Generation and characterization of new alleles of quiver (qvr) that encodes an extracellular modulator of the Shaker potassium channel.

Our earlier genetic screen uncovered a paraquat-sensitive leg-shaking mutant quiver ¹ (qvr ¹ ), whose gene product interacts with the Shaker (Sh) K ⁺ channel. We also mapped the qvr locus to EY04063 and noticed altered day-night activity patterns in these mutants. Such circadian behavioral defects were independently reported by another group, who employed the qvr ¹ allele we supplied them, and attributed the extreme restless phenotype of EY04063 to the qvr gene. However, their report adopted a new noncanonical gene name sleepless (sss) for qvr. In addition to qvr ¹ and qvr ^EY , our continuous effort since the early 2000s generated a number of novel recessive qvr alleles, including ethyl methanesulfonate (EMS)-induced mutations qvr ² and qvr ³ , and P-element excision lines qvr ^ip6 (imprecise jumpout), qvr ^rv7 , and qvr ^rv9 (revertants) derived from qvr ^EY . Distinct from the original intron-located qvr ¹ allele that generates abnormal-sized mRNAs, qvr ² , and qvr ³ had their lesion sites in exons 6 and 7, respectively, producing nearly normal-sized mRNA products. A set of RNA-editing sites are nearby the lesion sites of qvr ³ and qvr ^EY on exon 7. Except for the revertants, all qvr alleles display a clear ether-induced leg-shaking phenotype just like Sh, and weakened climbing abilities to varying degrees. Unlike Sh, all shaking qvr alleles (except for qvr ^f01257 ) displayed a unique activity-dependent enhancement in excitatory junction potentials (EJPs) at larval neuromuscular junctions (NMJs) at very low stimulus frequencies, with qvr ^EY displaying the largest EJP and more significant NMJ overgrowth than other alleles. Our detailed characterization of a collection of qvr alleles helps to establish links between novel molecular lesions and different behavioral and physiological consequences, revealing how modifications of the qvr gene lead to a wide spectrum of phenotypes, including neuromuscular hyperexcitability, defective motor ability and activity-rest cycles.