Figure 2.

The developmental program of Malawi cichlid dentitions. (a) Expression of pitx2 in the lower jaw (dorsal view) of three Malawi cichlid species, Cynotilapia afra (CA), Metriaclima zebra (MZ), Labeotropheus fuelleborni (LF), during tooth initiation and development. OB, odontogenic band (around 4 days post-fertilization (dpf)); 1^st, first tooth to initiate (around 5 dpf); 3–4 t, 3–4-teeth stage (around 6–7 dpf). Black arrowhead in LF OB shows the extent of the initial field of odontogenic competence prior to tooth germ initiation. Black arrowheads in CA, MZ, LF 1^st indicate the formation of the first tooth, note the extensive region of competence in LF, later marking competent epithelium reflecting the future distribution of teeth (arrowhead, 3–4-teeth stage; refer to Figure 1c). Scale bar 100 μm. All panels are to the same scale. (b) Expression of pax9 in the lower jaw (dorsal view) of three Malawi cichlid species CA, MZ, LF, during tooth initiation and development. OB, 1^st, and 3–4 t as in (a). Black arrows in OB for CA, MZ and LF mark the extent of the odontogenic field of expression within mesenchymal cells along the mesiodistal jaw axis; the point of the arrow indicates the position along this axis where the first tooth will initiate. Black arrowheads in 1^st for CA, MZ and LF point to up-regulated expression in the mesenchyme surrounding the thickening dental epithelium. Black arrowheads in CA, MZ and LF 3–4 t, show developing teeth with pax9 expression in the dental mesenchyme surrounding the epithelial tooth germ, and not within the dental papilla. Scale bar 100 μm. All panels are to the same scale. (c) Expression of shh in the lower jaw (dorsal view) of three Malawi cichlid species CA, MZ, LF, during tooth initiation and development. OB, 1^st, and 3–4 t as in (a). Black arrowhead in LF OB marks the onset of tooth initiation within the primary OB (note the asymmetry of dental initiation, left half of the dentary initiating first); tooth initiation will occur within this restricted band although the area of dental competence is extended lingually (black arrow). Black arrowhead in LF 1^st shows the extended OB. MZ and LF 3–4 t shows the order of initiation and spacing of the first teeth. Numbers refer to the order of appearance. Black arrowhead marks the future position of tooth 5, which is placed differently in MZ versus LF. Scale bar 100 μm. All panels are to the same scale.