Fig. 2.

Egr2^Lo/Lo sciatic nerves are congenitally hypomyelinated. Gross examination revealed that at P14, wild-type (WT) nerves (A, arrow) were opaque white because of abundant myelination, whereas P14 Egr2^Lo/Lo nerves (B, arrow) were transparent because of defective myelination. Toluidine blue-stained sections (C and D) and electron micrographs (E and F) illustrate that WT nerves (C and E Inset) have thick and abundant myelination of medium- and large-caliber axons, whereas Egr2^Lo/Lo (D and F Inset) nerves have densely packed Schwann cells that show minimal myelination of a few axons. BrdUrd incorporation (red nuclei) showed that P14 nerves from Egr2^Lo/Lo mice (H) have higher numbers of proliferating Schwann cells than do wild-type nerves (G). Immunohistochemical analysis with antibodies against the promyelinating Schwann cell marker SCIP demonstrated that P14 wild-type nerve has few SCIP-immunoreactive cells (red nuclei) (I), whereas Egr2^Lo/Lo nerve has abundant SCIP-positive cells (J).