Conotoxins: discovery using new assays and  applications in the characterization  of pruriceptors in the mouse  dorsal root ganglion (drg)
Creators: name: Espino, Samuel Sindingan
Publisher: name: University of Utah
Year: 2018
Subjects: subject: Biological sciences
subject: FOS: Biological sciences
subject: Conotoxins
subject: Conus araneosus
subject: Conus aulicus
subject: DRG neurons
subject: NET
subject: Pruriceptors

description: Cone snails are predatory marine gastropods that use venom to capture prey. Components of the cone snail venom are small peptidic compounds called conotoxins which target ion channels, receptors, and transporters in the preyâ€™s nervous system.  Conotoxins are highly potent and specific towards their molecular target, thus, they are used as tools for the understanding of how the nervous system works. Moreover, conotoxins are also powerful leads for developing new drugs. A conotoxin, omega-MVIIA is now sold as the drug Prialt for the treatment of pain. Given the tremendous research and pharmacological applications of these compounds, it is thus important to pursue further research aimed at discovering novel conotoxins. For this research I aimed to discover novel conotoxins using two biological assays that were not previously used in conotoxin discovery. One assay measured the activity of the norepinephrine transporter (NET) expressed in human embryonic kidney (HEK) cells to reuptake radiolabeled norepinephrine and another assay used calcium imaging of dissociated mouse dorsal root ganglion (DRG) neurons. Further, I focused my research on cone snail clades with limited toxinological information. Chapter 2 describes two conotoxins whose activities were identified using the NET assay. These conotoxins chi-AuID and chi-AoIC were isolated from the   venom of mollusk-hunters Conus aulicus and Conus araneosus, respectively. The conotoxin fv1a from Conus furvus another mollusk-hunting cone snail is also reported. The conotoxin fv1a does not inhibit NET, however, this conotoxin shows activity in vivo in mice and in calcium imaging of DRG neurons. The three conotoxins presented in Chapter 2 are homologous, however, they do not have the same pharmacological property. Thus, a comparison of the sequences of chi-AuID, chi-AoIC, and fv1a allowed for the identification of amino acids important for NET inhibition. Chapter 3 describes glycine-rich conotoxins identified from the venom of worm-hunting snails in the Virgiconus clade. vi6a, the first conotoxin identified in this group, was purified from the venom of Conus virgo using calcium imaging. This conotoxin elicited an excitatory behavior in mice when injected intracranially (IC) and intraperitoneally (IP). Conotoxins homologous to vi6a were further identified from Conus terebra and Conus kintoki using molecular biology techniques. Interestingly, C. virgo expresses two additional conotoxins homologous to vi6a.  Chapter 4 describes the characterization of pruriceptors in the mouse DRG that are responsive to histamine and chloroquine. Three major populations of neurons were identified and these populations were further characterized using various pharmacological agents to identify the constellation of ion channels and receptors expressed in the membrane of these neurons. Using the conotoxin mu-PIIIA, the expression of Nav1.7 and Nav1.8 in these pruriceptor populations were identified.