The C-terminal of CASY-1/Calsyntenin regulates GABAergic synaptic transmission at the Caenorhabditis elegans neuromuscular junction

Aged Biodegradable Nanoplastics Enhance Body Accumulation Associated with Worse Neuronal Damage in Caenorhabditis elegans

The environmental and health challenges posed by petroleum-based biodegradable plastics, such as polybutylene succinate (PBS) and polybutyleneadipate-co-terephthalate (PBAT), are a significant concern because they are increasingly present in the environment and contribute a substantial proportion of microplastics (MPs) or nanoplastics (NPs). In this study, ultraviolet (UV)-aged PBS-NPs and PBAT-NPs are found to have a higher propensity to accumulate within the body of Caenorhabditis elegans (C. elegans) by prolonging the defecation interval, which could induce severe neuronal damage compared to pristine NPs. The increased accumulation of biodegradable nanoplastics (BNPs) and subsequent impairments of neurobehavior are highly attributed to their reduced particle size and altered surface properties, including changed chemical bonds and functional groups after photoaging. Aged BNPs also cause more severe damage to GABAergic neurons and neurotransmitter receptors, resulting in disrupted neuronal homeostasis and behaviors. Overall, BNPs of both PBS and PBAT components show no significant differences in biological accumulation and mechanisms of neural damage, highlighting the commonalities and characteristics of the adverse effects of petroleum-based BNPs on the nervous system. Our study opens up the exploration of the health impacts of photoaging and the degradation state of BNPs that are increasingly present in the environment.

Nervous system-wide analysis of all C. elegans cadherins reveals neuron-specific functions across multiple anatomical scales

Differential expression of cell adhesion proteins is a hallmark of cell-type diversity across the animal kingdom. Gene family-wide characterization of their organismal expression and function is, however, lacking. Using genome-engineered reporter alleles, we established an atlas of expression of the entire set of 12 cadherin gene family members in the nematode Caenorhabditis elegans, revealing differential expression across neuronal classes, a dichotomy between broadly and narrowly expressed cadherins, and several context-dependent temporal transitions in expression across development. Engineered mutant null alleles of cadherins were analyzed for defects in morphology, behavior, neuronal soma positions, neurite neighborhood topology and fasciculation, and localization of synapses in many parts of the nervous system. This analysis revealed a restricted pattern of neuronal differentiation defects at discrete subsets of anatomical scales, including a novel role of cadherins in experience-dependent electrical synapse formation. In total, our analysis results in previously little explored perspectives on cadherin deployment and function.

Sensory modulation of neuropeptide signaling by CASY-1 gates cholinergic transmission at Caenorhabditis elegans neuromuscular junction

The neuromuscular junction (NMJ) is crucial for understanding the fundamentals of synaptic transmission and activity. Various modulators operate within neuronal circuits, from sensory to motor neurons, to influence synaptic transmission at the NMJ. This study sheds light on the regulation of sensory-evoked cholinergic neurotransmission at motor neurons orchestrated by CASY-1, the mammalian calsyntenin orthologue. We report that the increased excitation-inhibition (E-I) ratio at the NMJ in casy-1 mutants is likely due to its interactions with neuromodulators in sensory neurons. We explored the intricate genetic interactions of CASY- 1 with the neuropeptide FLP-21 and its receptor, NPR-1, both of which display simultaneous alterations in cholinergic signaling at the NMJ. Through genetic, pharmacological, and bioimaging-based experiments, we proposed a mechanism by which CASY-1 potentially interacts with the neuropeptide-carrying vesicles to regulate synaptic transmission. The nematode Caenorhabditis elegans serves as an ideal model system for this study, enabling detailed insights into neuromodulatory mechanisms in the neuronal circuit.

