Characterizing genetic variation in natural populations is vital to evolutionary biology; however, many non-model species lack genomic resources. Here, we demonstrate that reference bias significantly affects population genomic analyses by mapping whole-genome sequence data from gray foxes (Urocyon cinereoargenteus) to a conspecific reference and two heterospecific canid genomes (dog and Arctic fox). Mapping to the conspecific genome improved read pairing by ∼5% and detected 26%-32% more SNPs and 33%-35% more singletons. Nucleotide diversity estimates increased by over 30%, FST increased from 0.189 to 0.197, and effective population size estimates were 30%-60% higher with the conspecific reference. Recombination rates varied by up to 3-fold at chromosome ends with heterospecific references. Importantly, FST outlier detection differed markedly, with heterospecific genomes identifying twice as many unique outlier windows. These findings highlight the impact of reference genome choice and the importance of conspecific genomic resources for accurate evolutionary inference.

In this issue of Cell, Huang and colleagues reveal how ancient hybridization between ancestors of tomato and a related wild species, Solanum etuberosum, enabled the origin of tuber formation and the diversification of potato species. Their genomic analyses highlight how interactions between genes derived from distinct progenitors can drive development of novel traits in hybrids.

Personalized cancer vaccines aim to broaden the anti-tumor T cell repertoire by targeting neoantigens unique to each patient's tumor, but immunogenicity has been inconsistent. In this issue of Cell, Blass, Keskin, Tu et al. evaluate NeoVaxMI, a multi-adjuvant personalized synthetic long-peptide vaccine administered with nivolumab in patients with melanoma. NeoVaxMI elicited stronger CD4+ and CD8+ responses than earlier iterations, and vaccine-induced T cells trafficked to regressing metastatic lesions.

Evaluating the innate value of objects is critical for expressing adaptive behaviors. However, where and how this computation takes place in the brain remain elusive. By recording from virtually every neuron in Drosophila higher olfactory areas, we show that the lateral horn is a site of innate odor value computation, where distinct neurons represent opposing innate values. A connectome-based spiking network model recapitulating the neural activity indicates that representations of aversive odors emerge through specific convergence of feedforward excitation, whereas those of attractive odors emerge through additional local inhibition. This inhibition is broad yet balanced with excitation and implements gain control and thresholding to shape attractive odor tuning. Manipulation of local inhibition biased neuronal and behavioral odor responses according to the prediction of the model. Thus, odors at the opposite ends of the hedonic spectrum are processed in sub-circuits that are not only segregated but also distinct in connectivity motifs.

A significant complication of Crohn's disease (CD) is intestinal fibrosis, which narrows the bowel lumen to form a stricture. Creeping fat (CF) is the wrapping of mesenteric adipose tissue around diseased bowel, of which the role in CD stricture progression is unclear. By constructing a human single-cell CD fibroblast atlas, we identified CF-derived, CTHRC1+ fibroblasts enriched for Yes-associated protein (YAP)/transcriptional co-activator with PDZ-binding motif (TAZ) signatures and localized to a fibrotic CF-bowel wall interface within the stricture. We further showed that analogous Cthrc1+ mouse fibroblasts derive from mesenteric adipose tissue stromal cells, infiltrate fibrotic bowel, and deposit extracellular matrix in a YAP/TAZ-dependent manner in a mouse model of intestinal fibrosis. Our findings identify CF as a key source of pro-fibrotic fibroblasts and raise the possibility of improving future clinical management of stricture progression by targeting not only the bowel but also CF.

Totipotency enables single cells to regenerate an organism, yet how differentiated somatic cells reacquire this potential remains unclear. Here, we show that LEAFY COTYLEDON2 (LEC2) reprograms SPEECHLESS (SPCH)-expressing meristemoid mother cells (MMCs) away from stomatal-lineage progression, driving their conversion into totipotent somatic embryo founder cells (SEFCs) in Arabidopsis cotyledons. Using time-course live imaging, single-nucleus RNA sequencing (snRNA-seq), and spatial laser capture microdissection combined with RNA sequencing (LCM-RNA-seq), we uncover a lineage bifurcation point where MMC derivatives either commit to guard cells or transition into a guard mother cell (GMC)-auxin intermediate, an auxin-enriched state that enables transcriptional reprogramming and embryonic gene activation. LEC2 and SPCH cooperatively activate TRYPTOPHAN AMINOTRANSFERASE OF ARABIDOPSIS 1 (TAA1) and YUCCA4 (YUC4), establishing a local auxin biosynthesis circuit essential for SEFC specification. Genetic and promoter analyses confirm MMCs as the origin of somatic embryos, with TAA1/YUC-mediated auxin production indispensable for totipotency and embryogenesis. These findings define an auxin-driven, transcriptionally regulated trajectory linking stomatal progenitors to somatic embryogenesis, revealing a direct route that advances mechanistic understanding of plant regenerative plasticity.

