Knock-in mice and MEFs expressing active site mutant Rev3l have knockout phenotypes.
(A) Diagram of the mouse Rev3l ASM knock-in allele, with the wild-type (WT) locus shown at the top. Green rectangles indicate Rev3l coding sequences and the gray line represents chromosomal sequence. In the middle diagram, FRT sites are represented by double red triangles, loxP sites by blue triangles and lox511 sites by yellow triangles. The targeted exon 27 (starred) carries D2773A and D2775A point mutations and is inserted in an inverted orientation between wild-type exons 26 and 27. Splicing donor and acceptor sites flanking wild-type and ASM exon 27 are kept intact. The knock-in was produced by a Cre-dependent genetic switch. First, the neomycin positive selection cassette (neo) was excised by breeding with C57BL/6 Flp deleter mice. A subsequent cross with Cre-expressing mice led to excision of the wild-type exon 27 and inversion of ASM mutant exon 27 into the functional orientation. In the constitutive ASM knock-in locus shown in the lower diagram, the D2773A/D2775A Rev3l gene is expressed under the control of the endogenous Rev3l promoter and wild-type Rev3l exon 27 is absent from the locus. Heterozygous ASM knock-in mice (Rev3L+/M) were then used for breeding. (B) Example of Southern blot analysis of (left) the inducible knock-in locus (neo+) and (right) the constitutive ASM knock-in locus. Genomic DNA of the tested animals was compared with C57BL/6 wild-type genomic DNA (WT). EcoRV digested DNA was blotted on a nylon membrane and hybridized with the external 3’ probe with the position shown at the top of part A. Restriction fragments of 15 kb, 11.5 kb and 9.5 kb were observed for the wild-type, inducible knock-in locus (neo+) and constitutive ASM knock-in locus, respectively. Genomic DNA was further analyzed extensively and confirmed by specific PCR assays and complete DNA sequencing as described in the Materials and Methods. (C) Genotypes of mouse pups produced by breeding parental Rev3l+/M mice. (D) Growth of Rev3l+/Δ and Rev3lM/Δ cells. These cells were produced by addition of AdCre to Rev3lM/lox or Rev3l+/lox MEFs, deleting the floxed allele of Rev3l. (E) Survival of Rev3l+/lox, Rev3lM/lox, Rev3l+/Δ and Rev3lM/Δ primary MEFs 120 hr after addition of cisplatin, as measured by ATP content. (F) The MEFs as in (E) were stained with DAPI, and for 53BP1 and γ-H2AX by immunofluorescence as in Fig 2 to detect foci of DNA double-strand breaks. The quantification shows the percentage of cells with >2 53BP1 and γ-H2AX foci in Rev3l+/lox, Rev3lM/lox, Rev3l+/Δ and Rev3lM/Δ primary MEFs 9 days after AdCre treatment. (*) p < 0.01. Data represent mean ± SEM.