LSD1 is required for euchromatic origin firing and replication timing

Area of Science:

• Epigenetics
• Molecular Biology
• Cell Cycle Regulation

Background:

• DNA replication initiates from specific origins, typically in open chromatin.
• The precise epigenetic mechanisms controlling replication origin selection and activation are not fully understood.
• Lysine-specific demethylase 1 (LSD1) is known to promote chromatin condensation via H3K4me1/2 demethylation.

Purpose of the Study:

• To investigate the role of LSD1 in DNA replication and origin firing.
• To elucidate the mechanism by which LSD1 influences replication timing.
• To understand the implications of LSD1's role in replication for epigenetic regulation and cancer therapy.

Main Methods:

• Co-immunoprecipitation to detect LSD1 interaction with replication machinery.
• Cellular fractionation and western blotting to assess LSD1 levels during S phase.
• Chromatin immunoprecipitation followed by sequencing (ChIP-seq) to identify pre-replicative complex (pre-RC) binding sites.
• Analysis of DNA replication timing using genome-wide assays in LSD1-deficient cells.
• Investigating the recruitment of TICRR and CDC45 to replication origins.

Main Results:

• LSD1 interacts with the DNA replication machinery and peaks in early S phase.
• LSD1 facilitates origin firing in euchromatic regions enriched with H3K4me2.
• LSD1 deficiency causes a genome-wide shift in DNA replication from early to late S phase.
• LSD1's function in origin firing involves the loading of TICRR and recruitment of CDC45 to the pre-RC.
• These findings reveal an unexpected role for LSD1 in regulating replication timing through epigenetic mechanisms.

Conclusions:

• LSD1 plays a critical, previously unrecognized role in activating euchromatic replication origins.
• Epigenetic regulation by LSD1 is crucial for determining DNA replication timing.
• Understanding LSD1's role in replication is important for managing side effects of anti-LSD1 cancer therapies.