Local changes in gap junctional permeability accompany regionalization of the mesoderm in early fish (loach, Misgurnus fossilis) embryos.

It was revealed that the marginal area of early leach (Misgurnus fossilis) embryos, situated in the proximity of the yolk cell (YC), - the zone of early activation of mesoderm-specific genes - is characterized by regional changes in the permeability and selectivity of gap junctional (GJ) channels. Comparison of the efficiency of GJ transfer of negatively (Lucifer yellow, LY, and fluorescein, FL) and positively (4',6-diamidino-2-phenylindole, DAPI) charged dyes showed that, at the early gastrula stage, GJs formed between blastomeres of the presumptive mesoderm layer and the YC acquired higher permeability for LY and FL and became virtually impenetrable for DAPI over most of the germ ring area, except for its dorsal side. GJs in the dorsal-anterior region were permeable for both LY and DAPI. The dorsal-posterior area was labeled with neither of the dyes. Observations on the fate of embryonic shield blastomeres stained with both LY and DAPI showed that their progenies were confined to the head mesoderm, whereas the paraxial somite mesoderm and the ventral mesoderm contained the cells labeled with solely LY or FL. The presumptive notochord region was not labeled at all. These data support the hypothesis that GJs between the embryonic cells may be involved in the spatial organization of development due to their ability to transfer different regulatory factors in different directions, filtering molecules in accordance with the electric charge and configuration as well as with their size.