Spatial and temporal coincidence of induction processes and gap-junctional communication in Patella vulgata (Mollusca,Gastropoda)

In the early development of the gastropod mollusc Patella vulgata, two inductive processes take place between the animal and vegetal hemispheres. One is the induction of the vegetally-located stem cell of the mesoderm (the 3D macromere) by the first-quartet micromeres (which are located in the animal hemisphere). The other is the induction of dorsoventral symmetry in the first-quartet micromeres by the 3D macromere. As a consequence of the latter induction process, a dorsoventrally-organised prototroch is formed. In this paper, the moment of 3D induction is determined by deleting the inducing first-quartet micromeres at successive stages of development. Furthermore, the role of gap junctions in the two above-mentioned induction processes is investigated. This was done by studying lucifer yellow dye transfer between the 3D macromere and the first-quartet micromeres, in relation to these two induction processes. Analysis of the pattern of dye-transfer in vivo, in sections and with confocal laser scanning microscopy demonstrated that the moment of dye transfer coincides with the moment of 3D induction and with the moment of induction of the dorsoventral pattern of the prototroch. This indicates that gap-junctional communication may be involved in these two induction processes.