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.
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.