Cell cycling and DNA replication in a mutant blocked in cell division in the nematode Caenorhabditis elegans

The postembryonic development of the nematode Caenorhabditis elegans has been described at the level of individual cell lineages. A mutant of postembryonic development, lin-5 II, causes a failure of postembryonic nuclear and cell divisions. Mitosis in living animals is seen by light microscopy to proceed through prophase and nuclear envelope breakdown, but an abnormal-looking metaphase plate forms in the mutant, after which the interphase nuclear morphology reappears until the next attempted round of division. The precursor cells which give rise to the ventral nerve cord have been studied in lin-5. In the wild type these cells divide asymmetrically to give six descendants (one hypodermal cell and five neurons). In the mutant these precursors accumulate approximately six times the diploid quantity of DNA within a single nucleus, while attempting mitosis up to three times. These polyploid cells display characteristics of the cells they would have produced ordinarily.