Calcineurin regulates enteric muscle contraction through EXP-1, excitatory GABA-gated channel, in C. elegans

JM-20 affects GABA neurotransmission in Caenorhabditis elegans

Along with the discovery of new candidate molecules for pharmaceuticals, several studies have emerged showing different mechanisms of action and toxicological aspects. 3-ethoxycarbonyl-2-methyl-4- (2-nitrophenyl)4,11-dihydro-1H-pyrido [2,3-b] [1,5] benzodiazepine (JM-20) is a hybrid molecule. It is derived from 1,5-benzodiazepines and structurally differentiated by the addition of 1,4-dihydropyridine bonded to the benzodiazepine ring. This gives this molecule potential neuroprotective, antioxidant, and anxiolytic activity. As this is a promising multi-target molecule, further studies are necessary to improve the knowledge about its mechanism of action. In our study, we used Caenorhabditis elegans (C. elegans) to investigate the effects of chronic treatment with JM-20. Nematodes from the wild-type strain (N2) were treated chronically at different concentrations of JM-20. Our results show that JM-20 does not cause mortality, but higher concentrations can delay the development of worms after 48h exposure. We assessed basic behaviors in the worm, and our data demonstrate decreased defecation cycle. Our results suggest that JM-20 acts on the C. elegans GABAergic system because GABA neurotransmission is associated with the worm intestine. We also observed increased locomotor activity and decreased egg-laying after JM-20 treatment. When both behaviors were evaluated in mutants with have reduced levels of GABA (unc-25), this effect is no observed, suggesting the GABAergic modulation. Still, the JM-20 exert similar effect of Diazepam in basic behaviors observed. To reinforce neuromodulatory action, computational analysis was performed, and results showed a JM-20 binding on allosteric sites of nematodes GABA receptors. Overall, this work provided a better understanding of the effects of JM-20 in C. elegans as well as showed the effects of this new molecule on the GABAergic system in this animal model.

Abnormal neurotransmission of GABA and serotonin in Caenorhabditis elegans induced by Fumonisin B1

Fumonisin B1 (FB1) is a neurodegenerative mycotoxin synthesized by Fusarium spp., but the potential neurobehavioral toxicity effects in organisms have not been characterized clearly. Caenorhabditis elegans (C. elegans) has emerged as a promising model organism for neurotoxicological studies due to characteristics such as well-functioning nervous system and rich behavioral phenotypes. To investigate whether FB1 has neurobehavioral toxicity effects on C. elegans, the motor behavior, neuronal structure, neurotransmitter content, and gene expression related with neurotransmission of C. elegans were determined after exposed to 20-200 μg/mL FB1 for 24 h and 48 h, respectively. Results showed that FB1 caused behavioral defects, including body bends, head thrashes, crawling distance, mean speed, mean amplitude, mean wavelength, foraging behavior, and chemotaxis learning ability in a dose-, and time-dependent manner. In addition, when C. elegans was exposed to FB1 at a concentration of 200 μg/mL for 24 h and above 100 μg/mL for 48 h, the GABAergic and serotonergic neurons were damaged, but no effect on dopaminergic, glutamatergic, and cholinergic neurons. The relative content of GABA and serotonin decreased significantly. Furthermore, abnormal expression of mRNA levels associated with GABA and serotonin were found in nematodes treated with FB1, such as unc-30, unc-47, unc-49, exp-1, mod-5, cat-1, and tph-1. The neurobehavioral toxicity effect of FB1 may be mediated by abnormal neurotransmission of GABA and serotonin. This study provides useful information for understanding the neurotoxicity of FB1.

Heterogeneous expression of GABA receptor-like subunits LCCH3 and GRD reveals functional diversity of GABA receptors in the honeybee Apis mellifera

BACKGROUND AND PURPOSE

Despite a growing awareness, annual losses of honeybee colonies worldwide continue to reach threatening levels for food safety and global biodiversity. Among the biotic and abiotic stresses probably responsible for these losses, pesticides, including those targeting ionotropic GABA receptors, are one of the major drivers. Most insect genomes include the ionotropic GABA receptor subunit gene, Rdl, and two GABA-like receptor subunit genes, Lcch3 and Grd. Most studies have focused on Rdl which forms homomeric GABA-gated chloride channels, and a complete analysis of all possible molecular combinations of GABA receptors is still lacking.

