Disease relevance of Sh

• We have compared functional expression of the Drosophila Shaker H4 potassium channel in stable insect cell lines and in baculovirus-infected insect cells, using three different baculovirus promoters [1].
• To modify excitability by gene transfer, we created a recombinant adenovirus designed to overexpress a Drosophila Shaker potassium channel (AdShK) [2].
• We constructed a recombinant baculovirus, A. californica nuclear polyhedrosis virus, containing the Drosophila Shaker H4 K+ channel cDNA under control of the polyhedrin promoter [3].
• Expression of Drosophila Shaker potassium channels in mammalian cells infected with recombinant vaccinia virus [4].
• However, voltage-dependent Drosophila Shaker H4 K+ channels and Escherichia coli beta-galactosidase were expressed efficiently in all four cell types with VV vectors [5].

Psychiatry related information on Sh

• Genetic analysis of oxygen defense mechanisms in Drosophila melanogaster and identification of a novel behavioural mutant with a Shaker phenotype [6].
• We show that mns flies perform normally in a number of tasks, have preserved sleep homeostasis, but are not impaired by sleep deprivation [7].

High impact information on Sh

• The Drosophila Shaker (Sh) gene appears to encode a type of voltage-sensitive potassium (K+) channel called the A channel [8].
• We studied the role of the prototypical inactivating K+ conductance, Shaker, in Drosophila photoreceptors by recording intracellularly from wild-type and Shaker mutant photoreceptors [9].
• Multiple potassium-channel components are produced by alternative splicing at the Shaker locus in Drosophila [10].
• Expression studies in frog oocytes confirm that Shaker encodes a component of a potassium channel (the A channel) that conducts a fast transient potassium current [11].
• Here we report the isolation of complementary DNA clones from the mouse brain, the nucleotide sequences of which predict a protein remarkably similar to the Shaker protein [11].

Biological context of Sh

• Coexpression of Hk with Sh in Xenopus oocytes increases current amplitudes and changes the voltage dependence and kinetics of activation and inactivation, consistent with predicted functions of Hk in vivo [12].
• Synaptic transmission at the larval neuromuscular junction was increased in the qvr(1) mutant to the level of Sh mutants [13].
• The IA potassium channel is encoded by the Shaker (Sh) locus on the X chromosome of D.m. Because this channel may be one of those involved in volatile anesthetic action, we tested the sensitivity to isoflurane in three Shaker strains with different degrees of dysfunctional IA conductance (Shnull greater than ShKS133 greater than Sh5) [14].
• The IC50 values for Sh 5 (0.89), Sh133 (1.29), and Shnull (1.37) were significantly different from the wild type (0.56) [14].
• These findings suggest that an embryonic form of the Shaker IA channel is present during early myogenesis [15].

Anatomical context of Sh

• The temporal expression pattern of Sh in muscle was different from that in the central nervous system: muscle expression was transient and limited to mid-pupal stage while nervous system expression was observed throughout pupation, apparently peaking at the late-pupal stage [16].
• In particular, Shaker and slowpoke mutations enhanced the size and dynamics of the depolarization-induced Ca(2+) increase in the growth cone [17].
• Loss of Shaker currents increased the size of lamellipodia and the number of filopodia, structures associated with the actin cytoskeleton [17].
• By combining experiments with modelling, we show that the inactivation of Shaker K+ channels amplifies voltage signals and enables photoreceptors to use their voltage range more effectively [9].
• We also determined that the remaining delayed-rectifier current in cultured myocytes was carried by the Shaker ortholog SHK-1 [18].

Associations of Sh with chemical compounds

• We used Sh, slo and quinidine to remove specifically one or more K+ currents, so as to study physiological properties of these currents not previously characterized, and to examine their role in membrane excitability [19].
• In mature adults, selective elimination of IA either with Shaker (Sh) mutations or with 4-aminopyridine (4-AP), had no effect on spike duration or on the delay in excitation [20].
• Contrary to most potassium channel modulations, serotonin induced a reversible positive shift in the voltage operating range, of +30 mV for the Shaker channels and +10-14 mV for the delayed rectifier [21].
• In the Shaker channel, substitution of the gating hinge glycine with alanine and several other amino acids prevents pore opening, but the ability to open is recovered if a secondary glycine is introduced at an adjacent position [22].
• A proline at the gating hinge favors the open state of the Shaker channel as if by preventing inner helix straightening [22].

Physical interactions of Sh

• We have examined the effects of mutations in two loci--the Shaker complex and shaking-B-on the taste pathway of Drosophila melanogaster Meigen at the behavioural and electrophysiological levels [23].

Regulatory relationships of Sh

• The modulatory effects of the Hk beta subunit appeared to be specific to the Sh alpha subunit because other voltage- and Ca(2+)-activated K+ currents were not affected by Hk mutations [24].
• Similarly, the slowpoke mutation significantly suppresses the increased transmitter release conferred either by a mutation in Shaker or by application of 4-aminopyridine, which blocks the Shaker-encoded potassium channel at the Drosophila nerve terminal [25].
• Synthetic Reaper and Grim N terminus peptides induced fast inactivation of Shaker-type K+ channels when applied to the cytoplasmic side of the channel that was qualitatively similar to the inactivation produced by other K+ channel inactivation particles [26].

Other interactions of Sh

• However, in combinations of eag and Sh alleles, the basic pattern of innervation was altered [27].
• Fura-2-based imaging revealed in cultured embryonic neurons that the loss of either voltage-gated, inactivating Shaker channels or Ca(2+)-gated Slowpoke BK channels led to robust spontaneous Ca(2+) transients that preferentially occurred within the growth cone [17].
• In muscles, a genetic mutation of Shab removes virtually all the whole cell delayed rectifier current (IK), while leaving unaltered the transient A-current encoded by the Shaker gene [28].
• In contrast, we show that Shal is as important in these neuronal cell bodies as Shaker is in muscles [29].
• Shaw encodes a 42 pS noninactivating channel distinctive for its extremely low voltage sensitivity; Shaw channels have a total equivalent gating charge of 0.90 e- charges, in sharp contrast to 7 e- reported for Shaker channels [29].

Analytical, diagnostic and therapeutic context of Sh

• Recombinational dissection of the ShrK0120 strain of Drosophila melanogaster demonstrated that its extremely prolonged neuromuscular transmission, a defect qualitatively different from other Sh alleles, results from a synergistic interaction with a second site mutation [30].
• In whole-cell recordings of photoreceptors, rapidly inactivating Shaker channels are characterized by a conspicuously negative voltage operating range; together with a delayed rectifier, these channels are specifically modulated by the putative efferent neurotransmitter serotonin [21].
• To identify the molecular basis of these alterations, Sh transcript sequences were amplified using the polymerase chain reaction after reverse transcription of mutant RNA [31].
• However, RKShIIIA cannot be assigned to either of the two known classes of Sh-family genes in mammals based on sequence analysis [32].
• Site-directed mutagenesis of the S4 sequence of the Shaker potassium channel and electrophysiological analysis suggest that voltage-dependent activation involves the S4 sequence but is not solely due to electrostatic interactions [33].

References