Cre Lox Breeding for Beginners, Part 1

Overview of Cre/Lox System

• Cre/Lox System: A critical tool in mouse genetics enabling tissue-specific and inducible knockouts.
  • Allows precise control over gene expression location and timing.
  • Useful to avoid embryonic lethal phenotypes by controlling gene deletion.
  • Applications: activating/deactivating transgene expression, tracking cells, generating chromosomal inversions or translocations, and reporting gene expression.
  • Constantly evolving with novel applications.

Breeding Schemes

• Complex Models: Involves generating double, triple, quadruple, or n-tuple mutant/transgenic mice.
  • Breeding is complex and often requires technical support.

Efficient Breeding Scheme for Knockouts

• First Cross: Mate a homozygous loxP-flanked mouse with a cre transgenic mouse.
  • 50% offspring: heterozygous for loxP allele and hemizygous/heterozygous for cre transgene.
• Second Cross: Mate these offspring back to homozygous loxP-flanked mice.
  • 25% progeny: homozygous for loxP allele and hemizygous/heterozygous for cre transgene (experimental mice).
  • 25%: homozygous for loxP allele with no cre transgene (potential controls).
• Adaptation is necessary depending on specific genotypes and strains.

Cre Switch for Transgenes

• Gene Activation: loxP-flanked stop sequence can be removed by Cre recombinase to activate gene expression.
  • Application: Mating transgenic strains for specific tissue expression (e.g., mammary tissue).

Inducible or Tissue-Specific Expression

• Inducible Strain: Design transgenes with loxP sites for activation/deactivation.
• Searching for Strains: JAX Cre Repository and Cre Portal at MGI.

Cre Reporter Strains

• Purpose: Confirm Cre activity in specific tissues.
  • Use of visible markers like GFP or LacZ after Cre excision of loxP-flanked stop sequence.
• Applications: Label tissues/organs for tracking in experiments.

Visual Representation

• Figures provided to illustrate breeding schemes and applications of Cre/Lox system:
  • Mating strategies and expected outcomes.
  • Activation and deactivation of transgenes through Cre recombinase.
  • Use of Cre reporter strains to confirm tissue-specific Cre activity.

Conclusion

• The Cre/Lox system is a versatile and powerful tool in mouse genetics, with applications in knockout and transgene research, and the development of reporter strains aids in visualizing and tracking experimental results.