Mouse L cell mitochondrial DNA molecules are selected randomly for replication throughout the cell cycle

Area of Science:

• Cell Biology
• Molecular Genetics
• Mitochondrial DNA Replication

Background:

• Mitochondrial DNA (mtDNA) copy number doubles per cell generation.
• Replication mechanisms for mtDNA remain incompletely understood.
• Possible models include random selection or deterministic replication of each molecule.

Purpose of the Study:

• To investigate the selection process for mitochondrial DNA replication rounds.
• To determine if mtDNA replication is a continuous or cell-cycle-dependent process in mouse L cells.

Main Methods:

• Mouse L cells were pulse-labeled with 3H-thymidine to label replicating mtDNA.
• Cells were chased for varying durations (1.5-22 hr).
• A second labeling with 5-bromodeoxyuridine was performed before mtDNA isolation and analysis.

Main Results:

• A consistent fraction of previously 3H-thymidine-labeled mtDNA incorporated 5-bromodeoxyuridine.
• This incorporation occurred across all chase intervals.
• Demonstrates random selection of mtDNA molecules for replication.

Conclusions:

• Mitochondrial DNA replication in mouse L cells is a random process.
• Replication of mitochondrial DNA occurs continuously throughout the cell cycle.