title: Smooth muscle protein 22 alpha-Cre is expressed in myeloid cells in mice.
abstract: BACKGROUND
  Experiments using Cre recombinase to study smooth muscle specific functions rely on strict specificity of Cre transgene expression. Therefore, accurate determination of Cre activity is critical to the interpretation of experiments using smooth muscle specific Cre.
  
  
  RESULTS
  Two lines of smooth muscle protein 22 α-Cre (SM22α-Cre) mice were bred to floxed mice in order to define Cre transgene expression. Southern blotting demonstrated that SM22α-Cre was expressed not only in tissues abundant of smooth muscle, but also in spleen, which consists largely of immune cells including myeloid and lymphoid cells. PCR detected SM22α-Cre expression in peripheral blood and peritoneal macrophages. Analysis of SM22α-Cre mice crossed with a recombination detector GFP mouse revealed GFP expression, and hence recombination, in circulating neutrophils and monocytes by flow cytometry.
  
  
  CONCLUSIONS
  SM22α-Cre mediates recombination not only in smooth muscle cells, but also in myeloid cells including neutrophils, monocytes, and macrophages. Given the known contributions of myeloid cells to cardiovascular phenotypes, caution should be taken when interpreting data using SM22α-Cre mice to investigate smooth muscle specific functions. Strategies such as bone marrow transplantation may be necessary when SM22α-Cre is used to differentiate the contribution of smooth muscle cells versus myeloid cells to observed phenotypes.
authors.affiliation: Key Laboratory of Nutrition and Metabolism, Institute for Nutritional Sciences, Clinical Research Center of Institute for Nutritional Sciences, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai, China.
authors.forename: Zhuxia
authors.initials: Z
authors.lastname: Shen
authors.forename: Chao
authors.initials: C
authors.lastname: Li
authors.forename: Ryan A
authors.initials: RA
authors.lastname: Frieler
authors.forename: Alena S
authors.initials: AS
authors.lastname: Gerasimova
authors.forename: Soo Jung
authors.initials: SJ
authors.lastname: Lee
authors.forename: Jing
authors.initials: J
authors.lastname: Wu
authors.forename: Michael M
authors.initials: MM
authors.lastname: Wang
authors.forename: Carey N
authors.initials: CN
authors.lastname: Lumeng
authors.forename: Frank C
authors.initials: FC
authors.lastname: Brosius
authors.forename: Sheng Zhong
authors.initials: SZ
authors.lastname: Duan
authors.forename: Richard M
authors.initials: RM
authors.lastname: Mortensen
mesh_terms: D000818:Animals; D019426:Integrases / Q000235:genetics; D017737:Macrophages, Peritoneal / Q000378:metabolism; D051379:Mice; D008822:Mice, Transgenic; D008840:Microfilament Proteins / Q000235:genetics*; D009000:Monocytes / Q000378:metabolism; D009124:Muscle Proteins / Q000235:genetics*; D022423:Myeloid Cells / Q000378:metabolism*; D032389:Myocytes, Smooth Muscle / Q000378:metabolism; D009504:Neutrophils / Q000378:metabolism; D011995:Recombination, Genetic; D013154:Spleen / Q000378:metabolism
chemical_list: D008840:Microfilament Proteins; D009124:Muscle Proteins; C058992:Tagln protein, mouse; C045073:Cre recombinase; D019426:Integrases