Worm Breeder's Gazette 10(3): 21
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 have previously reported results consistent with a cell- autonomous requirement for tra-1 function in development of hermaphrodite structures (WBG Nov. 1987; May 1988). The intersexual phenotypes of several tra-1 mosaics suggested that tra-1 function may also be required in descendants of E, the founder cell of the intestine, for production of the hermaphrodite specific gene product vitellogenin. These intersexes were either hermaphrodite in all respects but failed to express vitellogenins or were hermaphrodite for all AB- and P2-derived structures but male for all EMS-derived structures. We have further tested this suggestion by analyzing tra-1 mosaic intestines, using in situ hybridization with a vit-5 probe to detect presence or absence of vitellogenin mRNA production in individual cells of dissected intestines as described previously (e.g. Schedin and Wood, WBG Nov. 1985). The free duplication ctDp2, which carries tra-1(+), is lost approximately once every 200 cell divisions. The E cell and its descendants undergo 19 divisions in generating the 20 cells of the adult intestine. Therefore, on average, 1 in 10 animals of a strain homozygous for a tra-1(lf) mutation and carrying ctDp2 should have genetically mosaic intestines. If tra-1 function is required cell-autonomously for intestinal vitellogenin synthesis, then tra-1(+) cells should express the vit genes and tra-1(+) cells should not. If the duplication is lost only once in the E lineage, then the cells not expressing the vit genes will be clonally related. Specific patterns of nonexpressing cells are predicted, because some cells in the lineage exchange places during development, giving rise to noncontiguous sister cells in the adult intestine (Sulston et al., Dev. Biol, 100:64, 1983). To assay vit gene expression, [35S]-labelled vit-5 probe was hybridized in situ to partially dissected, fixed intestines (3:1 ethanol:acetic acid) from animals of the appropriate strain. On average, about half the intestine was available for hybridization. From 329 dissected hermaphrodites, 17 mosaic intestines were identified. As expected, most of these showed only a single cell or pair of cells not hybridizing to the vit-5 probe. However, one mosaic intestine contained 5 nonhybridizing cells, and another contained 10. In these mosaics, some of the nonhybridizing cells were not adjacent, but interspersed with hybridizing cells. However, in each mosaic, the nonhybridizing cells could be identified and shown to represent an exclusive clone, consistent with a single loss of the duplication during intestinal development and a cell- autonomous requirement for tra-1 function in vitellogenin synthesis.