Figure 1.

Synapses in mature biglycan null mice are abnormal. A, Biglycan is expressed at the neuromuscular junction of wild-type mice. Frozen sections of quadriceps femoris (5 weeks old) were labeled with α-bungarotoxin (red) and anti-biglycan (green). Biglycan is expressed at both the neuromuscular junctions and the noninnervated regions of the sarcolemma. No immunoreactivity is observed when sections from biglycan null muscle are stained in the same fashion (data not shown). Scale bar, 10 μm. B, C, The NMJs of biglycan null mice are hypersegmented. Sternomastoid muscle was dissected from perfusion-fixed 5-week-old wild-type (B) and biglycan null (C) littermates and then double-labeled (left) with rh-α-bungarotoxin to visualize the AChRs (red) and anti-SV/anti-neurofilament (green) to show the nerve. Merged images, left; AChR distribution only, right. Note the segmentation (arrowheads) of the biglycan null endplate in contrast to the continuous postsynaptic domains observed in the wild-type. Scale bar, 10 μm. D, The number of segments per endplate from muscles fixed and imaged as described above were scored. Endplates in biglycan null mice were significantly more segmented than those of their littermate controls (n = 60 endplates from 4 animals for each condition; Mann–Whitney U test; p < 0.01).