Fig. 7. Specificity of anti-keratin and anti-Hu antibodies.

Control lamprey spinal cord stained with anti-glial keratin antibody LCM 29 (magenta in A) or the anti-Hu antibody (green in B) imaged with an epifluorescence microscope. D = dorsal; V = ventral; ^* = the giant axons of Müller neurons. Arrows point to neurons stained with anti-Hu but not with the anti-keratin antibody. C, images in A and B merged, showing segregation of stained profiles. Scale bar = 20 μm. The small amount of pale labeling in a few cells is due to overlap of different cells in the section, and not to co-expression of Hu and keratin in the same cell. This is shown by the absence of pale label on confocal imaging in the region of the central canal (cc) in D. Two large Müller axons are indicated by ^*. E, cc region stained with anti-acetylated tubulin antibody showing subependymal cells sending processes to the cc. These are the CSF-contacting neurons described by others (see text). F, a section double-labeled with antibodies to BrdU (brown) and neurofilament (red). N = dorsal cells (primary sensory neurons). Note the absence of NF stain in the ependymal and subependymal cells surrounding the central canal, even though some of these cells would be labeled by anti-Hu, as in D. The arrowhead points to a BrdU-positive cell that has no NF stain, at the base of the dorsal column.