Patterning multiple tooth rows in Malawi cichlids. shh and pitx2 are co-expressed in an odontogenic band (OB) for every new tooth row. shh is expressed in a second OB in Cynotilapia afra (CA) (arrow, 2) (around 12 days post-fertilization (dpf)); the second row has started the process of initiation (pitx2 CA arrow, 2). pitx2 is absent from the lingual extent of the jaw margin and we propose that this lack of pitx2 (and therefore combinatorial expression of both pitx2 and shh) is in part responsible for the lack of additional rows (3, 4 and so on) in CA. Metriaclima zebra (around 12 dpf) initiates a third row and Labeotropheus fuelleborni (around 12 dpf) row 4, concomitant with OBs labelled by both shh and pitx2. Expression is also visible in replacement teeth in the first rows. Scale bar 100 μm.
Fraser et al. BMC Biology 2008 6:32 doi:10.1186/1741-7007-6-32