231: Transcription start sites as a germline mutational hotspot

Cortés Guzmán M et al., Nat Commun - This study identifies a pronounced germline mutational hotspot centered on transcription start sites (TSSs) driven in part by early embryonic mosaic variants and transcription-associated DNA damage. Key terms: transcription-start-sites, early-mosaicism, double-strand-breaks, mutational-signatures, promoter-mutations.

Study Highlights:
Extremely rare variants show a localized excess of non(CpG > TpG) mutations around TSSs extending several hundred base pairs, reaching ~35% enrichment at the 100-bp scale and ~14% at 1 kb. The hotspot is largely absent from de novo mutation calls because early mosaic variants are significantly enriched downstream of the TSS and are often filtered from family sequencing data. Regression and feature analyses link the TSS excess to divergent transcription, RNA polymerase II stalling, R-loop formation and somatic (mitotic) double-strand breaks rather than meiotic PRDM9-associated breaks. Mutational signature decomposition implicates non-canonical DSB repair (including TMEJ) and transcription-associated processes, and the hotspot preferentially affects genes related to cancer and developmental phenotypes.

Conclusion:
Transcription initiation regions are focal points of heritable variation shaped by early-development mosaicism and transcription-linked mitotic DNA damage, with implications for disease genetics and evolutionary constraint

Music:
Enjoy the music based on this article at the end of the episode.

First author:
Cortés Guzmán M

Journal:
Nature Communications

DOI:
10.1038/s41467-025-66201-0

Reference:
Cortés Guzmán M, Castellano D, Serrano Colomé C, Seplyarskiy V, Weghorn D. Transcription start sites experience a high influx of heritable variants fueled by early development. Nat Commun. 2025;16:10120. https://doi.org/10.1038/s41467-025-66201-0

License:
This episode is based on an open-access article published under the Creative Commons Attribution 4.0 International License (CC BY 4.0) – https://creativecommons.org/licenses/by/4.0/

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Episode link: https://basebybase.com/episodes/tss-hotspot-early-development

️ Episode:
231: Transcription start sites as a germline mutational hotspot

️ Season:
1

Article title:
Transcription start sites experience a high influx of heritable variants fueled by early development

QC:
This episode was checked against the original article PDF and publication metadata for the episode release published on 2025-12-17.

QC Scope:
- article metadata and core scientific claims from the narration
- excludes analogies, intro/outro, and music
- transcript coverage: Substantive audit of the transcript's articulation of the TSS mutational hotspot, early mosaic enrichment, drivers (divergent transcription, RNAP II stalling, R-loops), mitotic DSBs vs meiotic DSBs, mutational signatures, timing in early embryogenesis, and disease/evolutionary implications of the hotspot.
- transcript topics: Germline transcription start-site (TSS) mutational hotspot; Early mosaic variants and DNMs vs ERVs; Divergent transcription, RNAP II stalling, and R-loop formation as drivers; Mitotic vs meiotic double-strand breaks; Mutational signatures around the TSS (SBS3, SBS40b, SBS40c, SBS39); Timing during early embryogenesis (4-cell to 8-cell transition)

QC Summary:
- factual score: 10/10
- metadata score: 10/10
- supported core claims: 7
- claims flagged for review: 0
- metadata checks passed: 4
- metadata issues found: 0

Metadata Audited:
- article_d...