Abstract Single-cell RNA sequencing and spatial transcriptomics have transformed our understanding of the transcriptional landscape by enabling high-resolution profiling of gene expression. Yet most experimental pipelines and their associated analysis frameworks collapse transcript diversity into gene-level counts, obscuring alternative splicing and isoform usage. The increasing ability of long-read sequencing to recover full-length transcripts from single cells and spatially barcoded tissues has created a pressing need for computational frameworks to support the storage, analysis, and visualisation of isoform-resolved data. Existing tools for isoform and splicing analysis either specialise in bulk, single-cell, or spatial RNA-seq assays in isolation and remain fragmented across languages and data models, limiting interoperability and hindering widespread adoption. We present Allos, a Python framework for isoform-level single-cell and spatial transcriptomics analysis. Built on the AnnData data model, Allos natively represents transcript-level quantification and integrates directly with GTF/GFF and FASTA annotations. Allos enables differential isoform usage screening, multi-panel visualisation, structural transcript interpretation, and protein-level analysis across bulk, single-cell, and spatial assays from both long- and short-read sequencing. Its modular design and scverse compatibility allow isoform-resolved analyses to run alongside established gene-level workflows, linking transcript-level screening with structure-aware visualisation and downstream interpretation. Allos is open-source and available at https://github.com/cobioda/allos , with comprehensive documentation and tutorials provided online.

The human nasal region arises from neural crest and placodal lineages, yet its early development remains poorly understood owing to limited fetal tissue access and structural complexity. Here we present an integrated single-nucleus and spatial transcriptomic atlas of the human fetal nasal region, generated from male and female fetuses between 7 and 12 post-conceptional weeks. Single-nucleus RNA sequencing [snRNA-seq] resolved 32 distinct cell types, while integration with multiplexed error-robust fluorescence in situ hybridization (MERFISH) enabled spatial and temporal mapping of gene expression dynamics across the olfactory epithelium (OE) and adjacent tissues. We identify markers of olfactory sensory neuron differentiation and pathways governing epithelial patterning and OE morphogenesis. Notably, spatially resolved snRNA-seq profiles of 169 olfactory receptor genes reveal molecular support for the "one neuron-one receptor" principle already in the first trimester. Together, this work establishes a molecular and spatial framework of early human olfactory development and provides a resource for studies of sensory neurogenesis and congenital disorders.

Rapid advances in single-cell technologies now allow measurement of thousands of transcripts and other molecular features of individual cells offering unprecedented insight into lung biology in homeostasis and in disease. The accelerated generation of multimodal data has, however, been accompanied by the reporting of putatively "novel" cell types described without consensus regarding their ontogeny, identity, function, or defining markers. To fully realize the value of the technological advances and to enable rigorous comparison across studies, respiratory research will benefit from standardized, quantitative, and biologically grounded cell classifications and nomenclature. Achieving the transformative potential of the multimodal data will depend on common, machine- and human-readable nomenclature, structured and expandable dictionary and atlas resources, and clear methodological standards that ensure consistency as technologies evolve. The American Thoracic Society (ATS) recognized the importance of promoting a common nomenclature to enhance equitable access and utility of the vast amounts of multimodal data generated by the lung research community. The Collaborative Cross-Consortium and Country Lung Cell Nomenclature Project (C3LCN) was adopted as an ATS Assembly Project in 2024. This is the consensus report outlining the goals and framework of the Project to foster coordinated progressive lung cell research to include: 1) providing best practices for analysis, publication and reporting of lung single-cell transcriptomic datasets; 2) establishing a contemporary lexicon for healthy adult human cells of the lower respiratory tract with structured, persistent, and resolvable identifiers; 3) defining a scalable taxonomy to organize a common lung cell nomenclature; 4) offering tools to support collaboration, knowledge dissemination, and translational advances rooted in modern lung biology augmenting, not replacing, pre-genomic biological knowledge; and 5) describing an infrastructure capable of incorporating new ontological refinements as higher-resolution, multimodal single-cell and spatial datasets emerge, cellular heterogeneity is better defined, and disease-associated abnormal cell types and reactive cell states are increasingly recognized and mechanistically interrogated. Together, this coordinated effort aims to provide the foundation necessary for a robust, harmonized, and expandable nomenclature for lung science.

Meiosis, endoreplication, and asynthetic fissions are variations of the canonical cell cycle where either replication or mitotic divisions are muted. Here, we identify a cell cycle variantconserved across organs and mammals, where both replication and mitosis are muted, and that orchestrates the differentiation of post-mitotic progenitors into multiciliated cells (MCCs). MCC progenitors reactivate most of the cell cycle transcriptional program but replace the temporal expression of cyclins E2 and A2 with non-canonical cyclins O and A1. In addition, the primary APC/C inhibitor Emi1 is silenced. Re-expressing cyclins E2 and A2 and/or Emi1 can induce partial replication or mitosis. This shows that a cell can co-opt the cell cycle genetic program and regulate only certain elements to qualitatively and quantitatively divert CDK activity toward differentiation rather than division. We propose this cell cycle variant to exploit the existence of a cytoplasmic—or centriolar—CDK threshold lower than the S-phase threshold.

