Nicotinamide is an endogenous agonist for a C. elegans TRPV OSM-9 and OCR-4 channel

Insect transient receptor potential vanilloid channels as potential targets of insecticides

Chordotonal organs are miniature sensory organs present in insects. Chordotonal organs depend on transient receptor potential (TRP) channels. Transient receptor potential vanilloid (TRPV) channels are the only TRPs identified that can act as targets of insecticides. By binding with TRPV channels, insecticides targeting the chordotonal organs trigger the inflow of calcium ions, resulting in abnormal function of the chordotonal organ to achieve the goal of eliminating pests. TRPV channels are highly expressed in various developmental stages and tissue parts of insects and play an important role in the whole life history of insects. In this review, we will discuss the structure and types of TRPV channels as well as their genetic relationships in different species. We also systematically reviewed the recent progress of TRPV channels as insecticide targets, demonstrating that TRPV channels can be used as the target of new high-efficiency insecticides.

The modes of action of ion-channel-targeting neurotoxic insecticides: lessons from structural biology

Insecticides are indispensable tools for plant protection in modern agriculture. Despite having highly heterogeneous structures, many neurotoxic insecticides use similar principles to inhibit or deregulate neuronal ion channels. Insecticides targeting pentameric ligand-gated channels are structural mimetics of neurotransmitters or manipulate and deregulate the proteins. Those binding to (pseudo-)tetrameric voltage-gated(-like) channels, on the other hand, are natural or synthetic compounds that directly block the ion-conducting pore or prevent conformational changes in the transmembrane domain necessary for opening and closing the pore. The use of a limited number of inhibition mechanisms can be problematic when resistances arise and become more widespread. Therefore, there is a rising interest in the development of insecticides with novel mechanisms that evade resistance and are pest-insect-specific. During the last decade, most known insecticide targets, many with bound compounds, have been structurally characterized, bringing the rational design of novel classes of agrochemicals within closer reach than ever before.

An insecticide target in mechanoreceptor neurons

Hundreds of neurotoxic insecticides are currently in use. However, only a few direct targets have been identified. Here, using Drosophila and the insecticide flonicamid, we identified nicotinamidase (Naam) as a previous unidentified molecular target for an insecticide. Naam is expressed in chordotonal stretch-receptor neurons, and inhibition of Naam by a metabolite of flonicamid, TFNA-AM (4-trifluoromethylnicotinamide), induces accumulation of substrate nicotinamide and greatly inhibits negative geotaxis. Engineered flies harboring a point mutation in the active site show insecticide resistance and defects in gravity sensing. Bees are resistant to flonicamid because of a gene duplication, resulting in the generation of a TFNA-AM-insensitive Naam. Our results, in combination with the absence of genes encoding Naam in vertebrate genomes, suggest that TFNA-AM and potential species-specific Naam inhibitors could be developed as novel insecticides, anthelmintics, and antimicrobials for agriculture and human health.

Flonicamid metabolite 4-trifluoromethylnicotinamide is a chordotonal organ modulator insecticide†

BACKGROUND

The selective aphicide flonicamid is known to cause symptoms in aphids that are like those of chordotonal organ TRPV channel modulator insecticides such as pymetrozine, pyrifluquinazon and afidopyropen. Flonicamid is classified by the Insecticide Resistance Action Committee as a chordotonal organ modulator with an undefined target site. However, although it has been shown not to act on TRPV channels, flonicamid's action on chordotonal organs has not been documented in the literature.

RESULTS

Flonicamid causes locusts to extend their hindlegs, indicating an action on the femoral chordotonal organ. In fruit flies, it abolishes negative gravitaxis behavior by disrupting transduction and mechanical amplification in antennal chordotonal neurons. Although flonicamid itself only weakly affects locust chordotonal organs, its major animal metabolite 4-trifluoromethylnicotinamide (TFNA-AM) potently stimulates both locust and fly chordotonal organs. Like pymetrozine, TFNA-AM rapidly increases Ca²⁺ in antennal chordotonal neurons in wild-type flies, but not iav¹ mutants, yet the effect is nonadditive with the TRPV channel agonist.

