The SLO-1 BK channel of Caenorhabditis elegans is critical for muscle function and is involved in dystrophin-dependent muscle dystrophy

Wnt-Ror-Dvl signalling and the dystrophin complex organize planar-polarized membrane compartments in C. elegans muscles

Cell polarity mechanisms allow the formation of specialized membrane domains with unique protein compositions, signalling properties, and functional characteristics. By analyzing the localization of potassium channels and proteins belonging to the dystrophin-associated protein complex, we reveal the existence of distinct planar-polarized membrane compartments at the surface of C. elegans muscle cells. We find that muscle polarity is controlled by a non-canonical Wnt signalling cascade involving the ligand EGL-20/Wnt, the receptor CAM-1/Ror, and the intracellular effector DSH-1/Dishevelled. Interestingly, classical planar cell polarity proteins are not required for this process. Using time-resolved protein degradation, we demonstrate that -while it is essentially in place by the end of embryogenesis- muscle polarity is a dynamic state, requiring continued presence of DSH-1 throughout post-embryonic life. Our results reveal the unsuspected complexity of the C. elegans muscle membrane and establish a genetically tractable model system to study cellular polarity and membrane compartmentalization in vivo.

Caenorhabditis elegans as a Model System for Duchenne Muscular Dystrophy

The nematode worm Caenorhabditis elegans has been used extensively to enhance our understanding of the human neuromuscular disorder Duchenne Muscular Dystrophy (DMD). With new arising clinically relevant models, technologies and treatments, there is a need to reconcile the literature and collate the key findings associated with this model.

Mitochondrial hydrogen sulfide supplementation improves health in the C. elegans Duchenne muscular dystrophy model

Duchenne muscular dystrophy (DMD) is an X-linked recessive disorder characterized by progressive muscle degeneration and weakness due to mutations in the dystrophin gene. The symptoms of DMD share similarities with those of accelerated aging. Recently, hydrogen sulfide (H2S) supplementation has been suggested to modulate the effects of age-related decline in muscle function, and metabolic H2S deficiencies have been implicated in affecting muscle mass in conditions such as phenylketonuria. We therefore evaluated the use of sodium GYY4137 (NaGYY), a H2S-releasing molecule, as a possible approach for DMD treatment. Using the dys-1(eg33) Caenorhabditis elegans DMD model, we found that NaGYY treatment (100 µM) improved movement, strength, gait, and muscle mitochondrial structure, similar to the gold-standard therapeutic treatment, prednisone (370 µM). The health improvements of either treatment required the action of the kinase JNK-1, the transcription factor SKN-1, and the NAD-dependent deacetylase SIR-2.1. The transcription factor DAF-16 was required for the health benefits of NaGYY treatment, but not prednisone treatment. AP39 (100 pM), a mitochondria-targeted H2S compound, also improved movement and strength in the dys-1(eg33) model, further implying that these improvements are mitochondria-based. Additionally, we found a decline in total sulfide and H2S-producing enzymes in dystrophin/utrophin knockout mice. Overall, our results suggest that H2S deficit may contribute to DMD pathology, and rectifying/overcoming the deficit with H2S delivery compounds has potential as a therapeutic approach to DMD treatment.

Physical exertion exacerbates decline in the musculature of an animal model of Duchenne muscular dystrophy

Duchenne muscular dystrophy (DMD) is a genetic disorder caused by loss of the protein dystrophin. In humans, DMD has early onset, causes developmental delays, muscle necrosis, loss of ambulation, and death. Current animal models have been challenged by their inability to model the early onset and severity of the disease. It remains unresolved whether increased sarcoplasmic calcium observed in dystrophic muscles follows or leads the mechanical insults caused by the muscle's disrupted contractile machinery. This knowledge has important implications for patients, as potential physiotherapeutic treatments may either help or exacerbate symptoms, depending on how dystrophic muscles differ from healthy ones. Recently we showed how burrowing dystrophic (dys-1) C. elegans recapitulate many salient phenotypes of DMD, including loss of mobility and muscle necrosis. Here, we report that dys-1 worms display early pathogenesis, including dysregulated sarcoplasmic calcium and increased lethality. Sarcoplasmic calcium dysregulation in dys-1 worms precedes overt structural phenotypes (e.g., mitochondrial, and contractile machinery damage) and can be mitigated by reducing calmodulin expression. To learn how dystrophic musculature responds to altered physical activity, we cultivated dys-1 animals in environments requiring high intensity or high frequency of muscle exertion during locomotion. We find that several muscular parameters (e.g., size) improve with increased activity. However, longevity in dystrophic animals was negatively associated with muscular exertion, regardless of effort duration. The high degree of phenotypic conservation between dystrophic worms and humans provides a unique opportunity to gain insight into the pathology of the disease as well as the initial assessment of potential treatment strategies.

Calnexin revealed as an ether-a-go-go chaperone by getting mutant worms up and going

Pierce examines new work revealing that calnexin controls the biogenesis of ERG-type K⁺ channels in Caenorhabditis elegans.

The role of ion channels in cell excitability was first revealed in a series of voltage clamp experiments by Hodgkin and Huxley in the 1950s. However, it was not until the 1970s that patch-clamp recording ushered in a revolution that allowed physiologists to witness how ion channels flicker open and closed at angstrom scale and with microsecond resolution. The unexpectedly tight seal made by the patch pipette in the whole-cell configuration later allowed molecular biologists to suck up the insides of identified cells to unveil their unique molecular contents. By refining these techniques, researchers have scrutinized the surface and contents of excitable cells in detail over the past few decades. However, these powerful approaches do not discern which molecules are responsible for the dynamic control of the genesis, abundance, and subcellular localization of ion channels. In this dark territory, teams of unknown and poorly understood molecules guide specific ion channels through translation, folding, and modification, and then they shuttle them toward and away from distinct membrane domains via different subcellular routes. A central challenge in understanding these processes is the likelihood that these diverse regulatory molecules may be specific to ion channel subtypes, cell types, and circumstance. In work described in this issue, Bai et al. (2018. J. Gen. Physiol.https://doi.org/10.1085/jgp.201812025) begin to shed light on the biogenesis of UNC-103, a K⁺ channel found in Caenorhabditis elegans.