Following eukaryotic genome replication, the ring-shaped cohesin complex embraces the two newly synthesized sister chromatids, enabling their faithful segregation during cell divisions. Replisome passage through cohesin rings has been envisioned as a fail-safe mechanism that ensures co-entrapment of replication products-whether replisomes can indeed pass through cohesin rings remains unknown. Here, we use biochemical reconstitution and single-molecule fluorescence microscopy to directly visualize replisome-cohesin encounters. We find that the translocating eukaryotic replicative Cdc45-Mcm2-7-GINS (CMG) helicase, unlike other obstacles of similar size, readily passes through cohesin rings. Fully reconstituted replisomes also pass cohesin rings to leave both replication products trapped inside. Replisome passage is primarily aided by DNA polymerases α and ε, a finding that necessitates re-evaluation of canonical cohesion establishment factor roles. Our findings demonstrate the existence of a simple mechanism that links genome replication with chromosome segregation: replisome passage through cohesin rings.

Tuberculosis (TB) is the leading cause of death from infectious disease worldwide, and Bacillus Calmette-Guérin (BCG) remains the only clinically approved vaccine. An enduring challenge in TB vaccine development is systematic antigen selection from a large repertoire of potential candidates. We performed an efficacy screen in mice of antigens that are targets of CD4 T cells in humans. We found striking heterogeneity in protective efficacy, and most of the top protective antigens are not currently in clinical development. We observed immunologic cross-reactivity among phylogenetically clustered antigens, reflecting common CD4 epitopes. We developed a trivalent mRNA vaccine consisting of PPE20 (Rv1387), EsxG (Rv0287), and PE18 (Rv1788), which augmented and exceeded BCG protection in multiple mouse models. Finally, we observed cellular immune responses to these antigens in 84% of humans exposed to M. tuberculosis. These data advance our understanding of TB vaccine immunology and define a vaccine concept for clinical development.

A hallmark of HIV infection is disruption of intestinal barrier integrity that persists in people with HIV (PWH) despite treatment with antiretroviral therapy (ART). This disruption is central to HIV disease progression, yet the causes remain incompletely understood. We report a mechanism by which immunometabolic defects in colon-resident CD8+ T cells in PWH lead to intestinal epithelial apoptosis and disruption of intestinal barrier integrity. We show that in PWH, these cells downregulate the lipid sensor peroxisome proliferator-activated receptor-γ (PPARγ), which results in reduced intracellular lipid droplets, impaired fatty acid oxidation, and acquisition of lipids by CD8+ T cells from intestinal epithelial cells, which then contributes to epithelial cell death. Our findings indicate that HIV-associated immunometabolic dysregulation of colon CD8+ T cells leads to loss of intestinal epithelial homeostasis. These results identify potential strategies to reduce comorbidities in PWH and other disorders with disrupted intestinal barrier integrity.

The innate attraction to sweet mediates appetitive and consummatory responses. Here, we dissected the circuit driving responses to sweet and showed that amygdala neurons tuned to sweet connect to the bed nucleus of the stria-terminalis (BNST) to promote sweet-evoked consumption. Next, we demonstrate that the BNST functions as a central hub, transforming appetitive signals into consumption and linking sensory inputs to the internal state, not only for sweet but also for other stimuli such as salt or food, to flexibly regulate consummatory behaviors. Using single-cell functional imaging, we show that ensemble activity in the BNST encodes stimulus identity and the animal's internal state. Finally, we demonstrate that manipulating BNST activity can bidirectionally transform consummatory responses. Together, these findings illustrate how the internal state modulates sensory responses, characterize a general brain dial for consumption, and provide fresh insights into sites of action of GLP1R agonists and a strategy to help promote weight gain in pathological states.