EXPERIMENTAL APPROACH

We cloned the Rdl, Grd, and Lcch3 genes of Apis mellifera and systematically characterized the resulting GABA receptors expressed in Xenopus oocytes, using electrophysiological assays, fluorescence microscopy and co-immunoprecipitation techniques.

KEY RESULTS

The cloned subunits interacted with each other, forming GABA-gated heteromeric channels with particular properties. Strikingly, these heteromers were always more sensitive than AmRDL homomer to all the pharmacological agents tested. In particular, when expressed together, Grd and Lcch3 form a non-selective cationic channel that opens at low concentrations of GABA and with sensitivity to insecticides similar to that of homomeric Rdl channels.

CONCLUSION AND IMPLICATIONS

For off-target species like the honeybee, chronic sublethal exposure to insecticides constitutes a major threat. At these concentration ranges, homomeric RDL receptors may not be the most pertinent target to study and other ionotropic GABA receptor subtypes should be considered in order to understand more fully the molecular mechanisms of sublethal toxicity to insecticides.

WNT regulates programmed muscle remodeling through PLC-β and calcineurin in Caenorhabditis elegans males

The ability of a muscle to break down and reform fibers is vital for development; however, if unregulated, abnormal muscle remodeling can occur, such as in the heart following cardiac infarction. To study how normal developmental remodeling is mediated, we used fluorescently tagged actin, mutant analyses, Ca2+ imaging and controlled Ca2+ release to determine the mechanisms regulating a conspicuous muscle change that occurs in Caenorhabditis elegans males. In hermaphrodites and larval males, the single cell anal depressor muscle, used for waste expulsion, contains bilateral dorsal-ventral sarcomeres. However, prior to male adulthood, the muscle sex-specifically remodels its sarcomeres anteriorly-posteriorly to promote copulation behavior. Although WNT signaling and calcineurin have been implicated separately in muscle remodeling, we unexpectedly found that they participate in the same pathway. We show that WNT signaling through Gαo and PLC-β results in sustained Ca2+ release via IP3 and ryanodine receptors to activate calcineurin. These results highlight the utility of this new model in identifying additional molecules involved in muscle remodeling.

Calcineurin tax-6 regulates male ray development and counteracts with kin-29 kinase in Caenorhabditis elegans

Phosphorylation is one of the critical protein modifications, which can lead to changing the activity of the proteins and regulating a variety of biological processes. Therefore, it is essential to properly maintain the phosphorylation level on proteins by balancing the activity of kinases and phosphatases. In this study, we report that calcineurin, a serine/threonine phosphatase, counteracts with a salt inducible kinase (SIK) to control male tail development in Caenorhabditis elegans. The counteracting regulation is cell lineage-dependent; the number of defective rays from T lineage in animals lacking calcineurin tax-6 is decreased by knock-down of SIK kin-29. This result is in contrast with the knock-down of bone marrow protein (BMP) receptor kinase sma-6, which slightly aggravates the T lineage defect. Also, sma-6 knock-down results in modest defect in ray 1 of V5 lineage in the absence of tax-6 activity. Finally, knock-down of a tyrosine phosphatase cdc-25.3 does not affect the defective ray phenotype of calcineurin tax-6 loss-of-function(lf) mutants. Altogether, these results suggest that balanced phosphorylation mediated by tax-6 and kin-29 is required for proper development of T lineage rays, and tax-6 and sma-6 may function in a parallel pathway in the developmental process of V5 lineage ray 1. This study emphasizes the elaborated developmental process of male ray formation, in which carefully coordinated expression of various genes is essential.

The evolution of pentameric ligand-gated ion-channels and the changing family of anthelmintic drug targets

SUMMARY Pentameric ligand-gated ion-channels rapidly transduce synaptic neurotransmitter signals to an electrical response in post-synaptic neuronal or muscle cells and control the neuromusculature of a majority of multicellular animals. A wide range of pharmaceuticals target these receptors including ethanol, nicotine, anti-depressants and other mood regulating drugs, compounds that control pain and mobility and are targeted by a majority of anthelmintic drugs used to control parasitic infection of humans and livestock. Major advances have been made in recent years to our understanding of the structure, function, activity and the profile of compounds that can activate specific receptors. It is becoming clear that these anthelmintic drug targets are not fixed, but differ in significant details from one nematode species to another. Here we review what is known about the evolution of the pentameric ligand-gated ion-channels, paying particular attention to the nematodes, how we can infer the origins of such receptors and understand the factors that determine how they change both over time and from one species to another. Using this knowledge provides a biological framework in which to understand these important drug targets and avenues to identify new receptors and aid the search for new anthelmintic drugs.

