Worm Breeder's Gazette 10(1): 122
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.
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.