Astrocytes and microglia are emerging key regulators of activity-dependent synapse remodeling that engulf and remove synapses in response to changes in neural activity. Yet, the degree to which these cells communicate to coordinate this process remains an open question. Here, we use whisker removal in postnatal mice to induce activity-dependent synapse removal in the barrel cortex. We show that astrocytes do not engulf synapses in this paradigm. Instead, astrocytes reduce contact with synapses prior to microglia-mediated synapse engulfment. We further show that the reduced astrocyte-synapse contact is dependent on the release of Wnts from microglia downstream of neuron-to-microglia fractalkine ligand-receptor (CX3CL1-CX3CR1) signaling. These results demonstrate an activity-dependent mechanism by which microglia instruct astrocyte-synapse interactions, providing a permissive environment for microglia to remove synapses. We further show that this mechanism is critical to remodel synapses in a changing sensory environment and that this signaling is upregulated in several disease contexts.

Some mobile genetic elements spread among unrelated bacterial species through unknown mechanisms. Recently, we discovered that identical capsid-forming phage-inducible chromosomal islands (cf-PICIs), a new family of phage satellites, are present across multiple species and genera, raising questions about their widespread dissemination. Here, we have identified and characterized a new biological entity enabling this transfer. Unlike other satellites, cf-PICIs produce their own capsids and package their DNA, relying solely on phage tails for transfer. cf-PICIs release non-infective, tailless capsids containing their DNA into the environment. These subcellular entities then interact with phage tails from various species, forming chimeric particles that inject DNA into different bacterial species depending on the tail present. Additionally, we elucidated the structure of the tailless cf-PICIs and the mechanism behind their unique capsid formation. Our findings illuminate the mechanisms used by satellites to spread in nature, contributing to bacterial evolution and the emergence of new pathogens.

Artificial intelligence (AI) models have been proposed for hypothesis generation, but testing their ability to drive high-impact research is challenging since an AI-generated hypothesis can take decades to validate. Here, we challenge the ability of a recently developed large language model (LLM)-based platform, AI co-scientist, to generate high-level hypotheses by posing a question that took years to resolve experimentally but remained unpublished: how could capsid-forming phage-inducible chromosomal islands (cf-PICIs) spread across bacterial species? Remarkably, the AI co-scientist's top-ranked hypothesis matched our experimentally confirmed mechanism: cf-PICIs hijack diverse phage tails to expand their host range. We critically assess its five highest-ranked hypotheses, showing that some opened new research avenues in our laboratories. We benchmark its performance against other LLMs and outline best practices for integrating AI into scientific discovery. Our findings suggest that AI can act not just as a tool but as a creative engine, accelerating discovery and reshaping how we generate and test scientific hypotheses.

The human gut microbiome is linked to child malnutrition, yet traditional microbiome approaches lack resolution. We hypothesized that complete metagenome-assembled genomes (cMAGs), recovered through long-read (LR) DNA sequencing, would enable pangenome and microbial genome-wide association study (GWAS) analyses to identify microbial genetic associations with child linear growth. LR methods produced 44-64× more cMAGs per gigabase pair (Gbp) than short-read methods, with PacBio (PB) yielding the most accurate and cost-effective assemblies. In a Malawian longitudinal pediatric cohort, we generated 986 cMAGs (839 circular) from 47 samples and applied this database to an expanded set of 210 samples. Machine learning identified species predictive of linear growth. Pangenome analyses revealed microbial genetic associations with linear growth, while genome instability correlated with declining length-for-age Z score (LAZ). This resource demonstrates the power of comparing cMAGs with health trajectories and establishes a new standard for microbiome association studies.

Early organogenesis is a crucial stage in embryonic development, characterized by extensive cell fate specification to initiate organ formation but also by a high susceptibility to developmental defects. Here, we profiled 285 serial sections from six E7.5-E8.0 embryos to generate full spatiotemporal transcriptome and signal maps during early organogenesis at single-cell resolution. By developing SEU-3D, we reconstructed digital embryos, enabling investigation of regionalized gene expression in the native spatial context. We established a space-informed gene-cell co-embedding approach, systematically characterized the spatial atlas of endoderm and mesoderm derivatives, and elucidated signaling networks across germ layers and cell types. Furthermore, we characterized a primordium determination zone (PDZ) formed along the anterior embryonic-extraembryonic interface at E7.75, and it revealed that the coordinated signaling communications contribute to the formation of cardiac primordium. Collectively, the high-resolution "digital embryo" provides significant insights into early organogenesis and a unique spatial platform for studying development and diseases.

