Mutations in the X-linked gene
sdc-2 disrupt both the processes of sex determination and dosage compensation in XX animals (hence: sdc= sex determination and dosage compensation), but have no apparent effect on XO animals. Mutant
sdc-2 XX animals adopt the male modes of both sex determination and dosage compensation, resulting in masculinization and specific over-expression of X-linked transcripts, respectively. Strong alleles exhibit XX specific lethality as homozygotes and in trans to deficiencies. There are now twenty-two alleles of
sdc-2. They define an allelic series of increasing lethality and masculinization. For strong alleles, XX animals are inviable. Rare surviving XX homozygotes are Dpy and Tra. For weak alleles, XX animals develop as Tra or intersexual animals or rare self fertile Egl hermaphrodites. XX lethality and Tra phenotype vary with the strength of the allele. A
her-1 mutation can be used to block the Tra effect of an allele with substantial XX viability, producing a strain of
her-1; phrodites. Seven weak alleles allow some survival of XX animals and can be kept as homozygous strains in the presence of a
her-1 mutation. In order to look directly at dosage compensation defects of
sdc-2 in XX animals, we looked at weaker alleles in
her-1 homozygous strains. We have done Northern blot analysis of RNA prepared from mixed-stage cultures of
her-1(
e1520); ) XX animals. [Since XO
her-1 animals are hermaphrodite, and since XO hermaphrodites in this strain may be healthier than XXs, 20 animals from the culture were verified genetically to be XX rather than XO.] An approximate twofold over-experession of X-linked mRNAs was seen. This was observed for the X-linked trancript
uvt-4 as normalized to the autosomal transcript
act-1, and also with the X-linked transcript
myo-2 as normalized to the autosomal trancript
myo-1.
sdc-2(
y55) is an intermediate strength allele. The majority of homozygous XX animals are masculinized and intersexual. Egg counts of progeny from rare
sdc-2(
y55)/sdc-2
(y55) XX homozygous hermaphrodites reveal that some lethality (about 5%) is observable, as either dead eggs or arrested L1 larvae. 6% of surviving adult animals are Egl hermaphrodites. The remaining 94% are Tra and pseudomale, and many of these are very unhealthy. They range from sterile intersexual animals with a vulval blip, through (often Dpy) animals of various intersexual character with deformed male tails, all the way to animals that appear very close to wild-type males in phenotype. The male structures of the latter can approach those of the wild-type male. Animals have been observed under Nomarski optics with tail structures including 9 rays on each side, hook, spicules, and near wild type fan, and with wild type male gonad morphology. These animals can exhibit male mating behavior but fail to produce cross progeny. Consistent with this, the gonads of these animals are seen to be packed with sperm, as if their mating defect resides in an inability to emit sperm. Interestingly, a single mutant copy of
her-1 is sufficient to block
sdc-2(
y55) masculinization. Surviving
sdc-2(
y55)/sdc-2
(y55) XX animals are 6% hermaphrodite, 94% Tra. Adult
her-1(
e1520)/+; ) /sdc-2
(y55) XX animals are 98% hermaphrodite, 2% Tra.
her-1(
e1520); ) XX animals are fully hermaphrodite, but are small, dumpy, egg laying defective, and have protruding vulvae; phenotypes associated with mutations that disrupt hermaphrodite dosage compensation. We have examined
y55 in trans to nDf19 and to
y39, a strong
sdc-2 allele. 52% of
y55/nDf19 animals survive and are Tra, 3% of these are self fertile.
y55/y39 animals are 15% viable and strongly Tra. Three factor crosses involving
dpy-6(
e14) and
lin-14(
n179ts), and
lin-14(
n179ts) and
unc-9(
e101) now place
sdc-2 within 0.1 map units to the right of
lin-14. In addition, two small deficiencies from the Ambros lab, maDf1 and maDf2, uncover both
sdc-2 and
lin-14 and fail to uncover
egl-15, located 1 map unit to the left of
lin-14 (M. Stern personal communication) and
sma-5, located 1.2 map units to the right. Both the strong allele
y39 (XX lethal) and the intermediate strength allele
y55 (XX Tra) have been mapped to within 0.2 map units of
lin14. We have shown several alleles of both classes to be uncovered by the small deficiency maDf1. This mapping helps to establish that mutations of both classes appear to occur at the same locus. Further, as the
lin-14 contig is now very large, this genetic position along with 4 gamma-radiation induced alleles and one allele generated in a mutator background, will facilitate cloning of
sdc-2.