Overexpression of MTERFD1 or MTERFD3 impairs the completion of mitochondrial DNA replication

Area of Science:

• Mitochondrial biology
• Molecular genetics
• Cellular metabolism

Background:

• The physiological functions of the mitochondrial transcription termination factor (mTERF) family remain largely unknown.
• While in vitro studies suggest mTERF proteins influence transcriptional readthrough and replication pausing, their in vivo roles in mitochondrial DNA (mtDNA) metabolism are unclear.

Purpose of the Study:

• To investigate the in vivo roles of two mTERF family members, MTERFD1 and MTERFD3, in mtDNA metabolism.
• To determine if MTERFD1 and MTERFD3 impact mtDNA replication and transcription processes.

Main Methods:

• Generation of cell lines with inducible expression of epitope-tagged MTERFD1 and MTERFD3.
• Utilized shRNA constructs to target MTERFD1 and MTERFD3 for knockdown.
• Confirmed mitochondrial localization and absence of sequence-specific DNA binding for both factors.
• Assessed mtDNA copy number and replication intermediates following protein overexpression.

Main Results:

• Overexpression of MTERFD1 or MTERFD3 led to a moderate decrease in mtDNA copy number.
• Specific mtDNA replication intermediates accumulated, indicating a blockage in the later stages of replication.
• MTERF proteins were confirmed to localize to mitochondria and do not bind DNA in a sequence-specific manner.

Conclusions:

• The mTERF family, specifically MTERFD1 and MTERFD3, is implicated in regulating mtDNA replication.
• These factors appear to restrain replication fork progression, potentially facilitating coordinated replication and transcription.
• The findings support a role for mTERF proteins in maintaining mitochondrial genome stability.