Biology subjects

Barker, C. M.

Publications and source records attributed to Barker, C. M..

9 recordsLinked to original sources

bioRxiv2026

Human iPSC-derived neurons identify West Nile virus neuropathogenesis signatures and reveal strain-dependent neuroattenuation

West Nile virus (WNV) is one of the leading causes of arthropod-transmitted encephalitis in the world, yet its effects on neurons, the principal target of WNV in the brain, remain poorly defined. Here we establish and use Ngn2-induced human iPSC-derived glutamatergic neurons to define the neuronal response to WNV through integrated temporal proteomics and transcriptomics. Temporal multi-omic profiling revealed that infection activated innate immunity and the Unfolded Protein Response while suppressing axonogenesis and synaptic programs. WNV infection also disrupted calcium homeostasis, reduced STMN2 abundance, and promoted cytoplasmic redistribution of TDP-43. Applying this neuronal model to characterize contemporary California isolates, we identified LA24, a lineage 1 strain that replicates efficiently in non-neuronal cell lines but is selectively attenuated in neurons, with reduced viral burden in the brain and attenuated pathogenicity in mice. Together, these findings uncover neuron-specific signatures of WNV pathogenesis and demonstrate that neuronal replication phenotypes can reveal strain-dependent virulence differences not captured by conventional cell lines.

microbiology↗

bioRxiv2026

Complete mitochondrial genomes of Arizona West Nile virus vectors, Culex quinquefasciatus and Culex tarsalis

Here we report a newly developed method utilizing long-range PCR and long-read Pacific Biosciences HiFi sequencing that successfully obtained two full-length and annotated mitochondrial genomes from Culex quinquefasciatus Say, 1823 and Culex tarsalis Coquillett, 1896, both from Maricopa County, Arizona, USA. Given the substantial burden of West Nile virus in Maricopa County over the past decade, and that these vectors are primarily responsible for spillover to human populations in the county, it is critical to better understand their distribution over time and space. This study begins to approach this need by contributing a novel approach that has resulted in the first West Nile virus vector mitochondrial genomes from Arizona. Our circular Cx. quinquefasciatus mitogenome is 15,587 bp in length, making it the first USA-based mitogenome sequenced through the AT-rich control region. The Cx. tarsalis mitochondrial genome is 16,416 bp long, longer than recently published California-based CTarK1 and Texas-based PQ585801 mitogenomes. The increased length of the Cx. tarsalis mitogenome is a result of a 905 bp insertion in the AT-rich control region, not present in the species publicly available mitogenomes. A maximum likelihood-based phylogenetic reconstruction supports the species designation of these newly-sequenced mitogenomes. The newly developed methodology offers a unique approach to study medically-important vector species around the globe, providing a solution to study populations through pooled vector pathogen surveillance programs.

genomics↗

bioRxiv2025

Evaluation of the safety and insecticidal efficacy of ivermectin-treated bird feed formulations in different avian species

BackgroundWest Nile virus (WNV) is maintained in an enzootic cycle between reservoir host birds and Culex (Cx.) spp. mosquitoes. This relationship presents a potential target for vector control strategies. Ivermectin (IVM), an endectocidal drug that selectively affects invertebrates while remaining safe at high concentrations in mammals and birds, can be delivered to Cx. tarsalis via blood meals from birds fed IVM-treated bird feed. In this study we evaluated the safety, efficacy, and utility of IVM-treated bird feed as a novel vector control strategy by assessing its impact on multiple bird species and mosquitoes. MethodsMosquitoes were collected during peak WNV transmission season in Northern Colorado and DNA extracted from blood meals to determine host species. Chickens, pigeons, zebra finches, and house sparrows were fed different formulations of IVM-treated bird feed and observed for clinical signs, and their sera were fed to Cx. tarsalis mosquitoes to evaluate mosquitocidal efficacy. Feeding rates and IVM serum concentrations in birds were analyzed by unpaired t-test and one-way ANOVA, and mosquito survivorship was analyzed by Kaplan-Meier curves and compared using paired log-rank tests. IVM serum concentration and mosquito survivorship were compared using Spearman correlation. ResultsSpeciation analyses conducted on blood meals from Cx. tarsalis collected during peak WNV transmission season in Northern Colorado determined that they feed primarily on songbird species that commonly visit bird feeders, with house sparrows representing the most frequent blood meal host. In laboratory experiments using multiple formulations and doses of IVM, chickens, pigeons, zebra finches, and house sparrows ate comparable amounts of IVM-treated bird feed compared to untreated feed, had similar weight gain, and exhibited no clinical signs of toxicity. Both colony-reared and locally captured Cx. tarsalis showed significant mortality after feeding on sera from IVM-treated birds compared to controls. ConclusionsThese results suggest that targeting songbirds with IVM-treated bird feed should be safe for wildlife and may elicit high rates of IVM-induced mortality by reaching a large proportion of WNV vector mosquitoes via their proclivity for feeding on passerine birds.

