Hormonal gatekeeping via the blood-brain barrier governs caste-specific behavior in ants.

Here, we reveal an unanticipated role of the blood-brain barrier (BBB) in regulating complex social behavior in ants. Using scRNA-seq, we find localization in the BBB of a key hormone-degrading enzyme called juvenile hormone esterase (Jhe), and we show that this localization governs the level of juvenile hormone (JH3) entering the brain. Manipulation of the Jhe level reprograms the brain transcriptome between ant castes. Although ant Jhe is retained and functions intracellularly within the BBB, we show that Drosophila Jhe is naturally extracellular. Heterologous expression of ant Jhe into the Drosophila BBB alters behavior in fly to mimic what is seen in ants. Most strikingly, manipulation of Jhe levels in ants reprograms complex behavior between worker castes. Our study thus uncovers a remarkable, potentially conserved role of the BBB serving as a molecular gatekeeper for a neurohormonal pathway that regulates social behavior.

Long ant life span is maintained by a unique heat shock factor.

Eusocial insect reproductive females show strikingly longer life spans than nonreproductive female workers despite high genetic similarity. In the ant Harpegnathos saltator (Hsal), workers can transition to reproductive "gamergates," acquiring a fivefold prolonged life span by mechanisms that are poorly understood. We found that gamergates have elevated expression of heat shock response (HSR) genes in the absence of heat stress and enhanced survival with heat stress. This HSR gene elevation is driven in part by gamergate-specific up-regulation of the gene encoding a truncated form of a heat shock factor most similar to mammalian HSF2 (hsalHSF2). In workers, hsalHSF2 was bound to DNA only upon heat stress. In gamergates, hsalHSF2 bound to DNA even in the absence of heat stress and was localized to gamergate-biased HSR genes. Expression of hsalHSF2 in Drosophila melanogaster led to enhanced heat shock survival and extended life span in the absence of heat stress. Molecular characterization illuminated multiple parallels between long-lived flies and gamergates, underscoring the centrality of hsalHSF2 to extended ant life span. Hence, ant caste-specific heat stress resilience and extended longevity can be transferred to flies via hsalHSF2. These findings reinforce the critical role of proteostasis in health and aging and reveal novel mechanisms underlying facultative life span extension in ants.

SARS-CoV-2 disrupts host epigenetic regulation via histone mimicry.

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) emerged at the end of 2019 and caused the devastating global pandemic of coronavirus disease 2019 (COVID-19), in part because of its ability to effectively suppress host cell responses1-3. In rare cases, viral proteins dampen antiviral responses by mimicking critical regions of human histone proteins4-8, particularly those containing post-translational modifications required for transcriptional regulation9-11. Recent work has demonstrated that SARS-CoV-2 markedly disrupts host cell epigenetic regulation12-14. However, how SARS-CoV-2 controls the host cell epigenome and whether it uses histone mimicry to do so remain unclear. Here we show that the SARS-CoV-2 protein encoded by ORF8 (ORF8) functions as a histone mimic of the ARKS motifs in histone H3 to disrupt host cell epigenetic regulation. ORF8 is associated with chromatin, disrupts regulation of critical histone post-translational modifications and promotes chromatin compaction. Deletion of either the ORF8 gene or the histone mimic site attenuates the ability of SARS-CoV-2 to disrupt host cell chromatin, affects the transcriptional response to infection and attenuates viral genome copy number. These findings demonstrate a new function of ORF8 and a mechanism through which SARS-CoV-2 disrupts host cell epigenetic regulation. Further, this work provides a molecular basis for the finding that SARS-CoV-2 lacking ORF8 is associated with decreased severity of COVID-19.

An NK-like CAR T cell transition in CAR T cell dysfunction.

Chimeric antigen receptor (CAR) T cell therapy has achieved remarkable success in hematological malignancies but remains ineffective in solid tumors, due in part to CAR T cell exhaustion in the solid tumor microenvironment. To study dysfunction of mesothelin-redirected CAR T cells in pancreatic cancer, we establish a robust model of continuous antigen exposure that recapitulates hallmark features of T cell exhaustion and discover, both in vitro and in CAR T cell patients, that CAR dysregulation is associated with a CD8+ T-to-NK-like T cell transition. Furthermore, we identify a gene signature defining CAR and TCR dysregulation and transcription factors, including SOX4 and ID3 as key regulators of CAR T cell exhaustion. Our findings shed light on the plasticity of human CAR T cells and demonstrate that genetic downmodulation of ID3 and SOX4 expression can improve the efficacy of CAR T cell therapy in solid tumors by preventing or delaying CAR T cell dysfunction.

Kr-h1 maintains distinct caste-specific neurotranscriptomes in response to socially regulated hormones.

