A REACTION-DIFFUSION MODEL CAN ACCOUNT FOR THE ANATOMICAL PATTERN OF THE CARDIAC CONAL VALVES IN FISH

The conus arteriosus of fish bears a variable number of swallownest-li ke valves arranged in transverse rows. We propose that a reaction-diff usion mechanism coupled with the specific growth dynamics of the conus arteriosus, and probably, with a system of positional information, ca n account for the pattern formation of the conal valves in these primi tive vertebrates. The reaction-diffusion mechanism, according to our h ypothesis, would determine the regular arrangement of the places where the endocardial cells are activated and they transform into mesenchym al cells. These cells populate the subendocardial space, giving rise t o the primordia of the conal valves. We have carried out simple comput er simulations, based on reaction-diffusion/lateral inhibition models, which were able to generate all the anatomical diversity of the fish conal valves allowing changes only in the growth rate of the structure . Furthermore, we have found similarities between the sequential morph ologies generated by our simulations and those actually occurring in e mbryos of Scyliorhinus canicula. We have derived three testable predic tions from our hypothesis: (1) the number of discrete areas of epithel ial-mesenchymal transition should correlate with the definitive number of valves in the conus arteriosus; (2) the small valves intercalated between the large ones should develop later than these latter; and (3) the longitudinal growth rate of the conus arteriosus in fish should b e proportional to the number of transverse rows of valves. (C) 1997 Ac ademic Press Limited.