinion in Cell Biology review some of the most exciting recent advances in our understanding of how various such dynamic assemblies function at the molecular level. As (to use the much-quoted phrase of Theodosius Dobzhansky) “nothing in biology makes sense except in the light of evolution”, Peroxisomes are vesicle-like packets containing specialized enzymes that rid cells of toxins and utilize fats as an energy source. They can be called into being or dismissed depending upon the metabolic needs of the cell, which may therefore have few or many peroxisomes at different times. Significant recent progress has been made in understanding peroxisomal biogenesis, and it turns out both fission and de novo assembly occur, depending on the cellular circumstances. The ER provides membranous materials for both processes, while the contents of the peroxisomes are imported by a long-mysterious mechanism that is only now being revealed. The coatomer family of vesicle coating complexes are shown to have significant structural relationships among themselves and, tellingly, to the nuclear pore complex; while the ESCRT system has been found to have a lineage that extends back into the Archea. Analyses of these factors indicate that a complex endomembrane system predates the initial radiation of eukaryotic lineages, and suggest new insights on the origins of eukaryotes. The biogenesis of cellular organelles represent another huge leap in complexity, generally involving either division of pre-existing organelles or de novo assembly from precursors generated by other organelles. With an insightful discussion of informational and algorithmic complexity, he argues persuasively that the problem is not as insurmountable as some had thought, and does not require the elaborate assumptions made by some previous theories. A mainstay of this review series has been the relentless and exciting progress made on the cytoskeleton. As several topics including septins, intermediate filaments, and the bacterial cytoskeleton were covered in excellent reviews in last year’s issue, this year we focused instead on recent progress on actin and microtubule function in cells.