Behavioral plasticity is key to animal survival. Harpegnathos saltator ants can switch between worker and queen-like status (gamergate) depending on the outcome of social conflicts, providing an opportunity to study how distinct behavioral states are achieved in adult brains. Using social and molecular manipulations in live ants and ant neuronal cultures, we show that ecdysone and juvenile hormone drive molecular and functional differences in the brains of workers and gamergates and direct the transcriptional repressor Kr-h1 to different target genes. Depletion of Kr-h1 in the brain caused de-repression of "socially inappropriate" genes: gamergate genes were upregulated in workers, whereas worker genes were upregulated in gamergates. At the phenotypic level, loss of Kr-h1 resulted in the emergence of worker-specific behaviors in gamergates and gamergate-specific traits in workers. We conclude that Kr-h1 is a transcription factor that maintains distinct brain states established in response to socially regulated hormones.

Tramtrack acts during late pupal development to direct ant caste identity.

A key question in the rising field of neuroepigenetics is how behavioral plasticity is established and maintained in the developing CNS of multicellular organisms. Behavior is controlled through systemic changes in hormonal signaling, cell-specific regulation of gene expression, and changes in neuronal connections in the nervous system, however the link between these pathways is unclear. In the ant Camponotus floridanus, the epigenetic corepressor CoREST is a central player in experimentally-induced reprogramming of caste-specific behavior, from soldier (Major worker) to forager (Minor worker). Here, we show this pathway is engaged naturally on a large genomic scale during late pupal development targeting multiple genes differentially expressed between castes, and central to this mechanism is the protein tramtrack (ttk), a DNA binding partner of CoREST. Caste-specific differences in DNA binding of ttk co-binding with CoREST correlate with caste-biased gene expression both in the late pupal stage and immediately after eclosion. However, we find a unique set of exclusive Minor-bound genes that show ttk pre-binding in the late pupal stage preceding CoREST binding, followed by caste-specific gene repression on the first day of eclosion. In addition, we show that ttk binding correlates with neurogenic Notch signaling, and that specific ttk binding between castes is enriched for regulatory sites associated with hormonal function. Overall our findings elucidate a pathway of transcription factor binding leading to a repressive epigenetic axis that lies at the crux of development and hormonal signaling to define worker caste identity in C. floridanus.

Social reprogramming in ants induces longevity-associated glia remodeling.

In social insects, workers and queens arise from the same genome but display profound differences in behavior and longevity. In Harpegnathos saltator ants, adult workers can transition to a queen-like state called gamergate, which results in reprogramming of social behavior and life-span extension. Using single-cell RNA sequencing, we compared the distribution of neuronal and glial populations before and after the social transition. We found that the conversion of workers into gamergates resulted in the expansion of neuroprotective ensheathing glia. Brain injury assays revealed that activation of the damage response gene Mmp1 was weaker in old workers, where the relative frequency of ensheathing glia also declined. On the other hand, long-lived gamergates retained a larger fraction of ensheathing glia and the ability to mount a strong Mmp1 response to brain injury into old age. We also observed molecular and cellular changes suggestive of age-associated decline in ensheathing glia in Drosophila.

Gene content evolution in the arthropods.

BACKGROUND: Arthropods comprise the largest and most diverse phylum on Earth and play vital roles in nearly every ecosystem. Their diversity stems in part from variations on a conserved body plan, resulting from and recorded in adaptive changes in the genome. Dissection of the genomic record of sequence change enables broad questions regarding genome evolution to be addressed, even across hyper-diverse taxa within arthropods. RESULTS: Using 76 whole genome sequences representing 21 orders spanning more than 500 million years of arthropod evolution, we document changes in gene and protein domain content and provide temporal and phylogenetic context for interpreting these innovations. We identify many novel gene families that arose early in the evolution of arthropods and during the diversification of insects into modern orders. We reveal unexpected variation in patterns of DNA methylation across arthropods and examples of gene family and protein domain evolution coincident with the appearance of notable phenotypic and physiological adaptations such as flight, metamorphosis, sociality, and chemoperception. CONCLUSIONS: These analyses demonstrate how large-scale comparative genomics can provide broad new insights into the genotype to phenotype map and generate testable hypotheses about the evolution of animal diversity.

Epigenetic Regulator CoREST Controls Social Behavior in Ants.

Ants acquire distinct morphological and behavioral phenotypes arising from a common genome, underscoring the importance of epigenetic regulation. In Camponotus floridanus, "Major" workers defend the colony, but can be epigenetically reprogrammed to forage for food analogously to "Minor" workers. Here, we utilize reprogramming to investigate natural behavioral specification. Reprogramming of Majors upregulates Minor-biased genes and downregulates Major-biased genes, engaging molecular pathways fundamental to foraging behavior. We discover the neuronal corepressor for element-1-silencing transcription factor (CoREST) is upregulated upon reprogramming and required for the epigenetic switch to foraging. Genome-wide profiling during reprogramming reveals CoREST represses expression of enzymes that degrade juvenile hormone (JH), a hormone elevated upon reprogramming. High CoREST, low JH-degrader expression, and high JH levels are mirrored in natural Minors, revealing parallel mechanisms of natural and reprogrammed foraging. These results unveil chromatin regulation via CoREST as central to programming of ant social behavior, with potential far-reaching implications for behavioral epigenetics.

