A polyray-l suppressor Julin Maloof and Cynthia Kenyon, Dept of Biochemistry, U.C.S.F, San Francisco, CA 94143 The polyray-l (pry-l) gene is required to keep homeotic selector (HOM-C) genes repressed where their expression has not been initiated (see accompanying abstract and WBG 12(5):39). pry-l mutant worms have numerous homeotic transformations and are very sick, so we were intrigued by a plate of pry-l mutant worms which appeared much healthier than normal. I outcrossed the strain and found F2s with the full pry-l mutant phenotype, suggesting that the "healthy" strain contained both pry-l and an extragenic suppressor. Does the suppressor have a phenotype on its own? Since pry-l causes homeotic transformations due to ectopic HOM-C expression, it seemed possible that the suppressor would cause transformations in the opposite direction, similar to those seen in HOM-C loss of function mutants. Indeed some F2s from the outcross had descendants of the QL neuroblast in the anterior of the worms, a phenotype also caused by loss-of function mutations in the HOM-C gene
mab-5. We are calling this newly identified gene spy-l for suppressor of polyray-l. spy-l seems to suppress all of the pry-l mutant-phenotypes: pry-l; spy-l double mutant worms do not have extra rays, are no longer Muv, are not Unc, and have anteriorly placed QR descendants. spy-l could suppress pry-l either by preventing ectopic HOM-C expression, or by preventing ectopically expressed HOM-C genes from having any effect.
mab-5-lacZ expression was examined and found to be normal in the
p1y-l; spy-l double, so wild-type spy-l is required for the ectopic HOM-C expression seen in pry-l mutant animals. The fact that there is a QL migration defect in worms mutant for spy-l alone suggests that spy-l may normally be required to turn on
mab-5 in QL. We compared expression of
mab-5-lacZ in wild- type and spy-l mutant worms at 3.5-5 hours and at 8-10 hours after hatching. At 3.5-5 hours 100% (n=20) of the mutant and 95% (n=20) of the wild-type worms had expression in QL. At 8- 10 hours 0% (n=30) of the mutant worms has expression of mab- 5 in the descendants of QL, but 87% (n=30) of the wild-type worms showed expression. It appears that spy-l is not required to initiate
mab-5 expression in QL, but that it is required to maintain expression once it is initiated. It is possible that spy-l is required to maintain the ON state of a number of HOM-C genes, in a manner analogous to the brahma and trithorax genes of Drosophila. spy-l is located on X, in a region well covered by cosmids. Hopefully a molecular analysis of spy-l along with the isolation and study of more spy-l alleles will enable us to determine how similar the C. elegans and Drosophila maintenance systems are, and how spy-l and other maintenance genes are used to maintain and specify pattern.