Ca²(+) /calmodulin-dependent protein kinase II mediates the octopamine-induced increase in sensitivity in spider VS-3 mechanosensory neurons

Single-cell transcriptomics reveals the brain evolution of web-building spiders

Spiders are renowned for their efficient capture of flying insects using intricate aerial webs. How the spider nervous systems evolved to cope with this specialized hunting strategy and various environmental clues in an aerial space remains unknown. Here we report a brain-cell atlas of >30,000 single-cell transcriptomes from a web-building spider (Hylyphantes graminicola). Our analysis revealed the preservation of ancestral neuron types in spiders, including the potential coexistence of noradrenergic and octopaminergic neurons, and many peptidergic neuronal types that are lost in insects. By comparing the genome of two newly sequenced plesiomorphic burrowing spiders with three aerial web-building spiders, we found that the positively selected genes in the ancestral branch of web-building spiders were preferentially expressed (42%) in the brain, especially in the three mushroom body-like neuronal types. By gene enrichment analysis and RNAi experiments, these genes were suggested to be involved in the learning and memory pathway and may influence the spiders' web-building and hunting behaviour. Our results provide key sources for understanding the evolution of behaviour in spiders and reveal how molecular evolution drives neuron innovation and the diversification of associated complex behaviours.

Is direct bodyguard manipulation a parasitoid-induced stress sleep? A new perspective

Bodyguard manipulation is a behavioural manipulation in which the host's behaviour is altered to protect the inducer's offspring from imminent biotic threats. The behaviour of a post-parasitoid-egressed host resembles a quiescence state with a characteristic reduction in motor activities like feeding, locomotion, respiration, and metabolic rate. Yet, they respond aggressively through a defensive response when disturbed, which ensures better fitness for the parasitoid's offspring. The behavioural changes in the parasitized host appear after the parasitoid egression. Several hypotheses have been proposed to elucidate how the parasitized host's behaviour is manipulated for the fitness benefits of the inducers, but the exact mechanism is still unknown. We review evidence to explain the behavioural changes and their mechanism in the parasitized hosts. The evidence suggests that parasitoid pre-pupal egression may drive the host to stress-induced sleep. The elevated octopamine concentration also reflects the stress response in the host. Given the theoretical links between the behavioural and the physiological changes in the post-parasitoid-egressed host and stress-induced sleep of other invertebrates, we suggest that behavioural studies combined with functional genomics, proteomics, and histological analyses might give a better understanding of bodyguard manipulation.

Octopamine signaling via OctαR is essential for a well-orchestrated climbing performance of adult Drosophila melanogaster

The biogenic amine octopamine (OA) orchestrates many behavioural processes in insects. OA mediates its function by binding to OA receptors belonging to the G protein-coupled receptors superfamily. Despite the potential relevance of OA, our knowledge about the role of each octopaminergic receptor and how signalling through these receptors controls locomotion still limited. In this study, RNA interference (RNAi) was used to knockdown each OA receptor type in almost all Drosophila melanogaster tissues using a tubP-GAL4 driver to investigate the loss of which receptor affects the climbing ability of adult flies. The results demonstrated that although all octopaminergic receptors are involved in normal negative geotaxis but OctαR-deficient flies had impaired climbing ability more than those deficient in other OA receptors. Mutation in OA receptors coding genes develop weak climbing behaviour. Directing knockdown of octαR either in muscular system or nervous system or when more specifically restricted to motor and gravity sensing neurons result in similar impaired climbing phenotype, indicating that within Drosophila legs, OA through OctαR orchestrated the nervous system control and muscular tissue responses. OctαR-deficient adult males showed morphometric changes in the length and width of leg parts. Leg parts morphometric changes were also observed in Drosophila mutant in OctαR. Transmission electron microscopy revealed that the leg muscles OctαR-deficient flies have severe ultrastructural changes compared to those of control flies indicating the role played by OctαR signalling in normal muscular system development. The severe impairment in the climbing performance of OctαR-deficient flies correlates well with the completely distorted leg muscle ultrastructure in these flies. Taken together, we could conclude that OA via OctαR plays an important multifactorial role in controlling locomotor activity of Drosophila.

