Worm Breeder's Gazette 14(4): 34 (October 1, 1996)

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.

Large communication channels in C. elegans embryos

Oliver Wiegner1, Olaf Bossinger2, Einhard Schierenberg1

1 Zoological Institute, University of Koeln, 50923 Germany
2 Dept. of Biology, Indiana University, Bloomington, IN 47405, USA

The pattern of cell-cell communication in embryos of C.elegans has
beeninvestigated by injecting tracer dyes into individual blastomeres
(Bossinger and Schierenberg, 1992). It has been shown that in embryos
from the 4-cell stage onward all blastomeres are well coupled for the
diffusion of negatively charged Lucifer Yellow (LY; MW 457 Da) while
uncharged Rhodamin-coupled dextran (MW 4.000 - 70.000 Da) remains
restricted to the injected cell and its descendants. However, in
Cephalobus spec. (another soil nematode), LY  and Rhodamin-dextran
(even at a  molecular weight of 70.000 Da) diffuse along discrete
pathways from cell to cell (Bossinger and Schierenberg, 1996).

We extended our dye-coupling studies in C. elegans using negatively
charged dextrans (LY-dextran and FITC-dextran) with  molecular
weights of 10.000 and 70.000 Da. Suprisingly, we found that in
embryos between the 4-and the 24-cell stage all blastomeres are
coupled for negatively charged dextrans whereas under all tested
conditions uncharged Rhodamin-dextran (MW 10.000 Da) remains in the
injected cell and its descendants. The diffusion of the negatively
charged dyes appears to occur quickly and freely between all
blastomeres. In contrast to Cephalobus we did not observe
preferential pathways of dye spread from the injected cell,
suggesting that all blastomeres are equally coupled. However at the
24-cell stage, when the primordial germline cell P4 has been
generated, diffusion into D and P4 cells becomes retarded.The
diffusion block lasts approximately 5 minutes until D joins the
somatic compartment and P4 remains uncoupled for at least 20 min. A
similar observation has been made for the much smaller LY in C.
elegans indicating that it is a diffusion block and not a reduction
in channel diameter.
In summary, our findings suggest that in the developing C. elegans
embryo all somatic blastomeres are coupled by communication channels
much larger than conventional gap junctions. These channels seem to
be permeable for negatively charged molecules up to a molecular
weight of at least 70.000 Da but are impermeable to uncharged
dextrans. Moreover, these channels seem to be equally present between
all blastomeres of the somatic cells. Presently we can only speculate
about the function of these communication pathways.

Bossinger, O; Schierenberg, E. (1992) Dev. Biol. 151: 401-409
Bossinger, O; Schierenberg, E. (1996) Dev. Genes Evol. 206: 25-34