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Fig. 3
The MSE is highly active in Schwann cells during the initiation of myelination, but activity is downregulated in the mature nerve. (A-D) Lateral views (anterior to the left, dorsal to the top) of wild-type zebrafish imaged live at the indicated stage carrying the MSE:EGFP transgene. EGFP expression is first detected in the PLL nerve at 60 hpf (A), and increases by 5 dpf (B) and 30 dpf (C). At 10 months, only a few Schwann cells express EGFP (D). (E,F) Lateral view of the PLLn from a wild-type fish fixed and stained for MBP expression at 6 months. EGFP expression is nearly undetectable (E), although the nerve is heavily myelinated at this time as indicated by MBP staining (F). The white dashed lines in D-F outline the nerve, and the white arrows mark EGFP-positive Schwann cells. n=at least five transgenic fish at each stage shown. Scale bars: 50 μm.