Chromosome-level genome assembly of the black widow spider Latrodectus elegans illuminates composition and evolution of venom and silk proteins

BACKGROUND

The black widow spider has both extraordinarily neurotoxic venom and three-dimensional cobwebs composed of diverse types of silk. However, a high-quality reference genome for the black widow spider was still unavailable, which hindered deep understanding and application of the valuable biomass.

FINDINGS

We assembled the Latrodectus elegans genome, including a genome size of 1.57 Gb with contig N50 of 4.34 Mb and scaffold N50 of 114.31 Mb. Hi-C scaffolding assigned 98.08% of the genome to 14 pseudo-chromosomes, and with BUSCO, completeness analysis revealed that 98.4% of the core eukaryotic genes were completely present in this genome. Annotation of this genome identified that repetitive sequences account for 506.09 Mb (32.30%) and 20,167 protein-coding genes, and specifically, we identified 55 toxin genes and 26 spidroins and provide preliminary analysis of their composition and evolution.

CONCLUSIONS

We present the first chromosome-level genome assembly of a black widow spider and provide substantial toxin and spidroin gene resources. These high-qualified genomic data add valuable resources from a representative spider group and contribute to deep exploration of spider genome evolution, especially in terms of the important issues on the diversification of venom and web-weaving pattern. The sequence data are also firsthand templates for further application of the spider biomass.

Modulation of octopaminergic and cholinergic pathways induced by Caatinga tree Manilkara rufula chemical compounds in Nauphoeta cinerea cockroaches

The entomotoxic potential of Manilkara rufula crude extract (CEMR) and its aqueous (AFMR) and methanolic (MFMR) fractions were evaluated against Nauphoeta cinerea cockroaches. The results point out to a direct modulation of octopaminergic and cholinergic pathways in insect nervous system. CEMR induced an anti-acetylcholinesterase (AChE) effect in cockroach brain homogenates. CEMR significantly decreased the cockroach heart rate in semi-isolated heart preparations. CEMR also caused a broad disturbance in the insect behavior by reducing the exploratory activity. The decreased antennae and leg grooming activities, by different doses of CEMR, mimicked those of phentolamine activity, a selective octopaminergic receptor antagonist. The lethargy induced by CEMR was accompanied by neuromuscular failure and by a decrease of sensilla spontaneous neural compound action potentials (SNCAP) firing in in vivo and ex vivo cockroach muscle-nerve preparations, respectively. AFMR was more effective in promoting neuromuscular paralysis than its methanolic counterpart, in the same dose. These data validate the entomotoxic activity of M. rufula. The phentolamine-like modulation induced in cockroaches is the result of a potential direct inhibition of octopaminergic receptors, combined to an anti-AChE activity. In addition, the modulation of CEMR on octopaminergic and cholinergic pathways is probably the result of a synergism between AFMR and MFMR chemical compounds. Further phytochemical investigation followed by a bio-guiding protocol will improve the molecular aspects of M. rufula pharmacology and toxicology to insects.

Multiple Biogenic Amine Receptor Types Modulate Spider, Cupiennius salei, Mechanosensory Neurons

The biogenic amines octopamine (OA), tyramine (TA), dopamine (DA), serotonin (5-HT), and histamine (HA) affect diverse physiological and behavioral processes in invertebrates, but recent findings indicate that an additional adrenergic system exists in at least some invertebrates. Transcriptome analysis has made it possible to identify biogenic amine receptor genes in a wide variety of species whose genomes have not yet been sequenced. This approach provides new sequences for research into the evolutionary history of biogenic amine receptors and allows them to be studied in experimentally accessible animal models. The Central American Wandering spider, Cupiennius salei, is an experimental model for neurophysiological, developmental and behavioral research. We identified ten different biogenic amine receptors in C. salei transcriptomes. Phylogenetic analysis indicated that, in addition to the typical receptors for OA, TA, DA, and 5-HT in protostome invertebrates, spiders also have α1- and α2-adrenergic receptors, but lack TAR2 receptors and one invertebrate specific DA receptor type. In situ hybridization revealed four types of biogenic amine receptors expressed in C. salei mechanosensory neurons. We used intracellular electrophysiological experiments and pharmacological tools to determine how each receptor type contributes to modulation of these neurons. We show that arachnids have similar groups of biogenic amine receptors to other protostome invertebrates, but they lack two clades. We also clarify that arachnids and many other invertebrates have both α1- and α2-adrenergic, likely OA receptors. Our results indicate that in addition to an OAβ-receptor that regulates rapid and large changes in sensitivity via a G_s-protein activating a cAMP mediated pathway, the C. salei mechanosensory neurons have a constitutively active TAR1 and/or α2-adrenergic receptor type that adjusts the baseline sensitivity to a level appropriate for the behavioral state of the animal by a G_q-protein that mobilizes Ca²⁺.

