Worm Breeder's Gazette 11(1): 21

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.

Rescue of Lethal Mutations Using Cosmids and Germ-Line Transformation

Denise V. Clark and David L. Baillie

Figure 1

We have been studying essential genes in the unc-22 IV region of 
Caenorhabditis ntial genes have now been 
identified in this 2 map unit interval, and the minimum estimate of 
essential genes is 52.  Lately our focus has been on the 0.2 map unit 
interval between dpy-20 and unc-22 (see map below).  This region 
contains three identified essential genes with zygotic lethal mutant 
phenotypes.  The most severe alleles of let-56, 
e developmental arrest in early 
larval stages (L1 or L2).
dpy-20 (Clark and Baillie, unpublished results) and unc-22 [Moerman, 
Benian and Waterston, (1986) PNAS 83:2579] have both been cloned and 
placed on the physical map and between them lies a section of cosmid 
contig of about 200 kb.  Coding regions on four cosmids in this 
interval have been mapped and characterized by identifying regions of 
homology with C.  briggsae [Prasad and Baillie, (1989) Genomics, in 
In order to identify the cosmids that contain essential gene coding 
regions, we have been injecting cosmid DNA into strains carrying a 
lethal mutation [let-x unc-22 nT1(IV); +/nT1(V)] 
and screening the F1 generation for fertile Unc-22s or Unc-22 
s173) is rescued by the cosmid C11F2 and by 
ZK820.  Stable and transient rescues were achieved, and two stable 
lines containing s173 and C11F2 were kept.  C11F2 and ZK820 share two 
coding regions identified by C.  briggsae homology.  Two subclones 
containing each coding region were tried for rescue of s173 without 
success.  Three cosmids F47H9, C29E6 and ZK822 were injected together 
into individuals carrying let-653(s1733) and a stable line of Unc-22 
ated.  Later, transient rescue using C29E6 
was achieved.  The stable lines are being cultured for DNA isolation 
so that the copy number of cosmid sequences in these lines can be 
The map below shows the cosmids being used for transformation 
experiments.  Note that C35H3 rescues dpy-20 but not let-60.  Also 
note that all likely cosmids have been used in attempts to rescue let-
92(s504) and (s677), without success.
This work is supported by an MDA of Canada predoctoral fellowship to 
DVC, and MDA of Canada and NSERC grants to DLB.
[See Figure 1]

Figure 1