Biochemical and Functional Interplay Between Ion Channels and the Components of the Dystrophin-Associated Glycoprotein Complex

Dystrophin is a cytoskeleton-linked membrane protein that binds to a larger multiprotein assembly called the dystrophin-associated glycoprotein complex (DGC). The deficiency of dystrophin or the components of the DGC results in the loss of connection between the cytoskeleton and the extracellular matrix with significant pathophysiological implications in skeletal and cardiac muscle as well as in the nervous system. Although the DGC plays an important role in maintaining membrane stability, it can also be considered as a versatile and flexible molecular complex that contribute to the cellular organization and dynamics of a variety of proteins at specific locations in the plasma membrane. This review deals with the role of the DGC in transmembrane signaling by forming supramolecular assemblies for regulating ion channel localization and activity. These interactions are relevant for cell homeostasis, and its alterations may play a significant role in the etiology and pathogenesis of various disorders affecting muscle and nerve function.

BKIP-1, an auxiliary subunit critical to SLO-1 function, inhibits SLO-2 potassium channel in vivo

Auxiliary subunits are often needed to tailor K⁺ channel functional properties and expression levels. Many auxiliary subunits have been identified for mammalian Slo1, a high-conductance K⁺ channel gated by voltage and Ca²⁺. Experiments with heterologous expression systems show that some of the identified Slo1 auxiliary subunits can also regulate other Slo K⁺ channels. However, it is unclear whether a single auxiliary subunit may regulate more than one Slo channel in native tissues. BKIP-1, an auxiliary subunit of C. elegans SLO-1, facilitates SLO-1 membrane trafficking and regulates SLO-1 function in neurons and muscle cells. Here we show that BKIP-1 also serves as an auxiliary subunit of C. elegans SLO-2, a high-conductance K⁺ channel gated by membrane voltage and cytosolic Cl⁻ and Ca²⁺. Comparisons of whole-cell and single-channel SLO-2 currents in native neurons and muscle cells between worm strains with and without BKIP-1 suggest that BKIP-1 reduces chloride sensitivity, activation rate, and single-channel open probability of SLO-2. Bimolecular fluorescence complementation assays indicate that BKIP-1 interacts with SLO-2 carboxyl terminal. Thus, BKIP-1 may serve as an auxiliary subunit of SLO-2. BKIP-1 appears to be the first example that a single auxiliary subunit exerts opposite effects on evolutionarily related channels in the same cells.

De novo analysis of the transcriptome of Pratylenchus zeae to identify transcripts for proteins required for structural integrity, sensation, locomotion and parasitism

The root lesion nematode Pratylenchus zeae, a migratory endoparasite, is an economically important pest of major crop plants (e.g. cereals, sugarcane). It enters host roots, migrates through root tissues and feeds from cortical cells, and defends itself against biotic and abiotic stresses in the soil and in host tissues. We report de novo sequencing of the P. zeae transcriptome using 454 FLX, and the identification of putative transcripts encoding proteins required for movement, response to stimuli, feeding and parasitism. Sequencing generated 347,443 good quality reads which were assembled into 10,163 contigs and 139,104 singletons: 65% of contigs and 28% of singletons matched sequences of free-living and parasitic nematodes. Three-quarters of the annotated transcripts were common to reference nematodes, mainly representing genes encoding proteins for structural integrity and fundamental biochemical processes. Over 15,000 transcripts were similar to Caenorhabditis elegans genes encoding proteins with roles in mechanical and neural control of movement, responses to chemicals, mechanical and thermal stresses. Notably, 766 transcripts matched parasitism genes employed by both migratory and sedentary endoparasites in host interactions, three of which hybridized to the gland cell region, suggesting that they might be secreted. Conversely, transcripts for effectors reported to be involved in feeding site formation by sedentary endoparasites were conspicuously absent. Transcripts similar to those encoding some secretory-excretory products at the host interface of Brugia malayi, the secretome of Meloidogyne incognita and products of gland cells of Heterodera glycines were also identified. This P. zeae transcriptome provides new information for genome annotation and functional analysis of possible targets for control of pratylenchid nematodes.

The Cyclooctadepsipeptide Anthelmintic Emodepside Differentially Modulates Nematode, Insect and Human Calcium-Activated Potassium (SLO) Channel Alpha Subunits

The anthelmintic emodepside paralyses adult filarial worms, via a mode of action distinct from previous anthelmintics and has recently garnered interest as a new treatment for onchocerciasis. Whole organism data suggest its anthelmintic action is underpinned by a selective activation of the nematode isoform of an evolutionary conserved Ca²⁺-activated K⁺ channel, SLO-1. To test this at the molecular level we compared the actions of emodepside at heterologously expressed SLO-1 alpha subunit orthologues from nematode (Caenorhabditis elegans), Drosophila melanogaster and human using whole cell voltage clamp. Intriguingly we found that emodepside modulated nematode (Ce slo-1), insect (Drosophila, Dm slo) and human (hum kcnma1)SLO channels but that there are discrete differences in the features of the modulation that are consistent with its anthelmintic efficacy. Nematode SLO-1 currents required 100 μM intracellular Ca²⁺ and were strongly facilitated by emodepside (100 nM; +73.0 ± 17.4%; n = 9; p<0.001). Drosophila Slo currents on the other hand were activated by emodepside (10 μM) in the presence of 52 nM Ca²⁺ but were inhibited in the presence of 290 nM Ca²⁺ and exhibited a characteristic loss of rectification. Human Slo required 300nM Ca²⁺ and emodepside transiently facilitated currents (100nM; +33.5 ± 9%; n = 8; p<0.05) followed by a sustained inhibition (-52.6 ± 9.8%; n = 8; p<0.001). This first cross phyla comparison of the actions of emodepside at nematode, insect and human channels provides new mechanistic insight into the compound’s complex modulation of SLO channels. Consistent with whole organism behavioural studies on C. elegans, it indicates its anthelmintic action derives from a strong activation of SLO current, not observed in the human channel. These data provide an important benchmark for the wider deployment of emodepside as an anthelmintic treatment.

Filarial diseases affect an estimated 200 million people and the Drugs for Neglected Diseases initiative (DNDi) has identified development of macrofilaricidal drugs as a priority. Emodepside, currently used in companion animals, paralyses adult filarial worms and may address this unmet need for human medicine. Its receptor is an evolutionary conserved Ca²⁺-activated K⁺ channel, SLO-1. In this paper we address an important knowledge gap in terms of understanding the interaction of emodepside with its target receptor SLO-1 in nematodes in comparison to the human orthologue KCNMA1 and provide the first cross phyla analysis of the interaction of emodepside with slo channels, in nematode, insect and human. Intriguingly, this shows that emodepside modulates slo/BK currents from heterologously expressed channels from all three organisms, however there are discrete differences in the feature of modulation; only the nematode channel exhibits a sustained facilitation by emodepside. This is consistent with the effects of emodepside on C. elegans behaviour and indicates that this differential action of emodepside on the nematode channel likely underlies its potent anthelmintic effects. These data provide an important benchmark for the wider deployment of emodepside as an anthelmintic treatment.