CONCLUSIONS

Flonicamid is a pro-insecticide form of TFNA-AM, a potent chordotonal organ modulator. The functional effects of TFNA-AM on chordotonal organs of locusts and flies are indistinguishable from those of the TRPV agonists pymetrozine, pyrifluquinazon and afidopyropen. Because our previous results indicate that TFNA-AM does not act directly on TRPV channels, we conclude that it acts upstream in a pathway that leads to TRPV channel activation. © 2022 Society of Chemical Industry.

TRPV channel nanchung and TRPA channel water witch form insecticide-activated complexes

We have previously shown that insect vanilloid-type transient receptor potential (TRPV) channels Nanchung (Nan) and Inactive (Iav) form complexes, which can be over-stimulated and eventually silenced by commercial insecticides, afidopyropen, pymetrozine and pyrifluquinazon. Silencing of the TRPV channels by the insecticides perturbs function of the mechano-sensory organs, chordotonal organs, disrupting sound perception, gravitaxis, and feeding. In addition to TRPV channels, chordotonal organs express an ankyrin-type transient receptor potential (TRPA) channel, Water witch (Wtrw). Genetic data implicate Wtrw in sound and humidity sensing, although the signaling pathway, which links Wtrw to these functions has not been clearly defined. Here we show that, in heterologous system, Nan and Wtrw form calcium channels, which can be activated by afidopyropen, pymetrozine and an endogenous agonist, nicotinamide. Analogous to Nan-Iav heteromers, Nan forms the main binding interface for afidopyropen, whereas co-expression of Wtrw dramatically increases its binding affinity. Pymetrozine competes with afidopyropen for binding to Nan-Wtrw complexes, suggesting that these compounds have overlapping binding sites. Analysis of Drosophila single-nucleus transcriptomic atlas revealed co-expression of nan and wtrw in audio- and mechanosensory neurons. The observation that Nan can form insecticide-sensitive heteromers with more than one type of TRP channels, raises a possibility that Nan may partner with some other TRP channel(s). In addition, we show that Wtrw can be activated by plant-derived reactive electrophiles, allyl isothiocyanate and cinnamaldehyde, defining new molecular target for these repellents.

Effects of nicotinamide on follicular development and the quality of oocytes

BACKGROUND

Nicotinamide (NAM) is an important antioxidant, which is closely related to female fertility, but its role has not been clearly elucidated. The purpose of the present study was to investigate the effects of NAM on follicular development at different stages and the quality of oocytes.

METHODS

The concentration of NAM in follicular fluid (FF) of 236 women undergoing in vitro fertilization (IVF) was ascertained by enzyme-linked immunosorbent assay (ELISA), and the correlation between NAM and clinical indexes was analyzed. During the in vitro maturation (IVM) of mice cumulus-oocyte complexes (COCs), different concentrations of NAM were added to check the maturation rate and fertilization rate. The reactive oxygen species (ROS) levels in the oocytes treated with different hydrogen peroxide (H₂O₂) and NAM were assessed. Immunofluorescence staining was performed to measure the proportion of abnormal spindles.

RESULTS

The level of NAM in large follicles was significantly higher than that in small follicles. In mature FF, the NAM concentration was positively correlated with the rates of oocyte maturation and fertilization. Five mM NAM treatment during IVM increased maturation rate and fertilization rate in the oxidative stress model, and significantly reduced the increase of ROS levels induced by H₂O₂ in mice oocytes.

CONCLUSIONS

Higher levels of NAM in FF are associated with larger follicle development. The supplement of 5 mM NAM during IVM may improve mice oocyte quality, reducing damage caused by oxidative stress.

