Overview
C57BL/6 is the most widely used inbred mouse strain in biomedical research and serves as the reference strain for the mouse genome sequence. Since its establishment in 1921, C57BL/6 has become the standard background for gene targeting due to extensive phenotypic characterization, excellent breeding performance, ES cell compatibility, and widespread availability of Cre driver lines on this background.
Why C57BL/6 is Preferred for Gene Targeting
C57BL/6 mice dominate gene targeting projects for several key reasons: (1) They are the reference strain for the mouse genome sequence, ensuring accurate targeting vector design. (2) ES cell lines derived from C57BL/6N substrains (JM8 cells) have high germline transmission efficiency. (3) The majority of tissue-specific Cre driver lines are maintained on C57BL/6 backgrounds, enabling direct crosses without mixed background effects. (4) Extensive baseline phenotypic data exists for comparison across laboratories and publications.
C57BL/6 Substrain Considerations
Two major substrains exist: C57BL/6J (Jackson Laboratory) and C57BL/6N (NIH/Taconic). C57BL/6J carries an Nnt deletion affecting glucose metabolism. C57BL/6N has intact Nnt but some colonies carry the rd8 retinal degeneration allele. C57BL/6N is the standard background for IKMC knockout resources using JM8 ES cells. Researchers should specify substrain in publications for reproducibility.
Frequently Asked Questions
What makes C57BL/6 the reference strain?
C57BL/6J was the first mouse strain to have its complete genome sequenced (published 2002). This extensive genomic characterization, combined with decades of phenotypic data and widespread research community adoption, established C57BL/6 as the de facto reference strain for comparative genomics and gene targeting.
Can I use C57BL/6 for all research applications?
C57BL/6 is suitable for most applications including gene targeting, neuroscience, cancer, metabolism, and immunology. However, some specialized studies may benefit from alternative backgrounds. For example, BALB/c is preferred for myeloma production, FVB/N for pronuclear injection transgenics, and 129 strains for some ES cell applications.
How do I maintain genetic purity on C57BL/6 background?
Maintain lines through sibling crosses or backcross to C57BL/6 periodically. After ES cell targeting, backcross at least 5 generations (N5) to achieve >97% genetic purity. For critical studies, use speed backcrossing with SNP marker panels to accelerate background conversion while retaining the targeted allele.
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