Worm Breeder's Gazette 10(3): 10

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.

Stalking the dpy-21 Null Phenotype

Leslie DeLong, Martha Soto and Barbara Meyer

dpy-21 appears to be required in both XX and XO animals for proper 
dosage compensation.  In XX animals, mutations in dpy-21 result in a 
Dpy phenotype and elevated X-linked gene expression.  XO dpy-21 
animals appear wild-type in length, but they also have altered X-
linked gene expression.  To date dpy-21 is the only XX specific dpy 
mutation that appears to affect both XX and XO animals.
We have begun a systematic genetic analysis of dpy-21.  The mutant 
phenotype of dpy-21 was originally defined by the alleles e428 and 
e459 (J.  Hodgkin, Mol.  Gen.  Genet.  192: 452 (1983).  12 new EMS 
induced alleles have been isolated as suppressors of the XO-specific 
lethality of xol-1(y9).  Three of these alleles (y47am, y59am and 
y60am) are suppressible by sup-7(st5) X.  All alleles isolated to date 
resemble the original alleles: XX animals are Dpy, frequently have a 
protruding vulva (rare animals are Bivulva) and occasionally are Egl.  
XO animals appear wild-type.  In five of six alleles tested for 
viability at 20 C the progeny of homozygous mothers have reduced 
viability: e428 (83%), y47am (86%), y58 (96%), y60am (89%), y87 (93%) (
percent of zygotes that matured to adulthood).  The exception is y88ts,
which is slightly Dpy at 15 C, Dpy and fully viable at 20 C (99.8%), 
and Dpy with reduced viability at 25 C (90%).  Despite the isolation 
of amber suppressible alleles, it is possible that null alleles of dpy-
21 might not have been recovered from the xol-1 suppression screen.  
We have devised a complementation screen that has allowed the 
isolation of deficiencies of dpy-21 and we are now using this same 
screen to isolate additional EMS induced alleles of dpy-21.Using the 
complementation screen we have isolated 3 gamma ray induced mutations (
yDf4, yDf6 and yDf7) that fail to complement both dpy-21 and par-4(
it57), which lies to the right of dpy-21.  Since all three 
deficiencies complement mutations to the left of dpy-21, we must use 
molecular markers to show that the deficiencies do indeed span the dpy-
21 locus.  The 5S rRNA contig, which maps just to the left of dpy-21, 
will provide the initial probes for mapping the leftmost deficiency 
endpoints.  dpy-21(y88ts)/yDf6 hermaphrodites are Dpy and 70% viable (
compared to 99.8% viability for y88/y88).  In contrast, the viability 
of dpy-21(y88ts)/yDf4 and dpy-21(y88ts)/yDf7 hermaphrodites is reduced 
to 14% and 20%, respectively.  The severely reduced viability in these 
two stains may be explained in part by the additional mutant 
phenotypes associated with these two deficiencies.  yDf4/unc-76 and 
yDf7/unc-76 strains produce 35% and 41% dead eggs respectively and 
only 17% of zygotes mature to become Unc-76 hermaphrodites.  Since 
both deficiencies have been multiply backcrossed these results may 
indicate that yDf4 and yDf7 have some dominant maternal-effect 
lethality.  In addition, Df/unc-76 hermaphrodites are slow growing (
evidence of haploinsufficiency).  Our working hypothesis is that all 
three deficiencies span the dpy-21 locus and that the dominant effects 
of yDf4 and yDf7 are due to removal of some other locus or loci.
To determine if the available dpy-21 alleles are null we compared 
the viability of y88ts/yDf6 (70%) to that of y88ts/y60am (94%).  In 
this situation y60am does not act like a null allele, in that it does 
not resemble a deficiency when placed in trans to a hypomorphic allele.
Two possible interpretations of these data are: 1) we have not yet 
isolated a null allele of dpy-21 or 2) yDf6 removes a locus that acts 
synergistically with dpy-21.  This question will be settled once we 
know the nature of mutations obtainable from the complementation