Noncanonical necrosis in 2 different cell types in a Caenorhabditis elegans NAD+ salvage pathway mutant

Necrosis was once described as a chaotic unregulated response to cellular insult. We now know that necrosis is controlled by multiple pathways in response to many different cellular conditions. In our pnc-1 NAD⁺ salvage deficient Caenorhabditis elegans model excess nicotinamide induces excitotoxic death in uterine-vulval uv1 cells and OLQ mechanosensory neurons. We sought to characterize necrosis in our pnc-1 model in the context of well-characterized necrosis, apoptosis, and autophagy pathways in C. elegans. We confirmed that calpain and aspartic proteases were required for uv1 necrosis, but changes in intracellular calcium levels and autophagy were not, suggesting that uv1 necrosis occurs by a pathway that diverges from mec-4d-induced touch cell necrosis downstream of effector aspartic proteases. OLQ necrosis does not require changes in intracellular calcium, the function of calpain or aspartic proteases, or autophagy. Instead, OLQ survival requires the function of calreticulin and calnexin, pro-apoptotic ced-4 (Apaf1), and genes involved in both autophagy and axon guidance. In addition, the partially OLQ-dependent gentle nose touch response decreased significantly in pnc-1 animals on poor quality food, further suggesting that uv1 and OLQ necrosis differ downstream of their common trigger. Together these results show that, although phenotypically very similar, uv1, OLQ, and touch cell necrosis are very different at the molecular level.

Nanchung and Inactive define pore properties of the native auditory transduction channel in Drosophila

Auditory transduction is mediated by chordotonal (Cho) neurons in Drosophila larvae, but the molecular identity of the mechanotransduction (MET) channel is elusive. Here, we established a whole-cell recording system of Cho neurons and showed that two transient receptor potential vanilloid (TRPV) channels, Nanchung (NAN) and Inactive (IAV), are essential for MET currents in Cho neurons. NAN and IAV form active ion channels when expressed simultaneously in S2 cells. Point mutations in the pore region of NAN-IAV change the reversal potential of the MET currents. Particularly, residues 857 through 990 in the IAV carboxyl terminus regulate the kinetics of MET currents in Cho neurons. In addition, TRPN channel NompC contributes to the adaptation of auditory transduction currents independent of its ion-conduction function. These results indicate that NAN-IAV, rather than NompC, functions as essential pore-forming subunits of the native auditory transduction channel in Drosophila and provide insights into the gating mechanism of MET currents in Cho neurons.

Overactive EGF signaling suppresses a C. elegans pnc-1 egg-laying phenotype independent of known signaling mediators

Nicotinamide recycling is critical to the development and function of Caenorhabditis elegans. Excess nicotinamide in a pnc-1 nicotinamidase mutant causes the necrosis of uv1 and OLQ cells and a highly penetrant egg laying defect. An EGF receptor (let-23) gain-of-function mutation suppresses the Egl phenotype in pnc-1 animals. However, gain-of-function mutations in either of the known downstream mediators, let-60/ Ras or itr-1, are not sufficient. Phosphatidylcholine synthesis is neither required nor sufficient, in contrast to its role in the let-23gf rescue of uv1 necrosis. The mechanism behind the let-23gf suppression of the pnc-1 Egl phenotype is unknown.

Biophysics and Modeling of Mechanotransduction in Neurons: A Review

Mechanosensing is a key feature through which organisms can receive inputs from the environment and convert them into specific functional and behavioral outputs. Mechanosensation occurs in many cells and tissues, regulating a plethora of molecular processes based on the distribution of forces and stresses both at the cell membrane and at the intracellular organelles levels, through complex interactions between cells’ microstructures, cytoskeleton, and extracellular matrix. Although several primary and secondary mechanisms have been shown to contribute to mechanosensation, a fundamental pathway in simple organisms and mammals involves the presence of specialized sensory neurons and the presence of different types of mechanosensitive ion channels on the neuronal cell membrane. In this contribution, we present a review of the main ion channels which have been proven to be significantly involved in mechanotransduction in neurons. Further, we discuss recent studies focused on the biological mechanisms and modeling of mechanosensitive ion channels’ gating, and on mechanotransduction modeling at different scales and levels of details.

