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Cis-regulatory variation in the MdCKX6 promoter is associated with allele-specific expression and fruit size in apple.

Fruit size is a key determinant of apple fruit quality and market value and is strongly influenced by phytohormone-regulated cell proliferation and expansion during early fruit development. Cytokinin oxidase/dehydrogenase (CKX) enzymes regulate cytokinin homeostasis by irreversibly degrading active cytokinins, but the contribution of natural variation in CKX genes to fruit size remains poorly understood. Here, we identified MdCKX6 as a candidate regulator of fruit growth in apple (Malus domestica). MdCKX6 exhibited pronounced allele-specific expression during fruit development in the cultivar 'Royal Gala'. Sequence analysis identified a promoter SNP associated with differential promoter activity and allele-specific expression. Genotyping of diverse apple cultivars and wild Malus accessions revealed a significant association between MdCKX6 promoter genotype and fruit size. Cultivars carrying low-expression alleles produced larger fruits, whereas high-expression alleles were associated with smaller fruits. To investigate gene function, MdCKX6 was overexpressed in tomato, resulting in reduced fruit size. Histological analyses of the transgenic tomato fruit revealed smaller pericarp cells. Transcriptome analysis of transgenic fruits revealed widespread changes in genes associated with cell-cycle regulation, cell wall modification, hormone-related processes, and transcriptional regulation. Together, these results identify MdCKX6 as a potential negative regulator of apple fruit growth and reveal an association between cis-regulatory variants, gene expression, and fruit size. This study provides new insights into the role of cytokinin metabolism in fruit development and highlights regulatory variation in MdCKX6 as a potential target for apple breeding.

Malus

Network-based stratification of allele-specific expression reveals patient subgroups in Huntington's disease.

MOTIVATION: Huntington's disease (HD) exhibits substantial variability in age of onset and disease progression that is not fully explained by CAG repeat length alone. Part of this residual variation is heritable, implicating additional genetic mechanisms. cis-regulatory variation, genetic variants that alter transcription and splicing of nearby genes, represents one such mechanism that can be quantified through allele-specific expression (ASE) analysis. However, methods for integrating ASE profiles into patient stratification frameworks remain underdeveloped, particularly for rare diseases with small cohorts and sparse data. RESULTS: We adapt a network-based stratification algorithm, originally developed for somatic tumour mutations, to ASE data. By propagating gene-level ASE imbalance profiles through a protein-protein interaction network, we stratified 20 HD patients into three distinct biological patient subgroups. Differential gene expression analysis highlights neuroinflammatory pathways, including microglial activation, immune cell activation, and cytokine regulation, as key sources of inter-patient heterogeneity, while differential ASE analysis implicates proteasomal and ubiquitin-dependent protein catabolic processes, immune activation, and central nervous system development. Intersection of differentially imbalanced and expressed genes identified FAM181B as a candidate gene with potential eQTL-mediated regulation, supported by independent cis-eQTL evidence for rs3780 in the caudate and putamen, the primary HD-affected striatal regions. FAM181B encodes a nuclear protein expressed in neural tissues acting as an interactor of the Hippo pathway TEAD transcription factors, implicating transcriptional regulatory variation as a potential contributor to molecular heterogeneity between patient subgroups. Differences in cortical and striatal neuropathological scores between clusters, even when adjusted for CAG repeat length, provide clinical support for the biological relevance of the identified subgroups. AVAILABILITY: All analysis code, Docker containers, and conda environments are available at https://github.com/macsbio/HD-ASE-NBS.

Huntington Disease

Gene expression is stable despite widespread cis and trans regulatory divergence in Saccharomyces yeasts.

