Worm Breeder's Gazette 10(2): 27
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 are generating and analyzing genetic mosaics of the sex- determination gene tra-1 to determine whether its action determines sexual fates cell-autonomously or whether it can influence fates through cell interactions (Hunter and Wood, WBG 10(1):119-121,1987). Loss-of-function mutations in tra-1 transform hermaphrodites into males. Genetic mosaics of tra-1 can be obtained from a homozygous tra- 1 strain carrying tra-1(+) on a metastable free duplication. Mitotic loss of the duplication during development produces a clone of tra-1 mutant cells, in an otherwise wild-type hermaphrodite animal. If tra- 1 functions cell-autonomously, then only cells included in the clone will express male fates. Because the C. elegans lineage is invariant and completely known it is possible to ask whether all the male structures observed in a mosaic animal are clonally related. We have now isolated and characterized over 200 tra-1 mosaics. About one half of these were generated by loss of eDp6 and the other half by loss of ctDp2, a derivative of eDp6 (see our other abstract, this volume), that still carries tra-1(+) and dpy-18(+) but is lost mitotically at a much higher rate. In about half of the ctDp2 mosaics examined, the duplication appears to be lost more than once. To provide an additional marker for mosaic analysis, we have also determined that wild-type dpy-18 function is required only in the P1 lineage for a non Dpy phenotype. Use of ctDp2 and the dpy-18 marker has allowed us to isolate many tra-1 mosaics resulting from duplication loss in the P1 lineage. These animals appear to be Dpy hermaphrodites under a dissecting microscope, but Nomarski microscopy shows that all or some of the internal structures are male. The results summarized below were obtained using both eDp6 and ctDp2. Duplication loss in AB lineages: In examining many tra-1 mosaics, we have observed that all male structures derived from AB can be expressed independently of each other, and that in general all the cells expressing male fates in an individual animal are clonally related. That is, all the observed intersexual phenotypes are consistent with cell-autonomous tra-1 function and a single duplication loss, or in a few cases, more than one duplication loss. (A few cases of probable multiple losses of eDp6 have been identified, and about half of the ctDp2 mosaics appear to have sustained multiple losses.) A clear exception to this generalization, as expected, is induction of partial vulva development from AB-derived ventral hypodermal cells (tra-1 in genotype, i.e., lacking the duplication) by the MS-derived anchor cell (in a tra-1(+) hermaphrodite gonad, i.e., retaining the duplication). Duplication loss in P1 lineages: Previously we reported an intersex that appeared to be the result of a first-cleavage loss of eDp6 in P1 with retention in AB. This animal had a hermaphrodite tail but no vulva, a male gonad containing only sperm, and male sex muscles, and it did not express yolk proteins. We have now isolated five additional intersexes of this class. We have also isolated seven intersexes that are male for all EMS derived structures (intestine, gonad, sex muscles) but hermaphrodite for P2- derived cells (both oocytes and sperm in germ line) and AB-derived structures. (There is no apparent sexual dimorphism in the P2-derived C and D lineages.) Conversely we have isolated six intersexes that are male only for P2-derived structures (only sperm in the germ line). We have also found three intersexes that are consistent with duplication loss in the progenitor of the sex myoblast M, leading to expression of male sex muscles in an otherwise hermaphrodite animal. Finally, we have seen two animals that were hermaphrodite in all respects except that they failed to express yolk proteins. This phenotype is consistent with loss of the duplication in the E cell, the clonal founder for the intestine. (Because the tra-1(e1099) allele used in these studies is often associated with abnormal gonadogenesis we cannot draw any conclusions on the autonomy of tra-1 in this process.) Conclusion: all tra-1 mosaics analyzed so far are consistent with cell-autonomous function of tra-1, with the notable exception of vulval induction in tra-1 ventral hypodermis by a tra-1(+) anchor cell.