Biology subjects

Ahuja, N.

Publications and source records attributed to Ahuja, N..

10 recordsLinked to original sources

bioRxiv2026

Organisms associated with siphonophores revealed by short-read whole-genome sequencing

Siphonophores are associated with prey, parasites, microbes, and other organisms in the open ocean, but little is known about these siphonophore cobionts. To learn more about them, we investigated molecular bycatch: their DNA captured during siphonophore genome sequencing. We reanalysed 213 specimens of Physalia, Nanomia, Bargmannia and other siphonophores sequenced in four previously published studies. We recovered 104 bacterial genomes forming 32 genome clusters, including recurrent Metamycoplasmataceae and diverse proteobacteria, groups also found with other cnidarians. Bacterial communities differed among Physalia species sampled in the southwestern Pacific. We identified non-siphonophore eukaryotes from ribosomal markers in 38 specimens, including fish and copepods consistent with prey, parasitic flatworms, and Perkinsela-like relatives of amoeba endosymbionts. Alfonsino (Beryx) sequences in one Hawaiian P. utriculus specimen are consistent with capture of pelagic young of deepwater fishes. Molecular bycatch reveals the diversity of siphonophore associates from specimens already collected for genome research.

genomics↗

bioRxiv2025

Spatiotemporal remodeling of chromatin topology architecture and H3K27me3 redistribution underlies vascular pathology in Hutchinson-Gilford progeria syndrome

Hutchinson-Gilford progeria syndrome (HGPS) is a devastating premature aging disorder driven by the accumulation of the lamin A variant, progerin, leading to severe vascular pathology. While epigenetic alterations are implicated, the spatiotemporal reorganization of the higher-order chromatin and its functional impact on vascular smooth muscle cell (VSMC) transcription remain poorly defined. Through an integrated, longitudinal multi-omics approach combining in situ high-throughput chromosome conformation capture (Hi-C) and Cleavage Under Targets and Tagmentation (CUT&Tag) profiling of CTCF, SMC1A, H3K27me3, H3K27ac, and H3K36me3 with transcriptomic analyses from control and HGPS iPSC-derived VSMCs, we reveal that global topologically associating domain (TAD) architecture remains largely intact in HGPS. However, the internal chromatin states of TADs undergo dynamic, passage-specific remodeling, characterized by a progressive accumulation of broad H3K27me3-repressed domains. This is accompanied by a loss of A/B compartment segregation, as confirmed by DNA-FISH, and a pronounced depletion of interchromosomal intermingling, specifically surrounding downregulated genes, suggesting that these interchromosomal contacts are essential for maintaining transcriptional competence in normal VSMCs. Crucially, we uncover widespread rewiring of enhancer-promoter (E-P) loops, which is linked to the dysregulation of genes critical for vascular development, extracellular matrix organization, and atherosclerosis. Our study demonstrates that spatiotemporal redistribution of repressive histone marks and reorganization of E-P interactions within a structurally resilient TAD framework underpin widespread transcriptional dysregulation in HGPS vascular pathogenesis. This uncovers a critical dissociation between higher-order chromatin architecture and histone modification landscape, providing a mechanistic basis for the failure of vascular homeostasis in progeria.

genomics↗

bioRxiv2025

A Chromosome-Scale Genome of Nanomia septata Reveals Extensive Rearrangement But No Clear Driver of the Unique Colony-Level Organization of Siphonophores

Siphonophores (Cnidaria:Hydrozoa) are pelagic colonial marine invertebrates with many highly specialized bodies (zooids) within a single colony. Their unique biology and ecological importance have made them of particular interest. Recent work revealed siphonophore genomes to be larger than in most other cnidarians. To investigate siphonophores genome biology and develop resources for future studies, we sequenced the genome of a single Nanomia septata to chromosome scale. The haploid genome is 1.5GB across 8 chromosomes, a reduction relative to the 15 chromosomes seen in closely related hydrozoan genomes, and is highly rearranged, consistent with multiple mixing events. Genome expansion occurred through intergenic repeat expansion, with protein-coding genes shorter than in most cnidarians. We found no genomic features clearly associated with siphonophores exceptional colony-level complexity. Gene families that play critical roles in cnidarian development have not expanded, and gene proximity was not generally correlated to their expression across zooids, except in male gonophores. To contextualize these observations, we genome sequenced 20 additional Nanomia specimens across the globe and mapped them to our chromosome-scale reference. Population genomic analyses support three previously recognized species of Nanomia, and at least one additional undescribed species. Overlapping geographic distribution of some Nanomia species suggest reproductive isolation in sympatry. Phylogenetic analyses of genome size indicate Nanomia septata and Nanomia cara have similarly large genomes between 1.5-1.7GB, while Nanomia bijuga and an undescribed species show a secondary reduction to 0.7GB. These results highlight how genomic factors have shaped colony organization and genome diversity within Nanomia.