Spatial transcriptomics enables serial analysis of the expression of hundreds of genes in tissue sections by combining molecular biology and imaging approaches. This technique allows the exploration of large tissue sections (up to 3cm2) at the single-cell resolution, allowing cell-cell interactions and subcellular RNA expression analyses. Regions of interest having particular shapes raise specific computational problems that need to be addressed. In this manuscript, we propose a method for the analysis of elongated curved shape (set of connected pixels) or point cloud spread within a shape (cell centers or RNA molecules). We develop a method to unfold linear structures and analyze its content along its principal axis, in order to study cell or transcript type proportions. The centerline of the shape is automatically computed by combining k-means clustering and salesman problem optimization. Our method allows the analysis of spatial distribution of cells or transcripts along or perpendicular to the centerline.

A reduced sense of smell is a common condition in people with cystic fibrosis (CF) that negatively affects their quality of life. While often attributed to nasal mucosa inflammation, the underlying causes of the olfactory loss remain unknown. Here, we characterized gene expression in olfactory epithelium cells from patients with CF using single-nuclei RNA sequencing and found altered expression of olfactory receptors (ORs) and genes related to progenitor cell proliferation. We confirmed these findings in newborn, inflammation-free samples of a CF animal model and further identified ultrastructural alterations in the olfactory epithelium and bulbs of these animals. We established that CFTR, the anion channel whose dysfunction causes CF, is dispensable for odor-evoked signaling in sensory neurons, yet CF animals displayed defective odor-guided behaviors consistent with the morphological and molecular alterations. Our study highlights CF's major role in modulating epithelial structure and OR expression, shedding light on the mechanisms contributing to olfactory loss in CF.

Background: Chronic pulmonary inflammation strongly contributes to respiratory failure and mortality in patients with cystic fibrosis (pwCF). Effective anti-microbial immunity and maintaining lung homeostasis require continuous structural-immune cell communication. Whether and how this crosstalk is altered in CF remains poorly understood, obscuring potential new angles for therapy development to restore airway homeostasis in pwCF. Methods: We performed droplet-based single cell RNA-sequencing on bronchial biopsies from pwCF to investigate structural-immune cell crosstalk. Computational analyses were used to compare these data to samples obtained from healthy controls. Results: CF airway wall biopsies showed lower proportions and altered transcriptomes of basal cells, submucosal gland cells and endothelial cells, and a higher abundance of ciliated cells, monocytes, macrophages and T cells. Both B and T lymphocytes displayed aberrantly activated phenotypes with transcriptional changes linked to hypoxia and vascular endothelial growth factor signaling, indicative of crosstalk with endothelial cells. The CF lung displayed unique changes in intercellular communication potential involving ionocytes, macrophages, endothelial cells and lymphocytes. This included interactions between HLA-E on structural cells and the druggable CD94/NKG2A immune checkpoint on CD8+ T cells. Conclusions: We report the first single cell transcriptome atlas of the CF lung containing the full spectrum of structural and immune cells, providing a valuable resource for investigating changes to cellular composition, phenotypes and crosstalk linked to CF. Our analyses highlight dysregulated basal cell function and adaptive immunity in pwCF - despite favorable responses to CFTR modulator therapy. We identify novel aspects of CF pathophysiology and potential entry points for therapeutic strategies.

Aging increases the risk of developing fibrotic diseases by hampering tissue regeneration after injury. Using longitudinal single-cell RNA-seq and spatial transcriptomics, here we compare the transcriptome of bleomycin (BLM) -induced fibrotic lungs of young and aged male mice, at 3 time points corresponding to the peak of fibrosis, regeneration, and resolution. We find that lung injury shifts the transcriptomic profiles of three pulmonary capillary endothelial cells (PCEC) subpopulations. The associated signatures are linked to pro-angiogenic signaling with strong Lrg1 expression and do not progress similarly throughout the resolution process between young and old animals. Moreover, part of this set of resolution-associated markers is also detected in PCEC from samples of patients with idiopathic pulmonary fibrosis. Finally, we find that aging also alters the transcriptome of PCEC, which displays typical pro-fibrotic and pro-inflammatory features. We propose that age-associated alterations in specific PCEC subpopulations may interfere with the process of lung progenitor differentiation, thus contributing to the persistent fibrotic process typical of human pathology.