Regulatory evolution can alter phenotypes, but cis- and trans-regulatory mechanisms may also diverge extensively while total transcript abundance remains stable. Comparisons of parental expression with allele-specific expression in F1 hybrids provide a framework for separating cis- and trans-regulatory effects because both parental alleles are measured in a shared trans-regulatory environment. Here, we analyzed RNA sequencing data from Saccharomyces cerevisiae, Saccharomyces paradoxus, and their F1 hybrid. Among the 4,164 genes with sufficient allele-specific support for strict classification, 2,134 (51.2%) showed detectable cis and/or trans regulatory divergence. However, hybrid expression remained largely conserved, with 81.5% of genes not significantly different from either parent. Compensatory cis-trans divergence predominated over reinforcing divergence; cross-replicate estimation reduced the apparent magnitude of this excess, but opposite-sign effects remained predominant in all 20 non-overlapping replicate comparisons. To connect gene expression to genome sequence, we analyzed the strongly cis-diverged locus LYS2 and found species differences in promoter architecture, including an S. cerevisiae-specific AT-rich insertion, altered spacing among candidate regulatory features, and a promoter-proximal TATA-like element unique to S. cerevisiae. Sequence-based nucleosome prediction suggests that these differences create a broader promoter-proximal nucleosome-depleted region in S. cerevisiae than in S. paradoxus. We also quantified allele-resolved intron retention and found that allele-resolved intron retention was broadly conserved, with only rare locus-specific hybrid-associated shifts. Together, these results show that regulatory divergence is widespread but often buffered in the hybrid, whereas intron-retention divergence is comparatively limited.

Saccharomyces

Gene expression is stable despite widespread cis and trans regulatory divergence in Saccharomyces yeasts.

Regulatory evolution can alter phenotypes, but cis- and trans-regulatory mechanisms may also diverge extensively while total transcript abundance remains stable. Comparisons of parental expression with allele-specific expression in F1 hybrids provide a framework for separating cis- and trans-regulatory effects because both parental alleles are measured in a shared trans-regulatory environment. Here, we analyzed RNA sequencing data from Saccharomyces cerevisiae, Saccharomyces paradoxus, and their F1 hybrid. Regulatory divergence was widespread, with 61.3% of tested orthologs showing significant divergence in at least one cis or trans component. However, hybrid expression remained largely conserved, with 81.6% of genes not significantly different from either parent. Compensatory cis-trans divergence predominated over reinforcing divergence, consistent with widespread buffering of transcript abundance. To connect genome-wide patterns to mechanism, we analyzed the strongly cis-diverged locus LYS2 and found species differences in promoter architecture, including an S. cerevisiae-specific AT-rich insertion, altered spacing among candidate regulatory features, and a promoter-proximal TATA-like element unique to S. cerevisiae. Sequence-based nucleosome prediction suggests that these differences create a broader promoter-proximal nucleosome-depleted region in S. cerevisiae than in S. paradoxus. We also quantified allele-resolved intron retention and found that splicing was broadly conserved, with only rare locus-specific hybrid-associated shifts. Together, these results show that regulatory divergence is widespread but often buffered in the hybrid, whereas post-transcriptional divergence is comparatively limited.

Gene expression

DirectASRM: uncovering allele-specific post-transcriptional RNA modifications through direct RNA sequencing.

SUMMARY: We developed DirectASRM, a comprehensive database for the systematic identification, integration, and annotation of allele-specific RNA modifications (ASRMs) from direct RNA sequencing data. DirectASRM enables single-base, transcript-level detection of ASRMs across multiple RNA modification types, diverse organisms and condition-specific contexts. The database further evaluates the confidence of each ASRM-SNP pair association within isoform context by jointly considering statistical evidence of allelic modification imbalance and independent support from external next-generation sequencing (NGS) - based RNA modification resources. DirectASRM also provides extensive functional annotations for ASRMs and their associated variants, including intra-sample transcript-level allele-specific expression (ASE) and allele-specific splicing, as well as additional post-transcriptional regulatory features such as miRNA binding, circRNA, RNA-protein interactions, and disease relevance. Overall, DirectASRM serves as a comprehensive resource that supports systematic investigation of the potential functional impact of genetic variants in epitranscriptomic regulation. AVAILABILITY AND IMPLEMENTATION: DirectASRM database is freely accessible at http://modinfor.com/DirectASRM/. DirectASRM pipeline is available at GitHub (https://github.com/jiayin1101/DirectASRM_pipeline) and Zenodo (DOI: https://doi.org/10.5281/zenodo.19876077).

