Fig. 5. A kreisler-independent activity in the conserved block regulates late segmental expression. (A-C) A large (A,B) and a minimal (C) fragment containing the conserved block from mouse mediates both early (8.25 dpc) and late (9.5 dpc) reporter expression in r5/r6. (E-G) Mutation of the KrA sites eliminates the early but not the late phase of r5 expression in transgenic mouse embryos. (D) A fragment containing the conserved block from chick reproducibly (n=8) directs reporter expression in r5/r6 at late stages (HH14) when electroporated in ovo into the right side of the neural tube. (H) Similar to the result in the mouse, mutation of the KrA site in the chick enhancer (n=11) does not abolish its ability to mediate later stage expression. The relevant constructs used in each case are indicated below each panel with the stages assayed listed above.