Drosophila Mechanosensory Transduction

Mechanosensation in Drosophila relies on sensory neurons transducing mechanical stimuli into ionic currents. The molecular mechanisms of this transduction are in the process of being revealed. Transduction relies on mechanogated ion channels that are activated by membrane stretch or the tension of force-conveying tethers. NOMPC (no-mechanoreceptor potential C) and DmPiezo were put forward as bona fide mechanoelectrical transduction (MET) channels, providing insights into MET channel architecture and the structural basis of mechanogating. Various additional channels were implicated in Drosophila mechanosensory neuron functions, and parallels between fly and vertebrate mechanotransduction were delineated. Collectively, these advances put forward Drosophila mechanosensory neurons as cellular paradigms for mechanotransduction and mechanogated ion channel function in the context of proprio- and nociception as well as the detection of substrate vibrations, touch, gravity, and sound.

OSM-9 and OCR-2 TRPV channels are accessorial warm receptors in Caenorhabditis elegans temperature acclimatisation

Caenorhabditis elegans (C. elegans) exhibits cold tolerance and temperature acclimatisation regulated by a small number of head sensory neurons, such as the ADL temperature-sensing neurons that express three transient receptor potential vanilloid (TRPV) channel subunits, OSM-9, OCR-2, and OCR-1. Here, we show that an OSM-9/OCR-2 regulates temperature acclimatisation and acts as an accessorial warmth-sensing receptor in ADL neurons. Caenorhabditis elegans TRPV channel mutants showed abnormal temperature acclimatisation. Ectopic expression of OSM-9 and OCR-2 in non-warming-responsive gustatory neurons in C. elegans and Xenopus oocytes revealed that OSM-9 and OCR-2 cooperatively responded to warming; however, neither TRPV subunit alone was responsive to warming. A warming-induced OSM-9/OCR-2-mediated current was detectable in Xenopus oocytes, yet ADL in osm-9 ocr-2 double mutant responds to warming; therefore, an OSM-9/OCR-2 TRPV channel and as yet unidentified temperature receptor might coordinate transmission of temperature signalling in ADL temperature-sensing neurons. This study demonstrates direct sensation of warming by TRPV channels in C. elegans.

Nicotinamide inhibits melanoma in vitro and in vivo

Background

Even though new therapies are available against melanoma, novel approaches are needed to overcome resistance and high-toxicity issues. In the present study the anti-melanoma activity of Nicotinamide (NAM), the amide form of Niacin, was assessed in vitro and in vivo.

Methods

Human (A375, SK-MEL-28) and mouse (B16-F10) melanoma cell lines were used for in vitro investigations. Viability, cell-death, cell-cycle distribution, apoptosis, Nicotinamide Adenine Dinucleotide⁺ (NAD⁺), Adenosine Triphosphate (ATP), and Reactive Oxygen Species (ROS) levels were measured after NAM treatment. NAM anti-SIRT2 activity was tested in vitro; SIRT2 expression level was investigated by in silico transcriptomic analyses. Melanoma growth in vivo was measured in thirty-five C57BL/6 mice injected subcutaneously with B16-F10 melanoma cells and treated intraperitoneally with NAM. Interferon (IFN)-γ-secreting murine cells were counted with ELISPOT assay. Cytokine/chemokine plasmatic levels were measured by xMAP technology. Niacin receptors expression in human melanoma samples was also investigated by in silico transcriptomic analyses.

