The hedgehog pathway is essential for dental periodic patterning in Malawi cichlids. Control (1% DMSO) treated (a) and cyclopamine treated (b) Cynotilapia afra embryos (7 days post-fertilization (dpf)) showing shh expression in the lower jaw dentition (arrowheads). Cyclopamine (and DMSO) was administered to C. afra embryos at 5 dpf for 24 hours; embryos continued to develop for a further 24 hours under standard conditions and were fixed at 7 dpf. Weaker levels of shh expression in cyclopamine-treated fish along with a disturbed initial pattern of tooth germs and second odontogenic band (b) compared with the 1% DMSO control (a). Note three tooth germs on each half of the dentary in the control (a) compared with two tooth germs on each half of the dentary in embryos treated with cyclopamine (b) (arrowheads). C. afra that were treated for 24 hours at 5 dpf (as above) continued to develop for a further 6 days (12 dpf) to stages where teeth of the first row are expected to erupt and teeth should be developing in the second tooth row (see Figures 4 and 8). Compared with the 1% DMSO control (c) the cyclopamine-treated C. afra (d) failed to develop a dentition; a single tooth shard (arrowhead) is seen unattached within the epithelium above the ossified lower jaw (alizarin red preparation).