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 quiver¹ (qvr¹), 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 qvr¹ 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 qvr¹ and qvr^EY, our continuous effort since the early 2000s generated a number of novel recessive qvr alleles, including ethyl methanesulfonate (EMS)-induced mutations qvr² and qvr³, 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 qvr¹ allele that generates abnormal-sized mRNAs, qvr², and qvr³ 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 qvr³ 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.