Communication compartments in the axial mesoderm of the chick embryo.

Intracellular microinjection of the fluorescent tracer Lucifer Yellow into mesoderm cells along the rostrocaudal axis of the early chick embryo has revealed compartments where the intercellular diffusion of dye, presumably via gap junctions, is restricted at the borders between groups of cells. Cells in the segmental plate were dye-coupled, as were cells forming the epithelial somites. However, dye-coupling was not observed between different somites, nor was it observed between the outer epithelial cells and the cells in the somitocoele. On dispersal of the somite, dermatome cells were dye-coupled. However, sclerotome cells were found to be divided into rostral and caudal compartments separated by a group of cells bordering the intrasclerotomal fissure (of von Ebner) that also exhibited dye-coupling, restricted primarily to cells along the fissure. Some of these compartment borders can be accounted for by the presence of a morphological barrier which reduces cell-cell contact, but others are more difficult to explain, as there appears to be extensive cell-cell contact across the border. This would be analogous to some compartments found in insects. Some of the compartments also have borders similar to those described by cell lineage studies. The results also indicate that dye-coupling becomes restricted in a spatial and temporal manner as the mesodermal cells mature.