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Fig. 1 Sterlet Bmp5 is expressed early in developing ampullary organs and transiently in mature neuromasts. (A–R) In situ hybridisation in sterlet for Bmp5 or the hair cell and electroreceptor marker Cacna1d, which labels mature neuromasts and ampullary organs (also expressed in taste buds on the barbels). Black arrowheads indicate examples of developing neuromasts; white arrowheads indicate examples of developing ampullary organs. (A–D) At stage 37, Bmp5 expression is only detectable in developing gill filaments (A,B) although Cacna1d-positive neuromasts are present (C,D). (E–H) At stage 40, Bmp5 is expressed in neuromasts and ampullary organ primordia (E,F); only a few Cacna1d-positive ampullary organs are present at this stage (G, H). (I–L) At stage 42, Bmp5 is expressed in mature ampullary organs and more weakly in neuromasts (I,J); compare with Cacna1d expression (K,L). (M–P) At stage 45 (onset of independent feeding), Bmp5 expression is weaker in ampullary organs and no longer detectable in most neuromasts (M,N); compare with Cacna1d expression (O,P). (Q,R) At stage 45 on the trunk, Bmp5 expression is visible in primII-deposited secondary neuromasts (more strongly in more rostral neuromasts) as well as in primD and neuromasts of the dorsal line (Q). Compare with Cacna1d expression in all neuromasts (R): arrowheads indicate examples of dorsal-line neuromasts and primII-deposited secondary neuromasts (offset a little dorsal to the line of primI-deposited primary neuromasts). Low-power insets show the location of these trunk regions. (S–V) Schematic depictions of sterlet lateral line organ development at similar stages (stages 35, 39, 41, 45), previously published in Minařík et al., 2024a. Abbreviations: app, anterior preopercular ampullary organ field; b, barbel; di, dorsal infraorbital ampullary organ field; dot, dorsal otic ampullary organ field; ds, dorsal supraorbital ampullary organ field; e, eye; gf, gill filaments; m, mouth; n, naris; o, otic vesicle; ppp, posterior preopercular ampullary organ field; prim, migrating lateral line primordium (primI, primary; primII, secondary; primD, dorsal); S, stage; st, supratemporal ampullary organ field; vi, ventral infraorbital ampullary organ field; vs, ventral supraorbital ampullary organ field. Scale bar: 250 μm.