Fig. 6. Isolation of the MSE on a conserved 1.3 kb element. (A) Murine Krox20 gene and extragenic sequences extending from –4.5 kb to +40 kb (upper). Restriction enzymes used to generate overlapping subfragments are shown. These fragments were fused to a ß-globin minimal promoter/lacZ reporter and tested in transgenesis (lower). The number of mice that showed ß-galactosidase activity in sciatic nerve biopsies at P2/3 and P30 and the total number of transgenic mice analysed (n) is indicated. For fragments #4 and #5 the mice that expressed ß-galactosidase at P30 were among those that expressed at P2/3. (B) Homology plot generated using the VISTA algorithm (Mayor et al., 2000) between murine fragment #4 (horizontal axis; numbering in kb is relative to the Krox20 gene) and corresponding human sequences. The vertical axis indicates percent homology in a window of 100 bp with a resolution of 7 bp. Homology >80% is highlighted in gray. Note the base homology shown is 50%. Mice transgenic for construct #5 were tested for ß-galactosidase activity in the sciatic nerve at P3 (C) and P30 (D) as described in Fig. 3. Nonmyelinating Schwann cells were detected using an antibody to GFAP (D; red-brown deposit). The scale bars represent 25 µm.