From behavior to genes, and back again

• Main Author: Low, Sean E
• Format: Dissertation
• Language: English
• Published: ProQuest Dissertations & Theses 01-01-2008
• Subjects: Neurosciences
• ISBN: 054981860X; 9780549818601

The aim of this thesis was to use forward and reverse genetics to explore the contribution of unknown and known genes to the touch-evoked escape behaviors of zebrafish (Danio rerio). A forward genetic screen identified two mutants that displayed abnormal touch-evoked escape behaviors. The first mutant touchdown (tdo) lacked sensitivity to light touch, but responded to noxious stimuli. tdo mutants were shown to result from mutations in the gene encoding for TRPM7, an ion channel with an attached kinase. A combination of electrophysiological and molecular techniques revealed that ion channel function was sufficient to restore sensitivity to light touch within excitable mechanosensitive neurons. Therefore TRPM7 is a candidate for a vertebrate mechanoreceptor responsible for sensitivity to light touch. The second mutant identified from our forward genetic screen non-active (nav) initiated escape contractions, but failed to swim in response to touch. nav mutants were shown to result from mutations in the gene encoding Navl.6 that abolished channel activity. Electrophysiological recordings revealed that Nav1.6 is required to turn on a locomotor network capable of generating rudimentary swimming. Furthermore the requirement of Nav1.6 to turn this network might be its contribution of a persistent sodium current which is known to facilitate repetitive firing in other neurons. Finally the cloning and characterization of the ATP-gated P2X receptor subunits P2X 1 through P2X5.2 from zebrafish demonstrated that two subunits (P2X1 and P2X5.1) form functional homomeric receptors in contrast to previous reports. The use of reverse genetics (antisense knockdown) allowed the rejection of the hypothesis that signaling through P2X receptors is essential for myogenesis.