Characterization of Lamprey Emx gene: Bridging the Gap from Non-Vertebrate Chordates to Gnathostomes
Tank, Elizabeth M.H.
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Lampreys possess a unique phylogenetic position between non-vertebrate chordates and jawed vertebrates (gnathostomes) and thus provide important insights into the evolutionary transition between these groups. The Emx gene family plays a major role in the development of the forebrain, a system that gnathostomes possess and non-vertebrate chordates do not. Three copies of the Emx gene are seen in gnathostomes. Examination of Emx in lampreys can therefore shed light on forebrain evolution and gene duplication. An Emx gene was isolated and cloned from Petromyzon marinus and characterized through phylogenetic and expression analysis. Phylogenetic analysis concluded that lamprey Emx is as equally similar to Emxl as to Emx2 in gnathostomes. Emx transcript was found in lamprey embryos between day 6 and day 19. Initial expression in embryos was located in the neural tube and somites, an expression that is not characteristic of Emx in gnathostomes. Yet all other expression domains including the dorsal telencephalon, olfactory epithelium, otic vesicle, pronephrus and pharyngeal arches has been observed in gnathostomes. One Emx gene was isolated, yet it is not certain that only one exists. This suggests that the function and expression domains of Emx ,were already developed in lamprey and thus maintained in gnathostomes and the Emx gene duplication event occurred after the lamprey / gnathostome divergence.