This entry represents the Spire (Spir) family, including vertebrate Spire-1 and Spire-2, Ciona savignyi PEM-5 and Drosophila dSpire. They contain a KIND (kinase noncatalytic C-lobe) domain and four actin-binding WH2 (WASP homology 2) domains []. They act as actin nucleation factors []and are involved in a novel actin-dependent mechanism for long range vesicle transport []. Although Spire proteins are capable of nucleating actin polymerisation in vitro by themselves, they have been found to act in cooperation with members of another family of actin nucleators: the formin subgroup (FMN) of formins []. Spire/formin cooperation is considered to have a major regulatory function in mammalian oocyte maturation []. The structure of Spire has been revealed [, ]. The mammalian genome encodes two Spir proteins, Spir-1 and Spir-2. They have an identical structure and share a high degree of homology. Spir-2 has a broader expression pattern[].
