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Fig. 6 Sterlet larvae in which Bmp signalling was blocked prior to ampullary organ formation have supernumerary ampullary organs and ectopic supraorbital neuromasts. Sterlet larvae after in situ hybridisation (ISH) for the hair cell and electroreceptor marker Cacna1d (also expressed in taste buds on barbels) or the electroreceptor-specific marker Kcnab3. Black arrowheads indicate examples of neuromasts; white arrowheads indicate examples of ampullary organs. (A?H) Stage 45 larvae that had been treated for 20 hr from stage 36 (i.e., from hatching to approximately stage 38, just prior to the onset of ampullary organ development) with either DMH1 or DMSO as controls. Larvae are numbered for cross-referencing with ampullary organ counts in Supplementary file 3. ISH for Cacna1d (A?D) or Kcnab3 (E?H) shows that, relative to DMSO-treated controls (A,B,E,F), DMH1-treated larvae have many more ampullary organs (C,D,G,H). This phenotype is particularly prominent in the three dorsal-most ampullary organ fields, where the dorsal supraorbital, dorsal otic and supratemporal fields - clearly separate in DMSO-treated larvae (A,B,E,F) - almost fuse together in DMH1-treated larvae (C,D,G,H). (I,J) A much older wild-type larva (2.8 cm in length, ~65 dpf) after ISH for Cacna1d. The dorsal supraorbital, dorsal otic and supratemporal ampullary organ fields are clearly separated, suggesting the supernumerary ampullary organs in this region in DMH1-treated larvae (C,D,G,H) are ectopic, not precocious. (K?N1) Most DMH1-treated larvae also develop an ectopic offshoot from the supraorbital neuromast line. This is visible after ISH for Cacna1d (K,L; compare with DMSO control in A,B) and confirmed to represent neuromasts in DMH1-treated larvae via ISH for electroreceptor-specific Kcnab3 (M,N) followed by immunostaining for the supporting cell marker Sox2 to reveal neuromasts (M1,N1). Abbreviations: dot, dorsal otic ampullary organ field; ds, dorsal supraorbital ampullary organ field; e, eye; S, stage; so, supraorbital neuromast line; st, supratemporal ampullary organ field; WT, wild type. Scale bar: 250 ?m.