Primary-evidence overview

DNA Replication Sites: Dynamics and Imaging Resolution

Primary evidence separating visible foci from individual replication units

DNA Replication Site Dynamics Review.docx

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What a visible replication site measures

Leonhardt and colleagues followed GFP-PCNA in living mouse C2C12 cells. Colocalization with replication proteins and nucleotide incorporation supported using these foci as markers of active DNA synthesis. [leonhardt2000]

The foci changed distribution during S phase through gradual appearance and disappearance. The recorded sites showed little directional movement, supporting local assembly and disassembly rather than relocation of one persistent factory. [leonhardt2000]

The authors interpreted positional stability as anchoring. Imaging established relative position; it did not identify a physical nuclear anchor or prove that every focus contains a fixed number of replication units. [leonhardt2000]

Resolution changes the unit that is counted

Chagin and colleagues compared conventional and super-resolution imaging in human HeLa Kyoto and mouse C2C12 cells. Structures appearing as single conventional foci separated into multiple smaller sites at higher resolution. [chagin2016]

Combining site counts with genome size, S-phase duration and DNA-fiber measurements supported resolving many sites to individual-replicon scale. This assignment was an integrated inference, rather than direct identification of each origin from an image. [chagin2016]

Late-S clustering, optical resolution and non-diploid cell models limit a universal one-focus/one-replicon rule. The two studies therefore illustrate both local replication-site dynamics and the dependence of a visible factory on the scale of observation. [leonhardt2000] [chagin2016]

Access and biological limits

Primary Abstracts, selected descriptive Results and citation identities were inspected. These cultured-cell observations do not establish identical site kinetics in every tissue, a complete replication-timing programme or a structurally defined nuclear scaffold. [leonhardt2000] [chagin2016]

Primary references and access depth

  1. Leonhardt H et al. (2000). Dynamics of DNA replication factories in living cells. The Journal of cell biology 149:271-80. PMID 10769021. DOI 10.1083/jcb.149.2.271. Access: Abstract and selected descriptive Results.
  2. Chagin VO et al. (2016). 4D Visualization of replication foci in mammalian cells corresponding to individual replicons. Nature communications 7:11231. PMID 27052570. DOI 10.1038/ncomms11231. Access: Abstract and selected descriptive Results.

A newer spatial assay still needs a defined counting unit

The 3D-SPARK study combined nucleotide-analogue pulse labeling and super-resolution imaging to classify DNA-synthesis nanostructures in individual human cells. Reported size, abundance and spatial arrangement changed under several perturbations. These are labeled synthesis structures measured over specified pulses; the result does not turn every optical object into a mapped replication origin or replace a DNA-fibre measure of fork progression. Hawgood et al. (2025).

Additional primary references

  1. Hawgood et al. (2025). Spatial mapping of DNA synthesis reveals dynamics and geometry of human replication nanostructures. The EMBO Journal. DOI: 10.1038/s44318-025-00574-2. Primary study. Access in this reassessment: primary abstract and bibliographic record.

Reassessed 12 October 2026. Recent-source access is stated above; complete supplementary material and raw data were not reanalysed. The archived Word draft remains a separate, unreconciled document.