Alleles

Parent-of-origin effects on allelic expression bias in interspecific poplar hybrids.

In hybrid plants, phenotypic outcomes are governed by interactions between the two parental genomes. However, the mechanisms underlying the interplay of divergent regulatory networks from these genomes remain poorly understood. In this study, we compared gene-level and allele-specific expression patterns, as well as differentially enriched pathways between F₁ and complex backcross (CBC) lines derived from a natural interspecific hybrid population of Populus fremontii (Pf) and P. angustifolia (Pa). Metabolic differences between Pf and Pa which exhibit low and high levels respectively of phenylpropanoid-derived condensed tannins were leveraged. Using individualized transcriptome references, differential expression and clustering analyses revealed CBC-biased and F₁-biased expression for genes involved in phenylpropanoid metabolism and photosynthesis, respectively. Biased expression of these genes at the allele level was also observed in F1. At the whole-transcriptome level, Pa-biased genes predominated in F₁ hybrids, and Pa alleles displayed more conserved expression patterns than Pf alleles across examined samples. Further analyses indicated that allelic expression bias was significantly associated with parental origin, which could be driven by sequence variations in cis-regulatory elements and differences in CpG island length. Our findings demonstrate strong parent-of-origin effects on divergent regulatory networks governing gene expression in poplar hybrids and provide clues for strategic parental selection tailored to specific metabolic pathways of interest.

cis-regulation

Parent-of-origin specific allelic expression in outbreeding Arabidopsis arenosa identifies antagonistic parental enrichment in protein degradation pathways.

In plants, the epigenetic phenomenon of parent-of-origin allele-specific expression occurs mainly in the triploid endosperm. Although well studied in inbreeding Arabidopsis thaliana, genomic imprinting has been less investigated in outcrossers. In order to investigate a wider role of parental-specific allelic expression, we have analyzed imprinting in whole seeds of the obligate outbreeder Arabidopsis arenosa. High-throughput analysis of imprinting in outbreeding species is hampered by the lack of reference genomes and available sequenced accessions. High degree of allelic variation in outbreeding species may also limit the analysis to loci with less variation. We developed a reference-independent pipeline to detect parental-specific reads. Using different accessions in reciprocal crosses, we detected more than 70 paternally biased imprinted genes and > 500 maternally biased genes. Paternally biased genes showed major enrichment for proteins with ubiquitin protein transferase and ligase activity. Maternally biased genes were enriched for protein pathways directly counteracting paternally enriched genes. Here, we demonstrate an alignment-free protocol to identify imprinted genes that may be successfully applied for imprinting studies in other highly heterozygous outcrossing species. Our results suggest a unique role of genomic imprinting affecting post-transcriptional gene regulation in outbreeding A. arenosa.

Arabidopsis arenosa

Haplotype-specific expression of a terpene synthase underlies linalool variation in the grapevine cultivar Riesling.

