On the nature of undead cells in the nematode Caenorhabditis elegans

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Abstract
During the course of normal embryonic and post-embryonic development, 131 cells in a Caenorhabditis elegans hermaphrodite undergo programmed cell death. Loss of function mutations in either of the genes ced-3 or ced-4 abolish cell deaths, enabling these ‘undead’ cells to survive and be incorporated into the adult with no obvious deleterious consequences. Ultrastructural reconstructions have shown that undead cells exhibit many differentiated characteristics. Most of the reconstructed cells appeared to be neurons with all the characteristic features associated with such cells, such as processes, synaptic vesicles and presynaptic specializations. However, clear morphological differences were seen among the undead neurons, suggesting a diversity of cell type. One of the reconstructed cells was a rectal epithelial cell, which had displaced its lineal sister that normally functions in this role. Removal of the ability to undergo programmed cell death by mutation therefore reveals a diversity of cryptic differentiated states that are acquired by cells that normally are destined to die.