Results

NAM reduced up to 90% melanoma cell number and induced: i) accumulation in G1-phase (40% increase), ii) reduction in S- and G2-phase (about 50% decrease), iii) a 10-fold increase of cell-death and 2.5-fold increase of apoptosis in sub-G1 phase, iv) a significant increase of NAD⁺, ATP, and ROS levels, v) a strong inhibition of SIRT2 activity in vitro. NAM significantly delayed tumor growth in vivo (p ≤ 0.0005) and improved survival of melanoma-bearing mice (p ≤ 0.0001). About 3-fold increase (p ≤ 0.05) of Interferon-gamma (IFN-γ) producing cells was observed in NAM treated mice. The plasmatic expression levels of 6 cytokines (namely: Interleukin 5 (IL-5), Eotaxin, Interleukin 12 (p40) (IL12(p40)), Interleukin 3 (IL-3), Interleukin 10 (IL-10) and Regulated on Activation Normal T Expressed and Secreted (RANTES) were significantly changed in the blood of NAM treated mice, suggesting a key role of the immune response. The observed inhibitory effect of NAM on SIRT2 enzymatic activity confirmed previous evidence; we show here that SIRT2 expression is significantly increased in melanoma and inversely related to melanoma-patients survival. Finally, we show for the first time that the expression levels of Niacin receptors HCAR2 and HCAR3 is almost abolished in human melanoma samples.

Conclusion

NAM shows a relevant anti-melanoma activity in vitro and in vivo and is a suitable candidate for further clinical investigations.

Genetic and functional diversification of chemosensory pathway receptors in mosquito-borne filarial nematodes

Lymphatic filariasis (LF) afflicts over 60 million people worldwide and leads to severe pathological outcomes in chronic cases. The nematode parasites (Nematoda: Filarioidea) that cause LF require both arthropod (mosquito) intermediate hosts and mammalian definitive hosts for their propagation. The invasion and migration of filarial worms through host tissues are complex and critical to survival, yet little is known about the receptors and signaling pathways that mediate directed migration in these medically important species. In order to better understand the role of chemosensory signaling in filarial worm taxis, we employ comparative genomics, transcriptomics, reverse genetics, and chemical approaches to identify putative chemosensory receptor proteins and perturb chemotaxis phenotypes in filarial worms. We find that chemoreceptor family size is correlated with the presence of environmental (extrahost) stages in nematode life cycles, and that filarial worms contain compact and highly diverged chemoreceptor complements and lineage-specific ion channels that are predicted to operate downstream of chemoreceptor activation. In Brugia malayi, an etiological agent of LF, chemoreceptor expression patterns correspond to distinct parasite migration events across the life cycle. To interrogate the role of chemosensation in the migration of larval worms, arthropod and mammalian infectious stage Brugia parasites were incubated in nicotinamide, an agonist of the nematode transient receptor potential (TRP) channel OSM-9. Exposure of microfilariae to nicotinamide alters intramosquito migration, and exposure of L3s reduces chemotaxis toward host-associated cues in vitro. Nicotinamide also potently modulates thermosensory responses in L3s, suggesting a polymodal sensory role for Brugia osm-9. Reverse genetic studies implicate both Brugia osm-9 and the cyclic nucleotide-gated (CNG) channel subunit tax-4 in larval chemotaxis toward host serum, and these ion channel subunits partially rescue sensory defects in Caenorhabditis elegans osm-9 and tax-4 knock-out strains. Together, these data reveal genetic and functional diversification of chemosensory signaling proteins in filarial worms and encourage a more thorough investigation of clade- and parasite-specific facets of nematode sensory receptor biology.

The Na+-K+-ATPase is needed in glia of touch receptors for responses to touch in C. elegans

