Figure 2.

Expression of the targeted and randomly integrated versions of the Hoxb1/lacZ transgene during early development. Two 8.5-d.p.c. fetuses expressing either the randomly integrated (left), or the HoxD targeted (right) Hoxb1 transgene. (Left) The expected expression domains were scored, both in the fourth rhombomere of the hindbrain (r4, arrowhead) and in the posterior part of the developing trunk. (Right) Expression in r4 was no longer detected when the transgene was recombined upstream Hoxd13. However, early expression in the trunk was maintained, extending more anteriorly in somitic mesoderm than for the randomly integrated version (arrows). Black and red arrows indicate the anterior limits of transgene expression in TgNb1 (black) and TgHb1 (red) embryos, respectively.