Initiation of DNA replication requires actin dynamics and formin activity

Area of Science:

• Cell Biology
• Molecular Biology
• Biochemistry

Background:

• Nuclear actin's polymerization state and levels influence transcriptional regulation.
• Actin dynamics are controlled by nucleocytoplasmic shuttling and filament polymerization.

Purpose of the Study:

• To investigate the role of actin dynamics and formins in DNA replication.
• To elucidate the mechanisms by which nuclear actin regulates DNA synthesis.

Main Methods:

• Experiments conducted using Xenopus egg extracts and human somatic cells.
• Inhibition of formins to assess effects on nuclear transport and DNA replication.
• Analysis of nuclear actin regulators in transcriptionally silent Xenopus egg extracts.

Main Results:

• Formin inhibition disrupts nuclear transport, DNA replication initiation, and general transcription in proliferating cells.
• Disruption of actin dynamics in Xenopus egg extracts abrogates nuclear transport by preventing cargo release from importin complexes.
• Nuclear formin activity is essential for loading cyclin-dependent kinase (CDK) and proliferating cell nuclear antigen (PCNA) onto chromatin, and for DNA replication initiation and elongation.

Conclusions:

• Actin dynamics and formins are essential for DNA replication.
• Nuclear actin controls DNA replication through multiple direct and indirect mechanisms, including nuclear transport and chromatin loading of key replication factors.