Worm Breeder's Gazette 9(1): 64

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.

Early Embryogenesis of Caenorhabditis elegans is Unaffected by Phorbol Ester Tumor Promoters

Y. Tabuse and J. Miwa

We reported previously that the tumor promoting phorbol esters TPA 
and PDD cause severe disturbances in the growth, reproduction, and 
behavior of larval and adult C.  elegans.  Gravid hermaphrodites 
treated with the phorbol esters (e.g., 1ug/ml TPA) lay some eggs 
before they cease producing eggs.  These eggs hatch normally even in 
the presence of the phorbol esters.  We could explain this outcome 
assuming either of the following reasons: 1) the phorbol esters simply 
do not enter eggs both inside and outside mothers because some unknown 
mechanism blocks them from going inside before the egg shell is formed 
and because the egg shell is impermeable to the phorbol esters; 2) 
embryos are unaffected by the phorbol esters.  We tested assumption 2) 
by culturing permeabilized embryos.  Two-cell stage embryos were 
fractured in the culturing medium (L.  Edgar, personal communication), 
and permeability was ascertained by squeezing out the cytoplasm of 
either AB or P1 cell.  The partial embryo with AB or P1 cell so 
treated underwent many rounds of division to form a ball of many cells 
either in the presence or absence of 1ug/ml TPA, showing no sign of 
TPA effect on the embryonic cell division.  Also unaffected by TPA in 
early embryogenesis through the P3 division are the cell division rate 
and pattern both of the AB cell lineage characterized by synchronous 
equal cell divisions and of the P cell lineage with characteristically 
defined unequal cell divisions.  We also observed E cell specific 
autofluorescence in P1-derived cell masses and E cell aggregation.  (
Experiments using permeabilized whole intact embryos confirmed the 
result although the data should be interpreted with some reservation 
and caution because of difficulty in making sure that such whole 
embryos were indeed permeabilized.)  The result suggests that the 
assumption 2) is correct at least for the first several rounds of cell 
division.  As previously reported, newly hatched L1 larva are arrested 
in growth with the phorbol esters.  In arrested hatchees, neither Z1 
nor Z4 divides and either of Z2 and Z3 does not usually divide any 
more than once.  Thus, possibly C.  elegans becomes phorbol ester 
sensitive between the P3 cell division and hatching.
To add some speculation, according to the currently common idea that 
phorbol esters exert their effects on various biological systems 
through interaction with the specific receptor, the observation could 
mean 1) early embryos have yet to acquire receptors or 2) early 
embryonic programs by-pass receptors.  It is an interesting assumption 
but without supportive evidence yet that maternally derived programs 
by-pass phorbol ester receptors and that acquisition of sensitivity to 
phorbol esters requires zygotic gene expression.  Experiments are 
under way to ask when and how phorbol ester sensitivity arises as well 
as what causes this sensitivity.