Biology subjects

Shaw, D. K.

Publications and source records attributed to Shaw, D. K..

14 recordsLinked to original sources

bioRxiv2026

Borrelia burgdorferi bb0164 encodes a Na+/Ca2+ antiporter homolog with a novel role in Mn2+ homeostasis and infectivity

Borrelia burgdorferi, the Lyme disease causative agent, relies on trace metals for motility, growth, and virulence in the absence of metal transport homologues encoded in the genome. Previous studies characterized borrelial metal transporter (bmtA) as a manganese (Mn) transporter and speculated that it is the sole Mn transporter. An oxidative stress transposon library screen identified bb0164, annotated as a calcium/sodium antiporter, as having a putative metal binding domain. The transposon mutant lost the ability to internalize Mn suggesting B. burgdorferi is using a non-canonical protein for metal transport. In this study, a bb0164 deletion and complement were generated in B. burgdorferi 5A4-NP1 to evaluate for trace metal transport, virulence regulation, resistance to oxidative stress, and infectivity. Our data demonstrated that the loss of bb0164 resulted in a significant reduction in internalized Mn, increased sensitivity to oxidative stress, dysregulation of the BosR-RpoS virulence pathway, and a loss of infectivity in mice. The loss of bb0164 resulted in elevated rpoS, ospC, and dbpA expression and production, while bosR was not altered transcriptionally or post-transcriptionally. B. burgdorferi grown in chelated complete BSK-II media showed a similar sensitivity to oxidative stress and virulence dysregulation as the bb0164 mutant. These phenotypes were rescued by exogenous Mn and Zn without influencing the expression levels of bb0164 or bmtA. AlphaFold models of BB0164 were structurally divergent from the canonical bacterial Mn transporter, Bacillus subtilis MntH and B. burgdorferi BmtA, but shared high similarity with a calcium/cation antiporter superfamily member. Together, this study characterized BB0164 as a second non-canonical Mn transporter in B. burgdorferi that is essential for mammalian pathogenesis and likely supports metal homeostasis along with bmtA. More broadly, B. burgdorferi uses unique and uncharacterized mechanisms for metal homeostasis that supports physiology and pathogenesis of the spirochete during mammalian infection. Author SummaryLyme disease, caused by Borrelia burgdorferi, is the most common vector-borne illness in the United States and can result in a chronic inflammatory disease. B. burgdorferi acquires most of the necessary nutrients, including trace metals, from the host due to its limited metabolic capacity. B. burgdorferi has evolved a manganese-centric metabolism in place of the iron primarily used by other bacteria. Little is understood about manganese homeostasis in B. burgdorferi with a single transporter, BmtA, characterized to date. Here, we describe a second manganese transporter, encoded by bb0164, that is essential for infection, protects against oxidative stress, and alters genetic regulation. We found that BB0164, an annotated ion antiporter, does not structurally align with conserved manganese transporters from other bacteria. Interestingly, our work suggests bb0164 and bmtA are not subject to transcriptional regulation dependent on temperature or metal availability, differing from other bacterial manganese transporters. These findings indicate B. burgdorferi is uniquely using an antiporter protein for metal transport to support metal homeostasis, which further demonstrates the importance of manganese in borrelial pathogenesis.

microbiology↗

bioRxiv2026

An Nrf2-Nup214 positive feedback loop sustains the antioxidant response and promotes microbial infection in ticks