Identification and characterization of a putative basic helix-loop-helix (bHLH) transcription factor interacting with calcineurin in C. elegans

Calcineurin is a Ca(2+)/Calmodulin activated Ser/Thr phosphatase that is well conserved from yeast to human. It is composed of catalytic subunit A (CnA) and regulatory subunit B (CnB). C. elegans homolog of CnA and CnB has been annotated to tax-6 and cnb-1, respectively and in vivo function of both genes has been intensively studied. In C. elegans, calcineurin play roles in various signaling pathways such as fertility, movement, body size regulation and serotonin-mediated egg laying. In order to understand additional signaling pathway(s) in which calcineurin functions, we screened for binding proteins of TAX-6 and found a novel binding protein, HLH-11. The HLH-11, a member of basic helix-loop-helix (bHLH) proteins, is a putative counterpart of human AP4 transcription factor. Previously bHLH transcription factors have been implicated to regulate many developmental processes such as cell proliferation and differentiation, sex determination and myogenesis. However, the in vivo function of hlh-11 is largely unknown. Here, we show that hlh-11 is expressed in pharynx, intestine, nerve cords, anal depressor and vuvla muscles where calcineurin is also expressed. Mutant analyses reveal that hlh-11 may have role(s) in regulating body size and reproduction. More interestingly, genetic epistasis suggests that hlh-11 may function to regulate serotonin-mediated egg laying at the downstream of tax-6.

Calcineurin interacts with KIN-29, a Ser/Thr kinase, in Caenorhabditis elegans

Calcineurin is a Ca2+/Calmodulin activated Ser/Thr phosphatase that is well conserved from yeast to human. In Caenorhabditis elegans, tax-6 and cnb-1 encode catalytic and regulatory subunits of calcineurin, respectively. We performed yeast two-hybrid screening using TAX-6 as a bait to identify calcineurin interacting proteins. KIN-29 is one of proteins that specifically interacted with TAX-6. KIN-29 is a Ser/Thr kinase previously shown to be involved in regulating gene expression of a subset of chemoreceptors in specific neurons. Both TAX-6 and KIN-29 are expressed in hypodermis, muscles, and neurons. Moreover, both calcineurin and kin-29 mutants exhibit similar phenotypes, namely small body size, small brood size, and slow growth. Here we describe specific genetic interaction between tax-6 and kin-29 in regulating body size, serotonin mediated egg laying, and chemoreceptor expression.

Casein kinase II and calcineurin modulate TRPP function and ciliary localization

Cilia serve as sensory devices in a diversity of organisms and their defects contribute to many human diseases. In primary cilia of kidney cells, the transient receptor potential polycystin (TRPP) channels polycystin-1 (PC-1) and polycystin-2 (PC-2) act as a mechanosensitive channel, with defects resulting in autosomal dominant polycystic kidney disease. In sensory cilia of Caenorhabditis elegans male-specific neurons, the TRPPs LOV-1 and PKD-2 are required for mating behavior. The mechanisms regulating TRPP ciliary localization and function are largely unknown. We identified the regulatory subunit of the serine-threonine casein kinase II (CK2) as a binding partner of LOV-1 and human PC-1. CK2 and the calcineurin phosphatase TAX-6 modulate male mating behavior and PKD-2 ciliary localization. The phospho-defective mutant PKD-2(S534A) localizes to cilia, whereas a phospho-mimetic PKD-2(S534D) mutant is largely absent from cilia. Calcineurin is required for PKD-2 ciliary localization, but is not essential for ciliary gene expression, ciliogenesis, or localization of cilium structural components. This unanticipated function of calcineurin may be important for regulating ciliary protein localization. A dynamic phosphorylation-dephosphorylation cycle may represent a mechanism for modulating TRPP activity, cellular sensation, and ciliary protein localization.