Worm Breeder's Gazette 10(3): 154
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 part of my seemingly never-ending effort to find out whether functional neurons persist after laser killing, I recently shot out the 19 dispensable pharyngeal neurons in each of 4 newly hatched larvae, allowed them to grow for 2, 3, 3, or 5 days, and prepared them for EM (with Nichol Thomson manning the microtome). There were no surprises with respect to neuron persistence: of 52 neurons that could be easily checked only 2 retained full length processes. More unexpectedly, there were several cases of membrane fusions. This shouldn't have been a surprise, since laser-induced cell fusion has been seen in embryos (E. Schierenberg, Dev Biol 101: 240-245). Possibly the laser causes pressure waves that spread out from the aiming point and break membranes. There are 6 large cells in a cross-section through the pharynx: 3 binucleate muscle cells in dorsal and subventral positions, and 3 marginal cells in ventral and subdorsal positions (see figure). The muscle cells contain radial actomyosin filaments that open the lumen when they contract. The marginal cells lie at the apices of the triradiate lumen and contain radial intermediate filaments. Most pharyngeal neuron cell bodies lie in invaginations of the membranes of syncytial muscle cells as shown, and fusion of the muscle membranes on either side of lasered neurons was the most common fusion event. This had no obvious functional consequence. However, in three cases an mc2 marginal cell was fused to an m4 muscle cell (2 in one worm, 1 in a second). These fusions were local events, so it was still possible to distinguish a muscle portion and a marginal cell portion. The muscle portions looked normal, but the three marginal cells appeared to have been transformed. They did not contain visible intermediate filaments, but instead contained radial thick filaments, and looked like normal muscle cells. This was true throughout the fused marginal cells, even in the regions around the nucleus and most distant from the fusion. Furthermore, the shape of the pharyngeal lumen had changed slightly: the apices corresponding to the fused marginal cells were less pronounced. Cultured differentiated vertebrate cells of many different types can be transformed by fusion with muscle cell (Miller et al, Genes & Dev 2: 330-340). The above observations suggest this can happen in differentiated worm cells as well. [See Figure 1]