Worm Breeder's Gazette 8(3): 40

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.

Mutations Exhibiting Differential Expression in XO and XX Animals

J. Plenefisch, R. Rho, B. Meyer

The level of X-linked gene expression in C.  elegans is regulated by 
a dosage compensation mechanism, which in turn depends upon the 
assessment of the ratio of X chromosomes to autosomes.  In order to 
identify loci involved in either or both of these processes, we have 
employed a screen to isolate mutations which are differentially 
expressed in XO and XX animals.  The rationale behind this approach is 
that some mutations which perturb these processes might be 
preferentially lethal in either XO or XX animals.  (For example, in 
Drosophila males which fail to hyperactivate their single X chromosome 
because of a mutation in a gene essential for dosage compensation are 
inviable.  Females homozygous for the same mutation are viable).  The 
screen uses a strain carrying a mutation in the gene him-5(e1490); 
animals homozygous for the him-5 marker produce broods with up to 33% 
XO males, rather than the usual 0.1%, due to an increased frequency of 
meiotic non-disjunction.  Hermaphrodites homozygous for him-5 were 
mutagenized and the progeny of 10,000 F2 descendents were examined.  
The following five classes of mutations were obtained: 
1.  An abundant class of mutants (15 mutants) which resulted in an 
apparent male-specific lethal phenotype in a him-5 background proved 
ultimately to be closely linked lethals on the X chromosome in trans 
to one another.  A common property of this class was the appearance of 
0.2% (or fewer) spontaneous wild-type males that failed to transfer 
the male-specific lethal phenotype.  
2.  A mutation with a maternal-effect hermaphrodite-lethal phenotype.
Hermaphrodites homozygous for this mutation produce apparently wild-
type males (in combination with e1490) but almost no viable 
hermaphrodite progeny.  The few escapers from this lethality are Dpy 
and produce progeny.  The mutant phenotype (in the absence of e1490) 
is similar to that of dpy-26 (except that dpy-26 is also associated 
with a Him phenotype that causes 5% males among its progeny).  This 
mutation (y1) maps to the right of lon-1 on chromosome III; it 
complements dpy-27(rh18), a mutation with a very similar phenotype.  
y1 represents a new gene, dpy-28.  
3.  A mutant which fails to produce any wild-type male progeny in an 
e1490 background.  The hermaphrodite progeny are variably dumpy in 
phenotype, egg-laying defective and occasionally weakly transformed 
toward male development.  The mutation (y) produces nullo-X oocytes 
and therefore is not an 'anti-Him'.  It is either a male-specific 
recessive lethal mutation or a new her mutation.  It maps to the 
cluster of genes on chromosome II.  
4.  A maternal-effect mutation which produces wild-type males in 
combination with e1490 but very sick, egg-laying defective and weakly 
sexually transformed hermaphrodites.  This mutation (y4) maps to the X 
5.  A mutation with a male-specific lethal phenotype which behaves 
as a homozygous viable translocation involving chromosomes X and IV.  
An animal homozygous for this mutation and e1490 fails to produce 
viable nullo-X oocytes and thus it has an 'anti-Him' phenotype.  In a 
heterozygote, however, the mutation leads to a dominant Him phenotype 
in the absence of e1490, as would be expected if it were a 
translocation that interfered with normal meiotic disjunction of the 
homologous X chromosomes.  This is similar to mnT12 isolated by 
Sigurdson and Herman.
The three new mutations, y1, y2, and y4 are being analyzed more 
completely.  This analysis includes determining the interactions of 
these mutations with mutations in the her, fem, and tra genes and the 
dpy genes resulting in differential expression in XO and XX animals.  
The level of X-specific gene expression is also being assayed in the 
new mutations.