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.

Transformation of Differentiated Cells by Laser-Induced Cell Fusion

Leon Avery

Figure 1

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 
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]

Figure 1