genomics↗

bioRxiv2025

SPINK1-COL18A1 Crosstalk Shapes Epigenome and Drives Cancer Stemness in Pancreatic Ductal Adenocarcinoma

Pancreatic ductal adenocarcinoma (PDAC) is a devastating cancer with an increasing incidence and extremely dismal prognosis. Discovery and mechanistic understanding of the genetic and epigenetic drivers of PDAC is therefore of critical importance. Here, we uncover serine protease inhibitor Kazal type 1 (SPINK1) as a putative determinant of clinical progression and demonstrate that it can have a non-canonical function as a regulator of epigenomic states of PDAC cells and associated extensive changes in gene expression. We show that SPINK1 expression, which varies in PDAC, is associated with key aggressive phenotypic cancer states and is correlated with the expression of stemness markers both in vitro and in patient samples. Mechanistically, our results strongly suggest that SPINK1 acts through a new signaling axis, by interacting with COL18A1 in the Golgi apparatus, promoting endostatin release and eventually inducing extensive histone H3 modifications. These results reveal a new function of SPINK1 in PDAC and suggest a potential therapeutic route to combat PDAC aggressiveness by targeting the SPINK1-COL18A1-endostatin signaling.

cancer biology↗

bioRxiv2025

Zonal endothelial cell heterogeneity underlies murine renal vascular development.

The renal vasculature consists of highly specialized blood vessels that carry out distinct physiological functions. Defining their transcriptional signatures and tracing their developmental ontogeny has thus far been challenging due to a lack of regionally specific endothelial biomarkers. Here, we performed single nuclear RNA sequencing (snucRNA-Seq) to interrogate embryonic renal endothelial cells. We identified nine different endothelial cell types, and validated expression of novel candidates using multiplex RNAScope. We interrogate biological characteristics, including cell cycle stage, of developmental blood vessels with a variety of in vivo tools. Using genetic tools based on expression of tip cell marker Esm1, we performed detailed lineage tracing, demonstrating multi-clonal and multi-directional endothelial contribution to glomerular vasculature. Together, this study provides the first validated, tool-focused developmental atlas of the murine renal vasculature and elucidates several novel cellular mechanisms of nephron vascularization.

developmental biology↗

bioRxiv2024

Global genomics of the man-o'-war (Physalia) reveal biodiversity at the ocean surface

The open ocean is a vast, highly connected environment, and the organisms found there have been hypothesized to represent massive, well-mixed populations. Of these, the Portuguese man-o-war (Physalia) is uniquely suited to dispersal, sailing the ocean surface with a muscular crest. We tested the hypothesis of a single, panmictic Physalia population by sequencing 133 genomes, and found five distinct lineages, with multiple lines of evidence showing strong reproductive isolation despite range overlap. We then scored thousands of citizen-science photos and identified four recognizable morphologies linked to these lineages. Within lineages, we detected regionally endemic subpopulations, connected by winds and currents, and identified individual long-distance dispersal events. We find that, even in these sailing species, genetic variation is highly partitioned geographically across the open ocean. SummaryThe open ocean is a vast and highly connected environment. The organisms that live there have a significant capacity for dispersal and few geographic boundaries to separate populations. Of these, the Portuguese man-o-war or bluebottle (genus Physalia) is uniquely suited to long-distance travel, using its gas-filled float and muscular crest to catch the wind and sail the sea surface. Physalia are distributed across the globe, and like many pelagic organisms, have been hypothesized to represent a massive, well-mixed population that extends across ocean basins. We tested this hypothesis by sequencing whole genomes of 133 samples collected from waters of over a dozen countries around the globe. Our results revealed five distinct lineages, with multiple lines of evidence indicating strong reproductive isolation, despite regions of range overlap. We combined these data with an independent dataset of thousands of images of Physalia uploaded to the citizen-science website inaturalist.org, which we scored for morphological characters including sail size, tentacle arrangement, and color. From these images, we identified four recognizable morphologies, described their geographical distribution, and linked them to four of the lineages identified with genomic data. We conclude there are at least four species, three of which correspond to species proposed by scientists in the 18th and 19th centuries: P. physalis, P utriculus, and P. megalista, along with one as yet unnamed species Physalia sp. from the Tasman Sea. Within each species, we observe significant population structure, with evidence of persistent subpopulations at a regional scale, as well as evidence for individual long-distance dispersal events. Our findings indicate that, instead of one well-mixed, cosmopolitan species, there are in fact multiple Physalia species with distinct but overlapping ranges, each made up of regionally endemic subpopulations that are connected by major ocean currents and wind patterns.

