title: Utility and limits of Hprt-Cre technology in generating mutant mouse embryos.
abstract: BACKGROUND
  Hprt-Cre doubles the prevalence of homozygous null embryos per litter versus heterozygous breedings without decreasing litter size. Resulting mutant embryos are genotypically and phenotypically equivalent between strategies. We set out to confirm the effectiveness of this approach with other alleles and hypothesized that it would increase efficiency in generating compound mutants.
  
  
  METHODS
  Null mutants for Cyp26b1, Pitx2, and Shh were generated with Hprt-Cre from conditional alleles as were double and triple allelic combinations of Fgfr2IIIb, Raldh2, and Cyp26b1. Embryos were genotyped and phenotyped by whole mount photography, histology, and immunohistochemistry.
  
  
  RESULTS
  Fifty percent of Hprt-Cre litters were homozygous null for Cyp26b1 (15/29) and Pitx2 (75/143), with phenotypic and genotypic equivalence to mutants from standard heterozygous breedings. In multi-allele breedings, mutant embryos constituted half of litters without significant embryo loss. In contrast, Shh breedings yielded a smaller ratio of embryos carrying two recombined alleles (6 of 16), with a significant litter size reduction because of early embryonic lethality (16 live embryos from 38 deciduae).
  
  
  CONCLUSIONS
  Hprt-Cre can be used to efficiently generate large numbers of mutant embryos with a number of alleles. Compound mutant generation was equally efficient. However, efficiency is reduced for genes whose protein product potentially interacts with the Hprt pathway (e.g., Shh).
authors.affiliation: Division of Pediatric Surgery, Department of Surgery, University of Wisconsin SMPH Madison, Madison, Wisconsin.
authors.forename: Krzysztof M
authors.initials: KM
authors.lastname: Zaremba
authors.affiliation: Division of Pediatric Surgery, Department of Surgery, University of Wisconsin SMPH Madison, Madison, Wisconsin.
authors.forename: Amy L
authors.initials: AL
authors.lastname: Reeder
authors.affiliation: Division of Pediatric Surgery, Department of Surgery, University of Wisconsin SMPH Madison, Madison, Wisconsin.
authors.forename: Anna
authors.initials: A
authors.lastname: Kowalkowski
authors.affiliation: Division of Pediatric Surgery, Department of Surgery, University of Wisconsin SMPH Madison, Madison, Wisconsin.
authors.forename: Eden
authors.initials: E
authors.lastname: Girma
authors.affiliation: Division of Pediatric Surgery, Department of Surgery, University of Wisconsin SMPH Madison, Madison, Wisconsin. Electronic address: nichol@surgery.wisc.edu.
authors.forename: Peter F
authors.initials: PF
authors.lastname: Nichol
mesh_terms: D000445:Aldehyde Oxidoreductases / Q000235:genetics; D000818:Animals; D001947:Breeding / Q000379:methods*; D003577:Cytochrome P-450 Enzyme System / Q000235:genetics; D003656:Decidua / Q000502:physiology; D004622:Embryo, Mammalian / Q000502:physiology; D005260:Female; D018507:Gene Expression Regulation, Developmental; D005818:Genetic Engineering / Q000379:methods*; D053823:Hedgehog Proteins / Q000235:genetics; D006579:Heterozygote; D018398:Homeodomain Proteins / Q000235:genetics; D006720:Homozygote; D008098:Litter Size; D008297:Male; D051379:Mice; D008817:Mice, Mutant Strains / Q000235:genetics*; D011247:Pregnancy; D051497:Receptor, Fibroblast Growth Factor, Type 2 / Q000235:genetics; D000072516:Retinoic Acid 4-Hydroxylase; D015398:Signal Transduction / Q000235:genetics*; D014157:Transcription Factors / Q000235:genetics; D000097577:Homeobox Protein PITX2
chemical_list: D000445:Aldehyde Oxidoreductases; D003577:Cytochrome P-450 Enzyme System; D053823:Hedgehog Proteins; D018398:Homeodomain Proteins; D051497:Receptor, Fibroblast Growth Factor, Type 2; D000072516:Retinoic Acid 4-Hydroxylase; D014157:Transcription Factors; D000097577:Homeobox Protein PITX2; C465570:Shh protein, mouse; C000607081:Cyp26b1 protein, mouse; C470579:RALDH2 protein, mouse; C496354:Fgfr2 protein, mouse
keywords: Compound mutants; Cyp26b1; Efficiency; Fgfr2IIIb; Homozygous null mutants; Hprt-Cre; Mouse; Pitx2; Raldh2; Shh