Leveraging technological innovations to investigate evolutionary transitions to eusociality.

The study of the major transition to eusociality presents several challenges to researchers, largely resulting from the importance of complex behavioral phenotypes and the shift from individual to group level selection. These challenges are being met with corresponding technological improvements. Advances in resource development for non-model taxa, behavioral tracking, nucleic acid sequencing, and reverse genetics are facilitating studies of hypotheses that were previously intractable. These innovations are resulting in the development of new model systems tailored to the exploration of specific behavioral phenotypes and the querying of underlying molecular mechanisms that drive eusocial behaviors. Here, we present a brief overview of how methodological innovations are advancing our understanding of the evolution of eusociality.

Epigenetics in Insects: Genome Regulation and the Generation of Phenotypic Diversity.

Epigenetic inheritance is fundamentally important to cellular differentiation and developmental plasticity. In this review, we provide an introduction to the field of molecular epigenetics in insects. Epigenetic information is passed across cell divisions through the methylation of DNA, the modification of histone proteins, and the activity of noncoding RNAs. Much of our knowledge of insect epigenetics has been gleaned from a few model species. However, more studies of epigenetic information in traditionally nonmodel taxa will help advance our understanding of the developmental and evolutionary significance of epigenetic inheritance in insects. To this end, we also provide a brief overview of techniques for profiling and perturbing individual facets of the epigenome. Doing so in diverse cellular, developmental, and taxonomic contexts will collectively help shed new light on how genome regulation results in the generation of diversity in insect form and function.

Conserved Genes Underlie Phenotypic Plasticity in an Incipiently Social Bee.

Despite a strong history of theoretical work on the mechanisms of social evolution, relatively little is known of the molecular genetic changes that accompany transitions from solitary to eusocial forms. Here, we provide the first genome of an incipiently social bee that shows both solitary and social colony organization in sympatry, the Australian carpenter bee Ceratina australensis. Through comparative analysis, we provide support for the role of conserved genes and cis-regulation of gene expression in the phenotypic plasticity observed in nest-sharing, a rudimentary form of sociality. Additionally, we find that these conserved genes are associated with caste differences in advanced eusocial species, suggesting these types of mechanisms could pave the molecular pathway from solitary to eusocial living. Genes associated with social nesting in this species show signatures of being deeply conserved, in contrast to previous studies in other bees showing novel and faster-evolving genes are associated with derived sociality. Our data provide support for the idea that the earliest social transitions are driven by changes in gene regulation of deeply conserved genes.

The Toxicogenome of Hyalella azteca: A Model for Sediment Ecotoxicology and Evolutionary Toxicology.

Hyalella azteca is a cryptic species complex of epibenthic amphipods of interest to ecotoxicology and evolutionary biology. It is the primary crustacean used in North America for sediment toxicity testing and an emerging model for molecular ecotoxicology. To provide molecular resources for sediment quality assessments and evolutionary studies, we sequenced, assembled, and annotated the genome of the H. azteca U.S. Lab Strain. The genome quality and completeness is comparable with other ecotoxicological model species. Through targeted investigation and use of gene expression data sets of H. azteca exposed to pesticides, metals, and other emerging contaminants, we annotated and characterized the major gene families involved in sequestration, detoxification, oxidative stress, and toxicant response. Our results revealed gene loss related to light sensing, but a large expansion in chemoreceptors, likely underlying sensory shifts necessary in their low light habitats. Gene family expansions were also noted for cytochrome P450 genes, cuticle proteins, ion transporters, and include recent gene duplications in the metal sequestration protein, metallothionein. Mapping of differentially expressed transcripts to the genome significantly increased the ability to functionally annotate toxicant responsive genes. The H. azteca genome will greatly facilitate development of genomic tools for environmental assessments and promote an understanding of how evolution shapes toxicological pathways with implications for environmental and human health.

Variation in DNA Methylation Is Not Consistently Reflected by Sociality in Hymenoptera.

