(A) Schematic of the mouse TRF1 locus on chromosome 1 (NCBI locus ID 21749), the targeting construct, and the altered alleles of TRF1. R: EcoRI, P: PvuII, H: HindIII. F1. F2 and R: PCR primers.
(B) TRF1 PCR on tail DNA from mice of the indicated genotypes using the F1 and F2 forward primers and the R reverse primer. PCR products: wild type, 100 bp; flox, 152 bp; null allele, 500 bp.
(C) Immunoblot monitoring loss of TRF1 upon Cre-treatment of TRF1F/F MEFs. TRF1 (Ab1449) was detected 3 days after Cre treatment of TRF1F/F and TRF1F/+ MEFs. -Cre: mock infection, γ-tubulin: loading control.
(D) IF-FISH to monitor TRF1 at telomeres of TRF1F/F MEFs at day 3 post Cre. TRF1 IF, red; telomeric FITC PNA probe, green.
(E) Graph representing proliferation of TRF1-deficient MEFs.
(F) Phase-contrast microscopic images of primary TRF1F/F MEFs before and after Cre treatment. Cells were stained for SA-β-galactosidase at day 7 post Cre.
(G) Metaphase spreads showing the fragile telomere phenotype in TRF1 null cells. Telomeres highlighted by FISH (green) and DNA was stained with DAPI (red) at day 4 post Cre.