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-like valves arranged in transverse rows. We propose that a reaction-diffusion mechanism coupled with the specific growth dynamics of the conus arteriosus, and probably, with a system of positional information, can account for the pattern formation of the conal valves in these primitive vertebrates. The reaction-diffusion mechanism, according to our hypothesis, would determine the regular arrangement of the places where the endocardial cells are activated and they transform into mesenchymal cells. These cells populate the subendocardial space, giving rise to the primordia of the conal valves. We have carried out simple computer 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 morphologies generated by our simulations and those actually occurring in embryos of Scyliorhinus canicula. We have derived three testable predictions from our hypothesis: (1) the number of discrete areas of epithelial-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 be proportional to the number of transverse rows of valves. Copyright 1997 Academic Press Limited