Grapevine cultivars vary widely in monoterpenoid content, yet the genetic and regulatory mechanisms underlying this variation remain poorly characterized beyond highly aromatic Muscat types. We profiled free volatiles and monoterpenoid glycosides in a Riesling × Cabernet Sauvignon F1 mapping population, revealing extensive variation and transgressive segregation consistent with multigenic control. QTL mapping identified 70 significant loci associated with 48 volatile compounds and monoterpene glycosides, including two major QTLs explaining 33.6% and 33.4% of phenotypic variance in (3S)-linalool accumulation. Integration of haplotype-resolved transcriptomics with metabolite data, enabled by a chromosome-scale diploid Riesling genome assembly, resolved a (3S)-linalool/nerolidol synthase cluster on chromosome 10 and identified VviTPS54 as the strongest candidate underlying linalool variation. VviTPS54 exhibited haplotype-specific expression strongly correlated with (3S)-linalool accumulation across genotypes, while no QTL was detected at the 1-deoxy-D-xylulose-5-phosphate synthase 1 (VviDXS1) locus previously identified in Muscat cultivars. In addition, VviDXS1 expression was not correlated with terpene levels, indicating that regulatory variation within terpene synthase clusters, rather than methylerythritol phosphate (MEP) pathway flux, drives monoterpenoid composition in this population. These results establish regulatory variation of terpene synthases as a key mechanism underlying monoterpenoid diversity in grapevine and demonstrate that resolving such variation requires haplotype-phased genome assemblies coupled with haplotype-resolved transcriptomics to detect allele-specific expression differences at complex, heterozygous loci.

Grapevine

SNP-derived CpG variation and DNA methylation linking genetic susceptibility to metabolic disease.

DNA methylation at CpG dinucleotides represents a key epigenetic mechanism linking genetic variation to gene regulation in complex human diseases. Single-nucleotide polymorphisms (SNPs) that create or disrupt CpG sites can alter local DNA methylation and transcriptional activity, thereby influencing disease susceptibility. These CpG-modifying variants provide a functional interface between inherited genetic variation and epigenetic regulation in complex metabolic disorders. This review summarizes current evidence on SNP-derived CpG variation and its role in allele-specific DNA methylation and gene regulation in metabolically relevant tissues. By integrating findings from genome-wide association studies, epigenome-wide association studies, and multi-omics research, this review provides a mechanistic framework explaining how CpG-modifying polymorphisms influence adipogenesis, pancreatic β-cell function, inflammation, and glucose metabolism. Special emphasis is placed on South Asian populations, who exhibit early β-cell dysfunction and increased visceral adiposity. Many CpG-modifying variants act as methylation quantitative trait loci (meQTLs), influencing allele-specific methylation and gene expression. Understanding SNP-CpG-methylation interactions may improve functional interpretation of disease-associated genetic variants, enhance biomarker discovery, and support precision medicine strategies for metabolic disease.

Humans

Allele-specific chromatin architecture shapes imprinted domains and coordinates a distal enhancer and antisense transcription at the mouse Mest-Copg2 domain.

Genomic imprinting results in parent-of-origin-dependent gene expression, but how three-dimensional genome organization contributes to imprinted gene regulation remains unclear. Using Capture Hi-C in mouse cortex and primary cortical neurons, we identified parental allele-specific chromatin architectures across multiple imprinted domains. These architectures largely originate from imprinting control regions and correlate with DNA methylation-sensitive CTCF binding. Active and inactive alleles of imprinted genes show distinct promoter interaction profiles and differential engagement with distal regulatory elements in both contact frequency and the epigenetic state of distal regions. A CRISPR interference screen identified a distal enhancer that regulates Mest-Copg2 imprinted expression through allele-specific chromatin interactions. In neurons, this enhancer activates Copg2 on the maternal allele, whereas on the paternal allele it drives Mest isoforms transcribed antisense to Copg2 and contributes to Copg2 repression. In summary, we show that allele-specific chromatin architecture coordinates maternal enhancer activity and paternal antisense transcription to control imprinted expression in neurons.

Animals

Epi-Allele elicits compensatory expression of the non-targeted allele and prevents haploinsufficiency in dominant genetic diseases.

Epigenetic regulation may underlie asymmetric allelic expression of many genes during development and disease pathogenesis. Allele-specific epigenetic modification could provide an efficient therapy for dominant genetic diseases due to heterozygous mutations. We developed an allele-specific epigenetic editing method ("Epi-Allele") for silencing pathogenic alleles and found surprisingly elevated expression of the non-targeted alleles, leaving total gene expression unchanged. Genome-wide screening revealed that such compensated allelic expression represents a common phenomenon, suggesting that the Epi-Allele approach could avoid the haploinsufficiency induced by current allele-specific silencing therapies. This notion was validated by allele-specific epigenetic remodeling of Myh6 and MYH7 genes in ameliorating cardiac phenotypes in a hypertrophic cardiomyopathy (HCM) mouse model and HCM patient iPSC-derived cardiomyocytes, respectively. Thus, Epi-Allele offers an allele-specific haploinsufficiency-free therapeutic approach for treating dominant genetic diseases.