Pulmonary arterial hypertension (PAH) and hereditary hemorrhagic telangiectasia (HHT) are two distinct vascular diseases linked to impaired signaling through bone morphogenetic protein (BMP) receptor complexes in endothelial cells. Although BMP-9 plays a central role in activating this pathway by binding to ALK1 and BMPR-II, its precise function in the pulmonary microvasculature has remained unclear. In this study, we demonstrate a role for BMP-9 in regulating pulmonary vascular architecture and homeostasis. Our findings reveal that BMP-9 signaling intersects with VEGF pathways and contributes to the delicate balance between vascular growth and remodeling in the lungs. We also show that disruption of this pathway can shift vascular responses toward an HHT-like state, potentially altering disease susceptibility. These insights offer a unique perspective on how BMP-9 and ALK1 shape pulmonary vascular biology and suggest that targeting this axis could inform future strategies for treating complex vascular diseases such as PAH.

The increasing number of single-cell gene expression atlases available represent a potential revolution in understanding physio-pathological processes. To fully leverage this single-cell revolution, we need to enhance data integration and cell annotation strategies, with a particular emphasis on addressing the challenges posed by imbalanced cell type proportions and substantial batch effects. scMusketeers, a deep learning model, optimizes the latent data representation and solves all at once these challenges. scMusketeers features three neural modules: (1) an autoencoder for noise and dimensionality reductions; (2) a focal loss classifier to enhance rare cell type predictions; and (3) an adversarial domain adaptation (DANN) module for batch effect correction. Benchmarking against state-of-the-art tools, including the UCE foundation model, showed that scMusketeers performs on par or better, particularly in identifying rare cell types. It also allows to transfer cell labels from single-cell RNA sequencing to spatial transcriptomics. With its modular and adaptable design, scMusketeers offers a versatile framework that can be generalized to other large-scale biological projects requiring deep learning approaches, establishing itself as a valuable tool for single-cell data integration and analysis. ### Competing Interest Statement The authors have declared no competing interest.

Rationale: Bronchiectasis is a pathological dilatation of the bronchi in the respiratory airways associated with environmental or genetic causes (e.g., cystic fibrosis, primary ciliary dyskinesia, and primary immunodeficiency disorders), but most cases remain idiopathic. Objectives: To identify novel genetic defects in unsolved cases of bronchiectasis presenting with severe rhinosinusitis, nasal polyposis, and pulmonary Pseudomonas aeruginosa infection. Methods: DNA was analyzed by next-generation or targeted Sanger sequencing. RNA was analyzed by quantitative PCR and single-cell RNA sequencing. Patient-derived cells, cell cultures, and secretions (mucus, saliva, seminal fluid) were analyzed by Western blotting and immunofluorescence microscopy, and mucociliary activity was measured. Blood serum was analyzed by electrochemiluminescence immunoassay. Protein structure and proteomic analyses were used to assess the impact of a disease-causing founder variant. Measurements and Main Results: We identified biallelic pathogenic variants in WAP four-disulfide core domain 2 (WFDC2) in 11 individuals from 10 unrelated families originating from the United States, Europe, Asia, and Africa. Expression of WFDC2 was detected predominantly in secretory cells of control airway epithelium and also in submucosal glands. We demonstrate that WFDC2 is below the limit of detection in blood serum and hardly detectable in samples of saliva, seminal fluid, and airway surface liquid from WFDC2-deficient individuals. Computer simulations and deglycosylation assays indicate that the disease-causing founder variant p.Cys49Arg structurally hampers glycosylation and, thus, secretion of mature WFDC2. Conclusions: WFDC2 dysfunction defines a novel molecular etiology of bronchiectasis characterized by the deficiency of a secreted component of the airways. A commercially available blood test combined with genetic testing allows its diagnosis.

Single-cell CRISPR-based transcriptome screens are potent genetic tools for concomitantly assessing the expression profiles of cells targeted by a set of guides RNA (gRNA), and inferring target gene functions from the observed perturbations. However, due to various limitations, this approach lacks sensitivity in detecting weak perturbations and is essentially reliable when studying master regulators such as transcription factors. To overcome the challenge of detecting subtle gRNA induced transcriptomic perturbations and classifying the most responsive cells, we developed a new supervised autoencoder neural network method. Our Sparse supervised autoencoder (SSAE) neural network provides selection of both relevant features (genes) and actual perturbed cells. We applied this method on an in-house single-cell CRISPR-interference-based (CRISPRi) transcriptome screening (CROP-Seq) focusing on a subset of long non-coding RNAs (lncRNAs) regulated by hypoxia, a condition that promote tumor aggressiveness and drug resistance, in the context of lung adenocarcinoma (LUAD). The CROP-seq library of validated gRNA against a subset of lncRNAs and, as positive controls, HIF1A and HIF2A, the 2 main transcription factors of the hypoxic response, was transduced in A549 LUAD cells cultured in normoxia or exposed to hypoxic conditions during 3, 6 or 24 h. We first validated the SSAE approach on HIF1A and HIF2 by confirming the specific effect of their knock-down during the temporal switch of the hypoxic response. Next, the SSAE method was able to detect stable short hypoxia-dependent transcriptomic signatures induced by the knock-down of some lncRNAs candidates, outperforming previously published machine learning approaches. This proof of concept demonstrates the relevance of the SSAE approach for deciphering weak perturbations in single-cell transcriptomic data readout as part of CRISPR-based screening.

