Conditional Genetic Manipulation in Mice

All mouse experiments were carried out at Baylor College of Medicine (BCM) and The Hospital for Sick Children with the approval of their respective Institutional Animal Care and Use Committees. All mice were housed in a pathogen-free facility. Mouse lines included: Gt(ROSA)26Sor^tm1Jus – ‘R26PR’ (Carofino et al., 2013 (link)), Gt(ROSA)26Sor^tm2Jus – ‘R26FLPR’ (both generated by Justice Laboratory), Tg(MMTV-cre)4Mam/J – ‘MMTV-cre’ (The Jackson Laboratory, Bar Harbor, Maine, US), Tg(Mx1-cre)1Cgn/J – ‘Mx1-cre’ (from Dr Margaret A. Goodell, Baylor College of Medicine, Houston, Texas, US), and Rag1^tm1Mom/J – ‘Rag1^−/−’ (from Dr David Corry, Baylor College of Medicine, Houston, Texas, US). All lines were on a C57BL/6 (J or N) background, with the exception of MMTV-cre (B6.129 F1 hybrid). The R26FLPR line was generated as previously described (Carofino et al., 2013 (link)), except for the addition of an N-terminal FLAG tag and the addition of P2A-eGFP rather than IRES-eGFP. P2A-eGFP was amplified from OCT4-2A-eGFP-PGK-Puro, which was a gift from Rudolf Jaenisch (Addgene plasmid # 31938). Mx1-cre was activated in both the R26PR;Mx1-cre and R26FLPR;Mx1-cre lines via intraperitoneal injection of 250 µg polyinosinic:polycytidylic acid (pIpC) (Sigma-Aldrich), with three doses spaced two days apart and one dose, respectively, at 8 weeks of age.