Figure.Figure 2(A) Schematic outline of the Tamoxifen (TM) administration used in the study and experimental design for testing the effect of YY1 deletion on Cardiotoxin (CTX) induced muscle regeneration process for control (Ctrl), Pax7CreERT2/+; YY1+/+ and inducible knock Out (YY1iKO), Pax7CreERT2/+; YY1f/f mice. (B) SCs were FACS sorted 3 days after the last TM injection and cultured for 1.5 days; RT-qPCR detection of YY1 mRNA shows the ablation in YY1iKO cells. (C) IF staining for Pax7 and YY1 on freshly isolated FISCs or (D) single myofibers from EDL muscles or (E) cryosections from TA muscles showing the deletion of YY1 protein from YY1iKO cells. Scale bar =100 µm in (C) or 50 µm in (D-E). (F) Representative FACS plots. About 100,000 cells from 2-month-old Ctrl and YY1iKO mice were sorted by FACS 3 weeks post-TM injection. The percentage of SCs was shown. (n=3 mice, each). (G) H&E staining was performed on the injured TA muscles collected from the designated times post-CTX injection to visualize the degree of regeneration. Scale bar = 100 µm. (H) IF staining for eMyHC on the TA muscles 5 days post-CTX injury. Quantifications of the number of eMyHC+ fibers are shown on the right (n=3, each). Scale bar = 50 µm. (I) Left: representative images of TA muscles isolated from Ctrl or YY1iKO mice 60 days post-CTX injury. Right: Masson's Trichrome staining of the above muscles to visualize the degree of fibrosis. Scale bar = 100 µm. (J) Cross-section area (CSA) of individual myofibers in TA muscles 4 weeks after injury was measured. The distribution for CSA was calculated (n=3 mice). (K) Representative FACS plots showing the percentage of SCs sorted from TA muscles 3 days after CTX injury of Ctrl and YY1iKO mice. Immunostaining for Pax7 together with Laminin was performed on the TA muscles 3 days post-CTX injury. Scale bar = 100 µm. Quantifications of the numbers of Pax7+ SCs per area are shown on the right (n=3 mice, each). Immunostaining for MyoD together with Laminin was performed on the TA muscles 3 days post-CTX injury. Scale bar = 100 µm. Quantifications of the numbers of MyoD+ SCs per area are shown on the right (n=3 mice, each). (N) IF staining for Pax7 and Laminin on TA muscles 4 weeks after CTX injury of Ctrl or YY1iKO mice. Quantifications of the numbers of Pax7+ SCs per 100 fibers are shown on the right (n=3 mice, each). Scale bar = 100 μm. (O) Schematic outline of the second CTX injury 28 days after the first injury. (P) H&E staining was performed on TA muscles of Ctrl or YY1iKO mice 7 day after second CTX injury. Scale bar = 400 μm (left) or 100 μm (right). (Q) Representative images of above TA muscles 7 days after second injury. (R) Quantifications of the weight above TA muscles from three pairs of littermate mice. (S) IF staining for eMyHC and Laminin on TA muscles 7 days after the second CTX injury of Ctrl or YY1iKO mice. Quantifications of the number of eMyHC+ fibers per area are shown on the right (n=3 mice, each). Scale bar = 100 μm. (T) IF staining for Pax7 and Laminin on the above muscles and the quantifications of the number of Pax7+ SCs per area are shown on the right (n=3 mice, each). Scale bar = 100 μm. Error bars represent s.d.'s of the mean. Student's t-test (two-sided): N.S = non-significant, *P<0.05, **P<0.01, ***P<0.001.