Worm Breeder's Gazette 10(1): 118
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 showed previously by in situ hybridization with vit gene probes that the decision to express vitellogenin transcripts appears to be positionally influenced in intestinal cells of triploid intersex mosaic animals (3A;2X plus a large X duplication; Schedin and Wood, 1985, C. elegans Meeting Abstracts, p. 102; Schedin and Wood, 1985, Worm Breeder's Gazette 9:72.) All mosaics have a region of 8 to 12 contiguous positive cells at the anterior end, with the remaining observable portion of the intestine negative. In addition, about half the mosaics show a gradient of intensity, with more anterior positive cells hybridizing more strongly than more posterior positive cells. ( In diploid or triploid adult hermaphrodites, all 20 intestinal cells hybridize uniformly to the vit probes.) One possible explanation for these results would be that initiation of vitellogenin synthesis during larval development normally occurs in a gradient pattern, which is preserved in some triploid intersex adults. To test this possibility, a highly synchronous population of L1 larvae was prepared from N2 hermaphrodites and then assayed for vitellogenin (vit-5) transcripts by in situ hybridization at several larval stages. A gradient of transcription initiation was in fact observed, but surprisingly, with a polarity opposite to that described above. Autoradiographic grains were first seen over nuclei in the posterior portion of the intestine, shortly after condensation of the germ line nuclei undergoing spermatogenesis in the proximal arm of the gonad. Grains were then observed over the cytoplasm of the posterior intestinal cells with the more posterior cells hybridizing more strongly than the more anterior cells. At subsequent times, hybridization was observed more anteriorly. The most anterior cells, Int 1 and 2, were consistently the last to show hybridization. By the young adult stage, after the L4 molt but before initiation of oocyte production, the hybridization appeared uniform in all 20 intestinal cells. Therefore, the pattern of intestinal vitellogenin expression in the intersex animals is opposite to that found during larval development of normal diploid animals. These two results are not necessarily contradictory or even paradoxical. The first shows that intestinal cells can have positionally correlated differences in their final levels of vitellogenin expression in sexually ambiguous triploid intersexes; the second illustrates the kinetics of the normal hermaphrodite response. One of several possibilities, for example, would be that the normal hermaphrodite signal for vitellogenin expression is posteriorly initiated, causing posterior intestinal cells to respond first, whereas the ability of intestinal cells to respond is determined by the X/A ratio, which is somehow interpreted as being higher in the more anterior intestinal cells of triploid intersexes.