Expression patterns of the mouse Spir-2 actin nucleator.

Spir proteins are the founding members of the novel class of WH2 domain containing actin nucleation factors. They initiate actin polymerization by binding of actin monomers to four WH2 domains in the central part of the proteins. Despite their ability to nucleate actin polymerization in vitro by themselves, Spir proteins form a regulatory complex with the distinct actin nucleators of the formin subgroup of formins. The mammalian genome encodes two spir genes, spir-1 and spir-2. The corresponding proteins have an identical structural array and share a high degree of homology. Here, we have addressed the yet unknown expression of the mouse spir-2 gene. Northern blot analysis revealed that the spir-2 gene is expressed as a single mRNA. During embryogenesis in situ hybridizations show spir-2 to be expressed in the developing nervous system and intestine. In adult mouse tissues highest expression of spir-2 was detected in the epithelial cells of the digestive tract and in neuronal cells of the nervous system. High expression was also detected in testical spermatocytes. In contrast to the restricted expression of the mouse spir-1 gene, which is mainly found in the nervous system, our data presented here show a distinct and broader expression pattern of the spir-2 gene and by this support a more general cell biological function of the novel actin nucleators.