Fig. 7. Teratogenic dose of RA induces anterior shifts in the Cyp26c1 expression domain and the Hoxb1/vHnf1 expression boundary. All embryos were subjected to a 20 mg/kg dose of RA at E7.5, then analyzed 18 hours later at E8.25 (see Figs 2, 3, 4 for untreated controls). (B,C,F,H) Lateral view; (G,I) dorsal view; (A) ventral view; (D,E) anterior view. (A) RARE-lacZ expression is observed to the anterior tip of some embryos (left embryo), but in other embryos RARE-lacZ expression is reduced at the anterior tip (upper arrowhead in right embryo). RARE-lacZ expression in all embryos is greatly reduced posteriorly in the tailbud (lower arrowheads) when compared with the trunk. (B-C) Cyp26a1 expression is observed in the tailbud (arrowhead) similar to untreated embryos (MacLean et al., 2001), whereas Cyp26c1 expression has been shifted to the anterior-most region of the embryo (arrowhead). A lateral view shows that most Cyp26c1 expression is neural, with mesodermal expression being greatly reduced. (D,E) Comparison of anterior expression patterns of RARE-lacZ and Cyp26c1 demonstrates that the abnormal domain of Cyp26c1 expression lies in the region where RARE-lacZ expression first clears anteriorly. (F,G) The anterior domain of Hoxb1 expression (arrowhead) has been shifted further anteriorly from where it should normally reside at r4. (H-I) The anterior border of vHnf1 expression (arrowhead) has been shifted further anteriorly. This abnormal anterior border of vHnf1 expression lies posterior to the abnormal expression domains of Cyp26c1 and Hoxb1.