The distribution of cholinergic neurons and their co-localization with FMRFamide, in central and peripheral neurons of the spider Cupiennius salei

The spider Cupiennius salei is a well-established model for investigating information processing in arthropod sensory systems. Immunohistochemistry has shown that several neurotransmitters exist in the C. salei nervous system, including GABA, glutamate, histamine, octopamine and FMRFamide, while electrophysiology has found functional roles for some of these transmitters. There is also evidence that acetylcholine (ACh) is present in some C. salei neurons but information about the distribution of cholinergic neurons in spider nervous systems is limited. Here, we identify C. salei genes that encode enzymes essential for cholinergic transmission: choline ACh transferase (ChAT) and vesicular ACh transporter (VAChT). We used in-situ hybridization with an mRNA probe for C. salei ChAT gene to locate somata of cholinergic neurons in the central nervous system and immunohistochemistry with antisera against ChAT and VAChT to locate these proteins in cholinergic neurons. All three markers labeled similar, mostly small neurons, plus a few mid-sized neurons, in most ganglia. In the subesophageal ganglia, labeled neurons are putative efferent, motor or interneurons but the largest motor and interneurons were unlabeled. Groups of anti-ChAT labeled small neurons also connect the optic neuropils in the spider protocerebrum. Differences in individual cell labeling intensities were common, suggesting a range of ACh expression levels. Double-labeling found a subpopulation of anti-VAChT-labeled central and mechanosensory neurons that were also immunoreactive to antiserum against FMRFamide-like peptides. Our findings suggest that ACh is an important neurotransmitter in the C. salei central and peripheral nervous systems.

Extended spider cognition

There is a tension between the conception of cognition as a central nervous system (CNS) process and a view of cognition as extending towards the body or the contiguous environment. The centralised conception requires large or complex nervous systems to cope with complex environments. Conversely, the extended conception involves the outsourcing of information processing to the body or environment, thus making fewer demands on the processing power of the CNS. The evolution of extended cognition should be particularly favoured among small, generalist predators such as spiders, and here, we review the literature to evaluate the fit of empirical data with these contrasting models of cognition. Spiders do not seem to be cognitively limited, displaying a large diversity of learning processes, from habituation to contextual learning, including a sense of numerosity. To tease apart the central from the extended cognition, we apply the mutual manipulability criterion, testing the existence of reciprocal causal links between the putative elements of the system. We conclude that the web threads and configurations are integral parts of the cognitive systems. The extension of cognition to the web helps to explain some puzzling features of spider behaviour and seems to promote evolvability within the group, enhancing innovation through cognitive connectivity to variable habitat features. Graded changes in relative brain size could also be explained by outsourcing information processing to environmental features. More generally, niche-constructed structures emerge as prime candidates for extending animal cognition, generating the selective pressures that help to shape the evolving cognitive system.