Changes in gene regulation that underlie phenotypic evolution can be encoded directly in the DNA sequence or mediated by chromatin modifications such as DNA methylation. It has been hypothesized that the evolution of eusocial division of labor is associated with enhanced gene regulatory potential, which may include expansions in DNA methylation in the genomes of Hymenoptera (bees, ants, wasps, and sawflies). Recently, this hypothesis garnered support from analyses of a commonly used metric to estimate DNA methylation in silico, CpG content. Here, we test this hypothesis using direct, nucleotide-level measures of DNA methylation across nine species of Hymenoptera. In doing so, we generated new DNA methylomes for three species of interest, including one solitary and one facultatively eusocial halictid bee and a sawfly. We demonstrate that the strength of correlation between CpG content and DNA methylation varies widely among hymenopteran taxa, highlighting shortcomings in the utility of CpG content as a proxy for DNA methylation in comparative studies of taxa with sparse DNA methylomes. We observed strikingly high levels of DNA methylation in the sawfly relative to other investigated hymenopterans. Analyses of molecular evolution suggest the relatively distinct sawfly DNA methylome may be associated with positive selection on functional DNMT3 domains. Sawflies are an outgroup to all ants, bees, and wasps, and no sawfly species are eusocial. We find no evidence that either global expansions or variation within individual ortholog groups in DNA methylation are consistently associated with the evolution of social behavior.

The Neuropeptide Corazonin Controls Social Behavior and Caste Identity in Ants.

Social insects are emerging models to study how gene regulation affects behavior because their colonies comprise individuals with the same genomes but greatly different behavioral repertoires. To investigate the molecular mechanisms that activate distinct behaviors in different castes, we exploit a natural behavioral plasticity in Harpegnathos saltator, where adult workers can transition to a reproductive, queen-like state called gamergate. Analysis of brain transcriptomes during the transition reveals that corazonin, a neuropeptide homologous to the vertebrate gonadotropin-releasing hormone, is downregulated as workers become gamergates. Corazonin is also preferentially expressed in workers and/or foragers from other social insect species. Injection of corazonin in transitioning Harpegnathos individuals suppresses expression of vitellogenin in the brain and stimulates worker-like hunting behaviors, while inhibiting gamergate behaviors, such as dueling and egg deposition. We propose that corazonin is a central regulator of caste identity and behavior in social insects.

Genome of the Asian longhorned beetle (Anoplophora glabripennis), a globally significant invasive species, reveals key functional and evolutionary innovations at the beetle-plant interface.

BACKGROUND: Relatively little is known about the genomic basis and evolution of wood-feeding in beetles. We undertook genome sequencing and annotation, gene expression assays, studies of plant cell wall degrading enzymes, and other functional and comparative studies of the Asian longhorned beetle, Anoplophora glabripennis, a globally significant invasive species capable of inflicting severe feeding damage on many important tree species. Complementary studies of genes encoding enzymes involved in digestion of woody plant tissues or detoxification of plant allelochemicals were undertaken with the genomes of 14 additional insects, including the newly sequenced emerald ash borer and bull-headed dung beetle. RESULTS: The Asian longhorned beetle genome encodes a uniquely diverse arsenal of enzymes that can degrade the main polysaccharide networks in plant cell walls, detoxify plant allelochemicals, and otherwise facilitate feeding on woody plants. It has the metabolic plasticity needed to feed on diverse plant species, contributing to its highly invasive nature. Large expansions of chemosensory genes involved in the reception of pheromones and plant kairomones are consistent with the complexity of chemical cues it uses to find host plants and mates. CONCLUSIONS: Amplification and functional divergence of genes associated with specialized feeding on plants, including genes originally obtained via horizontal gene transfer from fungi and bacteria, contributed to the addition, expansion, and enhancement of the metabolic repertoire of the Asian longhorned beetle, certain other phytophagous beetles, and to a lesser degree, other phytophagous insects. Our results thus begin to establish a genomic basis for the evolutionary success of beetles on plants.

The caste- and sex-specific DNA methylome of the termite Zootermopsis nevadensis.

Epigenetic inheritance plays an important role in mediating alternative phenotype in highly social species. In order to gain a greater understanding of epigenetic effects in societies, we investigated DNA methylation in the termite Zootermopsis nevadensis. Termites are the most ancient social insects, and developmentally distinct from highly-studied, hymenopteran social insects. We used replicated bisulfite-sequencing to investigate patterns of DNA methylation in both sexes and among castes of Z. nevadensis. We discovered that Z. nevadensis displayed some of the highest levels of DNA methylation found in insects. We also found strong differences in methylation between castes. Methylated genes tended to be uniformly and highly expressed demonstrating the antiquity of associations between intragenic methylation and gene expression. Differentially methylated genes were more likely to be alternatively spliced than not differentially methylated genes, and possessed considerable enrichment for development-associated functions. We further observed strong overrepresentation of multiple transcription factor binding sites and miRNA profiles associated with differential methylation, providing new insights into the possible function of DNA methylation. Overall, our results show that DNA methylation is widespread and associated with caste differences in termites. More generally, this study provides insights into the function of DNA methylation and the success of insect societies.