The septins

The septins make up a family of guanine-nucleotide binding proteins, most of which polymerize to form filaments. Septin genes have been found in fungi and animals but not in protozoa or plants; yeasts have seven septin genes and humans have twelve, but Caenorhabditis elegans has only two. Some septin genes generate multiple polypeptides by alternative splicing or alternative translation start sites. Of the five conserved motifs found in other members of the GTPase superfamily, three are highly conserved in septins. Septin filaments are thought to form a cytoskeletal system that organizes higher-order structures by self-assembly and templated assembly. These multifunctional proteins are best known for their role in cytokinesis, but other functions in dividing and non-dividing cells have evolved in different lineages: budding yeast has septins specific for sporulation; nematode septins are implicated in postembryonic morphogenesis of multiple cell lineages; fly septins are associated with the development of germ cells, photoreceptor cells and nervous system; and mammalian septins are implicated in exocytosis, tumorigenesis, apoptosis, synaptogenesis and neurodegeneration.