Tissue-specific knockouts generated through Cre-loxP recombination have become an important tool to manipulate the mouse genome. Normally, two successive rounds of breeding are performed to generate mice carrying two floxed target-gene alleles and a transgene expressing Cre-recombinase tissue-specifically. We show herein that two promoters commonly used to generate endothelium-specific (Tie2) and smooth muscle-specific [smooth muscle myosin heavy chain (Smmhc)] knockout mice exhibit activity in the female and male germ lines, respectively. This can result in the inheritance of a null allele in the second generation that is not tissue specific. Careful experimental design is required therefore to ensure that tissue-specific knockouts are indeed tissue specific and that appropriate controls are used to compare strains.

Original languageEnglish
Pages (from-to)1-4
Number of pages4
JournalPhysiological genomics
Issue number1
StatePublished - Sep 2008


  • Conditional
  • Cre-loxP
  • Endothelium
  • Knockout
  • Smooth muscle myosin heavy chain
  • Vascular


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