Worm Breeder's Gazette 2(2): 7a
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.
The post-embryonic development of the nematode Caenorhabditis described at the level of individual cell lineages. A mutant of post-embryonic development, E1348, 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; the nuclear membrane breaks down, 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 set of precursor cells giving rise to the ventral nerve cord divides asymmetrically to give six daughters (1 hypodermal cell and 5 neurons) in the wild type, and in the mutant these precursors accumulate approximately 6 times the diploid quantity of DNA within a single nucleus, while attempting mitosis up to three times. These polyploid cells display characteristics of the daughter cells they would have produced ordinarily. It is not known why these ventral cord precursors should stop at 6 diploid copies. Precursor cells for lineages giving rise to a greater number of daughters display higher DNA contents in this mutant. Possibly postembryonic cell proliferation is limited by the run out of preformed products in the precursors, or by some means of marking chromosome sets for further replication in dividing daughters. Recently, Cairns (1975) proposed a model for stem cell propagation in which the oldest chromosome sets are always segregated to the stem cell and the newer ones to the non-dividing daughter. Evidence for asymmetric distribution of chromosome sets in the ventral cord lineage has been sought by looking at the differential fluorescence of Hoechst 33258 stained ventral cord nuclei in wild type animals pulse labelled with bromodeoxyundine during post-embryonic development.