Truncated TPPP – An Endopterygota-specific protein

TPPP proteins exhibiting microtubule stabilizing function constitute a eukaryotic protein superfamily, characterized by the presence of the p25alpha domain of various lengths. Vertebrate species possess three TPPP paralogs; all of them possess a full-length p25alpha domain of 160–170 amino acids and are encoded by three exons. Species of Endopterygota (Holometabola) have, besides a full-size TPPP ortholog, a protein with a truncated p25alpha domain as well, where the last coding exon, responsible for microtubule binding, is missing. It is not the result of an alternative splicing but is coded by another gene. In Drosophila melanogaster, they are named as CG45057 (long-type) and CG6709 (truncated). The truncated protein has been found in the Endopterygota orders Diptera, Coleoptera, Hymenoptera, Lepidoptera and Raphidioptera. In Lepidoptera, in several superfamilies (Gelechioidea, Bombycoidea, Noctuoidea, Pyraloidea) two paralogs of the truncated TPPP occur. Truncated orthologs (CG6709) were not found in other insects or in arthropods and are absent in any other organism, as well, while the long-type TPPPs (CG45057 orthologs) occur commonly in all animals. Thus it seems that CG6709 orthologs occur only in insects undergoing on metamorphosis.