Worm Breeder's Gazette 11(5): 81

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.

A Putative mab-5(gf) Allele, e1751, is a Large Duplication of the Entire Gene which may Alter the mab-5 Promoter Region

Stephen Salser and Cynthia Kenyon

Figure 1

Several lines of evidence suggest that e1751 might be a gain-of-
function allele of mab-5.  The effect of e1751 on the Q migrations is 
directly opposite that of mab-5 loss-of-function mutations.  (Ed 
Hedgecock, Dev.  100) In addition, e1751 causes generation of ectopic 
V ray papillae, whereas mab-5 loss-of-function alleles prevent V ray 
production.  (Andrew Chisholm, pers.  comm.) Mapping experiments by Ed 
Hedgecock showed that e1751 could not be easily separated from mab-5 
by recombination, and finally, a restriction length polymorphism 
associated with e1751 was observed on Southern blots probed with the 
mab-5 containing cosmid ZC102.  (R.  Hoskins, pers.  comm.) We have 
confirmed this observation and mapped the 
[See Figure 1]
The rearrangement is a large tandem duplication of approximately 100 
kb.  that includes the entire mab-5 coding region and about 4 kb.  of 
upstream sequences.  As might be expected for a tandem duplication, 
e1751 reverts spontaneously to wild-type.  These revertants no longer 
contain the duplication and presumable arise by recombination.  We do 
not believe that the increased number of mab-5 gene copies explains 
the gain-of-function phenotype of e1751 because neither e1751/nDf16 
nor e1751/mab-5(lf) is wildtype.  Instead, the rearrangement may 
change the activity of one of the promoters.  The truncation of one 
promoter (copy #1) 4 kb upstream of the gene could remove negative 
control elements or bring new enhancers close to the mab-5 gene.
Some of our earlier genetic experiments suggested to us that e1751 
was not an allele of mab-5.  In these experiments the phenotype of 
e1751/nDf16 was compared to the phenotype of e1751/mab-5(e1239).  
Assuming that e1751 is an allele of mab-5 one would expect it to look 
the same over null and over deficiency.  Instead, the QR migration in 
e1751/nDf16 is fully mutant while e1751/mab-5(e1239) has an 
intermediate phenotype like e1751/+.  We have repeated these 
experiments using e2088, another allele of mab-5 that is likely to be 
null, and the result is the same.  These results imply that something 
on the wild-type chromosome other than mab-5 is ameliorating the e1751 
phenotype.  We do not know how to interpret these results at present, 
but have cloned both copies of mab-5 from e1751 and plan to test their 
activities in transgenic lines.

Figure 1