Worm Breeder's Gazette 11(4): 63

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.

fem-3 Regulation is Getting Foggy

Tom Evans and Judith Kimble

The fem-3 gene is required for specifying male development.  In XO 
males, fem-3 is active in the soma and germline to specify male 
somatic tissues and sperm.  In XX hermaphrodites, fem-3 must be 
inactive in the soma to allow female development.  In the XX germline 
however, fem-3 is active in larvae to promote a brief period of 
spermatogenesis, and then it must be turned off in adults to allow 
oogenesis.  How is regulation of fem-3 achieved?
To determine whether specific regions of the fem-3 gene impart 
control of its expression, we constructed reporter gene plasmids that 
contain the E.  coli lacZ coding region flanked by fem-3 5' and 3' 
sequences.  These plasmids were then coinjected with rol-6 to generate 
transformed lines.  Although these lines had inconsistent patterns of 
lacZ expression, they all exhibited an interesting phenotype: 
feminization of the germline (or Fog).  Both XX and XO transgenic 
animals make only oocytes (in 85-98% of the animals), but show normal 
sexual development of the soma.  Thus, these lines behave as if they 
have lost fem-3 function specifically in the germline.  Deletion 
analysis has identified a 190 base region of the 5' untranslated 
region (5' UTR) that is necessary for inducing the Fog phenotype.  
These results suggest that excess 5' UTR sequences may sequester a 
regulatory factor that is necessary for fem-3 expression in the 
germline.  Several observations suggest that it may be RNA containing 
the 5' UTR that causes the FOG phenotype.  (1) A plasmid carrying the 
5' UTR alone is not sufficient; 5' flanking sequence is required for 
full activity.  (2) The complete Fog effect depends on the sense 
orientation of the 5' UTR relative to 5' flanking sequences.  (3) In 
preliminary experiments, we have found that the levels of endogenous 
fem-3 RNA are not substantially altered in Fog transgenic animals.  
Therefore, it is possible that a regulatory factor binds fem-3 mRNA in 
the 5' UTR to stimulate translation (directly or indirectly) of the 
fem-3 protein, and the presence of excess 5' UTR prohibits this 
interaction.  Other explanations (e.g.  titration of DNA-binding 
factor, or anti-sense RNA) have not been completely ruled out.