Tubulin polymerization promoting protein (TPPP) ortholog from Suberites domuncula and comparative analysis of TPPP/p25 gene family

Sponges are one of the oldest metazoan phyla that are, due to their highly conservative nature, often referred to as the living fossils of multicellular animals. As such, they are a very important model for evolutionary, developmental and functional studies of Metazoa. Tubulin polymerization promoting proteins (TPPPs) are defined by the presence of p25-alpha domain (Pfam05517). Their functional characteristics resemble those of microtubule-associated proteins. Presence of TPPP homologous genes has been postulated in all eukaryotes with ciliated cells and their primary function has been proposed as some basic cilia-connected function. We present here the genomic structure and the corresponding cDNA sequence of one poriferan TPPP homolog (SdTPPP) isolated from the marine sponge Suberites domuncula; and a comparative analysis of TPPP homolog sequences and genomic structures from other Eukaryotes. Our results confirm the radiation of one TPPP homolog into three distinct genes in the Vertebrate lineage, but the origin of different sequences and their phylogenetic relationships show to be influenced by alternative protein isoforms, independent gene duplications, modularity of the p25-alpha domain and possible adaptational requirements to environmental conditions.