In vivo diversification and migrations of chick embryo heart muscle cells: a morphometric analysis with ALV- and...

By means of a reporter gene we previously demonstrated that non-replicative Avian Leukemia Virus- and Spleen Necrosis Virus-based retroviral vectors were preferentially expressed in the heart of avian embryos from different species. Using a computer-assisted approach, we now compare clones tagged by the two types of vectors, for volume, anatomical and subanatomical localisation, number of Hoechst-stained cell nuclei and mean cell division time during the period of heart morphogenesis, i.e. from stages 17-19 to 34 of Hamburger and Hamilton (1951). This analysis demonstrates that clones labelled by the two types of viruses display similar features and bring about new insights on the relationships between mitotic and migratory properties of the myocardial cells and histogenesis of the heart. Since only exteriormost cells were tagged with our inoculation procedure, our analysis shows that: (1) at stages 17-19, the myocardium is composed of cells with diverse potentials; some cells still retain the capacity to divide extensively and participate to different heart muscle layers, whilst most are restricted in their multiplication potential and contribute to single muscle layers; (2) about half of the clones are located deep in the heart wall, revealing extensive cell migrations from the heart surface to the ventricular trabeculae, the first migrating cells tagged being detected 20 h after viral inoculation. The presence of these cells is consistent with the finding of a large number of compact trabecular clones 5 days later suggesting that these cells divide mainly after completing migration. Our approach provides new insights as well as quantitative data on the different processes involved in heart morphogenesis, namely multiplication, migration and localisation of heart muscle cells.