Diversity of septin scaffolds.

Septins are ubiquitous GTP-binding proteins generally regarded as cytoskeletal components. Higher-order septin assemblies represented by the yeast septin collar function as cytoskeleton, providing structural support and scaffolds for many cellular factors. In metazoans, however, typical higher-order septin assemblies are often less predominant than dispersed 'low-order' septin populations. Recent studies revealed that septin populations with no obvious structure that had previously escaped our attention serve as scaffolds for kinetochore motor proteins and as sequestering depots for microtubule regulators. Unlike classic cytoskeletal polymers, which form uniform, continuous networks, septin polymers, being diverse, discontinuous and relatively static, seem suited to form discrete scaffolds. Thus, the septin system might be redefined as discrete scaffolds that are conditionally united to behave like cytoskeleton.