Cell-cell communication in the embryo of Caenorhabditis elegans

We have investigated the pattern of cell-cell communication in embryos of the free-living soil nematode Caenorhabditis elegans. For this, we have established a method for microinjection of tracer dyes into individual blastomeres. After iontophoresis of fluorescent dyes of different molecular weights (Lucifer yellow, LY, M(r) 457; rhodamine-labeled dextran, RD, M(r) 4000), we can visualize intercellular communication pathways. The dye-spread of LY, indicating communication via gap junctions, becomes first visible in the late 2-cell stage. From the 4-cell stage onward all cells appear to be well coupled by communication channels, which allow the free diffusion of LY. In contrast, RD remains restricted to the injected cell and its descendants. After the primordial germcell P4 has been generated in the 24-cell stage, dye-spread of LY into this cell and its somatic sister D is delayed. However, the restricted dye-coupling of D is only temporary. After a brief period it joins the somatic compartment. With the beginning of the morphogenesis phase the two existing germline cells (the daughters of P4) are completely uncoupled from the soma, while the latter still forms a single dye-coupling compartment. Only during the second half of embryogenesis different separate somatic communication compartments are established. We followed the pattern of intercellular communication in the alimentary tract and found a progressive restriction into smaller dye-coupling units. Our data are compared to those found in other systems and discussed with respect to cellular determination and differentiation.