Figure 4(A) FACS-isolated SCs from Pax7-nGFP mice were cultured for the designated time (0, 24, 48 or 72 hrs). YY1 expression was quantified by RT-qPCR. 18S was used as the normalization control.(B) Flow cytometric analysis of YY1 protein or IgG control in FACS-isolated SCs cultured for the designated time (0, 24 or 48hrs). YY1 protein level is normalized to IgG levels. The numbers indicate the normalized level of YY1 protein relative to that of FISCs.(C) An equal number of FACS-isolated SCs from Ctrl or YY1iKO mice were cultured for 48 hrs and EdU labelled for 8 hrs, followed by immunostaining for Pax7 (green) and EdU (red). Quantifications of the percentage of EdU+ cells are shown on the right (n=3 mice, each). Scale bar = 100 µm.(D) The above cells were also IF stained for Pax7 (red) and MyoD (green). Quantifications of each population, Pax7+MyoD+, or Pax7-MyoD+, are shown on the right (n=3, each). Scale bar = 100 µm.(E) Single EDL myofibers were cultured for 48 hrs before staining for Pax7 (red) and MyoD (green). Quantifications of the numbers of each population, Pax7+MyoD-, Pax7-MyoD+, or Pax7+MyoD+, are shown on the right (n=3 mice, each). Scale bar = 50 µm.(F) Pax7 (green) and Ki67 (red) staining was performed on the above single EDL myofibers. Scale bar = 50 µm. Quantifications of the numbers of each population, Pax7+Ki67-, Pax7-Ki67+, or Pax7+Ki67+, are shown on the right (n= 3 mice, each).(G) SCs expansion in vivo was determined by EdU labeling for 12 hrs 2.5 days after CTX injury. Quantifications of the numbers of EdU+ cells are shown on the right (n=3 mice, each). Scale bar = 100 µm.(H) An equal number of FACS-isolated SCs from Ctrl or YY1iKO mice were cultured for 24hrs and EdU labeled for 12 hrs, followed by immunostaining for Pax7 (green) and EdU (red) was performed. Quantifications of the percentage of EdU+ cells are shown on the right (n=3 mice, each). Scale bar = 100 µm.Single EDL myofibers were cultured for 12 (I) hrs in growth media before staining for Pax7 (green) and MyoD (red). Scale bar = 50 µm. Quantifications of the proportion of MyoD+ cells are shown on the right (n=3 mice, each).Single EDL myofibers were cultured for 24 (J) hrs in growth media before staining for Pax7 (green) and MyoD (red). Scale bar = 50 µm. Quantifications of the proportion of MyoD+ cells are shown on the right (n=3 mice, each).(K) FACS-isolated SCs from YY1iKO mice were infected with YY1 expressing or control viruses, followed by immunostaining for Pax7 (green) and MyoD (red) 36 hrs post-transfection. Scale bar = 100 µm. Quantifications of the numbers of each population, Pax7+MyoD-, Pax7-MyoD+, or Pax7+MyoD+, are shown on the right (n=3 mice, each).(L) Single EDL myofibers were cultured for 3 days, followed by immunostaining for Myogenin (red) and MyoD (green). Scale bar = 50 µm. Quantifications of the numbers of each population, MyoD+Myog+, MyoD-Myog+, or MyoD+Myog-, are shown on the right (n=3 mice, each).(M) FACS-isolated SCs were cultured for 2 days in proliferation medium followed by 2 days in differentiation medium; the degree of differentiation was assessed by IF staining of MF20+. Scale bar = 100 µm. Quantifications of the numbers of MF20+ area per nucleus are shown on the right (n=3 mice, each). Error bars represent s.d.'s of the mean. Student's t-test (two-sided): *P<0.05, **P<0.01, ***P<0.001.