Worm Breeder's Gazette 10(2): 105

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deg-1 is a Large Gene

Eve Wolinsky and Marty Chalfie

Figure 1

The deg-1(u38) mutation causes the PVC interneurons to degenerate 
and die during the late L3-early L4 stage.  Thus, such mutants become 
insensitive to tail touch as they mature (other neurons, in the head, 
degenerate during the Ll stage).  The phenotype conferred by u38 is 
dominant and temperature sensitive.  We have obtained 26 pseudo-wild 
type revertants following EMS and transposition mutagenesis, including 
one deletion allele.  These results suggest that the wild type 
function of deg-1 is dispensable, and that the u38 mutant gene product 
somehow 'poisons' specific neurons at specific times during 
development.  We wish to learn more about the deg-1 gene product in 
order to understand the molecular basis of the u38 phenotype.
As reported in the last gazette, we have cloned the gene using Tc1 
tagging.  Since then we have l) localized two insertions and one 
deletion genetically linked to deg-1 to two cosmids within a contig 
mapping in the center of X (cosmids and map kindly provided by A.  
Coulson and J.  Sulston), 2) localized three different types of cDNA 
clones to the same two cosmids (cDNA library kindly provided by J.  
Ahringer and J.  Kimble), and 3) begun sequencing our genomic and cDNA 
A part of the relevant contig map is reproduced below.  Our 
conclusions are based on Southern blots of DNA from various u38 
revertants probed with the cosmids shown.  We have subcloned three 
regions of cosmid C47C12 corresponding to three deg-1 linked DNA 
rearrangements.  Two different Tc1 insertions map to adjacent 
fragments near the center of C47C12: a 3 Kb EcoRI-XbaI fragment, and a 
2.3 Kb EcoRl fragment.  Our deletion strain is missing DNA from an 
approximately 8.5 Kb EcoRl fragment hybridizing to both cosmids C47C12 
and R02A8.
We used our 3 deg-1 subclones to screen an approximately Ll-staged 
cDNA library (we have not yet detected deg-1 sequences on Northerns).  
Three different types of CDNA's were obtained.  All three hybridize to 
the 2.3 Kb EcoRl fragment which is the site of one of the Tc1 
insertions.  Additional hybridizing sequences are found in the center 
of R02A8 for two cDNAs which differ in the amount of R02A8 sequences 
they contain (they also differ in that only one of the two contains 
the repetitive element of the C47C12 2.3 Kb EcoRl fragment described 
below.  None of the cDNA's bind detectably to sequences outside the 
two cosmids.  Thus, the R02A8 hybridizing cDNA's delineate a probable 
new region of deg-1 not previously identified by mapping DNA 
rearrangements in our revertant strains.
We have begun sequencing our deg-1 cDNA and genomic clones.  The 
largest cDNA is about 2.5 Kb, comprised of mostly R02A8 sequences.  
More of the C47C12 2.3 Kb EcoRl fragment is represented on another 
cDNA clone approximately 2 Kb in length.
Our study of the structure of deg-1 has so far yielded three points 
of interest.  l) The gene is large, extending from the center of 
C47C12 to the center of R02A8.  It appears to be sandwiched between 
the vitellogenin and tubulin genes.  2) One type of deg-1 cDNA 
contains sequences separated on the cosmid map by more than 10 Kb, 
suggesting a possible large intron.  3) The 2.3 Kb EcoRl fragment from 
C47C12 hybridizes to 5 additional bands on high-stringency Southern 
blots of XbaI-EcoRI cut genomic DNA.  The extra bands amy correspond 
to members of a gene family related to deg-1.  The hypothesis of a deg-
1 gene family is a possible explanation for the non-essentiality of 
the gene.
[See Figure 1]

Figure 1