SLO-2 potassium channel is an important regulator of neurotransmitter release in Caenorhabditis elegans

Slo2 channels are prominent K(+) channels in mammalian neurons but their physiological functions are not well understood. Here we investigate physiological functions and regulation of the Caenorhabditis elegans homologue SLO-2 in motor neurons through electrophysiological analyses of wild-type and mutant worms. We find that SLO-2 is the primary K(+) channel conducting delayed outward current in cholinergic motor neurons, and one of two K(+) channels with this function in GABAergic motor neurons. Loss-of-function mutation of slo-2 increases the duration and charge transfer rate of spontaneous postsynaptic current bursts at the neuromuscular junction, which are physiological signals used by motor neurons to control muscle cells, without altering postsynaptic receptor sensitivity. SLO-2 activity in motor neurons depends on Ca(2+) entry through EGL-19, an L-type voltage-gated Ca(2+) channel (CaV1), but not on other proteins implicated in either Ca(2+) entry or intracellular Ca(2+) release. Thus, SLO-2 is functionally coupled with CaV1 and regulates neurotransmitter release.

CLHM-1 is a functionally conserved and conditionally toxic Ca2+-permeable ion channel in Caenorhabditis elegans

Disruption of neuronal Ca(2+) homeostasis contributes to neurodegenerative diseases through mechanisms that are not fully understood. A polymorphism in CALHM1, a recently described ion channel that regulates intracellular Ca(2+) levels, is a possible risk factor for late-onset Alzheimer's disease. Since there are six potentially redundant CALHM family members in humans, the physiological and pathophysiological consequences of CALHM1 function in vivo remain unclear. The nematode Caenorhabditis elegans expresses a single CALHM1 homolog, CLHM-1. Here we find that CLHM-1 is expressed at the plasma membrane of sensory neurons and muscles. Like human CALHM1, C. elegans CLHM-1 is a Ca(2+)-permeable ion channel regulated by voltage and extracellular Ca(2+). Loss of clhm-1 in the body-wall muscles disrupts locomotory kinematics and biomechanics, demonstrating that CLHM-1 has a physiologically significant role in vivo. The motility defects observed in clhm-1 mutant animals can be rescued by muscle-specific expression of either C. elegans CLHM-1 or human CALHM1, suggesting that the function of these proteins is conserved in vivo. Overexpression of either C. elegans CLHM-1 or human CALHM1 in neurons is toxic, causing degeneration through a necrotic-like mechanism that is partially Ca(2+) dependent. Our data show that CLHM-1 is a functionally conserved ion channel that plays an important but potentially toxic role in excitable cell function.

Effects of manipulating slowpoke calcium-dependent potassium channel expression on rhythmic locomotor activity in Drosophila larvae

Rhythmic motor behaviors are generated by networks of neurons. The sequence and timing of muscle contractions depends on both synaptic connections between neurons and the neurons' intrinsic properties. In particular, motor neuron ion currents may contribute significantly to motor output. Large conductance Ca(2+)-dependent K(+) (BK) currents play a role in action potential repolarization, interspike interval, repetitive and burst firing, burst termination and interburst interval in neurons. Mutations in slowpoke (slo) genes encoding BK channels result in motor disturbances. This study examined the effects of manipulating slo channel expression on rhythmic motor activity using Drosophila larva as a model system. Dual intracellular recordings from adjacent body wall muscles were made during spontaneous crawling-related activity in larvae expressing a slo mutation or a slo RNA interference construct. The incidence and duration of rhythmic activity in slo mutants were similar to wild-type control animals, while the timing of the motor pattern was altered. slo mutants showed decreased burst durations, cycle durations, and quiescence intervals, and increased duty cycles, relative to wild-type. Expressing slo RNAi in identified motor neurons phenocopied many of the effects observed in the mutant, including decreases in quiescence interval and cycle duration. Overall, these results show that altering slo expression in the whole larva, and specifically in motor neurons, changes the frequency of crawling activity. These results suggest an important role for motor neuron intrinsic properties in shaping the timing of motor output.

Current drug targets for helminthic diseases

More than 2 billion people are infected with helminth parasites across the globe. The burgeoning drug resistance against current anthelmintics in parasitic worms of humans and livestock requires urgent attention to tackle these recalcitrant worms. This review focuses on the advancements made in the area of helminth drug target discovery especially from the last few couple of decades. It highlights various approaches made in this field and enlists the potential drug targets currently being pursued to target economically important helminth species both from human as well as livestock to combat disease pathology of schistosomiasis, onchocerciasis, lymphatic filariasis, and other important macroparasitic diseases. Research in the helminths study is trending to identify potential and druggable targets through genomic, proteomic, biochemical, biophysical, in vitro experiments, and in vivo experiments in animal models. The availability of major helminths genome sequences and the subsequent availability of genome-scale functional datasets through in silico search and prioritization are expected to guide the experimental work necessary for target-based drug discovery. Organized and documented list of drug targets from various helminths of economic importance have been systematically covered in this review for further exploring their use and applications, which can give physicians and veterinarians effective drugs in hand to enable them control worm infections.

Direct molecular interaction of caveolin-3 with KCa1.1 channel in living HEK293 cell expression system

Caveolin family is supposed to be essential molecules for the formation of not only caveola structure on cell membrane but also functional molecular complexes in them with direct and/or indirect interaction with other membrane and/or submembrane associated proteins. The direct coupling of caveolin-1 (cav1) with large conductance Ca(2+)-activated K(+) channel, KCa1.1 has been established in several types of cells and in expression system as well. The possible interaction of caveolin-3 (cav3), which shows expression in some differential tissues from cav1, with KCa1.1 remains to be determined. In the present study, the density of KCa1.1 current expressed in HEK293 cells was significantly reduced by the co-expression of cav3, as well as cav1. The co-localization and direct interaction of GFP- or CFP-labeled cav3 (GFP/CFP-cav3) with YFP- or mCherry-labeled KCa1.1 (KCa1.1-YFP/mCherry) were clearly demonstrated by single molecular image analyses using total internal reflection fluorescence (TIRF) microscopy and fluorescence resonance energy transfer (FRET) analyses with acceptor photobleaching method. The deletion of suggested cav1-binding motif in C terminus region of KCa1.1 (KCa1.1ΔCB-YFP) resulted in the marked decrease in cell surface expression, co-localization and FRET efficiency with CFP-cav3 and CFP-cav1. The FLAG-KCa1.1 co-immunoprecipitation with GFP-cav3 or GFP-cav1 also supported their direct molecular interaction. These results strongly suggest that cav3 possesses direct interaction with KCa1.1, presumably at the same domain for cav1 binding. This interaction regulates KCa1.1 expression to cell surface and the formation of functional molecular complex in caveolae in living cells.

