Worm Breeder's Gazette 15(3): 28 (June 1, 1998)

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.

Multiple promoter regions contribute to apparent cooperative negative regulation of her-1 by sdc gene products in hermaphrodites

Weiqing Li¹, Barbara Robertson¹, Adrian Streit², Bill Wood¹

        The male-determining gene her-1 has two sex-specific
transcripts: the larger one, which is necessary and sufficient for
masculinization, driven by an upstream promoter P1 and the smaller one,
which has no known function, by an internal promoter P2 in the large
second intron of the gene.  We have reported previously that transgenic
arrays of a 3.4-kb P2-region fragment including all of intron 2 appear
to mimic phenotypes resulting from sdc loss-of-function [sdc(lf)]
mutants, including suppression of  XO lethality and masculinization of
XX and XO animals in a xol-1(lf) background.  We have obtained evidence
that these transgene effects are copy-number dependent, supporting our
view that they result from in vivo titration of negative regulators
encoded by the sdc genes.  We analyzed two lines that carried integrated
arrays of P2 sequences, driving a lacZ  reporter in one case (ctIs1) and
a GFP reporter in the other (ctIs32).  One copy of the ctIs1 array did
not suppress xol-1(lf) XO lethality whereas one copy of  ctIs32 did so. 
Moreover, the ctIs1 reporter was expressed male-specifically whereas the
ctIs32 reporter was expressed in both sexes, suggesting that the P2
promoter might be present in too many copies to be appropriately
regulated.  Southern blot analysis showed that ctIs32 includes 6.4 times
more P2 sequences than ctIs1, consistent with titration as the cause of
the observed sdc-like phenotypes.
        We have taken advantage of the masculinizing effects of P2
promoter sequences in xol-1(lf) XX animals to perform a deletion
analysis, in order to define the sites involved in causing these
effects. We prepared a series of deletion constructs missing various
segments of the 3.4-kb P2 region, injected each into xol-1(lf) animals,
and scored between 5 and 25 transmitting lines carrying each construct
for masculinized animals in the F2 progeny.  We find that multiple
regions in P2 contribute to the putative titration effects.  A 0.4-kb
segment near the middle of the intron masculinizes weakly alone, but its
effect is enhanced by the presence of sequences in other more
P2-proximal and P2-distal segments of the intron.  P1 sequences do not
masculinize alone.  They can enhance masculinization by P2 sequences,
but only if the putative negative regulatory site defined by her-1(gf)
mutations just upstream of the transcription start site is intact. 
These results suggest a cooperative mechanism of her-1 regulation,
specifically, that the repression of transcription from P1 in XX animals
is likely to be assisted by sequences in the P2 region.