The role of kinesin-1 in neuronal dense core vesicle transport, locomotion and lifespan regulation in C. elegans

Fast axonal transport is crucial for neuronal function and is driven by kinesins and cytoplasmic dynein. Here, we investigated the role of kinesin-1 in dense core vesicle (DCV) transport in C. elegans, using mutants in the kinesin light chains (klc-1 and klc-2) and the motor subunit (unc-116) expressing an ida-1::gfp transgene that labels DCVs. DCV transport in both directions was greatly impaired in an unc-116 mutant and had reduced velocity in a klc-2 mutant. In contrast, the speed of retrograde DCV transport was increased in a klc-1 mutant whereas anterograde transport was unaffected. We identified striking differences between the klc mutants in their effects on worm locomotion and responses to drugs affecting neuromuscular junction activity. We also determined lifespan, finding that unc-116 mutant was short-lived whereas the klc single mutant lifespan was wild type. The ida-1::gfp transgenic strain was also short-lived, but surprisingly, klc-1 and klc-2 extended the ida-1::gfp lifespan beyond that of wild type. Our findings suggest that kinesin-1 not only influences anterograde and retrograde DCV transport but is also involved in regulating lifespan and locomotion, with the two kinesin light chains playing distinct roles.

Calsyntenin-1 expression and function in brain tissue of lithium-pilocarpine rat seizure models

To present the expression of calsyntenin-1 (Clstn1) in the brain and investigate the potential mechanism of Clstn1 in lithium-pilocarpine rat seizure models. Thirty-five male SD adult rats were induced to have seizures by intraperitoneal injection of lithium chloride pilocarpine. Rats exhibiting spontaneous seizures were divided into the epilepsy (EP) group (n = 15), whereas those without seizures were divided into the control group (n = 14). Evaluate the expression of Clstn1 in the temporal lobe of two groups using Western blotting, immunohistochemistry, and immunofluorescence. Additionally, 55 male SD rats were subjected to status epilepticus (SE) using the same induction method. Rats experiencing seizures exceeding Racine's level 4 (n = 48) were randomly divided into three groups: SE, SE + control lentivirus (lentiviral vector expressing green fluorescent protein [LV-GFP]), and SE + Clstn1-targeted RNA interference lentivirus (LV-Clstn1-RNAi). The LV-GFP group served as a control for the lentiviral vector, whereas the LV-Clstn1-RNAi group received a lentivirus designed to silence Clstn1 expression. These lentiviral treatments were administered via hippocampal stereotactic injection 2 days after SE induction. Seven days after SE, Western blot analysis was performed to evaluate the expression of Clstn1 in the hippocampus and temporal lobe. Meanwhile, we observed the latency of spontaneous seizures and the frequency of spontaneous seizures within 8 weeks among the three groups. The expression of Clstn1 in the cortex and hippocampus of the EP group was significantly increased compared to the control group (p < .05). Immunohistochemistry and immunofluorescence showed that Clstn1 was widely distributed in the cerebral cortex and hippocampus of rats, and colocalization analysis revealed that it was mainly co expressed with neurons in the cytoplasm. Compared with the SE group (11.80 ± 2.17 days) and the SE + GFP group (12.40 ± 1.67 days), there was a statistically significant difference (p < .05) in the latency period of spontaneous seizures (15.14 ± 2.41 days) in the SE + Clstn1 + RNAi group rats. Compared with the SE group (4.60 ± 1.67 times) and the SE + GFP group (4.80 ± 2.05 times), the SE + Clstn1 + RNAi group (2.0 ± .89 times) showed a significant reduction in the frequency of spontaneous seizures within 2 weeks of chronic phase in rats (p < .05). Elevated Clstn1 expression in EP group suggests its role in EP onset. Targeting Clstn1 may be a potential therapeutic approach for EP management.

