Fig. 1: High expression of LRP4 in intrafusal fibers.
From: Intrafusal-fiber LRP4 for muscle spindle formation and maintenance in adult and aged animals
a Schematic diagram of muscle spindle and NMJ. γ MN, γ motor neuron; α MN, α motor neuron; DRG, dorsal root ganglia; b fiber, bag fiber; ch fiber, chain fiber. b Lrp4-CreERT2 crossed with reporter mice Ai9 and the schedule of tamoxifen administration. c tdTomato labeled a few fibers of leg muscles in Lrp4-CreERT2; Ai9 mice. Scale bar, 200 µm. This experiment was repeated three times independently with similar results. d Anti-NF/Syn antibodies labeled pretzel-like structures positive for CF568-labeled α-BTX. Scale bar, 50 µm. This experiment was repeated three times independently with similar results. e–i The enrichment of tdTomato in muscle spindle. e Representative images of muscle spindle in leg muscle of Lrp4-CreERT2; Ai9 mice at P14 stained by NF/Syn. Scale bar, 100 µm. f Enlarged images of blue rectangle and white rectangle in (e). Arrows, annulospiral endings; arrowheads, regular NMJs. Scale bar, 50 µm. This experiment was repeated three times independently with similar results. g The schematic diagram of transection view of a muscle spindle. h The schematic diagram of series transection view in (i). i Tdtomato was concentrated in the intrafusal fibers and capsules. Images of transection view of a muscle spindle in Lrp4-CreERT2; Ai9 leg muscle (P60) at different locations. The internal distance is 100 µm. Scale bar, 40 µm. This experiment was repeated three times independently with similar results. j Elevated expression of Lrp4 mRNA in muscle spindle. Tdtomato+ muscle spindles were isolated and proceed to quantitative RT-PCR analysis. The related Lrp4 mRNA was compared with the extrafusal fibers (t (4) = 12.046, ***p = 0.0003). Data are shown as mean ± SEM. n = 3 mice per group, unpaired two-tailed t test. k Representative images of transection view of Lrp4-CreERT2; Ai9 leg muscle (P60) stained by DAPI and S46. Scale bar, 10 µm. This experiment was repeated three times independently with similar results. Source data are provided as a Source Data file.