Denisovans have yet to be directly associated with a hominin cranium, limiting our understanding of their morphology and geographical distribution. We have attempted to retrieve DNA from a nearly complete Middle Pleistocene cranium from Harbin (>146 ka), northeastern China. Although no DNA could be retrieved from a tooth or the petrous bone, mitochondrial DNA (mtDNA) could be isolated from dental calculus. The mtDNA falls within Denisovan mtDNA variation and is related to an mtDNA branch carried by early Denisovan individuals in southern Siberia, previously observed in Denisova Cave. This suggests that Denisovans inhabited a large geographical range in Asia in the Middle Pleistocene. The association of Denisovan mtDNA with the Harbin cranium allows a better understanding of the morphological relationships between Denisovans and other East Asian Middle Pleistocene fossils. Furthermore, the retrieval of host DNA from dental calculus opens new possibilities for genetic research on Middle Pleistocene hominins.

Single-cell metabolomics (SCM) promises to reveal metabolism in its complexity and heterogeneity, yet current methods struggle with detecting small-molecule metabolites, throughput, and reproducibility. Addressing these gaps, we developed HT SpaceM, a high-throughput SCM method combining cell preparation on custom glass slides, small-molecule matrix-assisted laser desorption ionization (MALDI) imaging mass spectrometry (MS), and batch processing. We propose a unified framework covering quality control, characterization, structural validation, and differential and functional analyses. Profiling HeLa and NIH3T3 cells, we detected 73 small-molecule metabolites validated by bulk liquid chromatography tandem MS (LC-MS/MS), achieving high reproducibility and single-cell resolution. Interrogating nine NCI-60 cancer cell lines and HeLa, we identified cell-type markers in subpopulations and metabolic hubs. Upon inhibiting glycolysis in HeLa cells, we observed emerging glucose-centered metabolic coordination and intra-condition heterogeneity. Overall, we demonstrate how HT SpaceM enables robust, large-scale SCM across over 140,000 cells from 132 samples and provide guidance on how to interpret metabolic insights beyond population averages.

Adaptation of intestinal helminths to vertebrates involved the evolution of strategies to attenuate host tissue damage to support parasite reproduction and dissemination of offspring to the environment. Helminths initiate the IL-25-mediated tuft cell-type 2 innate lymphoid cell (ILC2) circuit that enhances barrier protection of the host, although viable parasites can target and limit this pathway. We used IL-25 alone to create small intestinal adaptation, marked by anatomic and immunologic changes that persisted months after induction. Adaptation was associated with heightened resistance to barrier pathogens, including in the lung, and was enforced by transcriptionally and epigenetically modified effector-memory ILC2s distinct from those described by innate "training"; epithelial stem cells remained unaltered. Despite requiring IL-25 for induction, effector-memory ILC2s maintained an activated state in the absence of multiple alarmins and supported mucosal resilience while avoiding adverse sensitization to chronic inflammation, revealing a pathway for deploying innate immune cells to coordinate a distributed mucosal defense.

Understanding epithelial lineages of breast cancer and genotype-phenotype relationships requires direct measurements of the genome and transcriptome of the same single cells at scale. To achieve this, we developed wellDR-seq, a high-genomic-resolution, high-throughput method to simultaneously profile the genome and transcriptome of thousands of single cells. We profiled 33,646 single cells from 12 estrogen-receptor-positive breast cancers and identified ancestral subclones in multiple patients that showed a luminal hormone-responsive lineage, indicating a potential cell of origin. In contrast to bulk studies, wellDR-seq enabled the study of subclone-level gene-dosage relationships, which showed near-linear correlations in large chromosomal segments and extensive variation at the single-gene level. We identified dosage-sensitive and dosage-insensitive genes, including many breast cancer genes as well as sporadic copy-number aberrations in non-cancer cells. Overall, these data reveal complex relationships between copy number and gene expression in single cells, improving our understanding of breast cancer progression.

RNA-binding proteins (RBPs) are best known as effectors along the entire gene expression pathway and as constituents of RNA-protein machines such as the ribosome and the spliceosome. Around 1,000 RBPs account for these functions in mammalian cells. The total number of RBPs has recently more than tripled to include many "well-known" proteins such as metabolic enzymes or membrane proteins, sparking debate about the biological relevance of their RNA binding. We examine the experimental basis underlying the dramatic expansion of the RBPome, consider arguments that challenge its relevance, and discuss recent data that describe new RBP and RNA functions. We suggest that the scope of interplay between RNA and proteins is underexplored and that riboregulation of proteins represents an emerging theme in cell biology and translational medicine.