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Browsing by Author "Edwards, Scott V."

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    Molecular Adaptations for Sensing and Securing Prey and Insight into Amniote Genome Diversity from the Garter Snake Genome
    Perry, Blair W.; Card, Daren C.; McGlothlin, Joel W.; Pasquesi, Giulia IM M.; Adams, Richard H.; Schield, Drew R.; Hales, Nicole R.; Corbin, Andrew B.; Demuth, Jeffery P.; Hoffmann, Federico G.; Vandewege, Michael W.; Schott, Ryan K.; Bhattacharyya, Nihar; Chang, Belinda SW W.; Casewell, Nicholas R.; Whiteley, Gareth; Reyes-Velasco, Jacobo; Mackessy, Stephen P.; Gamble, Tony; Storey, Kenneth B.; Biggar, Kyle K.; Passow, Courtney N.; Kuo, Chih-Horng; McGaugh, Suzanne E.; Bronikowski, Anne M.; de Koning, AP Jason P. J.; Edwards, Scott V.; Pfrender, Michael E.; Minx, Patrick; Brodie, Edmund D.; Brodie, Edmund D.; Warren, Wesley C.; Castoe, Todd A. (Oxford University Press, 2018-08-01)
    Colubridae represents themost phenotypically diverse and speciose family of snakes, yet nowell-assembled and annotated genome exists for this lineage. Here, we report and analyze the genome of the garter snake, Thamnophis sirtalis, a colubrid snake that is an important model species for research in evolutionary biology, physiology, genomics, behavior, and the evolution of toxin resistance. Using the garter snake genome, we show how snakes have evolved numerous adaptations for sensing and securing prey, and identify features of snake genomestructure that provide insight into the evolution of amniote genomes.Analyses of the garter snake andother squamate reptile genomes highlight shifts in repeat element abundance andexpansionwithin snakes, uncover evidence of genes under positive selection, and provide revised neutral substitution rate estimates for squamates. Our identification of Z andW sex chromosome-specific scaffolds provides evidence for multiple origins of sex chromosome systems in snakes and demonstrates the value of this genome for studying sex chromosome evolution. Analysis of gene duplication and loss in visual and olfactory gene families supports a dim-light ancestral condition in snakes and indicates that olfactory receptor repertoires underwent an expansion early in snake evolution. Additionally, we provide some of the first links between secreted venom proteins, the genes that encode them, and their evolutionaryorigins ina rear-fanged colubridsnake, togetherwith newgenomic insight into the coevolutionary arms race between garter snakes and highly toxic newt prey that led to toxin resistance in garter snakes.
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    Parallel Evolution of Tetrodotoxin Resistance in Three Voltage-Gated Sodium Channel Genes in the Garter Snake Thamnophis sirtalis
    McGlothlin, Joel W.; Chuckalovcak, John P.; Janes, Daniel E.; Edwards, Scott V.; Feldman, Chris R.; Brodie, Edmund D.; Pfrender, Michael E.; Brodie, Edmund D. (Oxford University Press, 2014-08-18)
    Members of a gene family expressed in a single species often experience common selection pressures. Consequently, the molecular basis of complex adaptations may be expected to involve parallel evolutionary changes in multiple paralogs. Here, we use bacterial artificial chromosome library scans to investigate the evolution of the voltage-gated sodium channel (Nav) family in the garter snake Thamnophis sirtalis, a predator of highly toxic Taricha newts. Newts possess tetrodotoxin (TTX), which blocks Nav’s, arresting action potentials in nerves and muscle. Some Thamnophis populations have evolved resistance to extremely high levels of TTX. Previous work has identified amino acid sites in the skeletal muscle sodium channel Nav1.4 that confer resistance to TTX and vary across populations. We identify parallel evolution of TTX resistance in two additional Nav paralogs, Nav1.6 and 1.7, which are known to be expressed in the peripheral nervous system and should thus be exposed to ingested TTX. Each paralog contains at least one TTX-resistant substitution identical to a substitution previously identified in Nav1.4. These sites are fixed across populations, suggesting that the resistant peripheral nerves antedate resistant muscle. In contrast, three sodium channels expressed solely in the central nervous system (Nav1.1–1.3) showed no evidence of TTX resistance, consistent with protection from toxins by the blood–brain barrier. We also report the exon–intron structure of six Nav paralogs, the first such analysis for snake genes. Our results demonstrate that the molecular basis of adaptation may be both repeatable across members of a gene family and predictable based on functional considerations.