Fig. 6. The SCE-driven HA-tagged Oct-6 transgene is expressed in Schwann cells and rescues the congenital hypomyelination phenotype in Oct-6β-geo/β-geo animals. (A) Developmental expression of HA-Oct-6 in the Schwann cells of Oct-6β-geo/β-geo animals (panels A, C and E) is qualitatively indistinguishable from that of endogenous Oct-6 in Oct-6β-geo/+ animals (panels B, D and F). Both the HA-tagged Oct-6 protein encoded by the transgene and the endogenous Oct-6 protein are detected here with an Oct-6-specific antibody (red fluorescence signal). P0 protein (green fluorescence signal) could not be detected in sciatic nerves of Oct-6β-geo/β-geo animals at P1 (panel G), while few Schwann cells express high levels of P0 protein in nerves of Oct-6β-geo/+ (H) and HA/Oct-6β-geo/β-geo (I) animals at this stage. At P11, high levels of P0 expression are seen in HA/Oct-6β-geo/β-geo and Oct-6β-geo/+ nerves (K and L), whereas in the Oct-6β-geo/β-geo only a small number of Schwann cells express high levels of the P0 protein (J). In adult sciatic nerve, high levels of P0 protein expression are observed in Schwann cells of all three genetic backgrounds, consistent with their myelination status (panels M, N and O; see also part B). The scale bar represents 10 µm. (B) Myelin appears on schedule in sciatic nerves of Oct-6β-geo/β-geo mice expressing the HA-Oct-6 transgene. Myelin is clearly visible as dark blue rings around axons in micrographs of nerves stained with methylene blue. At P1, no myelin could be detected in Oct-6β-geo/β-geo nerves (A), while few Schwann cells have elaborated a myelin sheath around axons in HA/Oct-6β-geo/β-geo and Oct-6β-geo/+ mice (B and C, respectively). At P11, myelin formation is well advanced in nerves of HA/Oct-6β-geo/β-geo and Oct-6β-geo/+ animals (E and F), while only a few myelin figures could be detected in nerves of Oct-6β-geo/β-geo animals. Although with considerable delay, myelination in Oct-6β-geo/β-geo animals does commence (Bermingham et al., 1996; Jaegle et al., 1996). The microscopic morphology of adult sciatic nerves of Oct-6β-geo/β-geo animals is nearly indistinguishable from that of adult HA/Oct-6β-geo/β-geo and Oct-6β-geo/+ sciatic nerves (H and I). The scale bar represents 10 µm and applies to all panels.