Genome-wide identification and spatiotemporal expression analysis of cadherin superfamily members in echinoderms

BACKGROUND

Cadherins are calcium-dependent transmembrane cell-cell adhesion proteins that are essential for metazoan development. They consist of three subfamilies: classical cadherins, which bind catenin, protocadherins, which contain 6-7 calcium-binding repeat domains, and atypical cadherins. Their functions include forming adherens junctions, establishing planar cell polarity (PCP), and regulating cell shape, proliferation, and migration. Because they are basal deuterostomes, echinoderms provide important insights into bilaterian evolution, but their only well-characterized cadherin is G-cadherin, a classical cadherin that is expressed by many embryonic epithelia. We aimed to better characterize echinoderm cadherins by conducting phylogenetic analyses and examining the spatiotemporal expression patterns of cadherin-encoding genes during Strongylocentrotus purpuratus development.

RESULTS

Our phylogenetic analyses conducted on two echinoid, three asteroid, and one crinoid species identified ten echinoderm cadherins, including one deuterostome-specific ortholog, cadherin-23, and an echinoderm-specific atypical cadherin that possibly arose in an echinoid-asteroid ancestor. Catenin-binding domains in dachsous-2 orthologs were found to be a deuterostome-specific innovation that was selectively lost in mouse, while those in Fat4 orthologs appeared to be Ambulacraria-specific and were selectively lost in non-crinoid echinoderms. The identified suite of echinoderm cadherins lacks vertebrate-specific innovations but contains two proteins that are present in protostomes and absent from mouse. The spatiotemporal expression patterns of four embryonically expressed cadherins (fat atypical cadherins 1 and 4, dachsous-2, and protocadherin-9) were dynamic and mirrored the expression pattern of Frizzled 5/8, a non-canonical Wnt PCP pathway receptor protein essential for archenteron morphogenesis.

CONCLUSIONS

The echinoderm cadherin toolkit is more similar to that of an ancient bilaterian predating protostomes and deuterostomes than it is to the suite of cadherins found in extant vertebrates. However, it also appears that deuterostomes underwent several cadherin-related innovations. Based on their similar spatiotemporal expression patterns and orthologous relationships to PCP-related and tumor-suppressing proteins, we hypothesize that sea urchin cadherins may play a role in regulating the shape and growth of embryonic epithelia and organs. Future experiments will examine cadherin expression in non-echinoid echinoderms and explore the functions of cadherins during echinoderm development.

Activation of the CaMKII-Sarm1-ASK1-p38 MAP kinase pathway protects against axon degeneration caused by loss of mitochondria

Mitochondrial defects are tightly linked to axon degeneration, yet the underlying cellular mechanisms remain poorly understood. In Caenorhabditis elegans, PVQ axons that lack mitochondria degenerate spontaneously with age. Using an unbiased genetic screen, we found that cell-specific activation of CaMKII/UNC-43 suppresses axon degeneration due to loss of mitochondria. Unexpectedly, CaMKII/UNC-43 activates the conserved Sarm1/TIR-1-ASK1/NSY-1-p38 MAPK pathway and eventually the transcription factor CEBP-1 to protect against degeneration. In addition, we show that disrupting a trafficking complex composed of calsyntenin/CASY-1, Mint/LIN-10, and kinesin suppresses axon degeneration. Further analysis indicates that disruption of this trafficking complex activates the CaMKII-Sarm1-MAPK pathway through L-type voltage-gated calcium channels. Our findings identify CaMKII as a pivot point between mitochondrial defects and axon degeneration, describe how it is regulated, and uncover a surprising neuroprotective role for the Sarm1-p38 MAPK pathway in this context.

Investigating the molecular mechanisms of learning and memory using Caenorhabditis elegans

Learning is an essential biological process for survival since it facilitates behavioural plasticity in response to environmental changes. This process is mediated by a wide variety of genes, mostly expressed in the nervous system. Many studies have extensively explored the molecular and cellular mechanisms underlying learning and memory. This review will focus on the advances gained through the study of the nematode Caenorhabditis elegans. C. elegans provides an excellent system to study learning because of its genetic tractability, in addition to its invariant, compact nervous system (~300 neurons) that is well-characterised at the structural level. Importantly, despite its compact nature, the nematode nervous system possesses a high level of conservation with mammalian systems. These features allow the study of genes within specific sensory-, inter- and motor neurons, facilitating the interrogation of signalling pathways that mediate learning via defined neural circuits. This review will detail how learning and memory can be studied in C. elegans through behavioural paradigms that target distinct sensory modalities. We will also summarise recent studies describing mechanisms through which key molecular and cellular pathways are proposed to affect associative and non-associative forms of learning.

