ABSTRACT
The precise organization of an embryo extremely depends on cellular contacts and recognition. One of the molecules certainly involved in the integrity of the sea urchin embryo is a large glycoprotein complex called toposome. Over the years we have demonstrated that the molecule is mediating cell adhesion, it is expressed on the cell surface, it is present in a precursor form in the coelomic fluid and it is stored in yolk granules of the unfertilized egg in an intermediate form. Here we have investigated on the origin of toposome in the circulating cellular population of the perivisceral coelom of the sea urchin Paracentrotus lividus. We traced, by Western blot and dot blot experiments, the presence of the molecule in lysates of total coelomocytes and in partially enriched cellular populations. We demonstrated that toposome precursor is present in a defined coelomocyte population, namely the so called colorless spherule cells. A model is proposed for the origin of toposome in the sea urchin embryo.
