Worm Breeder's Gazette 10(1): 113

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Invisible Alleles of tra-1 and tra-3

J. Hodgkin

Figure 1

Previously (WBG 7-2:24) I described an 'invisible' (cryptic) allele 
of tra-2, e1875, which has no obvious phenotype by itself, but fails 
to complement strong alleles of tra-2.  Invisible alleles of tra-1 and 
tra-3 have now been obtained, which have interesting properties.
Strong loss-of-function (lf) alleles of tra-1 cause recessive 
masculinization of XX animals, while gain-of-function (gf) alleles 
cause dominant feminization of both XX and XO.  The invisible tra-1 
allele, e2332, was isolated as a feminizing suppressor of a weak tra-2 
mutant, e1209.  Suppressors of e1209 were screened for using a strain 
mab-1(e1228); 09): XX populations of this genotype 
consist only of small weakly self-fertile intersexes, and revertants 
with a healthy female or hermaphrodite phenotype are easily detected.  
By itself, e2332 is almost wild type.  In trans with a deficiency, or 
an lf allele such as e1099, it behaves as a weak lf allele.  Animals 
of genotype e2332/e1099 XX exhibit variable gonad abnormalities, often 
confined to only one gonad arm.  Non-gonadal structures are normal.  
The modifying mutations mab-1 or mab-11 (which also affect tra-2(e1209)
) alter the phenotype of e2332, enhancing both somatic masculinization 
and germline feminization, as shown in this 
[See Figure 1]
Although e2232 is a spontaneous allele, apparently induced by mut-6, 
no Tc1 or Tc3 insertions in the tra-1 region have been detected.  
Alleles with similar properties have also been obtained with EMS, 
though all of these cause stronger masculinization than e2332.  The 
mab modification seems to convert them into gf alleles that are able 
to suppress e1209.  These observations suggest that the distinction 
between lf (masculinizing) and gf (feminizing) alleles of tra-1 may 
not be as tidy as previously appeared.
Mutations of tra-3 cause partial masculinization of XX animals.  The 
invisible tra-3 allele was found in a strain carrying lev-11(x21), as 
a linked mutation e2333.  By itself, or in trans with a tra-3 null 
allele (e1107), it causes no masculinization.  However, if an animal, 
genotype e2333/e1107 XX, is selfed, one quarter of the progeny (the 
e1107 homozygotes) exhibit a Tra-3 phenotype.  In contrast, e1107 
progeny of +/e1107 animals are hermaphrodite, only exhibiting a Tra-3 
phenotype in the next generation, because of a maternal rescue effect. 
Thus, e2233 eliminates the maternal rescue, perhaps by reducing the 
dowry of functional tra-3 product below a critical level.  However, a 
single zygotic dose of e2333 can supply sufficient activity to give a 
hermaphrodite phenotype.

Figure 1