Worm Breeder's Gazette 3(2): 20

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.

Segregation of Developmental Potential in Embryos of C. elegans

J. Laufer, P. Bazzicalupo, B. Wood

In 1973 Whittaker showed that when early ascidian blastulae are 
treated with a cleavage inhibitor and subsequently examined for 
appearance of tissue specific enzymes or pigments, these 
differentiation markers appear on schedule, and only in the precursor 
cells of the appropriate tissues.  The pattern changes at each of the 
first few cleavages, apparently reflecting segregation of 
developmental potential.  In order to carry out similar experiments 
with C.  elegans, the permeability barrier imposed by the eggshell 
must be circumvented to allow application of cleavage inhibitors.  
This can be accomplished using a permeable eggshell mutant (Laufer, 
this issue), or by gently bursting wild-type eggs between a slide and 
a coverslip.  When this procedure is carried out in a suitable culture 
medium (ibid.) many of the blastomeres of early cleavage stage embryos 
survive and continue development to twitching tissue masses.  Most of 
our experiments have been done with embryos from burst eggs, which 
generally appear healthier and give better results than the permeable 
shelI embryos.
As a differentiation marker we have used the 'rhabditin' granules 
that appear in gut cells late in embryonic development; they can be 
seen in the light microscope as fluorescent bodies when viewed with 
epifluorescence or as bright spots on a dark background when viewed 
with crossed polarizers (Ward, personal communication).  The 
precursors of the gut cell lineage are the P1, EMSt, and E blastomeres 
at the 2-, 4-, and 8- cell stages, respectively (Deppe et al., 1978).
Cleavage of burst egg preparations was stopped by addition of 20  
g/ml cytochalasin B and 50  g/ml colchicine to the medium.  Embryos 
then were incubated overnight at 16 C and scored for appearance of the 
marker.  In arrested 2-cell embryos, granules were observed in 17 out 
of 21 P1 cells and in 0 out of 24 AB cells; in some of these embryos 
granules were observed in the P1 cell even though the AB cell had been 
destroyed when the egg was burst.  In arrested 4-cell embryos, the 
granules were seen in 6 out of 20 EMSt cells and in none of the AB or 
P2 cells.  Although the biochemical nature of this marker is poorly 
defined, the results appear to show segregation of potential for a 
tissue-specific activity that can be expressed independently of cell 
division, in agreement with the findings of Whittaker.  We are in the 
process of examining other tissue-specific markers, and screening egg-
lethal mutants for anomalous segregation of developmental potential.