UBC-9 Acts in GABA Neurons to Control Neuromuscular Signaling in C. elegans

Regulation of excitatory to inhibitory signaling balance is essential to nervous system health and is maintained by numerous enzyme systems that modulate the activity, localization, and abundance of synaptic proteins. SUMOylation is a key post-translational regulator of protein function in diverse cells, including neurons. There, its role in regulating synaptic transmission through pre- and postsynaptic effects has been shown primarily at glutamatergic central nervous system synapses, where the sole SUMO-conjugating enzyme Ubc9 is a critical player. However, whether Ubc9 functions globally at other synapses, including inhibitory synapses, has not been explored. Here, we investigated the role of UBC-9 and the SUMOylation pathway in controlling the balance of excitatory cholinergic and inhibitory GABAergic signaling required for muscle contraction in Caenorhabditis elegans. We found inhibition or overexpression of UBC-9 in neurons modestly increased muscle excitation. Similar and even stronger phenotypes were seen with UBC-9 overexpression specifically in GABAergic neurons, but not in cholinergic neurons. These effects correlated with accumulation of synaptic vesicle-associated proteins at GABAergic presynapses, where UBC-9 and the C. elegans SUMO ortholog SMO-1 localized, and with defects in GABA-dependent behaviors. Experiments involving expression of catalytically inactive UBC-9 [UBC-9(C93S)], as well as co-expression of UBC-9 and SMO-1, suggested wild type UBC-9 overexpressed alone may act via substrate sequestration in the absence of sufficient free SUMO, underscoring the importance of tightly regulated SUMO enzyme function. Similar effects on muscle excitation, GABAergic signaling, and synaptic vesicle localization occurred with overexpression of the SUMO activating enzyme subunit AOS-1. Together, these data support a model in which UBC-9 and the SUMOylation system act at presynaptic sites in inhibitory motor neurons to control synaptic signaling balance in C. elegans. Future studies will be important to define UBC-9 targets at this synapse, as well as mechanisms by which UBC-9 and the SUMO pathway are regulated.

Molecular mechanisms governing axonal transport: a C. elegans perspective

Axonal transport is integral for maintaining neuronal form and function, and defects in axonal transport have been correlated with several neurological diseases, making it a subject of extensive research over the past several years. The anterograde and retrograde transport machineries are crucial for the delivery and distribution of several cytoskeletal elements, growth factors, organelles and other synaptic cargo. Molecular motors and the neuronal cytoskeleton function as effectors for multiple neuronal processes such as axon outgrowth and synapse formation. This review examines the molecular mechanisms governing axonal transport, specifically highlighting the contribution of studies conducted in C. elegans, which has proved to be a tractable model system in which to identify both novel and conserved regulatory mechanisms of axonal transport.

Calsyntenin-3 interacts with both α- and β-neurexins in the regulation of excitatory synaptic innervation in specific Schaffer collateral pathways

Calsyntenin-3 (Clstn3) is a postsynaptic adhesion molecule that induces presynaptic differentiation via presynaptic neurexins (Nrxns), but whether Nrxns directly bind to Clstn3 has been a matter of debate. Here, using LC-MS/MS-based protein analysis, confocal microscopy, RNAscope assays, and electrophysiological recordings, we show that β-Nrxns directly interact via their LNS domain with Clstn3 and Clstn3 cadherin domains. Expression of splice site 4 (SS4) insert-positive β-Nrxn variants, but not insert-negative variants, reversed the impaired Clstn3 synaptogenic activity observed in Nrxn-deficient neurons. Consistently, Clstn3 selectively formed complexes with SS4-positive Nrxns in vivo Neuron-specific Clstn3 deletion caused significant reductions in number of excitatory synaptic inputs. Moreover, expression of Clstn3 cadherin domains in CA1 neurons of Clstn3 conditional knockout mice rescued structural deficits in excitatory synapses, especially within the stratum radiatum layer. Collectively, our results suggest that Clstn3 links to SS4-positive Nrxns to induce presynaptic differentiation and orchestrate excitatory synapse development in specific hippocampal neural circuits, including Schaffer collateral afferents.

