The baculovirus  Autographa californica multiple nucleopolyhedrovirus (AcMNPV), a pathogen of lepidopteran insects, has a striking dependence on the host cell actin cytoskeleton. During the delayed-early stage of infection, AcMNPV was shown to induce the accumulation of actin at the cortex of infected cells. However, the dynamics and molecular mechanism of cortical actin assembly remained unknown. Here, we show that AcMNPV induces dynamic cortical clusters of dot-like actin structures that mediate degradation of underlying extracellular matrix and therefore function similarly to clusters of invadosomes in mammalian cells. Furthermore, we find that the AcMNPV protein actin-rearrangement-inducing factor-1 (ARIF-1), which was previously shown to be necessary and sufficient for cortical actin assembly and efficient viral infection in insect hosts, is both necessary and sufficient for invadosome formation. We mapped the sequences within the C-terminal cytoplasmic region of ARIF-1 that are required for invadosome formation and identified individual tyrosine and proline residues that are required for organizing these structures. Additionally, we found that ARIF-1 and the invadosome-associated proteins cortactin and the Arp2/3 complex localize to invadosomes, and Arp2/3 complex is required for their formation. These ARIF-1-induced invadosomes may be important for the function of ARIF-1 in systemic virus spread. [Media: see text] [Media: see text] [Media: see text] [Media: see text] [Media: see text] [Media: see text] [Media: see text] [Media: see text] [Media: see text] [Media: see text]

No abstract

Ticks are increasingly important vectors of human and agricultural diseases. While many studies have focused on tick-borne bacteria, far less is known about tick-associated viruses and their roles in public health or tick physiology. To address this, we investigated patterns of bacterial and viral communities across two field populations of western black-legged ticks (Ixodes pacificus). Through metatranscriptomic analysis of 100 individual ticks, we quantified taxon prevalence, abundance, and co-occurrence with other members of the tick microbiome. Our analysis revealed 11 novel RNA viruses from Rhabdoviridae, Chuviridae, Picornaviridae, Phenuiviridae, Reoviridae, Solemovidiae, Narnaviridae, and 2 highly divergent RNA viruses lacking sequence similarity to known viral families. The majority of these viruses were also detectable in lab-raised ticks at all developmental life stages, localize to tick salivary glands, and show evidence of circulation in mice fed on by ticks. These data suggest that viruses are stable, heritable, and transmissible members of the tick microbiota. We also unexpectedly identified numerous virus-like transcripts that are associated with tick genomic DNA, most of which are distinct from known endogenous viral element-mediated immunity pathways in invertebrates. Together, our work reveals that in addition to potentially serving as vectors for potential viral pathogens, I. pacificus ticks may also have symbiotic partnerships with their own vertically-transmitted viruses or with ancient viruses through evolutionarily acquired virus-like transcripts. Our findings highlight how pervasive and intimate tick–virus interactions are, with major implications for both the fundamental physiology and vector biology of I. pacificus ticks.

The baculovirus Autographa californica multiple nucleopolyhedrovirus (AcMNPV), a pathogen of lepidopteran insects, has a striking dependence on the host cell actin cytoskeleton during infection. During the delayed-early stage of AcMNPV infection, the virus was shown to induce the accumulation of filamentous actin at the cortex of infected cells. However, the dynamics and molecular mechanism of cortical actin assembly remained unknown. Using live cell imaging, we show that AcMNPV induces the formation of dynamic dot-like actin structures that are arranged in clusters, resembling clusters of invadosomes in mammalian cells. Furthermore, we find that the AcMNPV protein actin-rearrangement-inducing factor-1 (ARIF-1), which was previously shown to be necessary and sufficient for assembly of cortical actin and efficient viral infection in insect hosts, is both necessary and sufficient for invadosome-like structure formation. We mapped the regions of ARIF-1 required for invadosome-like structure formation to a segment of the predicted C-terminal cytoplasmic region, and further identified residues tyrosine 332 and proline 335 as being required for organizing clusters of invadosome-like structures. Additionally, we found that ARIF-1 and the invadosome-associated proteins cortactin and the Arp2/3 complex localize to invadosome-like structures, and structure formation requires Arp2/3 complex activity. The resemblance of ARIF-1-induced structures to invadosomes in mammalian cells, and the known role of such structures in extracellular matrix degradation, suggests that AcMNPV-induced invadosome-like structures accelerate viral spread through the insect body by degrading extracellular matrix barriers during infection.