Worm Breeder's Gazette 10(1): 122

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Update on sup-26: A Negative Regulator of tra-2??

J. Manser and W.B. Wood

In previous Newsletters (WBG 9, No. 1, p. 70; WBG 9, No. 2, p. 97; 
WBG 9, No. 3, p. 52) and at the 1987 CSH Meeting (Abstracts, p.63) we 
have described the properties of sup-26(n1091 and ct49) III mutations, 
which were isolated as EMS induced extragenic suppressors of the 
semidominant her-1(n695) mutation.  Briefly, sup-26 mutations can 
feminize both XX and XO animals and appear to act upstream of tra-2 
because: 1) the null tra-2(e1095) XX phenotype is not suppressed by 
sup-26 and 2) a sup-26 mutation can block the enhancement of the 
hypomorphic tra-2(n1106) phenotype by sdc-1 (n485), dramatically 
feminizing a tra-2(n1106); 5) XX strain.  The 
latter result would not be expected if sup 26 mutations exerted only 
weak effects downstream of tra-2.  A sup-26 mutation can substantially 
suppress the Egl (HSN-) phenotype exhibited by tra-2(n1106) XX animals,
suggesting that sup-26 mutations cause an elevation of tra-2 activity 
in XX animals.  Two possible mechanisms for this apparent elevation 
are:  1) sup-26 mutations result in decreased her-1 activity, which 
indirectly elevates tra-2 activity or 2) sup-26 mutations can cause 
direct effects on tra-2 activity without necessarily affecting her-1 
activity.  The former mechanism seems less likely because:  1) sup-26 
suppresses tra2(n1106) in XX animals, where her-1 activity is 
presumably OFF or LOW and, 2) neither of the loss-of-function 
mutations her-1(e1520) or her-1(y10) by itself suppresses tra-2(n1106) 
XX.  [Preliminary experiments involving small numbers of animals (WBG 
9, No. 3, p.52) suggested that her-1(e1520) might show weak 
suppression of tra-2(n1106) XX; however, examination of greater 
numbers of animals showed no significant suppression.
To help us in thinking about models for the role of wild-type sup-26 
gene activity in normal sex determination, we wanted to determine 
whether sup-26(n1091 and ct49) mutations represent gain or loss of 
gene function sup-26 mutations are weak semidominant suppressors of 
her-1(n695), suggesting that they may represent gain of function [5-
10% of sup-26/+; 5) XX animals are suppressed].  
However, the existence of two apparently identical alleles, each 
isolated at approximately the frequency expected for EMS-induced nulls,
suggests that they may represent loss-of-gene function.  To address 
the question of gain or loss more directly, we wished to perform gene 
dosage experiments on sup-26 using deficiencies or duplications.  
Attempts to isolate a deficiency of the sup-26 locus were unsuccessful.
Instead we have used the duplication mnDp37(III;f), which carries a 
wild-type sup-26 allele.  If sup-26 mutations result in a gain of wild-
type gene activity, or of a novel activity that does not compete with 
wild-type then mnDp37[sup-26(+)1/sup-26/sup-26 animals should resemble 
sup-26/sup-26 animals by exhibiting strong suppression of her-1(n695).  
If sup-26 mutations result in a novel activity that competes with wild-
type then mnDp37[sup-26(+)1/sup26/sup-26 animals should exhibit 
stronger suppression than +/sup-26 animals.  However, if sup-26 
mutations are loss-of-function alleles, then mnDp37[sup-26(+)1/sup-
26/sup-26 animals should resemble +/sup-26 animals by showing only 
weak suppression of her-1(n695).  We have found that mnDp37[sup-26(+)
1/sup26(n1091)/sup-26(n1091);her-1(n695) XX animals show very weak 
suppression, suggesting that sup-26(n1091) is a loss of function 
mutation.  As a control, we constructed mnDp37/+/+;her-1(n695) XX 
animals and found them to exhibit phenotypes indistinguishable from 
those of +/+;her-1(n695)XX animals; that is, the addition of mnDp37 by 
itself (which includes most of LG III) does not result in either 
dramatic enhancement or suppression of her-1(n695).Therefore, the gene 
dosage experiments suggest that loss of sup-26 gene function is 
responsible for the apparent increase in tra-2 activity caused by sup-
26 mutations.  Consequently, wild-type sup-26 activity may act to 
reduce tra-2 activity in XO (and also XX) animals.  If sup-26 acts 
directly on tra-2 without affecting her-1 activity, there are at least 
two possible mechanisms for sup-26 action: 1) sup-26 activity could be 
controlled by her-1 or 2) sup-26, like fog-2, could be controlled in 
some other fashion.