DNA methylation

GWAS-based identification of a candidate gene and development of a predictive KASP marker for seed protein and oil contents in soybean.

BACKGROUND: Soybean [Glycine max (L.) Merrill] is one of the most widely cultivated crops worldwide. Its seeds contain about 40% protein and 20% oil, serving as essential nutrient sources for humans. Given the nutritional importance of seed protein and oil, identifying genes that regulate their levels is crucial for improving soybean seed quality. OBJECTIVE: This study aimed to identify genetic factors associated with seed protein and oil content using a genome-wide association study (GWAS). METHODS: Seed protein and oil contents were quantified in 192 soybean mutant accessions in a mutant diversity pool (MDP), and GWAS was conducted using 17,631 SNPs filtered from genotyping-by-sequencing. Expression of a candidate gene was examined across seed developmental stages (R5 to R7), and a significant SNP was converted into a Kompetitive Allele-Specific PCR (KASP) marker for validation. RESULTS: GWAS detected significant SNPs associated with seed protein and oil content. Chr20_7635098 was identified as a nonsynonymous SNP located in the exon of Glyma.20g042400. This gene showed differential expression across seed developmental stages between mutant accessions with contrasting protein and oil contents. The KASP marker for Chr20_7635098 was validated using the MDP and six domestic soybean cultivars showing predictive accuracies of ≥ 80.50% for protein content and ≥ 61.18% for oil content. CONCLUSION: Overall, this study identified a candidate gene linked to both seed protein and oil content, providing valuable insights for molecular breeding strategies aimed at efficiently improving these nutritional traits.

Glycine max

A transcriptome-wide approach for rapid pathotype discrimination of Puccinia striiformis f. sp. tritici in north-western India.

Stripe rust of wheat caused by Puccinia striiformis f. sp. tritici (Pst) remains a major constraint to wheat production in India due to the rapid evolution and frequent emergence of virulent pathotypes. Rapid and reliable discrimination of Pst pathotypes is essential for effective resistance deployment and surveillance. In the present study, transcriptome-wide simple sequence repeats (SSRs) and single nucleotide polymorphisms (SNPs) were exploited to develop and validate molecular markers for pathotype-specific detection of Pst pathotypes prevalent in North India (110S119, 238S119, 46S119, 110S84 and 78S84). Microsatellite mining from 6103 core orthologous clusters comprising 51,127 transcripts mined 14,634 SSR loci, from which 93 primer pairs were synthesized. However, only three SSR markers exhibited polymorphism indicating limited discrimination potential of expressed sequence-derived (EST) SSRs for pathotype differentiation. In contrast, SNP discovery through stringent variant calling and filtration yielded 186 pathotype-specific homokaryotic SNPs, of which 56 high-confidence loci were selected for Kompetitive Allele-Specific PCR (KASP) assay development. A total of 48 KASP markers were synthesized and 14 demonstrated clear pathotype- or cluster-specific polymorphism representing substantially higher resolution than SSR markers. The high SNP-to-KASP conversion efficiency (~ 95%) and reproducible fluorescence-based clustering emphasize the robustness of KASP assay. Comparative evaluation revealed that SNP-based KASP markers provide superior discriminatory capacity for closely related Pst pathotypes and represent a promising complementary molecular approach for rapid identification of predominant Indian Pst pathotypes. The validated marker panel developed in this study can complement conventional virulence phenotyping and field pathogenomics approaches for surveillance of currently known pathotypes, while continued refinement may accommodate future changes in pathogen populations.