Interaction of α-catulin with dystrobrevin contributes to integrity of dystrophin complex in muscle

The dystrophin complex is a multimolecular membrane-associated protein complex whose defects underlie many forms of muscular dystrophy. The dystrophin complex is postulated to function as a structural element that stabilizes the cell membrane by linking the contractile apparatus to the extracellular matrix. A better understanding of how this complex is organized and localized will improve our knowledge of the pathogenic mechanisms of diseases that involve the dystrophin complex. In a Caenorhabditis elegans genetic study, we demonstrate that CTN-1/α-catulin, a cytoskeletal protein, physically interacts with DYB-1/α-dystrobrevin (a component of the dystrophin complex) and that this interaction is critical for the localization of the dystrophin complex near dense bodies, structures analogous to mammalian costameres. We further show that in mouse α-catulin is localized at the sarcolemma and neuromuscular junctions and interacts with α-dystrobrevin and that the level of α-catulin is reduced in α-dystrobrevin-deficient mouse muscle. Intriguingly, in the skeletal muscle of mdx mice lacking dystrophin, we discover that the expression of α-catulin is increased, suggesting a compensatory role of α-catulin in dystrophic muscle. Together, our study demonstrates that the interaction between α-catulin and α-dystrobrevin is evolutionarily conserved in C. elegans and mammalian muscles and strongly suggests that this interaction contributes to the integrity of the dystrophin complex.

The atypical calpains: evolutionary analyses and roles in Caenorhabditis elegans cellular degeneration

The calpains are physiologically important Ca²⁺-activated regulatory proteases, which are divided into typical or atypical sub-families based on constituent domains. Both sub-families are present in mammals, but our understanding of calpain function is based primarily on typical sub-family members. Here, we take advantage of the model organism Caenorhabditis elegans, which expresses only atypical calpains, to extend our knowledge of the phylogenetic evolution and function of calpains. We provide evidence that a typical human calpain protein with a penta EF hand, detected using custom profile hidden Markov models, is conserved in ancient metazoans and a divergent clade. These analyses also provide evidence for the lineage-specific loss of typical calpain genes in C. elegans and Ciona, and they reveal that many calpain-like genes lack an intact catalytic triad. Given the association between the dysregulation of typical calpains and human degenerative pathologies, we explored the phenotypes, expression profiles, and consequences of inappropriate reduction or activation of C. elegans atypical calpains. These studies show that the atypical calpain gene, clp-1, contributes to muscle degeneration and reveal that clp-1 activity is sensitive to genetic manipulation of [Ca²⁺]_i. We show that CLP-1 localizes to sarcomeric sub-structures, but is excluded from dense bodies (Z-disks). We find that the muscle degeneration observed in a C. elegans model of dystrophin-based muscular dystrophy can be suppressed by clp-1 inactivation and that nemadipine-A inhibition of the EGL-19 calcium channel reveals that Ca²⁺ dysfunction underlies the C. elegans MyoD model of myopathy. Taken together, our analyses highlight the roles of calcium dysregulation and CLP-1 in muscle myopathies and suggest that the atypical calpains could retain conserved roles in myofilament turnover.

Calpains are calcium activated non-lysosomal proteases that cleave proteins with exquisite selectivity. Proteins can be activated by calpain cleavage, because they are released from inhibitory constraints, or they can be targeted for further degradation to facilitate their normal physiological turnover or to promote cellular remodelling. Inappropriate calpain activity can lead to degenerative pathologies and cancers. Our understanding of calpain function is based primarily on typical calpains, which carry EF hand motifs that bind Ca²⁺ or mediate dimerization; however, typical and atypical calpains, which lack EF hand motifs, are both present in mammals. Hence, any therapeutic intervention designed to suppress degenerative conditions, particularly those caused by elevated Ca²⁺ levels, should also consider the potential involvement of atypical calpains. We have taken advantage of the model organism C. elegans, which only encodes atypical calpain proteins, to gain an understanding of the evolution and activities of these proteins. We show that the CLP-1 atypical calpain is normally expressed in muscle and localizes to sarcomeric sub-structures. We find that CLP-1 contributes to the muscle degeneration observed in a model of Duchenne muscular dystrophy. Our studies also highlight the importance of calcium dysregulation in promoting CLP-1 activity and muscle degeneration.

Dystrobrevin controls neurotransmitter release and muscle Ca(2+) transients by localizing BK channels in Caenorhabditis elegans

Dystrobrevin is a major component of a dystrophin-associated protein complex. It is widely expressed in mammalian tissues, including the nervous system, in which it is localized to the presynaptic nerve terminal with unknown function. In a genetic screen for suppressors of a lethargic phenotype caused by a gain-of-function isoform of SLO-1 in Caenorhabditis elegans, we isolated multiple loss-of-function (lf) mutants of the dystrobrevin gene dyb-1.dyb-1(lf) phenocopied slo-1(lf), causing increased neurotransmitter release at the neuromuscular junction, increased frequency of Ca(2+) transients in body-wall muscle, and abnormal locomotion behavior. Neuron- and muscle-specific rescue experiments suggest that DYB-1 is required for SLO-1 function in both neurons and muscle cells. DYB-1 colocalized with SLO-1 at presynaptic sites in neurons and dense body regions in muscle cells, and dyb-1(lf) caused SLO-1 mislocalization in both types of cells without altering SLO-1 protein level. The neuronal phenotypes of dyb-1(lf) were partially rescued by mouse α-dystrobrevin-1. These observations revealed novel functions of the BK channel in regulating muscle Ca(2+) transients and of dystrobrevin in controlling neurotransmitter release and muscle Ca(2+) transients by localizing the BK channel.