Four of the five types of mammalian mechanosensors are composed of nerve endings and accessory cells. In Caenorhabditis elegans we showed that glia support the function of nose touch neurons via the activity of glial Na+ and K+ channels. We show here that a third regulator of Na+ and K+, the Na+-K+-ATPase, is needed in glia of nose touch neurons for touch. Importantly, we show that two Na+-K+-ATPase genes are needed for the function rather than structural integrity and that their ion transport activity is crucial for touch. Finally, when glial Na+-K+-ATPase genes are knocked out, touch can be restored by activation of a third Na+-K+-ATPase. Taken together, these data show the requirement in glia of touch neurons of the function of the Na+-K+-ATPase. These data underscore the importance of the homeostasis of Na+ and K+, most likely in the space surrounding touch neurons, in touch sensation, a function that might be conserved across species.NEW & NOTEWORTHY Increasing evidence supports that accessory cells in mechanosensors regulate neuronal output; however, the glial molecular mechanisms that control this regulation are not fully understood. We show here in Caenorhabditis elegans that specific glial Na+-K+-ATPase genes are needed for nose touch-avoidance behavior. Our data support the requirement of these Na+-K+-ATPases for homeostasis of Na+ and K+ in nose touch receptors. Our data add to our understanding of glial regulation of mechanosensors.

Nicotinamide Inhibits Aphid Fecundity and Impacts Survival

Nicotinamide (NAM) alters behavior in C. elegans and Drosophila, serving as an agonist of TRPV channels affecting sensory neurons and mimicking the mode of action of insecticides used to control phloem-feeding insects. The impact of NAM on green peach aphid (Myzus persicae) behaviors was assessed in artificial diet assays and foliar applications to Arabidopsis plants. Aphids feeding on artificial diets supplemented with NAM impaired stylet movement causing feeding interruptions and ultimately starvation and death. Aphid feeding behaviors were negatively impacted on NAM sprayed plants at concentrations as low as 2.5 mM leading to increased mortality. In choice assays with NAM sprayed leaves aphids showed clear preference for untreated control leaves. NAM is an intermediate in the NAD salvage pathway that should accumulate in nicotinamidase (nic) mutants. LC-MS analysis showed NAM accumulates 60-fold in nic-1-1 Arabidopsis mutants as compared with Col-0. Aphid reproductive potential was significantly decreased on nic-1-1 mutant plants, resulting in a smaller colony size and arrested population development. The results support the hypothesis that dietary NAM causes behavioral changes in aphids, including altered feeding, reduced reproduction, and increased mortality. NAM is thought to bind to TRPV channels causing overstimulation of sensory neurons in the aphid feeding apparatus.

Molecular and cellular modulators for multisensory integration in C. elegans

In the natural environment, animals often encounter multiple sensory cues that are simultaneously present. The nervous system integrates the relevant sensory information to generate behavioral responses that have adaptive values. However, the neuronal basis and the modulators that regulate integrated behavioral response to multiple sensory cues are not well defined. Here, we address this question using a behavioral decision in C. elegans when the animal is presented with an attractive food source together with a repulsive odorant. We identify specific sensory neurons, interneurons and neuromodulators that orchestrate the decision-making process, suggesting that various states and contexts may modulate the multisensory integration. Among these modulators, we characterize a new function of a conserved TGF-β pathway that regulates the integrated decision by inhibiting the signaling from a set of central neurons. Interestingly, we find that a common set of modulators, including the TGF-β pathway, regulate the integrated response to the pairing of different foods and repellents. Together, our results provide mechanistic insights into the modulatory signals regulating multisensory integration.

The present study characterizes the modulation of a behavioral decision in C. elegans when the worm is presented with a food lawn that is paired with a repulsive smell. We show that multiple specific sensory neurons and interneurons play roles in making the decision. We also identify several modulatory molecules that are essential for the integrated decision when the animal faces a choice between the cues of opposing valence. We further show that many of these factors, which often represent different states and contexts, are common for behavioral decisions that integrate sensory information from different types of foods and repellents. Overall, our results reveal the molecular and cellular basis for integration of simultaneously present attractive and repulsive cues to fine-tune decision-making.

