Harold Zakon1, Weiming Li2, Nisha E. Pillai3, Sumanty Tohari3, Prashant Shingate3, Jianfeng Ren4, Byrappa Venkatesh3,5.
1 Department of Neuroscience and Integrative Biology, The University of Texas, Austin, Texas, USA 78712
2 Department of Fisheries and Wildlife, Michigan State University, East Lansing, Michigan, USA 48824
3 Comparative and Medical Genomics Lab, Institute of Molecular and Cell Biology, A*STAR, Biopolis, Singapore 138673
4 Key Laboratory of Exploration and Utilization of Aquatic Genetic Resources, Shanghai Ocean University, Shanghai, 201306, China.
5 Department of Paediatrics, Yong Loo Lin School of Medicine, National University of Singapore 119228.
Published in Proceedings of the Royal Society B online on 20th Sept 2017
Studies of the voltage-gated sodium (Nav) channels of extant gnathostomes have made it possible to deduce that ancestral gnathostomes possessed four voltage-gated sodium channel genes derived from a single ancestral chordate gene following two rounds of genome duplication early in vertebrates. We investigated the Nav gene family in two species of lampreys (the Japanese lamprey, Lethenteron japonicum and sea lamprey, Petromyzon marinus) (jawless vertebrates – agnatha) and compared them with those of basal vertebrates to better understand the origin of Nav genes in vertebrates. We noted six Nav genes in both lamprey species but orthology with gnathostome (jawed vertebrate) channels was inconclusive. Surprisingly, the Nav2 gene, ubiquitously found in invertebrates and believed to have been lost in vertebrates, is present in lampreys, elephant shark (Callorhinchus milii) and coelacanth (Latimeria chalumnae). Despite repeated duplication of the Nav1 family in vertebrates, Nav2 is only in single copy in those vertebrates in which it is retained, and was independently lost in ray-finned fishes and tetrapods. Of the other five Nav channel genes, most were expressed in brain, one in brain and heart, and one exclusively in skeletal muscle. Invertebrates do not express Nav channel genes in muscle. Thus, early in the vertebrate lineage Nav channels began to diversify and different genes began to express in heart and muscle.
Figure 1.: Japanese lamprey (Lethenteron japonicum) and its sucker-like mouth. Lampreys are ancient vertebrates that lack jaws and teeth, and instead possess a sucker-like mouth which is used for attaching to large fishes and sucking their blood and body fluid.
Figure 2.: Expression patterns (RNA-Seq; Transcripts per million-TPM) of Nav2 and Nav1 voltage-gated sodium channel genes in the brain, heart, kidney, muscle, notochord, ovary and testis of the Japanese lamprey. Nav2 gene is an ancient voltage-gated sodium channel gene ubiquitously present in invertebrates and retained in lamprey but lost in mammals and ray-finned fishes.
For more information on BV’s laboratory, click , please click here.