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.

More tra-1 Genetic Mosaics

Craig P. Hunter and W.B. Wood

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 
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 
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.