Replication landscape of the human genome

Area of Science:

• Genomics
• Molecular Biology
• Epigenetics

Background:

• Human DNA replication origins and termini have remained difficult to pinpoint, with existing data showing significant discrepancies.
• Understanding replication dynamics is crucial for comprehending genome stability and cell proliferation.

Purpose of the Study:

• To accurately map genome-wide replication initiation and termination zones in human cells.
• To investigate the relationship between replication fork directionality, transcription, and chromatin structure.
• To elucidate the factors modulating cell-type-specific replication programs.

Main Methods:

• Sequencing of highly purified Okazaki fragments from two human cell types.
• Quantification of replication fork directionality.
• Genome-wide delineation of replication initiation and termination zones.

Main Results:

• Replication initiates stochastically within broad, non-transcribed zones (up to 150 kb) that often border transcribed genes.
• Replication terminates dispersively between initiation zones, with fork progression significantly co-oriented with transcription.
• Initiation zones are enriched in open chromatin, enhancer marks, and origin recognition complex (ORC)-binding sites, and often border topologically associating domains (TADs).

Conclusions:

• A novel genome-wide map of human replication initiation and termination zones has been established.
• Chromatin and transcriptional activity play significant roles in modulating DNA replication initiation.
• These findings reveal the mechanisms underlying cell-type-specific replication programs.