Fig. 3.

Decreased numbers of satellite cells in single-fiber cultures and injured muscles from mice lacking Numb in the Pax7-lineage. (A) Single fibers and associated satellite cells from EDL muscles of Numb^fl/fl Nbl^−/− and Pax7-Numb^fl/fl Nbl^−/− mice bred with R26R^YFP mice were cultured for 66 h and stained with antibodies recognizing Syn4, Pax7, and GFP. Nuclei were DAPI stained. (Scale bar: 100 μm.) Note that ∼98% of the Syn4^+ve cells also express Pax7. A majority of Pax7^+ve satellite cells from Pax7-Numb^fl/fl Nbl^−/− are YFP^+ve, but YFP was not detected in Numb^fl/fl Nbl^−/− mice. (B) Pax7^+ve cells were quantified immediately (0 h) or after 72 h of culture (50 fibers per time point). Significantly fewer satellite cell progeny, P < 0.001, were found on the fibers from the Pax7-Numb^fl/fl Nbl^−/− muscle after 72 h. (C) Pax7 and Ki67 IF of TA muscles from Numb^fl/fl Nbl^−/− and Pax7-Numb^fl/fl Nbl^−/− mice 4 d after BaCl₂ injury. Nuclei were stained with DAPI. (Scale bar: 50 μm.) (D) The average number of Pax7^+ve cells per μm² and the percentage of Pax7^+ve cells that are Ki67^+ve were quantified 4 d after BaCl₂ injury. At least four fields were evaluated for each genotype (n = 3 experiments). There are fewer Pax7^+ve cells in Pax7-Numb^fl/fl Nbl^−/− muscle, but a similar proportion are proliferating (Ki67^+ve), in both Pax7-Numb^{fl/f l} Nbl^−/− and control muscle at this time point.