Figure 4.

Increased number of perijunctional folds in biglycan null synapses. A, Electron micrographs of synapses in sternomastoid muscles from 5-week-old wild-type and congenic biglycan null mice. In the wild-type muscle junctional folds are largely restricted to the region directly under the synaptic bouton. However, in biglycan null animals an increased number of perijunctional folds (arrowheads) are observed flanking the synapse. Scale bar, 2 μm. B, Frequency histogram of perijunctional folds in synapses from wild-type and biglycan null mice. The number of perijunctional folds within 0.5–2 μm from the edge of nerve terminal was scored for two wild-type (n = 36 perijunctional regions) and two biglycan null muscles (n = 72 perijunctional regions). There are significantly more perijunctional folds in mutant muscle (Kolmogorov–Smirnov; p < 0.01).