Ixodes scapularis ticks are obligate hematophagous ectoparasites that take a single bloodmeal per life stage. During blood digestion, large quantities of heme and iron are released, leading to the production of reactive oxygen species. To counter the oxidative stress, ticks have evolved robust antioxidant systems. We previously found that the antioxidant transcription factor Nrf2 is activated during infection and supports Anaplasma phagocytophilum colonization in ticks. To investigate the Nrf2 regulatory network, we queried promoter regions in the Ixodes genome for Nrf2 binding sites. The gene encoding the nuclear pore complex protein nucleoporin 214 was identified as a target that is induced during Anaplasma infection and putatively regulated by Nrf2. Ixodes nup214 was experimentally validated as an Nrf2-regulated gene through functional luciferase reporter assays, pharmacological manipulation, and RNA interference transcriptional repression. We found that elevated expression of Nup214 leads to binding of the nuclear export protein CRM1, thereby trapping Nrf2 in the nucleus. Increased nuclear retention of Nrf2 prolonged the antioxidant response and functionally supported Anaplasma survival. Our findings uncover a previously unknown mechanism potentiated by Nrf2 that supports Anaplasma infection in ticks. SIGNIFICANCETicks have evolved to rely on host blood for nutrition and development. However, blood feeding comes with drawbacks. During digestion, large quantities of heme and iron are released, which promote the production of reactive oxygen species. To counter this, ticks have evolved robust antioxidant responses to protect themselves against oxidative stress. How tick-transmitted microbes, such as Anaplasma phagocytophilum, withstand the oxidative challenge in the tick is not well understood. Here, we demonstrate that, during infection, host-driven antioxidant defenses coordinated by the transcription factor Nrf2 support Anaplasma infection and persistence in ticks. We show that Nrf2 upregulates the nuclear pore complex protein Nucleoporin 214, which sequesters Nrf2 in the nucleus. The prolonged nuclear retention of Nrf2 enhances the tick antioxidant response, thereby supporting Anaplasma survival in the arthropod vector.

microbiology↗

bioRxiv2026

Transient activation of potent progenitor cells is required for spinal cord regeneration

Adult zebrafish exhibit full recovery following spinal cord injury. Transient expansion of stem cell-like progenitors is thought to underlie their regenerative capacity. Yet, our understanding of the identities and contributions of the crucial stem cell populations that direct spontaneous neural repair remains limited. Moreover, while most neural regeneration research is centered on promoting proliferative repair, the regulatory mechanisms that reinstate quiescence post-repair are unknown. Here, we determined the molecular identities and cellular contributions of sox2+ progenitors during spinal cord repair. Genetic lineage tracing shows zebrafish spinal progenitors, while quiescent in uninjured tissues, self-renew and differentiate into neurons and glia after injury. By single-cell sequencing, sox2+ cells are heterogeneous and biased towards neuronal or glial fates in both homeostatic and regenerating tissues. By screening for transcription factors that are differentially expressed in acute versus chronic spinal cord injury, we find the Bach1 transcription factors control transient progenitor cell activation by acting as dual activators and repressors of sox2 expression. This study elucidates the molecular diversity and contributions of sox2 expressing cells during spinal cord repair and identifies a transcriptional regulatory switch by which progenitor cells expand after injury and restore quiescence after regeneration is completed.

neuroscience↗

bioRxiv2025

Adaptation of Anaplasma phagocytophilum to the tick vector is controlled by the transcriptional regulator Tr1

Rickettsial pathogens are strictly dependent on the cellular biology of their hosts for survival and replication. Predominantly transmitted by blood-feeding arthropods, these vector-borne pathogens are forced to adapt between the disparate environments of their mammalian host and arthropod vector. To achieve this, the Rickettsial bacteria Anaplasma phagocytophilum undergoes extensive transcriptional reprogramming with over 41% of its genes differentially transcribed between mammals and Ixodes scapularis ticks. How the bacterium orchestrates this dramatic transcriptional reprogramming is not understood. The gene tr1 encodes a Helix-Turn-Helix DNA-binding protein that is exclusively expressed during tick infection. Herein, we show that tr1 is essential for A. phagocytophilum survival in ticks and regulates the transcription of other genes necessary to adapt to the arthropod vector. We demonstrate that Tr1 is a DNA-binding protein and recognizes promotors of tick-specific genes in A. phagocytophilum, including secreted effector ateA, alternate components of type IV secretion system (T4SS), and membrane proteins. Our findings demonstrate that Tr1 is a master regulator of genes that are critical for A. phagocytophilum adaptation to the tick.

microbiology↗

bioRxiv2025

Acquired tick resistance in Peromyscus leucopus alters Ixodes scapularis infection