Electrophysiological methods for Caenorhabditis elegans neurobiology

Patch-clamp electrophysiology is a technique of choice for the biophysical analysis of the function of nerve, muscle, and synapse in Caenorhabditis elegans nematodes. Considerable technical progress has been made in C. elegans electrophysiology in the decade since the initial publication of this technique. Today, most, if not all, electrophysiological studies that can be done in larger animal preparations can also be done in C. elegans. This chapter has two main goals. The first is to present to a broad audience the many techniques available for patch-clamp analysis of neurons, muscles, and synapses in C. elegans. The second is to provide a methodological introduction to the techniques for patch clamping C. elegans neurons and body-wall muscles in vivo, including emerging methods for optogenetic stimulation coupled with postsynaptic recording. We also present samples of the cell-intrinsic and postsynaptic ionic currents that can be measured in C. elegans nerves and muscles.

Cell excitability necessary for male mating behavior in Caenorhabditis elegans is coordinated by interactions between big current and ether-a-go-go family K(+) channels

Variations in K(+) channel composition allow for differences in cell excitability and, at an organismal level, provide flexibility to behavioral regulation. When the function of a K(+) channel is disrupted, the remaining K(+) channels might incompletely compensate, manifesting as abnormal organismal behavior. In this study, we explored how different K(+) channels interact to regulate the neuromuscular circuitry used by Caenorhabditis elegans males to protract their copulatory spicules from their tail and insert them into the hermaphrodite's vulva during mating. We determined that the big current K(+) channel (BK)/SLO-1 genetically interacts with ether-a-go-go (EAG)/EGL-2 and EAG-related gene/UNC-103 K(+) channels to control spicule protraction. Through rescue experiments, we show that specific slo-1 isoforms affect spicule protraction. Gene expression studies show that slo-1 and egl-2 expression can be upregulated in a calcium/calmodulin-dependent protein kinase II-dependent manner to compensate for the loss of unc-103 and conversely, unc-103 can partially compensate for the loss of SLO-1 function. In conclusion, an interaction between BK and EAG family K(+) channels produces the muscle excitability levels that regulate the timing of spicule protraction and the success of male mating behavior.

The dystrophin-associated protein complex maintains muscle excitability by regulating Ca(2+)-dependent K(+) (BK) channel localization

The dystrophin-associated protein complex (DAPC) consists of several transmembrane and intracellular scaffolding elements that have been implicated in maintaining the structure and morphology of the vertebrate neuromuscular junction (NMJ). Genetic linkage analysis has identified loss-of-function mutations in DAPC genes that give rise to degenerative muscular dystrophies. Although much is known about the involvement of the DAPC in maintaining muscle integrity, less is known about the precise contribution of the DAPC in cell signaling events. To better characterize the functional role of the DAPC at the NMJ, we used electrophysiology, immunohistochemistry, and fluorescent labeling to directly assess cholinergic synaptic transmission, ion channel localization, and muscle excitability in loss-of-function (lf) mutants of Caenorhabditis elegans DAPC homologues. We found that all DAPC mutants consistently display mislocalization of the Ca(2+)-gated K(+) channel, SLO-1, in muscle cells, while ionotropic acetylcholine receptor (AChR) expression and localization at the NMJ remained unaltered. Synaptic cholinergic signaling was also not significantly impacted across DAPC(lf) mutants. Consistent with these findings and the postsynaptic mislocalization of SLO-1, we observed an increase in muscle excitability downstream of cholinergic signaling. Based on our results, we conclude that the DAPC is not involved in regulating AChR architecture at the NMJ, but rather functions to control muscle excitability, in an activity-dependent manner, through the proper localization of SLO-1 channels.

Selective toxicity of the anthelmintic emodepside revealed by heterologous expression of human KCNMA1 in Caenorhabditis elegans

Emodepside is a resistance-breaking anthelmintic of a new chemical class, the cyclooctadepsipeptides. A major determinant of its anthelmintic effect is the calcium-activated potassium channel SLO-1. SLO-1 belongs to a family of channels that are highly conserved across the animal phyla and regulate neurosecretion, hormone release, muscle contraction, and neuronal network excitability. To investigate the selective toxicity of emodepside, we performed transgenic experiments in which the nematode SLO-1 channel was swapped for a mammalian ortholog, human KCNMA1. Expression of either the human channel or Caenorhabditis elegans slo-1 from the native slo-1 promoter in a C. elegans slo-1 functional null mutant rescued behavioral deficits that otherwise resulted from loss of slo-1 signaling. However, worms expressing the human channel were 10- to 100-fold less sensitive to emodepside than those expressing the nematode channel. Strains expressing the human KCNMA1 channel were preferentially sensitive to the mammalian channel agonists NS1619 and rottlerin. In the C. elegans pharyngeal nervous system, slo-1 is expressed in neurons, not muscle, and cell-specific rescue experiments have previously shown that emodepside inhibits serotonin-stimulated feeding by interfering with SLO-1 signaling in the nervous system. Here we show that ectopic overexpression of slo-1 in pharyngeal muscle confers sensitivity of the muscle to emodepside, consistent with a direct interaction of emodepside with the channel. Taken together, these data predict an emodepside-selective pharmacophore harbored by SLO-1. This has implications for the development of this drug/target interface for the treatment of helminth infections.

An alpha-catulin homologue controls neuromuscular function through localization of the dystrophin complex and BK channels in Caenorhabditis elegans

The large conductance, voltage- and calcium-dependent potassium (BK) channel serves as a major negative feedback regulator of calcium-mediated physiological processes and has been implicated in muscle dysfunction and neurological disorders. In addition to membrane depolarization, activation of the BK channel requires a rise in cytosolic calcium. Localization of the BK channel near calcium channels is therefore critical for its function. In a genetic screen designed to isolate novel regulators of the Caenorhabditis elegans BK channel, SLO-1, we identified ctn-1, which encodes an α-catulin homologue with homology to the cytoskeletal proteins α-catenin and vinculin. ctn-1 mutants resemble slo-1 loss-of-function mutants, as well as mutants with a compromised dystrophin complex. We determined that CTN-1 uses two distinct mechanisms to localize SLO-1 in muscles and neurons. In muscles, CTN-1 utilizes the dystrophin complex to localize SLO-1 channels near L-type calcium channels. In neurons, CTN-1 is involved in localizing SLO-1 to a specific domain independent of the dystrophin complex. Our results demonstrate that CTN-1 ensures the localization of SLO-1 within calcium nanodomains, thereby playing a crucial role in muscles and neurons.

