Worm Breeder's Gazette 11(5): 36

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 in dpy-2 and dpy-10

Adam Levy, Jie Yang and Jim Kramer

Figure 1

dpy-2 and dpy-10 are tightly linked at the left end of the cluster 
of LGII.  Alleles of each display genetic interactions with other loci.
The dpy-2 alleles e8 and q292 and the dpy-10 alleles e128 and q291 
can suppress a temperature sensitive allele of glp-1 (Maine and Kimble,
Development 105: 133).  e128 can suppress a ts allele of mup-1 (T.  
Bogaert, personal communication).  Kusch and Edgar (Genetics 113: 621) 
showed interactions between the recessive Dpy allele dpy-10(e128) and 
the recessive Lrol allele sqt-1(sc13): e128 sc13/e128 + animals are 
DpyLRol.  We have since shown that at least three other sqt-1 alleies (
sc99, sc101, and sc1) behave in a similar manner in the e128 
background such that e128 sqt-1/e128 + animals are DpyLRol.  e128 sc13 
homozygous animals are DpyLRol.  All other e128 sqt-1 homozygotes 
tested were Dpy, however the character of the Dpy phenotype differs 
with different sqt-1 alleles.
Cosmid ZK857 is located in the predicted vicinity of dpy-10 and 
contains two collagen genes.  Using mutator induced alleles of dpy-10 (
kindly provided by Don Riddle and Tim Schedl), we were able to show 
that one of these collagens is dpy-10.  We have shown that the other 
is dpy-2 by sequencing of mutants.  dpy-2 and dpy-10 are located 3.5 
kb apart (dpy-2 on the left) and are transcribed in opposite 
directions.  Structurally, the dpy-2 and dpy-10 collagens are more 
similar to each other than to any other of the sequenced collagens and 
are probably a result of a gene duplication.  dpy-2 is trans-spliced 
with SL1; dpy-10 is not trans-spliced.  The point and Tc1 mutations 
that we have analyzed are diagrammed in the figure below.
Glycine Substitutions: Replacements of Gly with Arg or Glu in the 
Gly-X-Y repeat region were identified in alleles of both dpy-2 and dpy-
10.  Different substitutions produce different phenotypes and some are 
temperature sensitive.  In general, temperature affects the severity 
of the LRol phenotype much more than the Dpy phenotype.  The locations 
of the substitutions apparently dictate the Dpy or DpyLRol phenotype.  
These substitutions presumably result in the destabilization of the 
collagen triple helix, which requires a glycine at every third amino 
acid for proper folding.
A Splice Acceptor Mutant: dpy-10(e128) is a G->A transition in the 
conserved AG of the splice acceptor of intron 2.  Reverse 
transcription PCR of e128 RNA indicates the presence of approximately 
equal amounts of apparently normally spliced message and unspliced 
message.  Even though the AG of the splice acceptor sequence is 
normally required for splicing, the mutant acceptor appears to be 
utilized surprisingly well.  When intron 2 is not spliced a 16 amino 
acid insertion would be encoded by the intron (no nonsense codons or 
frameshift).  Whether the Dpy phenotype of e128 is a result of reduced 
level of normal dpy-10 product or the production of dpy-10 collagen 
with a 16 amino acid insertion is unknown.  No evidence for the 
utilization of cryptic splice acceptors was detected.
Another Dominant Gain of Cysteine Mutant: dpy-10(cn64) displays 
dominant LRol and recessive temperature-sensitive DpyLRol phenotypes.  
The cn64 mutation results in an Arg->Cys substitution in homology box 
A, the same Arg->Cys change seen in the dominant RRol sqt-1(e1350) and 
rol-6(su1006) mutations.  All dominant Rol mutations identified to 
date are Arg->Cys changes in the A Box.  However, the dpy-10 Arg->Cys 
mutation causes a dominant LRol phenotype while the sqt-1 and rol-6 
mutations are dominant RRol.  Thus, the equivalent mutation in 
different collagens can cause twisting in opposite directions.  These 
gain of Cys mutations probably allow the formation of abnormal 
disulfide bonds within the cuticle.
Tc1 Insertions at the Same Site Produce Different Phenotypes: Two of 
the three Tc1 insertions in dpy-10(q323 and m457) are located at 
exactly the same point in the gene, and are in the same orientation.  
It is interesting that these two strains have different phenotypes, 
q323 is DpyLRol and m457 is Dpy.  One possible explanation for the 
difference in phenotypes is that the excision rates of the two 
elements are different.  We examined the relative frequency of 
excision in the three Tc1 strains by PCR of individual worms.  We 
found that the amount of the excision-sized product is consistently 
about ten-fold less with q323 than with m457 or m481, indicating that 
the element in q323 excises less frequently.  The amounts of excision 
in m457 and m481 are approximately equal.  The lower frequency of 
excision in q323 animals may result in the production of less 
functional dpy-10 product than in m457 or m481 animals, resulting in 
the DpyLRol phenotype.  It is possible that the differences in 
excision rates may be caused by differences in the sequences of the 
elements.  However, the effect could also be due to dpy-10 linked 
differences In the genetic backgrounds of the strains.  
? Null phenotypes: Our observations suggest that the null phenotypes 
of dpy-2 and dpy-10 are DpyLRol and that the less severe phenotype is 
Dpy.  Analysis of Tc1 insertions indicate that a lower amount of 
excision Is correlated with the DpyLRol phenotype.  In addition, the 
temperature sensitive alleles of dpy-2 and dpy-10 show DpyLRol 
phenotypes at 25 C, but are Dpy nonLRol at 15 C.  Raising the 
temperature presumably causes destabilization of the triple helix, 
reducing the level of functional dpy-2 or dpy-10 collagen.  Since 
neither dpy-2 or dpy-10 are haploinsufficient, 50% of the normal level 
of these collagens is presumably sufficient for normal function.  The 
Dpy phenotype would appear when the level of functional gene product 
was some unknown amount less than 50%, whereas the DpyLRol phenotype 
would appear to represent a more severe reduction or compete absence 
of these collagens.
[See Figure 1]

Figure 1