Figure 4.
Transmission electron microscopy (TEM) of maxillary barbel myelination. Barbel tissues were collected from adult wild-type AB zebrafish, embedded, and cut at 70 nm. To improve focus, A, B, and D were enhanced with a digital filter (Unsharp Mask) in Adobe Photoshop. A: Overview of the axon-rich ventral area in a normal adult maxillary barbel. Multiple small (1-2 μm) myelinated axons are surrounded by accompanying Schwann cells. B: In each barbel, there are several ‘giant’ axons. C: High-magnification TEM showing a single barbel axon (a) with numerous closely packed myelin lamellae (m). The axoplasm is full of smaller, grayish microtubules. D: Normal barbels also contain bundles of small, unmyelinated axons completely or partially wrapped by the cytoplasm of supporting cells. a, Axon, c, collagen bundle, en, endothelial cell, m, myelin, s, Schwann cell nucleus.