Investigation of gene evolution in vertebrate genome reveals novel insights into spine study

Vertebrate genomes have been considered to have undergone a complicated evolution during their early period and to have generated a large number of genetic templates with novel functions, such as an extended spinal cord and a dorsal central nervous system. However, consistent gene evolution in vertebrate genomes has not been fully elucidated. In this study, we have systematically investigated the gene evolution in vertebrates utilizing a series of comparative genomics tools. We determined that three critical genes were consistently lost in vertebrate genomes, and 14 genes initially emerged in vertebrate formation. Furthermore, another 29 genes were identified with consistent amino acid variation between the vertebrates and invertebrates. A function analysis of five genes (TEP3, ABLIM2, ABLIM3, GAD1 and GAD2) was performed, and their evolution mechanisms in vertebrate genomes further investigated. These findings provide novel insights for studying the vertebrate evolution and spine development.

The S6 gate in regulatory Kv6 subunits restricts heteromeric K+ channel stoichiometry

Atypical substitutions in the S6 activation gate sequence distinguish “regulatory” Kv subunits, which cannot homotetramerize due to T1 self-incompatibility. Pisupati et al. show that such substitutions in Kv6 work together with self-incompatibility to restrict Kv2:Kv6 heteromeric stoichiometry to 3:1.

The Shaker-like family of voltage-gated K⁺ channels comprises four functionally independent gene subfamilies, Shaker (Kv1), Shab (Kv2), Shaw (Kv3), and Shal (Kv4), each of which regulates distinct aspects of neuronal excitability. Subfamily-specific assembly of tetrameric channels is mediated by the N-terminal T1 domain and segregates Kv1–4, allowing multiple channel types to function independently in the same cell. Typical Shaker-like Kv subunits can form functional channels as homotetramers, but a group of mammalian Kv2-related genes (Kv5.1, Kv6s, Kv8s, and Kv9s) encodes subunits that have a “silent” or “regulatory” phenotype characterized by T1 self-incompatibility. These channels are unable to form homotetramers, but instead heteromerize with Kv2.1 or Kv2.2 to diversify the functional properties of these delayed rectifiers. While T1 self-incompatibility predicts that these heterotetramers could contain up to two regulatory (R) subunits, experiments show a predominance of 3:1R stoichiometry in which heteromeric channels contain a single regulatory subunit. Substitution of the self-compatible Kv2.1 T1 domain into the regulatory subunit Kv6.4 does not alter the stoichiometry of Kv2.1:Kv6.4 heteromers. Here, to identify other channel structures that might be responsible for favoring the 3:1R stoichiometry, we compare the sequences of mammalian regulatory subunits to independently evolved regulatory subunits from cnidarians. The most widespread feature of regulatory subunits is the presence of atypical substitutions in the highly conserved consensus sequence of the intracellular S6 activation gate of the pore. We show that two amino acid substitutions in the S6 gate of the regulatory subunit Kv6.4 restrict the functional stoichiometry of Kv2.1:Kv6.4 to 3:1R by limiting the formation and function of 2:2R heteromers. We propose a two-step model for the evolution of the asymmetric 3:1R stoichiometry, which begins with evolution of self-incompatibility to establish the regulatory phenotype, followed by drift of the activation gate consensus sequence under relaxed selection to limit stoichiometry to 3:1R.

Chemoreceptor proteins in the Caribbean spiny lobster, Panulirus argus: Expression of Ionotropic Receptors, Gustatory Receptors, and TRP channels in two chemosensory organs and brain

