High mutation frequency in DNA transfected into mammalian cells

Area of Science:

• Molecular Biology
• Genetics
• Mammalian Cell Culture

Background:

• The lacI gene from Escherichia coli serves as a reporter for genetic mutations.
• Simian virus 40 (SV40)-based recombinant DNA vectors facilitate replication and selection in both bacterial and mammalian systems.
• Understanding mutation frequencies in mammalian cells is crucial for gene transfer studies.

Purpose of the Study:

• To quantify mutation rates in mammalian cells using a bacterial reporter gene within a shuttle vector.
• To characterize the types of mutations occurring in mammalian cells after DNA transfection and replication.

Main Methods:

• Recombinant DNA vectors containing the Escherichia coli lacI gene were constructed.
• Plasmid DNA was introduced into COS7 simian cells via DEAE-dextran transfection.
• Replicated plasmid DNA was recovered from mammalian cells and analyzed in E. coli for lacI mutations.

Main Results:

• Mutations in the lacI gene were detected at frequencies of 1-5% in mammalian cells.
• This is significantly higher than the spontaneous mutation rate in E. coli (<10^-5).
• Observed mutations included base substitutions, deletions, duplications, complex rearrangements, and insertions from the host genome.

Conclusions:

• Mammalian cells exhibit a high frequency of mutations in SV40-based shuttle vectors.
• The observed mutations are diverse, indicating complex DNA damage and repair processes.
• These findings have significant implications for gene therapy and genetic engineering experiments involving DNA transfer into mammalian cells.