In many mammalian neurons, dense clusters of ion channels at the axonal initial segment and nodes of Ranvier underlie action potential generation and rapid conduction. Axonal clustering of mammalian voltage-gated sodium and KCNQ (Kv7) potassium channels is based on linkage to the actin-spectrin cytoskeleton, which is mediated by the adaptor protein ankyrin-G. We identified key steps in the evolution of this axonal channel clustering. The anchor motif for sodium channel clustering evolved early in the chordate lineage before the divergence of the wormlike cephalochordate, amphioxus. Axons of the lamprey, a very primitive vertebrate, exhibited some invertebrate features (lack of myelin, use of giant diameter to hasten conduction), but possessed narrow initial segments bearing sodium channel clusters like in more recently evolved vertebrates. The KCNQ potassium channel anchor motif evolved after the divergence of lampreys from other vertebrates, in a common ancestor of shark and humans. Thus, clustering of voltage-gated sodium channels was a pivotal early innovation of the chordates. Sodium channel clusters at the axon initial segment serving the generation of action potentials evolved long before the node of Ranvier. KCNQ channels acquired anchors allowing their integration into pre-existing sodium channel complexes at about the same time that ancient vertebrates acquired myelin, saltatory conduction, and hinged jaws. The early chordate refinements in action potential mechanisms we have elucidated appear essential to the complex neural signaling, active behavior, and evolutionary success of vertebrates.
Pubmed ID: 19112491 RIS Download
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THIS RESOURCE IS NO LONGER IN SERVICE. Documented on March 17, 2022. Genome databases housed at the Genome Institute at Washington University. Included are genome databases from Humans/Primates, other vertebrates, microorganisms, plants and invertebrates.
View all literature mentionsTo explore the elephant shark genome, we have conducted a survey-sequencing and comparative analysis of the elephant shark genome in collaboration with J. Craig Venter Institute. The elephant shark sequences generated under this project have been deposited at GenBank under the project accession number AAVX01000000. The sequences can also be searched using BLAST and retrieved here. Cartilaginous fishes (Chondrichthyes) represented by sharks, rays, skates and chimaeras, are phylogenetically the oldest group of living jawed vertebrates. They constitute an important group for our understanding of the origins of the complex developmental and physiological systems of jawed vertebrates. They are also an useful outgroup for bony vertebrates such as tetrapods and teleost fishes and help in identifying specialized features that have led to the evolution of diverse groups of bony vertebrates. The elephant shark (Callorhinchus milii), also known as the elephant fish and ghost shark, is a chimaera belonging to the Order Chimaeriformes and Family Callorhynchidae. It has the smallest genome among the known cartilaginous fish genomes. Thus, it was proposed as a model cartilaginous fish genome for whole-genome sequencing and comparative analysis (Venkatesh et al. 2005. Curr. Biol. 15: R82-R83). The following resources of the elephant shark are available for the scientific community: *Elephant Shark 1.4x assembly fasta sequences zipped 227 megabytes *Genomic DNA *~8x coverage BAC library (average insert size, ~150 kb) *cDNA libraries (under construction) *cDNA (dated 11 April 2008) with orthologs in 5 vertebrates (human, opossum, chicken, frog, fugu)
View all literature mentionsSoftware package for analysis of microarray images. Microarray spot detection and characterization software package which extracts numerical information from cDNA microarrays.
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