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.

Graded Initiation of Intestinal Vitellogenin Expression During Larval Development of N2 Hermaphrodites

P. Schedin and W.B. Wood

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 
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