Novel roles for mammalian septins: from vesicle trafficking to oncogenesis

In recent years a convergence of various aspects of cell biology has become apparent, and yet investigators are only beginning to grasp the underlying unifying mechanisms. Among the proteins that participate in diverse aspect s of cell biology are the septins. These are a group of novel GTPase protei ns that are broadly distributed in many eukaryotes except plants. Although septins were originally identified as a protein family involved in cytokine sis in yeast, recent advances in the field have now ascribed additional fun ctions to these proteins. In particular, the number of known mammalian sept in family members has increased dramatically as more data has become availa ble through genome analyses. We suggest a classification for the mammalian septins based on the sequence homologies in their highly divergent N- and C -termini. Recent work suggests novel functions for septins in vesicle traff icking, oncogenesis and compartmentalization of the plasma membrane. Given the ability of the septins to bind GTP and phosphatidylinositol 4,5-bisphos phate in a mutually exclusive manner, these proteins might be crucial eleme nts for the spatial and/or temporal control of diverse cellular functions. As the functions of the septins become unraveled, our understanding of seem ingly different cellular processes may move a step further.