Ticks are obligate hematophagous parasites and pathogen vectors responsible for morbidity and mortality worldwide. Ixodes scapularis is a vector for at least seven pathogens relevant to human and animal health including the Lyme disease microbe, Borrelia burgdorferi, and the causative agent of anaplasmosis, Anaplasma phagocytophilum. Tick-host interactions are a driving influence on the maintenance of tick-borne pathogens in a population. Here, we report that repeated I. scapularis larval infestations on the wild host species Peromyscus leucopus leads to immune-mediated rejection of the tick, a phenomenon termed acquired tick resistance (ATR). We found that over 50% fewer larvae reached repletion and had decreased blood meal weights compared to larvae fed on naive hosts. Additionally, mice exhibited increasingly severe inflammation at tick bite sites characterized by an influx of basophils, eosinophils, neutrophils, and T lymphocytes. Larvae fed on sensitized mice ingested higher quantities of host leukocytes when compared to ticks fed on naive hosts, which rarely ingested nucleated cells. When challenged with B. burgdorferi or A. phagocytophilum, larvae fed on sensitized mice ingested more bacteria. Altogether, we demonstrate that reservoir host species develop ATR against larval I. scapularis, which reduces tick feeding success and affects pathogen ingestion by larvae. These results indicate that ATR could impact Ixodes population dynamics, prevalence of infected ticks, and pathogen circulation in the wild.

immunology↗

bioRxiv2025

ATF6 enables pathogen infection in ticks by inducing stomatin and altering cholesterol dynamics

How tick-borne pathogens interact with their hosts has been primarily studied in vertebrates where disease is observed. Comparatively less is known about pathogen interactions within the tick. Here, we report that Ixodes scapularis ticks infected with either Anaplasma phagocytophilum (causative agent of anaplasmosis) or Borrelia burgdorferi (causative agent of Lyme disease) show activation of the ATF6 branch of the unfolded protein response (UPR). Disabling ATF6 functionally restricts pathogen survival in ticks. When stimulated, ATF6 functions as a transcription factor, but is the least understood out of the three UPR pathways. To interrogate the Ixodes ATF6 transcriptional network, we developed a custom R script to query tick promoter sequences. This revealed stomatin as a potential gene target, which has roles in lipid homeostasis and vesical transport. Ixodes stomatin was experimentally validated as a bona fide ATF6-regulated gene through luciferase reporter assays, pharmacological activators, and RNAi transcriptional repression. Silencing stomatin decreased A. phagocytophilum colonization in Ixodes and disrupted cholesterol dynamics in tick cells. Furthermore, blocking stomatin restricted cholesterol availability to the bacterium, thereby inhibiting growth and survival. Taken together, we have identified the Ixodes ATF6 pathway as a novel contributor to vector competence through Stomatin-regulated cholesterol homeostasis. Moreover, our custom, web-based transcription factor binding site search tool "ArthroQuest" revealed that the ATF6-regulated nature of stomatin is unique to blood-feeding arthropods. Collectively, these findings highlight the importance of studying fundamental processes in non-model organisms. IMPORTANCEHost-pathogen interactions for tick-borne pathogens like Anaplasma phagocytophilum (causative agent of Anaplasmosis) have been primarily studied in mammalian hosts. Comparatively less is known about interactions within the tick. Herein, we find that tick-borne pathogens activate the cellular stress response receptor, ATF6, in Ixodes ticks. Upon activation, ATF6 is cleaved and the cytosolic portion translocates to the nucleus to function as a transcription factor that coordinates gene expression networks. Using a custom script in R to query the Ixodes ATF6 regulome, stomatin was identified as an ATF6-regulated target that supports Anaplasma colonization by facilitating cholesterol availability to the bacterium. Moreover, our custom, web-based tool "ArthroQuest" found that the ATF6-regulated nature of stomatin is unique to arthropods. Given that lipid hijacking is common among arthropod-borne microbes, ATF6-mediated induction of stomatin may be a mechanism that is exploited in many vector-pathogen relationships for the survival and persistence of transmissible microbes. Collectively, this study identified a novel contributor to vector competence and highlights the importance of studying molecular networks in non-model organisms.