2 Abstract A complex and conserved regulatory network drives the cell cycle. Individual components of this network are sometimes used in differentiated cells, i.e. to control organelle destruction in mammalian lens cells or light response in land plants. Some differentiated cells co-opt cell-cycle regulators more largely, to increase their ploidy using a cell cycle variant named endoreplication. Using single-cell RNA-seq profiling and functional assays in differentiating multiciliated cells, we identified a novel type of cell cycle variant that supports cytoplasmic organelle, rather than nuclear content amplification. This variant operates in post-mitotic, centriole-amplifying differentiating multiciliated cells and is characterized by (i) a circular trajectory of the transcriptome, (ii) sequential expression of more than 70% of the genes involved in S, G2 and M-like progression along this trajectory, and (iii) successive waves of cyclins. This cell cycle variant is tailored by the expression of the non-canonical cyclins O and A1 – which replace the transcriptionally silent cyclins E2 and A2 – and by the silencing of the APC/C inhibitor Emi1, two switches also detected in male meiosis, another variant of the canonical cell cycle where centriole and DNA replications are uncoupled. Re-expressing Cyclin E2, cyclin A2 or Emi1 is sufficient to induce partial replication and mitosis, suggesting that change in the regulation of expression of a few cell cycle key players drives a qualitative and quantitative tuning of Cdk activity, allowing the diversion of the cell cycle in the multiciliation variant. We also propose that this new cell cycle variant relies on the existence of a cytoplasmic – or centriolar – Cdk threshold, lower than the S-phase threshold, which affects only the cytoplasmic reorganization. One-Sentence Summary MCC progenitors undergo a final, tailored iteration of the cell cycle during differentiation, to drive centriole amplification without DNA replication or mitosis.

The human airway mucociliary epithelium can be recapitulated in vitro using primary cells cultured in an air-liquid interface (ALI), a reliable surrogate to perform pathophysiological studies. As tremendous variations exist among media used for ALI-cultured human airway epithelial cells, the aim of our study was to evaluate the impact of several media (BEGM, PneumaCult, Half & Half, and Clancy) on cell type distribution using single-cell RNA sequencing and imaging. Our work revealed the impact of these media on cell composition, gene expression profile, cell signaling, and epithelial morphology. We found higher proportions of multiciliated cells in PneumaCult-ALI and Half & Half, stronger EGF signaling from basal cells in BEGM-ALI, differential expression of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) entry factor ACE2, and distinct secretome transcripts depending on the media used. We also established that proliferation in PneumaCult-Ex Plus favored secretory cell fate, showing the key influence of proliferation media on late differentiation epithelial characteristics. Altogether, our data offer a comprehensive repertoire for evaluating the effects of culture conditions on airway epithelial differentiation and will aid in choosing the most relevant medium according to the processes to be investigated, such as cilia, mucus biology, or viral infection. We detail useful parameters that should be explored to document airway epithelial cell fate and morphology.

Metabolic dysregulation, including perturbed glutamine-glutamate homeostasis, is common among patients with cardiovascular diseases, but the underlying mechanisms remain largely unknown. Using the human MESA cohort, here we show that plasma glutamine-glutamate ratio is an independent risk factor for carotid plaque progression. Mice deficient in glutaminase-2 (Gls2), the enzyme that mediates hepatic glutaminolysis, developed accelerated atherosclerosis and susceptibility to catastrophic cardiac events, while Gls2 overexpression partially protected from disease progression. High-throughput transcriptional profiling and high-resolution structural biology imaging of aortas showed that Gls2 deficiency perturbed extracellular matrix composition and increased vessel stiffness. This results from an imbalance of glutamine- and glutamate-dependent cross-linked proteins within atherosclerotic lesions and cellular remodeling of plaques. Thus, hepatic glutaminolysis functions as a potent regulator of glutamine homeostasis, which affects the aortic wall structure during atherosclerotic plaque progression. Murcy et al. show that increasing the plasma glutamine-to-glutamate ratio in atherosclerosis can distally reprogram transcriptional and post-transcriptional remodeling of the aorta by GLS2-dependent hepatic glutaminolysis.