Fig. 7. CYP1B1 contributes to maintaining the appropriate expression of Hoxb1. (Aa-Ac) Hoxb1 expression in a HH17 normal embryo (Aa), the isolated neural tube (Ab) and flat-mount preparation of the hindbrain (Ac). (Ba-Bc) Hoxb1 expression is reduced (n=5/7) by implantation of a bead soaked in 10^-4 nM TMS, a specific inhibitor of CYP1B1 (green arrow represents bead position). Expression is less intense in r4, r6 (red arrow) and the anterior spinal cord (blue arrow). (Ca-Cc) A similar reduction was noted with 10^-5 nM TMS (n=5/6). In some cases (Cc), the borders of the Hoxb1 r4 expression domain appeared to be smaller in the treated embryos (black arrows). These effects were not seen in either untreated embryos (Aa-Ac) or embryos where a DMSO-soaked bead was implanted into r4 (data not shown). TMS-treated and untreated embryos were processed simultaneously using an in situ protocol in which the Hoxb1 probe was derived from a common mix and colour reactions were performed for the same length of time.