microbiology↗

bioRxiv2024

Elevated phagocytic capacity directs innate spinal cord repair

Immune cells elicit a continuum of transcriptional and functional states after spinal cord injury (SCI). In mammals, inefficient debris clearance and chronic inflammation impede recovery and overshadow pro-regenerative immune functions. We found that, unlike mammals, zebrafish SCI elicits transient immune activation and efficient debris clearance, without causing chronic inflammation. Single-cell transcriptomics and inducible genetic ablation showed zebrafish macrophages are highly phagocytic and required for regeneration. Cross-species comparisons between zebrafish and mammalian macrophages identified transcription and immune response regulator (tcim) as a macrophage-enriched zebrafish gene. Genetic deletion of zebrafish tcim impairs phagocytosis and regeneration, causes aberrant and chronic immune activation, and can be rescued by transplanting wild-type immune precursors into tcim mutants. Conversely, genetic expression of human TCIM accelerates debris clearance and regeneration by reprogramming myeloid precursors into activated phagocytes. This study establishes a central requirement for elevated phagocytic capacity to achieve innate spinal cord repair.

neuroscience↗

bioRxiv2023

Rab27 in tick extracellular vesicle biogenesis and infection

BackgroundThe blacklegged tick, Ixodes scapularis, transmits most vector-borne diseases in the United States. It vectors seven pathogens of public health relevance, including the emerging human pathogen Anaplasma phagocytophilum. Nevertheless, it remains critically understudied when compared to other arthropod vectors. I. scapularis releases a variety of molecules that assist in the modulation of host responses. Recently, it was found that extracellular vesicles (EVs) carry several of these molecules and may impact microbial transmission to the mammalian host. EV biogenesis has been studied in mammalian systems and is relatively well understood, but the molecular players important for the formation and secretion of EVs in arthropods of public health relevance remain elusive. RabGTPases are among the major molecular players in mammalian EV biogenesis. They influence membrane identity and vesicle budding, uncoating, and motility. MethodsUsing BLAST, an in-silico pathway for EV biogenesis in ticks was re-constructed. We identified Rab27 for further study. EVs were collected from ISE6 tick cells after knocking down rab27 to examine its role in tick EV biogenesis. I. scapularis nymphs were injected with small interfering RNAs to knock down rab27 then fed on naive and A. phagocytophilum infected mice to explore the importance of rab27 in tick feeding and bacterial acquisition. ResultsOur BLAST analysis identified several of the proteins involved in EV biogenesis in ticks, including Rab27. We show that silencing rab27 in I. scapularis impacts tick fitness. Additionally, ticks acquire less A. phagocytophilum after rab27 silencing. Experiments in the tick ISE6 cell line show that silencing of rab27 causes a distinct range profile of tick EVs, indicating that Rab27 is needed to regulate EV biogenesis. ConclusionsRab27 is needed for successful tick feeding and may be important for acquiring A. phagocytophilum during a blood meal. Additionally, silencing rab27 in tick cells results in a shift of extracellular vesicle size. Overall, we have observed that Rab27 plays a key role in tick EV biogenesis and the tripartite interactions among the vector, the mammalian host, and a microbe it encounters.