Expression of Cys-loop receptor subunits and acetylcholine binding protein in the mechanosensory neurons, glial cells, and muscle tissue of the spider Cupiennius salei

The central and peripheral nervous system transcriptomes of the spider Cupiennius salei have 15 Cys-loop receptor subunits and an acetylcholine-binding protein (AChBP). Twelve subunits are predicted to form anion channels gated by γ-aminobutyric acid (GABA), glutamate, histamine, or changes in pH, and three are putative ACh-gated cation channels. Spiders have a variety of mechanosensilla and proprioceptive organs that are innervated by efferents in their peripherally located parts, and efferents also innervate muscle fibers. We investigated Cys-loop gene expression in muscle tissue by qPCR and localized this expression in mechanosensilla via in situ hybridization. The cuticular mechanosensory neurons had only CsGABArdl and CspHCl2 subunits, whereas the muscle tissue expressed a wider variety of subunits, especially CsGABAgrd, CsGABA_A β, CsGluCl1 and CspHCl, but very low levels of the CsGABArdl or CsnACh subunits. An nACh non-α subunit was expressed in a group of unidentified cells in the hypodermis and at low level in the muscle tissue, but the physiological function of this subunit is unknown. The CsnAChα subunit was not expressed in sensory neurons and was expressed at extremely low level in the muscle tissue. None of the probes gave signals in proprioceptive joint receptors, suggesting that efferent innervation to this sense organ employs other receptor types. CsAChBP and a glia-specific homeodomain CsREPO were both expressed in glial cells that surround sensory neurons and also in muscle tissue, probably around the nerve endings of the neuromuscular junction. These locations have large numbers of synapses, suggesting that AChBP may have a function in modulating synaptic transmission. J. Comp. Neurol. 525:1139-1154, 2017. © 2016 Wiley Periodicals, Inc.

Physiological functions and pharmacological and toxicological effects of p-octopamine

p-Octopamine occurs naturally in plants, invertebrates and animals with diverse functions and effects. This review summarizes the chemistry, metabolism, receptor binding characteristics, known physiological functions, and pharmacological and toxicological effects of p-octopamine. Databases used included PubMed and Google Scholar Advanced. p-Octopamine binds to neuroreceptors in insects that are not present in humans, while exhibiting poor binding to α-1, α-2, β-1, and β-2 adrenergic receptors in mammalian systems. p-Octopamine modestly binds to β-3 adrenergic receptors and may therefore promote lipolysis and weight loss. p-Octopamine is produced in brain and nerve tissues of mammals and is present and can be measured in the blood of normal human subjects. p-Octopamine is considered to be a CNS stimulant in spite of the fact that it binds poorly to adrenergic receptors. Variations occur in blood levels in association with neurological and hepatic diseases. Its precise role in normal neurophysiology is unclear. No human studies have been reported that demonstrate adverse cardiovascular effects following oral administration. No human studies have examined the effects of p-octopamine on athletic performance or weight loss and weight management. A need exists for both animal and human safety and efficacy studies involving oral administration of p-octopamine.

Transcriptome walking: a laboratory-oriented GUI-based approach to mRNA identification from deep-sequenced data

Background

Deep sequencing technology provides efficient and economical production of large numbers of randomly positioned, relatively short, estimates of base identities in DNA molecules. Application of this technology to mRNA samples allows rapid examination of the molecular genetic environment in individual cells or tissues, the transcriptome. However, assembly of such short sequences into complete mRNA creates a challenge that limits the usefulness of the technology, particularly when no, or limited, genomic data is available. Several approaches to this problem have been developed, but there is still no general method to rapidly obtain an mRNA sequence from deep sequence data when a specific molecule, or family of molecules, are of interest. A frequent requirement is to identify specific mRNA molecules from tissues that are being investigated by methods such as electrophysiology, immunocytology and pharmacology. To be widely useful, any approach must be relatively simple to use in the laboratory by operators without extensive statistical or bioinformatics knowledge, and with readily available hardware.

Findings

An approach was developed that allows de novo assembly of individual mRNA sequences in two linked stages: sequence discovery and sequence completion. Both stages rely on computer assisted, Graphical User Interface (GUI)-guided, user interaction with the data, but proceed relatively efficiently once discovery is complete. The method grows a discovered sequence by repeated passes through the complete raw data in a series of steps, and is hence termed ‘transcriptome walking’. All of the operations required for transcriptome analysis are combined in one program that presents a relatively simple user interface and runs on a standard desktop, or laptop computer, but takes advantage of multi-core processors, when available. Complete mRNA sequence identifications usually require less than 24 hours. This approach has already identified previously unknown mRNA sequences in two animal species that currently lack any significant genome or transcriptome data.