zoology↗

bioRxiv2023

Giants among Cnidaria: large nuclear genomes and rearranged mitochondrial genomes in siphonophores

Siphonophores (Cnidaria:Hydrozoa) are abundant predators found throughout the ocean and are important components in worldwide zooplankton. They range in length from a few centimeters to tens of meters. They are gelatinous, fragile, and difficult to collect, so many aspects of the biology of these 190 species remain poorly understood. To survey siphonophore genome diversity, we performed Illumina sequencing of 32 species sampled broadly across the phylogeny. Sequencing depth was sufficient to estimate nuclear genome size from k-mer spectra in 8 specimens, ranging from 0.7-4.8Gb. In 6 specimens we got heterozygosity estimates between 0.7-5.3%. Rarefaction analyses indicate k-mer peaks can be absent with as much as 30x read coverage, suggesting minimum genome sizes range from 1.0-3.8Gb in the remaining 27 samples without k-mer peaks. This work confirms most siphonophore nuclear genomes are large, but also identifies several with reduced size that are tractable targets for future siphonophore nuclear genome assembly projects. We also assembled mitochondrial genomes for 32 specimens from these new data, indicating a conserved gene order among Hydrozoa, Cystonectae and some Physonectae, also revealing the ancestral gene organization of siphonophores. There then was extensive rearrangement of mitochondrial genomes within other physonects and in Calycophorae, including the repeated loss of atp8. Though siphonophores comprise a small fraction of cnidarian species, this survey greatly expands our understanding of cnidarian genome diversity. This study further illustrates both the importance of deep phylogenetic sampling and the utility of Illumina genome skimming in understanding genomic diversity of a clade. SignificanceDescriptions of basic genome features, such as nuclear genome size and mitochondrial genome sequences, remain sparse across many clades in the tree of life, leading to over generalizations from very small sample sizes and often limiting selection of optimal species for genome assembly efforts. Here we use Illumina genome skimming to assess a variety of genome features across 35 siphonophores (Cnidaria). This deep dive within a single clade identifies six species that are optimal candidates of future genomic work, and reveals greater range in nuclear genome size and diversity of mitochondrial genome orders within siphonophores than had been described across all Cnidaria.

evolutionary biology↗

bioRxiv2023

Uncovering the transcriptomic heterogeneity of pancreatic endothelial cells using integrative and comparative single cell gene expression analysis

The pancreatic islet vasculature displays tissue-specific physiological and functional adaptations that support rapid glucose sensing and insulin response by {beta}-cells. To uncover the transcriptomic basis of this specialization, we performed a meta-analysis of multi-organ single cell RNA sequencing atlases employing a unique strategy to avoid transcriptomic contamination. We identified biologically relevant genes involved in sphingosine-1-phosphate-mediated insulin-secretion (PLPP1, RDX, CDC42EP1), islet basement membrane formation (SPARC, COL15A1), endothelial cell (EC) permeability (PLVAP, EHD4), membrane transporters (CD320, SLCO2A1) and developmental transcription factors (NKX2-3, AHR). These were validated in silico in independent datasets. We further established the first integrated transcriptomic atlas of human pancreatic ECs and described two unique capillary subpopulations: exocrine and endocrine pancreas ECs. We validated the spatial localization of key markers using RNAscope and immunofluorescence staining on mouse pancreatic tissue cross-sections. Our findings provide novel insights into pancreatic EC heterogeneity and islet EC function with potential implications in therapeutic strategies.

cell biology↗

bioRxiv2022

Rab11 is essential to pancreas morphogenesis, lumen formation and endocrine mass.