microbiology↗

bioRxiv2023

PERK-mediated antioxidant response is key for pathogen persistence in ticks

A crucial phase in the lifecycle of tick-borne pathogens is the time spent colonizing and persisting within the arthropod. Tick immunity is emerging as a key force shaping how transmissible pathogens interact with the vector. How pathogens remain in the tick despite immunological pressure remains unknown. In persistently infected Ixodes scapularis, we found that Borrelia burgdorferi (Lyme disease) and Anaplasma phagocytophilum (granulocytic anaplasmosis) activate a cellular stress pathway mediated by the endoplasmic reticulum receptor PERK and the central regulatory molecule, eIF2. Disabling the PERK pathway through pharmacological inhibition and RNAi significantly decreased microbial numbers. In vivo RNA interference of the PERK pathway not only reduced the number of A. phagocytophilum and B. burgdorferi colonizing larvae after a bloodmeal, but also significantly reduced the number of bacteria that survive the molt. An investigation into PERK pathway-regulated targets revealed that A. phagocytophilum and B. burgdorferi induce activity of the antioxidant response regulator, Nrf2. Tick cells deficient for nrf2 expression or PERK signaling showed accumulation of reactive oxygen and nitrogen species in addition to reduced microbial survival. Supplementation with antioxidants rescued the microbicidal phenotype caused by blocking the PERK pathway. Altogether, our study demonstrates that the Ixodes PERK pathway is activated by transmissible microbes and facilitates persistence in the arthropod by potentiating an Nrf2-regulated antioxidant environment.

microbiology↗

bioRxiv2023

An Anaplasma phagocytophilum T4SS effector, AteA, is essential for tick infection

Pathogens must adapt to disparate environments in permissive host species, a feat that is especially pronounced for vector-borne microbes, which transition between vertebrate hosts and arthropod vectors to complete their lifecycles. Most knowledge about arthropod-vectored bacterial pathogens centers on their life in the mammalian host, where disease occurs. However, disease outbreaks are driven by the arthropod vectors. Adapting to the arthropod is critical for obligate intracellular rickettsial pathogens, as they depend on eukaryotic cells for survival. To manipulate the intracellular environment, these bacteria use Type IV Secretion Systems (T4SS) to deliver effectors into the host cell. To date, few rickettsial T4SS translocated effectors have been identified and have only been examined in the context of mammalian infection. We identified an effector from the tick-borne rickettsial pathogen Anaplasma phagocytophilum, HGE1_02492, as critical for survival in tick cells and acquisition by ticks in vivo. Conversely, HGE1_02492 was dispensable during mammalian cell culture and murine infection. We show HGE1_02492 is translocatable in a T4SS-dependent manner to the host cell cytosol. In eukaryotic cells, the HGE1_02492 localized with cortical actin filaments, which is dependent on multiple sub-domains of the protein. HGE1_02492 is the first arthropod-vector specific T4SS translocated effector identified from a rickettsial pathogen. Moreover, the subcellular target of HGE1_02492 suggests that A. phagocytophilum is manipulating actin to enable arthropod colonization. Based on these findings, we propose the name AteA for Anaplasma (phagocytophilum) tick effector A. Altogether, we show that A. phagocytophilum uses distinct strategies to cycle between mammals and arthropods. ImportanceTicks are the number one vector of pathogens for livestock worldwide and for humans in the US. The biology of tick transmission is an understudied area. Understanding this critical interaction could provide opportunities to affect the course of disease spread. In this study we examined the zoonotic tick-borne agent Anaplasma phagocytophilum and identified a secreted protein, AteA, that is expressed in a tick-specific manner. These secreted proteins, termed effectors, are the first proteins to interact with the host environment. AteA is essential for survival in ticks and appears to interact with cortical actin. Most effector proteins are studied in the context of the mammalian host; however, understanding how this unique set of proteins affect tick transmission is critical to developing interventions.

microbiology↗

bioRxiv2022

CD36 homologs determine microbial resistance to the Lyme disease spirochete

Pattern recognition receptors sense pathogens in arthropods and mammals through distinct immune processes. Whether these molecules share a similar function and recognize the same microbe in evolutionarily distant species remain ill-defined. Here, we establish that the CD36 superfamily is required for Borrelia burgdorferi resistance in both the arthropod vector and humans. Using the blacklegged tick Ixodes scapularis and an electronic health record-linked biobank, we demonstrate that CD36 members elicit immunity to the Lyme disease spirochete. In ticks, the CD36-like protein Croquemort recognizes lipids and initiates the immune deficiency and jun N-terminal kinase pathways against B. burgdorferi. In humans, exome sequencing and clinical information reveal that individuals with CD36 loss-of-function variants have increased prevalence of Lyme disease. Altogether, we discovered a conserved mechanism of anti-bacterial immunity. One Sentence SummaryLipid receptors belonging to the CD36 superfamily exhibit a shared immune function in both ticks and humans.

