Fig. 1. Temporal genetic ablation of Myomaker in satellite cells during development titrates myonuclear number in myofibers.

a Experimental design used to reduce myonuclear accretion during development. Mymk^loxP/loxP or Mymk^loxP/loxP; Pax7^CreER mice were treated with tamoxifen (Tam.) to generate control or fusion-incompetent mice, respectively. Tamoxifen was administered at either postnatal (P) day 0 (Δ1w) or P6 (Δ2w) and animals were sacrificed 4 weeks post-tamoxifen. b Single myofiber images (left) and quantified average number of nuclei per myofiber (right) in control and Δ1w EDL muscle at P28. Control myofibers had an average of 230 nuclei/myofiber, while Δ1w mice had an average of 55 nuclei/myofiber. Myonuclei are labeled with DAPI. c Single myofiber images (left) and average number of nuclei per myofiber (right) in Δ2w and control EDL muscle at P35. Control myofibers had an average of 225 nuclei/myofiber, while Δ2w mice had an average of 100 nuclei/myofiber. Myonuclei are labeled using DAPI. In (b) and (c), n = 3 biologically independent animals and 20 myofibers were analyzed per animal. Statistical analyses and data presentation: (b) and (c), two-sided unpaired t-test; ****P < 0.0001. Data are reported as mean ± SD. Scale bar: 200 μm. Source data are provided as a Source Data file.