microbiology↗

bioRxiv2025

The CaMKII D135N mutation blocks kinase activity and reduces GluN2B binding

Three recent studies claimed that induction of long-term potentiation (LTP) of synaptic strength requires structural rather than enzymatic functions of the Ca2+/Calmodulin(CaM)-dependent protein kinase II (CaMKII). One study utilized the CaMKII D135N mutation, which was claimed to abolish enzymatic activity without affecting the structural function, i.e. binding to GluN2B. We found here that the D135N mutant indeed abolished enzymatic kinase activity and autophosphorylation at T286 (pT286). However, D135N mutation additionally reduced binding to GluN2B and prevented persistence of co-condensation with GluN2B. Similar as with the T286A mutant, GluN2B binding of the D135N mutant could be partially rescued by AS283, an inhibitor that directly enhances GluN2B binding. This partial effect on GluN2B binding has to be taken into account when using D135N to distinguish between enzymatic versus structural functions of CaMKII. Nonetheless, as discussed here, the D135N mutant indeed supports a structural rather than enzymatic CaMKII function in LTP induction.

neuroscience↗

bioRxiv2025

CaMKII monomers are sufficient for GluN2B binding, co-condensation, and synaptic potentiation

Cognitive functions require synaptic plasticity, specifically long-term potentiation (LTP). LTP is thought to require CaMKII binding to the NMDA-type glutamate receptor subunit GluN2B, but this poses a major conundrum: Truncated CaMKII monomers (without the hub domain that forms 12meric holoenzymes) fail to bind GluN2B, but still potentiate synapses when made constitutively active. We hypothesized that CaMKII monomer binding to GluN2B has just eluded detection. Instead, even though full-length CaMKII monomers (with hub domain mutations) were found to indeed bind and even co-condensate with GluN2B, truncated monomers were not. Nonetheless, truncated monomers still potentiated synapses, even in neurons with GluN2B mutations that ablate CaMKII binding. However, potentiation occurred only with monomers that were made Ca2+-independent by artificial phosphatase-resistant thio-autophosphorylation, not by regular autophosphorylation of T286. These findings support that CaMKII binding to GluN2B is required during physiological LTP induction because it generates the phosphatase-resistant autonomous activity that mediates LTP expression.

neuroscience↗

bioRxiv2023

Synchronicity in zebrafish locomotive circuit development mediated by electrical pacemaker interneurons

The earliest motor output in vertebrate animals is generated by clusters of early-born motor neurons that occupy distinct regions of the spinal cord, innervating stereotyped muscle groups. Even the simplest movements require coordinated activity across these motor pools, yet motor neurons are not directly interconnected and instead project to the periphery. Instead, emerging motor circuits might be synchronized by pacemaker interneurons. We hypothesize that pacemaker interneurons are required for synchronization of motor neuron activity throughout the spinal cord, coupling motor pools through electrical gap junctions to ultimately drive coordinated motor behavior. With functional imaging in the embryonic zebrafish spinal cord, we show that ipsilateral caudal interneurons possess periodic activity profiles prior to widespread motor circuit activity that transition to synchronized Ca2+ events in motor neurons throughout the spinal cord. Importantly, we also show that blockade of electrical gap junctions and ablation of pioneer pacemakers leads to desynchronization in developing motor circuits. Further, we use a genetic model of hyperactivity to gain critical insight into the consequences of errors in motor circuit formation and function, finding that Fragile X syndrome (FXS) model mutant zebrafish are hyperexcitable from the earliest phases of spontaneous behavior, show reduced sensitivity to blockade of electrical gap junctions, and have increased expression of the gap junction protein Connexin 36. Taken together, our work highlights the importance of pacemakers in the development of motor circuits and suggests that the origins of hyperactivity in neurodevelopmental disorders may be established during the initiation of motor circuit formation.

