THE NEW-AGE OF THE CELL

The view that cells are just a bag of enzymes was seriously challenged in the early sixties. Electron microscopy studies, subcellular fracti onation and the discovery of an extensive cytoskeletal network led to the concept that cells are organized into functionally distinct compar tments. More recently, much progress was made in understanding the mec hanisms controlling the dynamics of these networks and the ability of the different subcellular structures to communicate through a sophisti cated vesicular transport system driven by ATP-dependent motors. Mecha nisms controlling basic cellular functions, namely to divide, to move, to adhere, to differentiate, or to die, have been found to be extreme ly conserved throughout the animal kingdom. The understanding of the e nzymatic network involved in the progression of the cell cycle benefit ed from original studies made in different species, including yeast, f rog and starfish. It led to the discovery of cyclin-dependent kinases which per-iodic activation represents the basic cell cycle engine, and of checkpoint mechanisms which ensure that the integrity of the genom e is preserved during DNA duplication (or repair) and chromosomes segr egation in mitosis. Different families of GTPases have now been identi fied and their functions partly unraveled in signaling from the cell s urface, as well as in the proper targeting of vesicules; these enzymes are associated with a multimolecular recognition complex. Many cytosk eleton-associated proteins have now been characterized and their role in the assembly of supramolecular complexes involved in adhesion, cell shape and motility, is currently under investigation. Cells assemble into tissues of increasing complexity during development under the con trol of master genes and effector molecules, including the different f amilies of adhesion molecules. A growing body of data suggests that di fferent modes of signalling are coupled to regulate the behavior of ce lls. This review, which concentrates on certain areas in the field of cell biology, shows the critical importance of institutional support. Many of the current approaches from the different fields in the life s ciences, as well as from physics and chemistry, will merge to yield a better understanding of cellular functions.