India

Identification of elements determining KIR gene demethylation at the CD56-bright stage of NK cell development.

The variegated expression of the KIR family of class I MHC receptors generates specialized natural killer (NK) cells capable of allele-specific HLA recognition. Understanding the mechanism of KIR gene activation will lead to improved methods for the generation of fully functional NK cells. A central RUNX-binding site in the KIR proximal promoter is required for gene activation. RUNX proteins recruit ten-eleven translocation (TET) proteins that generate 5-hydroxymethylcytosine (5hmC) and drive DNA demethylation. Assessment of 5-methylcytosine (5mC) and 5hmC residues at four stages of NK cell development reveals deposition of 5hmC primarily in a CREB site next to the RUNX site at the CD56Bright stage but not the subsequent CD56Dim stage representing fully mature NK cells. KIR promoter demethylation is delayed relative to other lineage-associated genes, indicating a high threshold for KIR gene demethylation in developing NK cells, and a window of opportunity for RUNX/TET-dependent KIR gene activation in CD56Bright NK cells.

6-base sequencing

HRAS promotes mutant NRAS-driven transformation with codon and allele specificity.

Wild-type RAS family members determine the signaling and therapeutic response in cancers driven by mutant HRAS and KRAS because they activate alternate RAS effector pathways. Here, we found that the requirement for wild-type RAS to support mutant NRAS-driven transformation correlated with codon-specific differences in GTP hydrolysis. NRAS with mutations at either Gly12 (G12X) or Gly13 (G13X), which retained the GDP-GTP cycling function, had modest autonomous transforming potential. In contrast, NRAS with GTP-locking mutations at Gln61 (Q61X mutants) was uncoupled from receptor tyrosine kinase (RTK) input, rendering wild-type RAS an obligate partner for RTK-stimulated signaling and oncogenesis. In RASless cells expressing mutant NRAS, reintroduction of wild-type HRAS was sufficient to restore signaling and transformation. Global dependency mapping in human cancer cells revealed functional partitioning, wherein mutant NRAS promoted MAPK signaling and wild-type HRAS promoted PI3K-AKT survival signaling. Consequently, allele-specific or pan-RAS(ON) inhibitors synergized with inhibitors of proximal RTK signaling or of wild-type HRAS or KRAS to overcome this signaling plasticity. Pan-RAS(ON) and HRAS inhibition was synergistic for all NRAS mutants tested, with Q61X mutants showing greater sensitivity. These findings define the signaling partnership between mutant NRAS and wild-type HRAS as a targetable vulnerability and provide a biochemical blueprint for dual RAS inhibition in NRAS-mutated malignancies.

Humans

Genetic diversity and molecular mechanisms in hypertrophic cardiomyopathy: toward personalized therapy.

Hypertrophic cardiomyopathy (HCM) is the most common inherited cardiac muscle disorder, yet contemporary genomic and mechanistic research still lacks a cohesive model explaining how diverse genetic architectures give rise to heterogeneous phenotypes. This review synthesizes advances across sarcomeric and nonsarcomeric mutations, including intermediate-effect variants, polygenic modifiers, and ancestry-dependent sources of variant misclassification to elucidate how these factors govern disease penetrance and clinical expression. It critically evaluates how genetic diversity intersects with key molecular pathways, including sarcomeric hypercontractility, calcium dysregulation, mitochondrial energy deficiency, and transforming growth factor-β (TGF-β) and protein kinase B (AKT)/mammalian target of rapamycin (mTOR) signaling, to drive hypertrophic and fibrotic remodeling. Emerging mechanism-based therapies, such as myosin inhibition, allele-specific silencing, clustered regularly interspaced short palindromic repeats (CRISPR)-based correction, and metabolic modulation, are examined with respect to their capacity to modify upstream molecular drivers rather than downstream hemodynamic consequences. Persistent challenges, including variants of uncertain significance classification, ancestry-biased databases, inequitable access to genetic testing, and unresolved safety concerns for gene-based therapies, are critically assessed as major barriers to precision-medicine integration. By linking genetic architecture, molecular pathogenesis, and targeted interventions, this review advances a contemporary, mechanistically grounded framework that informs both individualized management and future research directions. Future research should prioritize pathway-specific therapeutics, functional and mechanistic validation of emerging variants, deeper physiologic phenotyping to refine disease modeling, and accelerate translation throughout the continuum of HCM pathophysiology.