Calcium ions are essential for many physiological processes, including neurosecretion and neuronal and muscle excitation. Paradoxically, abnormal accumulation of calcium ions is associated with cell death and has been documented as an early event in muscle and neural degenerative diseases. One mechanism to avoid detrimental calcium accumulation is to link the calcium increase with activation of calcium-dependent potassium ion channels, thereby reducing cell excitability and preventing further calcium influx. This negative feedback requires these potassium channels to be localized in close proximity to sites of calcium entry. In a Caenorhabditis elegans genetic screen, we identified α-catulin, known as a cytoskeletal regulatory protein in mammals, important for the localization of calcium-dependent potassium channels in both muscles and neurons. In muscle, α-catulin controls the localization of the dystrophin complex, a multimeric protein complex implicated in muscular dystrophy. The dystrophin complex in turn tethers the calcium-dependent potassium channels near calcium channels. In neurons, the α-catulin-mediated localization of the potassium channels is independent of the dystrophin complex. Lack of α-catulin results in mislocalization of the potassium channels, and in turn causes defects in neuromuscular function. Our results support the idea that cytoskeletal proteins function as anchor molecules that localize ion channels to specific cellular domains.

Non-apoptotic cell death in Caenorhabditis elegans

The simple nematode worm Caenorhabditis elegans has been instrumental in deciphering the molecular mechanisms underlying apoptosis. Beyond apoptosis, several paradigms of non-apoptotic cell death, either genetically or extrinsically triggered, have also been described in C. elegans. Remarkably, non-apoptotic cell death in worms and pathological cell death in humans share numerous key features and mechanistic aspects. Such commonalities suggest that similarly to apoptosis, non-apoptotic cell death mechanisms are also conserved, and render the worm a useful organism, in which to model and dissect human pathologies. Indeed, the genetic malleability and the sophisticated molecular tools available for C. elegans have contributed decisively to advance our understanding of non-apoptotic cell death. Here, we review the literature on the various types of non-apoptotic cell death in C. elegans and discuss the implications, relevant to pathological conditions in humans.

C. elegans models of neuromuscular diseases expedite translational research

The nematode Caenorhabditis elegans is a genetic model organism and the only animal with a complete nervous system wiring diagram. With only 302 neurons and 95 striated muscle cells, a rich array of mutants with defective locomotion and the facility for individual targeted gene knockdown by RNA interference, it lends itself to the exploration of gene function at nerve muscle junctions. With approximately 60% of human disease genes having a C. elegans homologue, there is growing interest in the deployment of lowcost, high-throughput, drug screens of nematode transgenic and mutant strains mimicking aspects of the pathology of devastating human neuromuscular disorders. Here we explore the contributions already made by C. elegans to our understanding of muscular dystrophies (Duchenne and Becker), spinal muscular atrophy, amyotrophic lateral sclerosis, Friedreich’s ataxia, inclusion body myositis and the prospects for contributions to other neuromuscular disorders. A bottleneck to low-cost, in vivo, large-scale chemical library screening for new candidate therapies has been rapid, automated, behavioural phenotyping. Recent progress in quantifying simple swimming (thrashing) movements is making such screening possible and is expediting the translation of drug candidates towards the clinic.

The dystrophin complex controls bk channel localization and muscle activity in Caenorhabditis elegans

Genetic defects in the dystrophin-associated protein complex (DAPC) are responsible for a variety of pathological conditions including muscular dystrophy, cardiomyopathy, and vasospasm. Conserved DAPC components from humans to Caenorhabditis elegans suggest a similar molecular function. C. elegans DAPC mutants exhibit a unique locomotory deficit resulting from prolonged muscle excitation and contraction. Here we show that the C. elegans DAPC is essential for proper localization of SLO-1, the large conductance, voltage-, and calcium-dependent potassium (BK) channel, which conducts a major outward rectifying current in muscle under the normal physiological condition. Through analysis of mutants with the same phenotype as the DAPC mutants, we identified the novel islo-1 gene that encodes a protein with two predicted transmembrane domains. We demonstrate that ISLO-1 acts as a novel adapter molecule that links the DAPC to SLO-1 in muscle. We show that a defect in either the DAPC or ISLO-1 disrupts normal SLO-1 localization in muscle. Consistent with observations that SLO-1 requires a high calcium concentration for full activation, we find that SLO-1 is localized near L-type calcium channels in muscle, thereby providing a mechanism coupling calcium influx with the outward rectifying current. Our results indicate that the DAPC modulates muscle excitability by localizing the SLO-1 channel to calcium-rich regions of C. elegans muscle.

Dystrophin is a long rod-shaped protein that forms a complex with several membrane and cytoplasmic proteins in muscle. Genetic defects in components of this dystrophin complex are responsible for many forms of muscular dystrophy, including Duchenne muscular dystrophy. C. elegans possesses the dystrophin complex and mutations in its components cause muscular defects, indicating that the dystrophin complex has an evolutionary conserved role in muscle. Accumulating evidence in mammals indicates that dystrophic muscle exhibits an abnormal calcium homeostasis. It is not clear how defects in the dystrophin complex are linked to calcium homeostasis, however. In a C. elegans genetic study we found that a novel adaptor protein links the dystrophin complex to a calcium-sensitive potassium channel that mediates muscle inactivation. We further demonstrated that both the dystrophin complex and the adaptor protein localize the potassium channel in a close proximity to a muscle-activating calcium channel. This arrangement ensures that calcium increases accompanied by muscle activation are coupled to muscle inactivation. Defects in the dystrophin complex or the adaptor disrupt the localization of the potassium channel, thereby resulting in prolonged muscle activation and calcium ion increases. Our study provides a mechanism by which the dystrophin complex regulates cellular signaling and muscle excitability.

Loss of dystrophin and the microtubule-binding protein ELP-1 causes progressive paralysis and death of adult C. elegans

EMAP-like proteins (ELPs) are conserved microtubule-binding proteins that function during cell division and in the behavior of post-mitotic cells. In Caenorhabditis elegans, ELP-1 is broadly expressed in many cells and tissues including the touch receptor neurons and body wall muscle. Within muscle, ELP-1 is associated with a microtubule network that is closely opposed to the integrin-based adhesion sites called dense bodies. To examine ELP-1 function, we utilized an elp-1 RNA interference assay and screened for synthetic interactions with mutated adhesion site proteins. We reveal a synthetic lethal relationship between ELP-1 and the dystrophin-like protein, DYS-1. Reduction of ELP-1 in a dystrophin [dys-1(cx18)] mutant results in adult animals with motility defects, splayed and hypercontracted muscle with altered cholinergic signaling. Worms fill with vesicles, become flaccid, and die. We conclude that ELP-1 is a genetic modifier of a C. elegans model of muscular dystrophy.

