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bioRxiv · 10.1101/2025.10.25.684582

Ancestry-Aware Modeling of Dark Cyclobutane Pyrimidine Dimer Formation Integrating GTEx Skin Transcriptomes and Evolutionary Genomics

Essel Arthur, K.
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Abstract

Ultraviolet (UV) radiation induces cyclobutane pyrimidine dimers (CPDs) in DNA, initiating mutagenic cascades that underlie photocarcinogenesis. Even hours after irradiation, dark-CPDs photoproducts generated via melanin-mediated chemiexcitation continue to form in melanocytes (4-6). While melanin confers photoprotection, its oxidative by-products can paradoxically extend DNA damage. Here we empirically validate an ancestry-aware computational framework coupling population pigmentation genetics with transcriptional regulation of DNA-repair pathways using Genotype-Tissue Expression (GTEx v9) skin RNA-seq data. We analyzed 604 GTEx donors from sun-exposed and non-exposed skin (lower leg, suprapubic) across inferred ancestry axes. Expression modules for melanin synthesis (TYR, TYRP1, SLC24A5, MC1R) and nucleotide-excision/oxidative-repair (XPC, DDB2, POLH, OGG1) were examined through differential expression, random-forest modeling, and 1,000-fold bootstrap uncertainty quantification. POLH and DDB2 were significantly upregulated in sun-exposed tissue (log2FC = 0.88 +/- 0.12 and 0.64 +/- 0.18; FDR < 0.05), whereas SLC24A5 and TYR displayed ancestry-linked gradients consistent with prior GWAS (8-10, 15, 16). Predictive modeling of a composite dark-CPD index achieved mean R^2 = 0.62 +/- 0.04 and RMSE = 0.21 +/- 0.03 (95 % CI), highlighting SLC24A5 (27 %) and XPC (19 %) as major contributors. These results empirically demonstrate co-regulation between pigmentation and repair pathways within realistic transcriptomic uncertainty bounds. Our integrative approach provides a reproducible, ancestry-aware platform for equitable dermatogenomic risk assessment and mechanistic insight into delayed UV mutagenesis.

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Essel Arthur, K.. 2025-10-28. Ancestry-Aware Modeling of Dark Cyclobutane Pyrimidine Dimer Formation Integrating GTEx Skin Transcriptomes and Evolutionary Genomics. https://doi.org/10.1101/2025.10.25.684582

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