Worm Breeder's Gazette 9(1): 74

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.

X chromosome expression in X duplications and in some new mutations

P. Meneely and K. Nordstrom

We have used X-linked hypomorphic (i.e., leaky) mutations as a 
simple and versatile assay for the expression of X-linked genes.  
Particularly useful mutants are lin-15 (n765) and let-2 (b246), which 
result in a temperature-sensitive Muv phenotype and lethality (or 
sterility), respectively.  From this assay, we have suggested that dpy-
21 and dpy-26 mutants have higher X expression than wild-type and that 
dpy-22, and possibly dpy-23, have lower expression than wild-type.  
The fact that dpy-21 is an effective suppressor of X-linked hypomorphs 
led to a simple scheme for finding new dosage compensation mutants: 
Mutagenizing lin-15 (n765) hermaphrodites (or lin-15 [n765] let-2 
[b246] hermaphrodites) and picking non-mutant animals in the F1 and F2.
We have found more than 20 suppressors, at least 7 of which suppress 
both hypomorphs.  Such suppressors do not appear to be particularly 
rare.  Most of them are Dpy, some are male-abnormal, and some are Him. 
Because some mutants are dominant suppressors we do not know yet how 
many genes are represented; at least one, a recessive suppressor, is a 
dpy-21 allele.  Another mutant is a heterozygous suppressor and semi-
Dpy, but a homozygous lethal and extremely Dpy.  In a previous 
newsletter, and in our CSH poster, we reported that mnDp25, a fairly 
large X duplication, suppressed a lin-15 hypomorph.  We have extended 
this to other duplications and hypomorphs, and the conclusion is quite 
clear: X duplications suppress hypomorphs in the regions they do not 
duplicate.  Although the data are limited, the effect appears to be 
size-dependent; a big duplication like mnDp25 suppresses better than a 
medium-sized duplication like mnDp57, and both suppress better than a 
small duplication like   (mnDp57 includes the region 
from unc-2+ to lon-2+, and was kindly provided by Bob Herman).  
Likewise, two copies of a duplication suppress better than a single 
copy.  This is consistent with the simple idea that the duplication 
competes with the normal X for the 'repressors' encoded by dpy-21, 
s elevating overall X expression.  Working on 
the old dogs and new tricks principle, we are isolating more X-
chromosome duplications and deficiencies.