Synapsin I Cre transgene expression in male mice produces germline recombination in progeny

Genesis. 2006 Jan;44(1):44-9. doi: 10.1002/gene.20183.


The cre/LoxP system can produce conditional loss of gene function in specific cell types such as neurons. A transgenic mouse line, utilized by multiple studies, used the Synapsin I promoter to drive expression of cre (SynCre) to achieve neuronal-specific cre expression. Herein we describe that cre expression can also be observed in SynCre mice within the testes after being bred into a floxed transgenic mouse line. Cre transcript was expressed in testes resulting in recombination of the floxed substrate in testes. In the majority of cases, progeny of male SynCre mice inherited a germline recombined floxed allele, while this was never observed in progeny from female mice carrying the SynCre allele. This observation should alert investigators to a potential confound using these mice and enables male germ cell "deletor" strategies.

Publication types

  • Letter
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Base Sequence
  • DNA Primers
  • Germ Cells*
  • Integrases / genetics*
  • Male
  • Mice
  • Mice, Transgenic
  • Neurons / cytology
  • Neurons / metabolism
  • Polymerase Chain Reaction
  • Recombination, Genetic*
  • Synapsins / genetics*
  • Testis / metabolism
  • Transgenes*


  • DNA Primers
  • Synapsins
  • Cre recombinase
  • Integrases