The Search for Putative Mesoderm and Muscle Specific Genes in Pleurobrachia bachei
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There has been a long debate in the scientific community over the oldest surviving metazoan lineage. Traditionally it has been taught that Porifera, the sponges, occupy that nitche possessing a diploblastic body plan without true organs; however recent phylogentic analysis has suggests that Ctenophora may truly be the oldest lineage, free floating animals with a possible mesoderm layer and complex organs. In this study we searched for the presence of mesoderm in Ctenophora by examining the genome of Pleurobrachia bachei for the presence of tropomyosin, calponin, and β-catenin. Gene expression for all three were found not only in the muscular regions of P. bachei, but in the epidermal tissues as well, indicating there is an unknown function in the metazoan common ancestor. Homology comparisons to the rest of Metazoa reveal little about tropomyosin and calponin, however the ctenophore β-catenin protein appears to be to least derived of all metazoans and suggests Ctenophora may be the most basal extant metazoan lineage.