Species-Specific Differences Of Myosin Content In The Developing Cardiac Chambers Of Fish, Birds, And Mammals

Key morphogenetic events during heart ontogenesis are similar in different vertebrate species We report that in primitive vertebrates i e cartilaginous fishes both the embryonic and the adult heart show a segmental subdivision similar to that of the embryonic mammalian heart Early morphogenetic events during cardiac development in the dogfish are long lasting providing a suitable model to study changes in pattern of gene expression during these stages We performed a comparative study among dogfish chicken rat and mouse to assess whether species specific qualitative and/or quantitative differences in myosin heavy chain (MyHC) distribution arise during development indicative of functional differences between species MyHC RNA content was investigated by means of in situ hybridisation using an MyHC probe specific for a highly conserved domain and MyHC protein content was assessed by immunohistochemistry MyHC transcripts were found to be homogeneously distributed in the myocardium. of the tubular and embryonic heart of dogfish and rodents A difference between atrial and ventricular MyHC content (mRNA. and protein) was observed in the adult stage Interestingly differences in the MyHC content were observed at the tubular heart stage in chicken These differences in MyHC content illustrate the distinct developmental profiles of avian and mammalian species which might be ascribed to distinct functional requirements of the myocardial segments during ontogenesis The atrial. myocardium. showed the highest MyHC content in the adult heart of all species analysed (dogfish (S canicula) mouse (M musculus) rat (R norvegicus) and chicken (G gallus)) These observations indicate that in the adult heart of vertebrates the atrial myocardium contains more myosin than the ventricular myocardium.