immunology↗

bioRxiv2021

The unfolded protein response triggers the ancestral immune deficiency pathway

The insect immune deficiency (IMD) pathway is a defense mechanism that senses and responds to Gram negative bacteria. Ticks lack genes encoding upstream components that initiate the IMD pathway. Despite this deficiency, core signaling molecules are present and functionally restrict tick-borne pathogens. The molecular events preceding activation remain undefined. Here, we show that the Unfolded Protein Response (UPR) initiates the IMD network in Ixodes scapularis ticks. The endoplasmic reticulum (ER) stress receptor, IRE1, is phosphorylated in response to tick-borne bacteria, but does not splice the mRNA encoding XBP1. Instead, through protein modeling and reciprocal pulldowns, we show that Ixodes IRE1 complexes with TRAF2. Disrupting IRE1-TRAF2 signaling blocks IMD pathway activation and diminishes the production of reactive oxygen species. Through in vitro, in vivo, and ex vivo techniques we demonstrate that the UPR-IMD pathway circuitry limits the Lyme disease-causing spirochete Borrelia burgdorferi and the rickettsial agents Anaplasma phagocytophilum and A. marginale (anaplasmosis). Altogether, our study uncovers a novel linkage between the UPR and the IMD pathway in ticks.

immunology↗

bioRxiv2021

Efficient CRISPR/Cas9 mutagenesis for neurobehavioral screening in adult zebrafish

Adult zebrafish are increasingly used to interrogate mechanisms of disease development and tissue regeneration. Yet, the prospect of large-scale genetics in adult zebrafish has traditionally faced a host of biological and technical challenges. Here, we describe an experimental pipeline that combines high-efficiency CRISPR/Cas9 mutagenesis with functional phenotypic screening to identify genes required for spinal cord repair in adult zebrafish. Using CRISPR/Cas9 dual-guide ribonucleic proteins, we show selective and combinatorial mutagenesis of 17 genes at 28 target sites with efficiencies exceeding 85% in adult F0 crispants. We find that capillary electrophoresis is a reliable method to measure indel frequencies, while avoiding the limitations of restriction enzyme-based genotyping. Using a quantifiable behavioral assay, we identify 7 single- or duplicate-gene crispants with reduced functional recovery after spinal cord injury. To rule out off-target effects, we generate germline mutations that recapitulate the crispant regeneration phenotypes. This study provides a platform that combines high-efficiency somatic mutagenesis with a functional phenotypic readout to perform medium- to large-scale genetic studies in adult zebrafish.

genetics↗

bioRxiv2020

Smoothened Transduces Hedgehog Signals via Activity-Dependent Sequestration of PKA Catalytic Subunits

ABSTRACTThe Hedgehog (Hh) pathway is essential for organ development, homeostasis, and regeneration. Dysfunction of this cascade drives several cancers. To control expression of pathway target genes, the G protein-coupled receptor (GPCR) Smoothened (SMO) activates glioma-associated (GLI) transcription factors via an unknown mechanism. Here we show that, rather than conforming to traditional GPCR signaling paradigms, SMO activates GLI by binding and sequestering protein kinase A (PKA) catalytic subunits at the membrane. This sequestration, triggered by GPCR kinase 2 (GRK2)-mediated phosphorylation of SMO intracellular domains, prevents PKA from phosphorylating soluble substrates, releasing GLI from PKA-mediated inhibition. Our work provides a mechanism directly linking Hh signal transduction at the membrane to GLI transcription in the nucleus. This process is more fundamentally similar between species than prevailing hypotheses suggest. The mechanism described here may apply broadly to other GPCR- and PKA-containing cascades in diverse areas of biology.Competing Interest StatementThe authors have declared no competing interest.View Full Text

biochemistry↗