Here come the septins: novel polymers that coordinate intracellular functions and organization.

Septins are conserved GTP-binding proteins that associate with cellular membranes and the actin and microtubule cytoskeletons. They polymerize to form filamentous structures that act as diffusion barriers between different membrane domains and as molecular scaffolds for membrane- and cytoskeleton-binding proteins. In yeast, septins are central to the spatio-temporal coordination of membrane polarity and cell division, but the roles of their mammalian counterparts have remained poorly understood. However, recent findings have shed light on the dynamics and regulation of mammalian septin assembly and our understanding of septin functions in cytoskeleton and membrane organization. The mammalian septins appear to form a novel network of hetero-polymers that are multi-functional, inter-changeable and respond dynamically to signals that coordinate events at the interface between cytoskeleton and membrane biology. Hence, studies of these molecules might provide new insights not only into how cells coordinate their functions, but also into the pathogenesis of cancer and other diseases in which septins are abnormally expressed.