In situ hybridisation of chick embryos with p53-specific probe and their immunostaining with anti-p53 antibodies

Tumor-suppressor protein p53 is an important regulator of cell cycle and ap optosis. On the level of embryo extracts it has been shown earlier that bot h p53 protein and mRNA are expressed in developing chicken. Here we describ e the expression patterns of p53 mRNA and protein in developing chicken emb ryos (stages 2-12) using in situ hybridisation and immunostaining with p53- specific monoclonal antibody Mab421. p53 mRNA is equally localised all over the embryo in the stages observed. According to electron microscopy data a subfraction of p53 mRNA is bound to dissolving yolk granules expressing ac id phosphatase activity characteristic for lysosomes. Protein p53 is synthe sised starting from the medium primitive streak stage (stage 3) and reaches its maximum level at the full primitive streak stage. During these stages protein p53 is distributed evenly across the embryos. After gastrulation p5 3 protein remains visible at higher levels only in certain anlages and area s. In developing nervous system the expression is observable in neuroectode rm, during the closure of the neural tube and in mesenchyme in the area of migrating neural crest cells. In cardiogenesis protein p53 is expressed dur ing formation of tubular heart in the epidyocardium, endocardium and cardia c jelly. p53 protein localises in the neurocoele (obviously connected with cellular debris) and cardiac jelly. Our data support the role of p53 in ear ly development, especially during embryo gastrulation, the development of c entral nervous system, neural crest and heart. In some cases increased p53 amounts colocalise with the areas of intensive epithelium-mesenchyme transi tion.