Worm Breeder's Gazette 10(3): 8

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.

dpy-29 and tra V: Jekyll and Hyde?

John Plenefisch, Leslie DeLong and Barbara Meyer

We recently reported the discovery of a new gene, dpy-29, which is 
required in XX animals for proper dosage compensation, and displays 
the same repertoire of mutant phenotypes as do dpy-26, 
sch, DeLong, Meyer Genetics, in 
press, see also Plenefisch et al.  in WBG v10 n2).  We have 
subsequently isolated eight additional alleles of dpy-29 (all of which 
map between unc-61 and unc-76 on LG V): six EMS induced alleles and 
one gamma-irradiation induced allele were obtained on the basis of 
their failure to complement dpy-29(y100am); one EMS induced allele was 
obtained as a suppressor of xol-1 XO-specific lethality.  Preliminary 
characterization of these new alleles reveals that they result in the 
same phenotypes as the original dpy-29(y100am).  Homozygous dpy-29 XX 
progeny of heterozygous mothers are Dpy; homozygous progeny of 
homozygous mothers are inviable, with rare Dpy escapees.  XO animals 
appear unaffected.  None of the alleles appear to promote X-chromosome 
nondisjunction as do mutations in dpy-26 and dpy-28.  Finally, none of 
these dpy-29 mutations appear to result in sexual transformation of XX 
animals into males.
We have previously reported the isolation of the sex transformation 
mutation y52, which also maps within the unc-61 and unc-76 interval of 
LG V (DeLong and Meyer WBG v10 n2).  XX animals homozygous for y52 are 
wild-type in length and exhibit a range of phenotypes from Egl 
hermaphrodite to pseudomale.  The most strongly transformed animals 
are incomplete males with a normal male body and gonad but a deformed 
tail with stunted rays.  Complete transformation to a mating XX male 
can occur if the animal is also homozygous for a mutation in xol-1.  
her-1(e1520) is epistatic to y52, suggesting that y52 acts upstream of 
her-1 in the sex determination pathway.  X-linked gene expression in 
y52 animals is indistinguishable from wild type (by the lin-14 assay). 
We have recently isolated three new tra mutations at this locus: two 
gamma-irradiation induced alleles were obtained on the basis of 
failure to complement y52; one EMS induced allele was obtained as a 
mating X.Y male in a xol-1 background.
Although the dpy-29 mutations appear to affect only dosage 
compensation in XX animals and the tra mutations appear to affect only 
sex determination in XX animals, we performed complementation tests 
between the two since they map to the same small interval.  y52 
complements all dpy-29 alleles fully for dumpiness and lethality.  
Moreover, y52/dpy-29 cannot suppress the XO specific lethality of xol-
1.  Unexpectedly, y52/dpy-29 XX animals are masculinized, the exact 
proportion ranging from 2% to 90% depending on the dpy-29 allele.  The 
most transformed of these y52/dpy-29 animals are capable of mating if 
simultaneously homozygous for xol-1.  Preliminary results suggest the 
proportion of transformed y52/dpy-29 XX animals shows no correlation 
with the extent of the dumpiness or XX-specific lethality of the dpy-
29 alleles.  At least a second of these tra mutations, y121, also 
shows the same complementation pattern in trans to dpy-29 alleles (we 
are continuing to test all the possible combinations).  Although the 
amber suppressor sup-7(st5) suppresses dpy-29(y100) for both dumpiness 
and lethality, dpy-29(y100am)/y52; ) XX animals are 
still transformed.  The interaction between dpy-29 and the tra on V is 
specific; dpy-29 does not display a similar interaction with other 
transformation mutations.  For example tra-1/+; 
5sd)/dpy-29 are indistinguishable from 
tra-1/+ or her-1(n695sd)/+ respectively.
The interactions between dpy-29 and the tightly linked tra mutation 
might be explained if the dpy-29 and the tra mutations represent 
separate neighboring genes, and all the extant alleles of dpy-29 are, 
for example, small deficiencies that alter not only dpy-29 but also 
the neighboring gene.  Alternatively dpy-29 may be a cryptic sdc-like 
gene.  That is, dpy-29 may be a gene which contains both sex-
determination and dosage compensation functions required for the 
hermaphrodite modes of both processes.  (The position of the y52 
mutation in the hierarchy of sex-determination genes is consistent 
with this proposal.) If this latter case is true, any potential 
masculinization of dpy-29 XX might be masked by the dpy-29 dosage 
compensation defect.  There is a precedent for such a phenomena.  
Mutations in dpy-21 or dpy-27 can suppress the masculinization of y52 
XX animals, and substantial evidence has accumulated suggesting that 
the sex determination process is feminized in animals which over-
express their X-linked genes.  Thus any masculinizing effects mediated 
by dpy-29 mutations might be visible only in the absence of an 
elevation of X-chromosome expression.  Both the ease of obtaining tra 
mutations and the complementation pattern seen between y52 and dpy-29 (
i.e., complementation for dosage compensation defects [dumpiness, 
lethality] and failure to complement for sex-determination defects [XX 
transformation]) suggest that the two functions are at least partially 
separable, unlike what has been observed with sdc-1 and sdc-2.  We 
have not as yet identified any dpy-29 alleles that completely 
complement the tra function, nor have we identified any mutations 
which simultaneously display both an obvious sex determination and 
dosage compensation phenotypes.  We have isolated two putative 
deficiencies of this region in an attempt to clarify the genetic 
interactions; however, whether dpy-29 and the tra mutations represent 
two functions within one gene or two separate neighboring genes 
probably cannot be determined merely from genetic evidence.  A 
molecular approach may well be required to resolve this conundrum.