Establishment of intrafusal and extrafusal motor innervation and expression of alpha motor neuron markers in the absence of ERR2/3.

(A-F) P100 mouse soleus muscle spindles of control (heterozygous: Esrrbflox/+;Esrrgflox/+;ChatCre). (A-C) and ERR2/3cko (D-F) mice. (A-F) Comparable distribution of Ia sensory annulospiral endings in the central spindle segment (visualized by VGLUT1, green), motor innervation (CHAT, magenta) and their postsynaptic sites (BTX, alpha bungarotoxin, grey) between control (A-C) and ERR2/3cko (D-F) mice (scale bar: 100 μm). Arrowheads: Comparable motor innervation (CHAT, magenta) of postsynaptic sites on the peripheral segments of intrafusal fibers (BTX, alpha bungarotoxin, grey) in control (A-C) and ERR2/3cko (D-F) mice. Scale bars: 100 μm. (G-N) Sections through EDL (G,H, K, L) and soleus (I, J, M, N) muscle of P100 mice: comparable characteristic pretzel-like morphologies of neuromuscular junctions (NMJs) with extrafusal muscle fibers and consistent motor innervation (VACHT+) of all postsynaptic NMJs (BTX+) and innervation in control (G, H, I, J) and ERR2/3cko (K, L, M, N) mice. Scale bars: 100 μm. (TIF)