Organizing Malawi cichlid dentitions with the 'spacer' gene wnt7b and ectodysplasin. Left panel: wnt7b is expressed in the zone of inhibition (ZOI) and inter-germ/inter-row spaces in (a) Cynotilapia afra (CA), (b) Metriaclima zebra (MZ) and (c) Labeotropheus fuelleborni (LF). Red circles indicate shh-positive tooth germs; arrowheads point to expression associated with initiating first-row teeth; arrows mark a lingual band of expression demarcating the shh odontogenic band (OB) of the second tooth row. Right panel: eda expression is up-regulated lingually in association with the mesenchyme of the first teeth (red circles) of (a) CA, (b) MZ and (c) LF. Expression is strongest in CA and most diffuse in LF. Arrows mark a second band of expression (CA, MZ) or continued expression (LF) lingually. Middle panel: Composite jaws showing the expression of wnt7b (left) and eda (right) in overlay with shh (false-colour, white). Arrows and arrowheads indicate expression in the ZOI of first-row teeth and in association with the second-row OB. For MZ and LF, tooth positions are numbered in order of initiation and asterisks mark the position of tooth number 5. All images from the 3–4-teeth stage; all specimens were stage-matched based on external structures, that is, pectoral and caudal fin development and eye development and maturity (3–4-teeth stage for CA and LF was 6 days post-fertilization (dpf) and for MZ it was 7 dpf). Overlay images from different individuals may show artefacts from slight differences in alignment. Scale bars for the middle panel are 100 μm.