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.

Title unknown.

Authors unknown.

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.