Worm Breeder's Gazette 8(3): 91

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.

A Hybrid Dysgenesis-Like Phenomenon in C.elegans

L.A. Donati, D.L. Baillie

We are studying the unc-22 f linkage group 
IV .  Our experiments make use of R.  Horvitz's balancer nT1.  In one 
experiment devised to study the effect of heat shock mutagenesis in C. 
elegans , we noticed that when Bergerac (BO) hermaphrodites were 
mated to Bristol (N2) males, a high rate of mutation was detected both 
in our control and in our experimental.  unc-22 BO hermaphrodites (EMS 
induced by Teresa Rogalski) were mated to unc-22 1 
N2 males.  Single wild-type F1's were set and their progeny analyzed 
for the absence of Unc-22 individuals.  Of 537 chromosomes screened, 
24 lethal bearing chromosomes were recovered (4-5%).  This is an 
increase of approximately 50 fold over the spontaneous rate of lethal 
induction in the Bristol strain (Rosenbluth et.  al., Mutation 
Research 110:39-48).  Several of these mutations have been mapped 
relative to unc-22 .  One maps 8.5 map units from unc-22 , another 
maps 4 map units away.  Of interest are three independently derived 
mutations which fail to complement one another and let-52 and appear 
tightly linked to unc-22 .  These mutations may either be point 
mutations of let-52 or may be chromosomal rearrangements in this 
region.  We are able to detect lethal bearing chromosomes in the 
progeny of the F1 suggesting that the mutations are fixed in the F1.  
Therefore, two possibilities exist as to the nature of these mutations.
The unc-22 BO strain may have an unusually high spontaneous mutation 
rate.  Alternatively, the high mutation rate may be due to a hybrid 
dysgenesis-like phenomenon, occurring sometime after fertilization and 
prior to the development of the germline of the F1.  If the unc-22 BO 
strain had an endogenous high spontaneous mutation rate, one would 
expect a large number of clustered mutational events.  We have 
evidence of one such event.  We are in the process of establishing a 
N2/BO let-52 strain which has been repetitively backcrossed to 
Bergerac.  Examination of this strain may allow us to detect reversion.
Also of interest is the distribution of these lethals.  EMS induced 
lethals seem to be primarily to the left of unc-22 .  There is only 
one EMS induced allele of let-52 , while there are three N2/BO 
interstrain cross induced alleles.  The molecular basis of these 
mutations is being investigated.  If these mutations are due to 
transposable element insertions, either Tc1 or some other element, it 
will be possible to isolate insertional mutations in genes of interest.
These molecularly marked strains will be invaluable for the cloning 
and molecular identification of specific genes.