Regulation of Glutamate Signaling in the Sensorimotor Circuit by CASY-1A/Calsyntenin in Caenorhabditis elegans

Locomotion is one of the most prominent behaviors in the nematode Caenorhabditis elegans. Neuronal circuits that ultimately produce coordinated dorso-ventral sinusoidal bends mediate this behavior. Synchronized locomotion requires an intricate balance between excitation and inhibition at the neuromuscular junctions (NMJ), the complex cellular and molecular mechanisms of which are not fully understood. Here, we describe the role of a cell adhesion molecule CASY-1, which functions to maintain this balance at the NMJ. In this study, we dissect out mechanisms by which the longer CASY-1A isoform could be affecting the excitatory cholinergic signaling at the NMJ by modulating the activity of sensory neurons. Mutants in casy-1 appear to have hyperactive sensory neurons, resulting in accelerated locomotion and motor circuit activity. These sensory neurons mediate increased motor activity via enhanced glutamate release. Using genetic, pharmacological, and optogenetic manipulations, we establish that CASY-1A is required to monitor the activity of these neurons. Our study illustrates a novel neuromodulatory role of CASY-1-mediated signaling in regulating the excitation-inhibition balance of the motor circuit.

C. elegans Locomotion: Finding Balance in Imbalance

The excitation-inhibition (E-I) imbalance in neural circuits represents a hallmark of several neuropsychiatric disorders. The tiny nematode Caenorhabditis elegans has emerged as an excellent system to study the molecular mechanisms underlying this imbalance in neuronal circuits. The C. elegans body wall muscles receive inputs from both excitatory cholinergic and inhibitory GABAergic motor neurons at neuromuscular junctions (NMJ), making it an excellent model for studying the genetic and molecular mechanisms required for maintaining E-I balance at the NMJ. The cholinergic neurons form dyadic synapses wherein they synapse onto ipsilateral body wall muscles allowing for muscle contraction as well as onto GABAergic motor neurons that in turn synapse on the contralateral body wall muscles causing muscle relaxation. An alternating wave of contraction and relaxation mediated by excitatory and inhibitory signals maintains locomotion in C. elegans. This locomotory behavior requires an intricate balance between the excitatory cholinergic signaling and the inhibitory GABAergic signaling mechanisms.Studies on the C. elegans NMJ have provided insights into several molecular mechanisms that could regulate this balance in neural circuits. This review provides a discussion on multiple genetic factors including neuropeptides and their receptors, cell adhesion molecules, and other molecular pathways that have been associated with maintaining E-I balance in C. elegans motor circuits. Further, it also discusses the implications of these studies that could help us in understanding the role of E-I balance in mammalian neural circuits and how changes in this balance could give rise to brain disorders.

Pentylenetetrazole (PTZ)-induced Convulsion Assay to Determine GABAergic Defects in Caenorhabditis elegans

Pentylenetetrazole (PTZ) is a GABA_A receptor antagonist and is used to monitor presynaptic defects in the release of the inhibitory neurotransmitter GABA. PTZ is a competitive inhibitor of GABA, and prevents binding of GABA on the GABA_A receptors present on the surface of muscle. In the absence of GABA binding, the excitatory to inhibitory signal ratio increases resulting in a convulsive phenotype. This assay provides a fast and reliable method to detect presynaptic defects in GABAergic synaptic transmission. The assay is based on correlating the extent of convulsions with the degree of presynaptic GABA release defects.