Worm Breeder's Gazette 11(4): 113
These abstracts should not be cited in bibliographies. Material contained herein should be treated as personal communication and should be cited as such only with the consent of the author.
As described earlier (WBG 10(3)), Lucifer Yellow (LY; ca. 450 Daltons ) microinjected into early blastomeres of C. elegans accumulates in the gut primordium during embryogenesis. Improvement of our microinjection technique (Iontophoresis, Piezo-stepper for easier penetration), better visualization with a light-intensifying camera and application of additional fluorescent dyes allows us to study the process of dye incorporation into individual embryos and further development in more detail. Following injection, LY-CH spreads at first all over the embryo. After a few minutes it becomes coupled to granular cytoplasmic components (probably yolk granules). During morphogenesis the dye accumulates in the gut primordium. LY-VS directly binds to cytoplasmic components of the injected cell such that a diffusion into neighboring cells does not take place and only the descendants of the marked cell show fluorescence. Nevertheless, with the beginning of morphogenesis a transfer into the gut primordium starts. In the pretzel stage fluorescence is only present in the cytoplasm of the intestinal cells. We assume that this transfer occurs via the extracellular space rather than directly from cell to cell. On the one hand, if we inject into the AB cell of a 2- cell stage, we only observe fluorescence in AB descendants (decreasing) and gut cells (increasing) during the morphogenesis phase but never in muscle cells which are positioned between AB-derived hypodermis and intestine. By penetrating the eggshell with a laser microbeam during various phases of development, we can allow passage of LY from the surrounding medium into the perivitelline space. No uptake of dye into the embryo is observed during the proliferation phase. If the eggshell is penetrated during morphogenesis dye is instantaneously incorporated exclusively into the gut primordium. Fluorescently labeled Dextrane ( 4000 Daltons) is neither incorporated into the gut cells after injection nor after laser penetration at any stage. If 2-cell embryos are laser-penetrated in a medium containing LY plus Cytochlasin, we observe an accumulation of dye in the gut precursor cell P1. This demonstrates that cleavage is no prerequisite for this typical uptake process. In addition we find that a reversal of cell size takes place (P1>AB) in such blocked 2-cell stages during development overnight, supporting our assumption that the accumulation of LY goes along with a transfer of other cytoplasmic components. For interpretation of our observations two alternative explanations seem plausible. On the one hand a transfer of yolk components into the gut primordium may take place, serving as a storage organ for postembryonic development. Alternatively toxic waste products may be deposited in a water-insoluble form in the cytoplasm of the intestine. It appears likely that our observations are of general significance for nematode development because in two other species we have also observed such an uptake process.