The molecular links between tissue-level morphogenesis and the differentiation of cell lineages in the pancreas remain elusive despite a decade of studies. We previously showed that in pancreas both these processes depend on proper lumenogenesis. The Rab GTPase Rab11 has been shown to be essential to epithelial lumen formation in vitro, however few studies have addressed its functions in vivo and none have tested its requirement in pancreas. Here, we show that Rab11 is critical to proper pancreas development. Co-deletion of the Rab11 isoforms Rab11A and Rab11B in the developing pancreatic epithelium (Rab11pancDKO) results in ~50% neonatal lethality, and surviving adult Rab11pancDKO mice exhibit defective endocrine function. Loss of Rab11 in the embryonic pancreas results in morphogenetic defects of the epithelium linked to defective lumen formation and interconnection. In contrast to wildtype cells, Rab11pancDKO cells attempt to form multiple lumens, resulting in a failure to coordinate a single apical membrane initiation site (AMIS) between groups of cells. We show that these defects are due to failures in vesicle trafficking, as apical components remain trapped within Rab11pancDKO cells. Together, these observations suggest Rab11 directly regulates epithelial lumen formation and morphogenesis. Our report links intracellular trafficking to organ morphogenesis in vivo, and presents a novel framework for decoding pancreatic development. HIGHLIGHTSO_LIRab11Af/f;Rab11B-/-;Pdx1-Cre pancreas displays disruption of epithelial organization and reduction of endocrine cell mass. C_LIO_LILoss of Rab11 results in disruption of pancreatic lumen continuity due to a failure of lumen formation. C_LIO_LIEpithelial cells lacking Rab11 display abnormal polarity. C_LI

developmental biology↗

bioRxiv2021

Cyp26b1 restrains murine heart valve growth during development

Endothelial cells (ECs) are critical to proper heart valve development, directly contributing to the mesenchyme of the cardiac cushions, which progressively transform into mature valves. To date, investigators have lacked useful markers of valve ECs to fully evaluate their contributions during valve morphogenesis. As a result, it has been unclear whether the well-characterized regional differentiation of valves correlates with any endothelial domains in the heart. Furthermore, it has been difficult to ascertain whether endothelial heterogeneity in the heart influences underlying mesenchymal zones in an angiocrine manner. To identify regionally expressed EC genes in the heart valves, we screened publicly available databases and assembled a toolkit of endothelial-enriched genes. We identified Cyp26b1 as one of many endothelial enriched genes found to be expressed in the endocardium of the developing cushions and valves. Here, we show that Cyp26b1 is required for normal heart valve development. Genetic ablation of Cyp26b1 in mouse embryos leads to abnormally thickened aortic valve leaflets, which is due in part to increased endothelial and mesenchymal cell proliferation in the remodeling valves. In addition, Cyp26b1 mutant hearts display ventricular septal defects (VSDs) in a portion of null embryos. We show that loss of Cyp26b1 results in upregulation of retinoic acid (RA) target genes, supporting the observation that Cyp26b1 has RA-dependent roles. Together, this work identifies a novel role for Cyp26b1 in heart valve morphogenesis. Understanding the spatiotemporal expression dynamics of cardiac EC genes will likely prove useful to the investigation of both normal as well as dysfunctional heart valve development. HIGHLIGHTS{middle dot} A mouse heart valve gene expression atlas can be generated with publicly available online tools, such as Genepaint and other gene expression databases. {middle dot} Endothelium of developing mouse heart valves is regionally heterogeneous. {middle dot} Cyp26b1 is expressed in the endocardial/endothelial lining of developing heart valves. {middle dot} Loss of Cyp26b1 leads to significant enlargement of aortic valves and to ventricular septal defects. {middle dot} Cyp26b1 represses cell proliferation in valve mesenchyme. {middle dot} Retinoic acid targets are upregulated in Cyp26b1-/- heart valves, indicating dysregulation of RA metabolism.

developmental biology↗