IN-VIVO DIVERSIFICATION AND MIGRATIONS OF CHICK-EMBRYO HEART-MUSCLE CELLS - A MORPHOMETRIC ANALYSIS WITH ALV-BASED AND SNV-BASED NONREPLICATIVE VECTORS

By means of a reporter gene we previously demonstrated that non-replic ative Avian Leukemia Virus- and Spleen Necrosis Virus-based retroviral vectors were preferentially expressed in the heart of avian embryos f rom different species. Using a computer-assisted approach, we now comp are 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 an alysis demonstrates that clones labelled by the two types of viruses d isplay similar features and bring about new insights on the relationsh ips between mitotic and migratory properties of the myocardial cells a nd histogenesis of the heart. Since only exteriormost cells were tagge d with our inoculation procedure, our analysis shows that: (1) at stag es 17-19, the myocardium is composed of cells with diverse potentials; some cells still retain the capacity to divide extensively and partic ipate 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, reve aling extensive cell migrations from the heart surface to the ventricu lar trabeculae, the first migrating cells tagged being detected 20 h a fter viral inoculation. The presence of these cells is consistent with the finding of a large number of compact trabecular clones 5 days lat er suggesting that these cells divide mainly after completing migratio n. Our approach provides new insights as well as quantitative data on the different processes involved in heart morphogenesis, namely multip lication, migration and localisation of heart muscle cells.