title: Lactation defect in a widely used MMTV-Cre transgenic line of mice.
abstract: BACKGROUND
  MMTV-Cre mouse lines have played important roles in our understanding about the functions of numerous genes in mouse mammary epithelial cells during mammary gland development and tumorigenesis. However, numerous studies have not included MMTV-Cre mice as controls, and many investigators have not indicated which of the different MMTV-Cre founder lines were used in their studies. Here, we describe a lactation defect that severely limits the use of one of the most commonly used MMTV-Cre founder lines.
  
  
  RESULTS
  To explore the role of protein tyrosine phosphatase Shp1 in mammary gland development, mice bearing the floxed Shp1 gene were crossed with MMTV-Cre mice and mammary gland development was examined by histological and biochemical techniques, while lactation competency was assessed by monitoring pup growth. Surprisingly, both the Shp1fl/+;MMTV-Cre and MMTV-Cre female mice displayed a severe lactation defect when compared to the Shp1 fl/+ control mice. Histological and biochemical analyses reveal that female mice expressing the MMTV-Cre transgene, either alone or in combination with floxed genes, exhibit defects in lobuloalveolar expansion, presence of large cytoplasmic lipid droplets in luminal alveolar epithelial cells postpartum, and precocious induction of involution. Using a PCR-based genotyping method, the three different founder lines can be distinguished, and we determined that the MMTV-Cre line A, the most widely used MMTV-Cre founder line, exhibits a profound lactation defect that limits its use in studies on mammary gland development.
  
  
  CONCLUSIONS
  The identification of a lactation defect in the MMTV-Cre line A mice indicates that investigators must use MMTV-Cre alone mice as control in studies that utilize Cre recombinase to excise genes of interest from mammary epithelial cells. Our results also suggest that previous results obtained in studies using the MMTV-Cre line A line should be re-evaluated if the controls did not include mice expressing only Cre recombinase.
authors.affiliation: Department of Pathology, University of Colorado School of Medicine, University of Colorado, Aurora, Colorado, United States of America.
authors.forename: Taichang
authors.initials: T
authors.lastname: Yuan
authors.forename: Yongping
authors.initials: Y
authors.lastname: Wang
authors.forename: Lily
authors.initials: L
authors.lastname: Pao
authors.forename: Steve M
authors.initials: SM
authors.lastname: Anderson
authors.forename: Haihua
authors.initials: H
authors.lastname: Gu
mesh_terms: D000818:Animals; D017209:Apoptosis; D005260:Female; D019426:Integrases / Q000378:metabolism; D007774:Lactation / Q000235:genetics*; D008321:Mammary Glands, Animal / Q000378:metabolism* / Q000473:pathology; D008324:Mammary Tumor Virus, Mouse / Q000378:metabolism*; D051379:Mice; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D016133:Polymerase Chain Reaction / Q000379:methods; D053824:Protein Tyrosine Phosphatase, Non-Receptor Type 6 / Q000235:genetics*; D050796:STAT3 Transcription Factor / Q000235:genetics; D050799:STAT5 Transcription Factor / Q000235:genetics
chemical_list: D050796:STAT3 Transcription Factor; D050799:STAT5 Transcription Factor; C494087:Stat3 protein, mouse; C045073:Cre recombinase; D019426:Integrases; D053824:Protein Tyrosine Phosphatase, Non-Receptor Type 6