Vascular amyloid alters astrocytic water and potassium channels in mouse models and humans with Alzheimer's disease

The neurovascular unit (NVU) comprises cerebral blood vessels and surrounding astrocytes, neurons, perivascular microglia and pericytes. Astrocytes associated with the NVU are responsible for maintaining cerebral blood flow and ionic and osmotic balances in the brain. A significant proportion of individuals with Alzheimer's disease (AD) have vascular amyloid deposits (cerebral amyloid angiopathy, CAA) that contribute to the heterogeneous nature of the disease. To determine whether NVU astrocytes are affected by the accumulation of amyloid at cerebral blood vessels we examined astrocytic markers in four transgenic mouse models of amyloid deposition. These mouse models represent mild CAA, moderate CAA with disease progression to tau pathology and neuron loss, severe CAA and severe CAA with disease progression to tau pathology and neuron loss. We found that CAA and disease progression both resulted in distinct NVU astrocytic changes. CAA causes a loss of apparent glial fibrillary acidic protein (GFAP)-positive astrocytic end-feet and loss of water channels (aquaporin 4) localized to astrocytic end feet. The potassium channels Kir4.1, an inward rectifying potassium channel, and BK, a calcium-sensitive large-conductance potassium channel, were also lost. The anchoring protein, dystrophin 1, is common to these channels and was reduced in association with CAA. Disease progression was associated with a phenotypic switch in astrocytes indicated by a loss of GFAP-positive cells and a gain of S100 beta-positive cells. Aquaporin 4, Kir4.1 and dystrophin 1 were also reduced in autopsied brain tissue from individuals with AD that also display moderate and severe CAA. Together, these data suggest that damage to the neurovascular unit may be a factor in the pathogenesis of Alzheimer's disease.

Dystrophin deficiency in Drosophila reduces lifespan and causes a dilated cardiomyopathy phenotype

A number of studies have been conducted recently on the model organism Drosophila to determine the function of genes involved in human disease, including those implicated in neurological disorders, cancer and metabolic and cardiovascular diseases. The simple structure and physiology of the Drosophila heart tube together with the available genetics provide a suitable in vivo assay system for studying cardiac gene functions. In our study, we focus on analysis of the role of dystrophin (Dys) in heart physiology. As in humans, the Drosophila dys gene encodes multiple isoforms, of which the large isoforms (DLPs) and a truncated form (Dp117) are expressed in the adult heart. Here, we show that the loss of dys function in the heart leads to an age-dependent disruption of the myofibrillar organization within the myocardium as well as to alterations in cardiac performance. dys RNAi-mediated knockdown in the mesoderm also shortens lifespan. Knockdown of all or deletion of the large isoforms increases the heart rate by shortening the diastolic intervals (relaxation phase) of the cardiac cycle. Morphologically, loss of the large DLPs isoforms causes a widening of the cardiac tube and a lower fractional shortening, a phenotype reminiscent of dilated cardiomyopathy. The dilated dys mutant phenotype was reversed by expressing a truncated mammalian form of dys (Dp116). Our results illustrate the utility of Drosophila as a model system to study dilated cardiomyopathy and other muscular-dystrophy-associated phenotypes.

Other model organisms for sarcomeric muscle diseases

Model organisms are vital to our understanding of human muscle biology and disease. The potential of the nematode Caenorhabditis elegans, the fruitfly, Drosophila melanogaster and the zebrafish, Danio rerio, as model genetic organisms for the study of human muscle disease is discussed by examining their muscle biology, muscle genetics and development. The powerful genetic tools available with each organism are outlined. It is concluded that these organisms have already demonstrated potential in facilitating the study of muscle disease and in screening for therapeutic agents.

DYC-1, a protein functionally linked to dystrophin in Caenorhabditis elegans is associated with the dense body, where it interacts with the muscle LIM domain protein ZYX-1

In Caenorhabditis elegans, mutations of the dystrophin homologue, dys-1, produce a peculiar behavioral phenotype (hyperactivity and a tendency to hypercontract). In a sensitized genetic background, dys-1 mutations also lead to muscle necrosis. The dyc-1 gene was previously identified in a genetic screen because its mutation leads to the same phenotype as dys-1, suggesting that the two genes are functionally linked. Here, we report the detailed characterization of the dyc-1 gene. dyc-1 encodes two isoforms, which are expressed in neurons and muscles. Isoform-specific RNAi experiments show that the absence of the muscle isoform, and not that of the neuronal isoform, is responsible for the dyc-1 mutant phenotype. In the sarcomere, the DYC-1 protein is localized at the edges of the dense body, the nematode muscle adhesion structure where actin filaments are anchored and linked to the sarcolemma. In yeast two-hybrid assays, DYC-1 interacts with ZYX-1, the homologue of the vertebrate focal adhesion LIM domain protein zyxin. ZYX-1 localizes at dense bodies and M-lines as well as in the nucleus of C. elegans striated muscles. The DYC-1 protein possesses a highly conserved 19 amino acid sequence, which is involved in the interaction with ZYX-1 and which is sufficient for addressing DYC-1 to the dense body. Altogether our findings indicate that DYC-1 may be involved in dense body function and stability. This, taken together with the functional link between the C. elegans DYC-1 and DYS-1 proteins, furthermore suggests a requirement of dystrophin function at this structure. As the dense body shares functional similarity with both the vertebrate Z-disk and the costamere, we therefore postulate that disruption of muscle cell adhesion structures might be the primary event of muscle degeneration occurring in the absence of dystrophin, in C. elegans as well as vertebrates.

SLO, SLO, quick, quick, slow: calcium-activated potassium channels as regulators of Caenorhabditis elegans behaviour and targets for anthelmintics

Large-conductance calcium and voltage-activated potassium channels, termed SLO-1 (or BK), are pivotal players in the regulation of cell excitability across the animal phyla. Furthermore, emerging evidence indicates that these channels are key mediators of a number of neuroactive drugs, including the most recent new anthelmintic, the cyclo-octadepsipeptide emodepside. Detailed reviews of the structure, function and pharmacology of BK channels have recently been provided (Salkoff et al. in Nat Rev Neurosci 7:921-931, 2006; Ghatta et al. in Pharmacol Ther 110:103-116, 2006) and therefore these aspects will only briefly be covered here. The purpose of this review is to discuss how SLO-1 channels might function as regulators of neural transmission and network activity. In particular, we focus on the role of SLO-1 in the regulation of Caenorhabditis elegans behaviour and highlight the role of this channel as an effector for pleiotropic actions of neuroactive drugs, including emodepside. On the premise that C. elegans is a 'model nematode' with respect to many aspects of neural function, the intention is that this might inform a broader understanding of the role of these channels in the nematodes and their potential as novel anthelmintic targets.