Humans

Haplotype-resolved genome of Forsythia suspensa reveals the reticulate evolution in Oleaceae and a novel gene cluster regulating stamen development.

The olive family (Oleaceae) comprises numerous species of economic, horticultural, and medicinal importance. Despite its significance, the evolutionary history of this complex family remains enigmatic. Here, we generated a high-quality haplotype-resolved genome of Forsythia suspensa, a distylous species that occupies a key phylogenetic position in Oleaceae. The 2 haplotypes exhibit significant allelic divergence with potential allele-specific regulation. We reconstructed the polyploidization history of Oleaceae by confirming and precisely dating a shared whole-genome triplication and an independent whole-genome duplication event. We revealed a complex reticulate evolution that gave rise to the tribe Oleeae: an initial hybridization between Forsythieae (♂) and Jasmineae (♀), a subsequent backcrossing event, and a final whole-genome duplication. We identified a novel tandemly duplicated pectin methylesterase inhibitor gene cluster that regulates filament length and pollen size via restricting cell elongation in the long-styled morph. Dosage augmentation via stepwise cluster formation (0.99 to 3.83 Mya) may contribute to maintaining stamen traits of the long-styled morph. These FsPMEIs are co-expressed with many cell wall-related genes, suggesting a functional link in cell wall modification. Our study reveals the reticulate evolution in Oleaceae and a novel gene cluster controlling stamen development in F. suspensa and provides valuable haplotype-resolved genomic resources for heterostylous species, offering novel framework and molecular pathways to understand plant adaptive evolution.

Forsythia

Innovative CRISPR/Cas9-Based Strategy for Allele-Specific HLA Peptidome Analysis Using a Pan-HLA Antibody.

Human leukocyte antigen (HLA) immunopeptidomics is restricted by the limited availability of allele-specific antibodies and by potential artifacts introduced by HLA overexpression systems. To address these challenges, we developed a CRISPR/Cas9-based strategy that selectively deletes undesired classical class I alleles while preserving a single endogenous allele, thereby enabling allele-resolved peptidome profiling with a pan-HLA class I antibody. As a proof of concept, we edited JY cells to eliminate HLA-B∗07:02 and HLA-C∗07:02 while retaining HLA-A∗02:01 (ΔBC clones). Peptide-HLA complexes were immunoprecipitated from WT and ΔBC clones using either the pan-HLA class I antibody W6/32 or the A∗02:01-specific antibody PA2.1, followed by nanoLC-MS/MS and computational HLA assignment. Deletion of HLA-B and HLA-C alleles caused an expected ∼55% reduction in total class I surface expression. Despite this, W6/32 immunoprecipitation from ΔBC clones recovered a comparable peptide yield to PA2.1 in WT cells. Binding predictions showed that most peptides identified in ΔBC clones using W6/32 were assigned to HLA-A∗02:01, with near-complete loss of HLA-B∗07:02- and HLA-C∗07:02-derived peptides. Sequence logo analysis confirmed the canonical A∗02:01 motif across conditions. The ΔBC W6/32 immunopeptidome exhibited a high degree of overlap (∼88%) with the WT PA2.1 repertoire, supporting the specificity and fidelity of the approach. These findings establish CRISPR-based editing of HLA alleles as a viable strategy for allele-specific immunopeptidome analysis using pan-HLA antibodies, supporting its potential application beyond this proof-of-concept system, reducing reliance on allele-specific reagents and facilitating the study of underrepresented HLA alleles.

Humans