Conclusions

As deep sequencing data becomes more widely available, accessible methods for extracting useful sequence information in the biological or medical laboratory will be of increasing importance. The approach described here does not rely on detailed knowledge of bioinformatic algorithms, and allows users with basic knowledge of molecular biology and standard laboratory computing equipment, but limited software or bioinformatics experience, to extract complete gene sequences from deep-sequencing data.

GABA and glutamate receptors have different effects on excitability and are differentially regulated by calcium in spider mechanosensory neurons

GABA and glutamate receptors belonging to the ligand-gated chloride-channel family are primary targets of insecticides and antiparasitics, so their molecular structure, pharmacology and biophysical properties have attracted significant attention. However, little is known about the physiological roles of these channels or how they regulate neuronal excitability and animal behavior. Mechanosensory neurons of VS-3 slit sensilla in the patella of the tropical wandering spider, Cupiennius salei, react to the GABA(A)-receptor agonists, GABA and muscimol, with depolarization and an increase in intracellular [Ca(2+)] and, during random noise stimulation, with a mixed inhibitory-excitatory response. We established that the GABA(A)-receptors in all VS-3 neurons are identical, but there are at least two types of glutamate receptors and some neurons do not respond to glutamate at all. Immunohistochemistry with antibodies against Drosophila inhibitory glutamate receptor (GluCls) α-subunit suggests that in addition to VS-3 neurons, these receptors may also be present in the efferent neurons surrounding the sensory neurons. Most VS-3 neurons were inhibited but not depolarized by glutamate during random stimulation, but some depolarized and had a similar excitatory-inhibitory response to glutamate as to muscimol. The membrane-permeable Ca(2+)-chelator BAPTA-AM abolished muscimol effects but potentiated glutamate effects, indicating that GABA and glutamate receptors are differentially modulated by Ca(2+), leading to diverse regulation of neuronal excitability. We hypothesize that this could be achieved by different Ca(2+)-triggered phosphorylation processes at each receptor type. These findings are important for understanding the significance of Ca(2+)-mediated regulation of transmitter receptor molecules and its role in controlling excitability.

Octopaminergic modulation of contrast gain adaptation in fly visual motion-sensitive neurons

Locomotor activity like walking or flying has recently been shown to alter visual processing in several species. In insects, the neuromodulator octopamine is thought to play an important role in mediating state changes during locomotion of the animal [K.D. Longden & H.G. Krapp (2009) J. Neurophysiol., 102, 3606-3618; (2010) Front. Syst. Neurosci., 4, 153; S.N. Jung et al. (2011)J. Neurosci., 31, 9231-9237]. Here, we used the octopamine agonist chlordimeform (CDM) to mimic effects of behavioural state changes on visual motion processing. We recorded from identified motion-sensitive visual interneurons in the lobula plate of the blowfly Calliphora vicina. In these neurons, which are thought to be involved in visual guidance of locomotion, motion adaptation leads to a prominent attenuation of contrast sensitivity. Following CDM application, the neurons maintained high contrast sensitivity in the adapted state. This modulation of contrast gain adaptation was independent of the activity of the recorded neurons, because it was also present after stimulation with visual motion that did not result in deviations from the neurons' resting activity. We conclude that CDM affects presynaptic inputs of the recorded neurons. Accordingly, the effect of CDM was weak when adapting and test stimuli were presented in different parts of the receptive field, stimulating separate populations of local presynaptic neurons. In the peripheral visual system adaptation depends on the temporal frequency of the stimulus pattern and is therefore related to pattern velocity. Contrast gain adaptation could therefore be the basis for a shift in the velocity tuning that was previously suggested to contribute to state-dependent processing of visual motion information in the lobula plate interneurons.