The spiny lobster, Panulirus argus, has two classes of chemosensilla representing “olfaction” and “distributed chemoreception,” as is typical for decapod crustaceans. Olfactory sensilla are found exclusively on antennular lateral flagella and are innervated only by olfactory receptor neurons (ORNs) that project into olfactory lobes organized into glomeruli in the brain. Distributed chemoreceptor sensilla are found on all body surfaces including the antennular lateral flagella (LF) and walking leg dactyls (dactyls), and are innervated by both chemoreceptor neurons (CRNs) and mechanoreceptor neurons that project into somatotopically organized neuropils. Here, we examined expression of three classes of chemosensory genes in transcriptomes of the LF (with ORNs and CRNs), dactyls (with only CRNs), and brain of P. argus: Ionotropic Receptors (IRs), which are related to ionotropic glutamate receptors and found in all protostomes including crustaceans; Gustatory Receptors (GRs), which are ionotropic receptors that are abundantly expressed in insects but more restricted in crustaceans; and Transient Receptor Potential (TRP) channels, a diverse set of sensor-channels that include several chemosensors in diverse animals. We identified 108 IRs, one GR, and 18 homologues representing all seven subfamilies of TRP channels. The number of IRs expressed in the LF is far greater than in dactyls, possibly reflecting the contribution of receptor proteins associated with the ORNs beyond those associated with CRNs. We found co-receptor IRs (IR8a, IR25a, IR76b, IR93a) and conserved IRs (IR21a, IR40a) in addition to the numerous divergent IRs in the LF, dactyl, and brain. Immunocytochemistry showed that IR25a is expressed in ORNs, CRNs, and a specific type of cell located in the brain near the olfactory lobes. While the function of IRs, TRP channels, and the GR was not explored, our results suggest that P. argus has an abundance of diverse putative chemoreceptor proteins that it may use in chemoreception.

TRPV4-Mediated Anti-nociceptive Effect of Suberanilohydroxamic Acid on Mechanical Pain

Biological effects of suberanilohydroxamic acid (SAHA) have mainly been observed in the context of tumor suppression via epigenetic mechanisms, but other potential outcomes from its use have also been proposed in different fields such as pain modulation. Here, we tried to understand whether SAHA modulates specific pain modalities by a non-epigenetic unknown mechanism. From 24 h Complete Freund's Adjuvant (CFA)-inflamed hind paws of mice, mechanical and thermal inflammatory pain indices were collected with or without immediate intraplantar injection of SAHA. To examine the action of SAHA on sensory receptor-specific pain, transient receptor potential (TRP) ion channel-mediated pain indices were collected in the same manner of intraplantar treatment. Activities of primarily cultured sensory neurons and heterologous cells transfected with TRP channels were monitored to determine the molecular mechanism underlying the pain-modulating effect of SAHA. As a result, immediate and localized pretreatment with SAHA, avoiding an epigenetic intervention, acutely attenuated mechanical inflammatory pain and receptor-specific pain evoked by injection of a TRP channel agonist in animal models. We show that a component of the mechanisms involves TRPV4 inhibition based on in vitro intracellular Ca²⁺ imaging and electrophysiological assessments with heterologous expression systems and cultured sensory neurons. Taken together, the present study provides evidence of a novel off-target action and its mechanism of SAHA in its modality-specific anti-nociceptive effect and suggests the utility of this compound for pharmacological modulation of pain.

Epidermal Growth Factor Receptor Cell Survival Signaling Requires Phosphatidylcholine Biosynthesis

Identification of pro-cell survival signaling pathways has implications for cancer, cardiovascular, and neurodegenerative disease. We show that the Caenorhabditis elegans epidermal growth factor receptor LET-23 (LET-23 EGFR) has a prosurvival function in counteracting excitotoxicity, and we identify novel molecular players required for this prosurvival signaling. uv1 sensory cells in the C. elegans uterus undergo excitotoxic death in response to activation of the OSM-9/OCR-4 TRPV channel by the endogenous agonist nicotinamide. Activation of LET-23 EGFR can effectively prevent this excitotoxic death. We investigate the roles of signaling pathways known to act downstream of LET-23 EGFR in C. elegans and find that the LET-60 Ras/MAPK pathway, but not the IP₃ receptor pathway, is required for efficient LET-23 EGFR activity in its prosurvival function. However, activation of LET-60 Ras/MAPK pathway does not appear to be sufficient to fully mimic LET-23 EGFR activity. We screen for genes that are required for EGFR prosurvival function and uncover a role for phosphatidylcholine biosynthetic enzymes in EGFR prosurvival function. Finally, we show that exogenous application of phosphatidylcholine is sufficient to prevent some deaths in this excitotoxicity model. Our work implicates regulation of lipid synthesis downstream of EGFR in cell survival and death decisions.