neuroscience↗

bioRxiv2022

Fmrp regulates neuronal balance in embryonic motor circuit formation

Motor behavior requires the balanced production and integration of a variety of neural cell types. Motor neurons are positioned in discrete locations in the ventral spinal cord, targeting specific muscles to drive locomotive contractions. Specialized spinal interneurons modulate and synchronize motor neuron activity to achieve coordinated motor output. Changes in the ratios of spinal interneurons could drastically alter motor output by tipping the balance of inhibition and excitation onto target motor neurons. Importantly, individuals with Fragile X syndrome (FXS) and associated autism spectrum disorders often have significant motor challenges, including repetitive behaviors and epilepsy. FXS stems from the transcriptional silencing of the gene Fragile X Messenger Ribonucleoprotein 1 (FMR1), which encodes an RNA binding protein that is implicated in a multitude of crucial neurodevelopmental processes, including cell specification. We find that zebrafish fmr1 mutants generate surplus ventral lateral descending (VeLD) interneurons, an early-born cell derived from the pMN domain. These GABAergic interneurons are also associated with changes in synaptogenesis, as fmr1 mutants show increased early expression of the scaffold Gephyrin, but these postsynaptic sites fail to mature. Our work shows that Fmrp regulates the proportionate production of neurons that comprise early embryonic motor circuits. As VeLD interneurons are hypothesized to act as central pattern generators driving the earliest spontaneous movements, this imbalance could profoundly influence the formation and long-term function of motor circuits driving locomotion.

neuroscience↗

bioRxiv2022

Semi-field and surveillance data define the natural diapause timeline for Culex pipiens across the United States

Culex pipiens is a globally-distributed mosquito of medical and veterinary importance, serving as a primary vector of West Nile virus (WNV). To survive winter, female Cx. pipiens mosquitoes undergo adult reproductive diapause initiated by photoperiod and temperature cues. While well-studied under laboratory conditions, the environmental signals that promote Cx. pipiens diapause induction in natural settings are less understood. Here, we evaluate Cx. pipiens in laboratory and semi-field studies to examine diapause induction, defining an approximate timeline beginning in late-August where mosquitoes become receptive to diapause. Using gravid (reproductive) mosquito surveillance data as a proxy for adult diapause incidence for locations across the United States (California, Colorado, Connecticut, Illinois, Iowa, Minnesota, Pennsylvania, and Virginia), we demonstrate consistent population declines coinciding with periods of diapause receptivity except in hybridization zones where Cx. quinquefasciatus is present, suggesting that Culex population genetics can significantly impact end-season population trends. Together, this study defines a window for diapause induction across the United States, shaped by temperature, latitude, elevation, and mosquito population genetics. Coinciding with the cessation of WNV activity, these data can have important implications for mosquito control, where targeted efforts prior to diapause induction can decrease mosquito populations and WNV overwintering to reduce mosquito-borne disease incidence the following season.

ecology↗

bioRxiv2020

Whole genome assembly of Culex tarsalis

The mosquito, Culex tarsalis, is a key vector in the western United States due to its role in transmission of zoonotic arboviruses that affect human health. Extensive research has been conducted on Cx. tarsalis ecology, feeding behavior, vector competence, autogeny, diapause, genetics, and insecticide resistance. Population genetic analyses in the western U.S. have identified at least three genetic clusters that are geographically distinct. Salivary gland-specific gene expression has also revealed genes involved in blood feeding. However, genetic studies of this mosquito have been hindered by the lack of a reference genome. To facilitate genomic studies in Cx. tarsalis, we have assembled and annotated a reference genome (CtarK1) based on PacBio HiFi reads from a single male. Using the Cx. tarsalis transcriptome and protein sequences from Culex quinquefasciatus, approximately 17,456 protein-coding genes, including the para insecticide resistance gene, were annotated in the CtarK1 genome. Genome completeness was assessed using the Benchmarking Universal Single-Copy Orthologs (BUSCO) tool, which identified 84.8% of the 2799 Dipteran BUSCO genes. The CtarK1 assembly is 790Mb with an N50 of 58kb. Using full mitochondrial genome alignments with other sequenced mosquito genomes we present a Bayesian phylogeny, which estimates that the divergence of Cx. tarsalis from Culex quinquefasciatus, the most closely related mosquito species with a genome, occurred 15.8-22.2 million years ago.

genomics↗