Fig. 5. The POU domain transcription factor Oct6 acts upstream of the MSE to regulate Krox20. (A) Analysis of the –31/+7 and –4.5/+40 Krox20/lacZ transgenes in a Krox20 null-mutant background. (Left) 15.5 dpc Krox20^cre/cre embryo carrying the –31/+7 Krox20/lacZ transgene stained for ß-galactosidase activity. The arrowhead identifies the sciatic nerve. (Right) Section of a ß-galactosidase-stained sciatic nerve from a 18.5 dpc Krox20^cre/cre embryo carrying the –4.5/+40 Krox20/lacZ transgene. The section was counterstained with Nuclear Fast Red. (B upper) Immunofluorescent analysis of sections of P0 wild type (left) and Krox20^lacZ/lacZ mutant (right) nerves using an antibody to Oct6 (-Oct6). (B lower) Immunofluorescent analysis of sections of P8 wild-type (left) and Oct6^{ß–geo/ß–geo} mutant (right) nerves using an antibody to Krox20 (-Krox20). The scale bars in A and B represent 25 µm. (C) Semiquantitative RT-PCR analysis of endogenous Krox20 transcripts (447 bp) and transcripts from the –4.5/+40 Krox20/lacZ transgene (607 bp) from 18.5 dpc sciatic nerves from Oct6^ß–geo/+ and Oct6^{ß–geo/ß–geo} embryos without transgene (left) or carrying the –4.5/+40 Krox20/lacZ transgene (right). Analysis of the 18S rRNA (389 bp) was included as a control. The results are representative of two independent experiments.