Calcium buffering and clearance in spider mechanosensory neurons

Spider VS-3 mechanoreceptor neurons have a low-voltage-activated Ca2+ current that raises intracellular calcium concentration [Ca2+] when they are depolarized by agonists of GABAA receptors or fire action potentials. The Ca2+ rise produces negative feedback by modulating the mechanoreceptor current and regulates Ca2+- and voltage-activated K+ currents. However, nothing is known about Ca2+ buffering in VS-3 neurons. Dynamic changes in VS-3 neuron intracellular [Ca2+] were measured using the fluorescent Ca2+ indicator Oregon Green BAPTA-1 (OG488) to understand Ca2+ buffering and clearance. Intracellular OG488 concentration increased slowly over more than 2 h as it diffused through a sharp intracellular microelectrode and spread through the cell. This slow increase was used to measure endogenous Ca2+ buffering and clearance by the added buffer technique, with OG488 acting as both added exogenous buffer and Ca2+ indicator. [Ca2+] was raised for brief periods by regular action potential firing, produced by pulsed electric current injection through the microelectrode. The resulting rise and fall of [Ca2+] were well fitted by the single compartment model of Ca2+ dynamics. With earlier ratiometric [Ca2+] estimates, these data gave an endogenous Ca2+ binding ratio of 684. Strong Ca2+ buffering may assist these neurons to deal with rapid changes in mechanical inputs.

Increased expression of calcium/calmodulin-dependent protein kinase type II subunit δ after rat traumatic brain injury

Many cellular responses to Ca(2+) signals are mediated by Ca(2+)/calmodulin-dependent enzymes, among which is the Ca(2+)/calmodulin-dependent protein kinase II (CaMKII). CaMKII was originally described in rat brain tissue. In rat brain, four different subunits of the kinase have been identified: α, β, γ, and δ. This study aims to investigate changes of CaMKIIδ after traumatic brain injury and its possible role. Rat traumatic brain injury (TBI) model was established by controlled cortical injury system. In the present study, we mainly investigated the expression and cellular localization of CaMKIIδ after traumatic brain injury. Western blot analysis revealed that CaMKIIδ was present in normal rat brain cortex. It gradually increased, reached a peak at the third day after TBI, and then decreased. Importantly, more CaMKIIδ was colocalized with neuron. In addition, Western blot detection showed that the third day postinjury was also the apoptosis peak indicated by the elevated expression of caspase-3.Importantly, immunohistochemistry analysis revealed that injury-induced expression of CaMKIIδ was colabeled by caspase-3 (apoptosis cells marker). Moreover, pretreatment with the CaMKII inhibitor (KN62) reduced the injury-induced activation of caspase-3. Noticeably, the CaMKII inhibitor KN-62 could reduce TBI-induced cell injury assessed with lesion volume and attenuate behavioral outcome evaluated by motor test. These data suggested that CaMKIIδ may be implicated in the apoptosis of neuron and the recovery of neurological outcomes. However, the inherent mechanisms remained unknown. Further studies are needed to confirm the exact role of CaMKIIδ after brain injury.

Activation of GABAA receptors modulates all stages of mechanoreception in spider mechanosensory neurons

GABA(A) receptors mediate mainly inhibitory effects, but there are also many examples of excitatory effects in both mammalian and invertebrate preparations. Here, we aimed to create a complete, quantitative picture of GABA(A)-mediated excitation in a mechanosensory neuron where this phenomenon has been well established. We used muscimol to activate GABA(A) receptors in spider VS-3 neurons and measured the dynamic behavior independently and separately at each of three stages of mechanoreception (receptor current, receptor potential, and action potentials) before and during modulation. We calculated frequency response functions between each stage, estimated information as signal entropy, and estimated information capacity from coherence. Since coherence is sensitive to both noise and nonlinearity, we measured signal-to-noise separately at each stage by averaging responses to repeated mechanical inputs. Muscimol depolarized VS-3 neurons and, after brief inhibition, increased their firing rates. During this excitation, we found significant changes at each stage. Receptor current was attenuated but became more selective to high frequencies. Membrane impedance and time constant fell, favoring higher frequency transmission from receptor current to receptor potential. Action potential firing increased and had higher total entropy. Information capacity from signal-to-noise was always much higher than from coherence, confirming that intracellular noise does not limit signal transmission in these neurons. We conclude that GABA(A) receptor activation shifts each stage of mechanotransduction to higher frequency sensitivity, while the elevated firing rate increases the amount of information that can be encoded. These results show that a single neurotransmitter can finely modulate a sensory neuron's sensitivity and ability to transmit information.