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.