Muscular dystrophy associated mutations in caveolin-1 induce neurotransmission and locomotion defects in Caenorhabditis elegans

Mutations in human caveolin-3 are known to underlie a range of myopathies. The cav-1 gene of Caenorhabditis elegans is a homologue of human caveolin-3 and is expressed in both neurons and body wall muscles. Within the body wall muscle CAV-1 localises adjacent to neurons, most likely at the neuromuscular junction (NMJ). Using fluorescently tagged CAV-1 and pre- and post-synaptic markers we demonstrate that CAV-1 co-localises with UNC-63, a post-synaptic marker, but not with several pre-synaptic markers. To establish a model for human muscular dystrophies caused by dominant-negative mutations in caveolin-3 we created transgenic animals carrying versions of cav-1 with homologous mutations. These animals had increased sensitivity to levamisole, suggesting a role for cav-1 at the NMJ. Animals carrying a deletion in cav-1 show a similar sensitivity. Sensitivity to levamisole and locomotion were also perturbed in animals carrying a dominant-negative cav-1 and a mutation in dynamin, which is a protein known to interact with caveolins. Thus, indicating an interaction between CAV-1 and dynamin at the NMJ and/or in neurons.

The calcium-activated potassium channel, SLO-1, is required for the action of the novel cyclo-octadepsipeptide anthelmintic, emodepside, in Caenorhabditis elegans

The cyclo-octadepsipeptide anthelmintic, emodepside, has pleiotropic effects on the behaviour of the model genetic animal Caenorhabditis elegans: it inhibits locomotion, feeding, egg-laying and slows development. Previous studies on pharyngeal muscle indicated a role for latrophilin-dependent signalling and therefore prompted the suggestion that this is a common effector of this drug's actions. However, whilst a C. elegans functional null mutant for latrophilin (lat-1) is less sensitive to the effect of emodepside on the pharynx it remains sensitive to the inhibitory effects of emodepside on locomotion. Here we show that this is not due to functional redundancy between two C. elegans latrophilins, as the double mutant, lat-2, lat-1, also remains sensitive to the effects of emodepside on locomotion. Therefore, emodepside has latrophilin-independent effects. To define the molecular basis for this we performed a mutagenesis screen. We recovered nine alleles of slo-1, which encodes a Ca(2+)-activated K(+) channel. These mutants were highly resistant to the inhibitory effect of emodepside on both pharyngeal and locomotor activity. The slo-1 alleles are predicted to reduce or eliminate SLO-1 signalling, suggesting that emodepside may signal through a SLO-1-dependent pathway. The observation that gain-of-function slo-1 alleles phenocopy the effects of emodepside, but are not themselves emodepside hypersensitive, favours a model whereby emodepside directly acts through a SLO-1-dependent pathway. Tissue-specific genetic rescue experiments reveal that emodepside acts through SLO-1 expressed in either body wall muscle or in neurones to inhibit locomotion. In contrast, in the pharyngeal system, emodepside acts through SLO-1 in neurones, but not muscle, to inhibit feeding. These data further inform understanding of the mode of action of emodepside and suggest that emodepside causes inhibition of feeding via a neuronal SLO-1-dependent pathway which is facilitated by LAT-1 whilst it signals through a latrophilin-independent, SLO-1-dependent pathway, in either neurones or body wall muscle, to inhibit locomotion.

A decline in transcript abundance for Heterodera glycines homologs of Caenorhabditis elegans uncoordinated genes accompanies its sedentary parasitic phase

Background

Heterodera glycines (soybean cyst nematode [SCN]), the major pathogen of Glycine max (soybean), undergoes muscle degradation (sarcopenia) as it becomes sedentary inside the root. Many genes encoding muscular and neuromuscular components belong to the uncoordinated (unc) family of genes originally identified in Caenorhabditis elegans. Previously, we reported a substantial decrease in transcript abundance for Hg-unc-87, the H. glycines homolog of unc-87 (calponin) during the adult sedentary phase of SCN. These observations implied that changes in the expression of specific muscle genes occurred during sarcopenia.

Results

We developed a bioinformatics database that compares expressed sequence tag (est) and genomic data of C. elegans and H. glycines (CeHg database). We identify H. glycines homologs of C. elegans unc genes whose protein products are involved in muscle composition and regulation. RT-PCR reveals the transcript abundance of H. glycines unc homologs at mobile and sedentary stages of its lifecycle. A prominent reduction in transcript abundance occurs in samples from sedentary nematodes for homologs of actin, unc-60B (cofilin), unc-89, unc-15 (paromyosin), unc-27 (troponin I), unc-54 (myosin), and the potassium channel unc-110 (twk-18). Less reduction is observed for the focal adhesion complex gene Hg-unc-97.

Conclusion

The CeHg bioinformatics database is shown to be useful in identifying homologs of genes whose protein products perform roles in specific aspects of H. glycines muscle biology. Our bioinformatics comparison of C. elegans and H. glycines genomic data and our Hg-unc-87 expression experiments demonstrate that the transcript abundance of specific H. glycines homologs of muscle gene decreases as the nematode becomes sedentary inside the root during its parasitic feeding stages.

A noncanonical SH3 domain binding motif links BK channels to the actin cytoskeleton via the SH3 adapter cortactin

Calcium-activated potassium (BK) channels play a central role in regulating multiple physiological processes, from the control of blood flow to neuronal excitability. Coordinated regulation of BK channel activity by changes in actin cytoskeleton dynamics has been implicated in several of these processes and related disease states such as epilepsy and stroke. However, how BK channels interact with the actin cytoskeleton is essentially unknown. Here we demonstrate noncanonical Src homology domain 3 (SH3) binding site motifs in the intracellular C terminus of the BK channel pore-forming alpha-subunit that are conserved from fish to humans. These noncanonical motifs target multiple SH3 domain cellular signaling proteins to BK channels, including the SH3 adapter protein cortactin (EMS1). We demonstrate that cortactin provides a molecular bridge between BK channels and the cortical actin cytoskeleton in cells. Disruption of the SH3-mediated interaction prevents the regulation of BK channel activity controlled by changes in actin cytoskeletal dynamics. Targeting of cortactin to BK channels via a novel, noncanonical SH3 domain binding motif has important implications for the coordination of BK channel function in normal physiology and disease.