Worm Breeder's Gazette 9(3): 20

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.

Activation of Tc1 Excision

D. Moerman, I. Mori and B. Waterston

In the process of mapping mut-6(st702) we have observed a remarkable 
enhancement or activation of Tc1 excision from unc-22. The observation 
is as follows: Fl hybrids of the genotype mut-6(st702) 
192::Tc1) / daf-11 136::Tc1) 
ntly yield 5 - 20 revertants per 100 progeny: 
a reversion rate 10 to 40 times higher than we have previously 
observed with any Bergerac derived strains. The Fl hybrids were 
derived from a cross of daf-11 136::Tc1) 
males with mut-6 192::Tc1) 
hermaphrodites. The revertants represent germ-line events ( whether 
these events are premeiotic and/or meiotic in origin is not clear ) 
and both st136::Tc1 and st192::Tc1 revert at similar high frequencies 
often in the same brood. The parent strains revert at significantly 
lower frequencies: mut-6 0-3 and daf-11 
dpy-4 at << 10-6. This high frequency reversion 
can be propagated as long as the mut-6 activity is maintained either 
in a heterozygous or homozygous state. That is daf-11 
dpy-4 F2 progeny did not yield revertants in any 
of 18 broods, but about 50 % of either the heteroallelic combination 
or the unc-22(st192::Tc1) homozygotes will revert within a single 
brood. Curiously, during further propagation of a derived mut-6 
192::Tc1) homozygous line we consistently observed 
that only 50 % of the progeny in turn yielded the high proportion of 
revertants in the next generation. Further propagation of the animals 
that did not give a high proportion of revertants showed that they 
remained relatively stable. These animals had not simply lost mut-6 
because they could still revert at the lower frequency ascribed to the 
parental mut-6 192::Tc1) strain.
We are currently investigating the basis of this phenomenon and its 
generality; i.e., is it unique to this pair of strains, and does it 
apply to other genes and to transposition as well as excision? Our 
results on these important questions are as yet too preliminary to 
bother to pass on. But the phenomenon is so impressive we will leave 
you with a specific example to stimulate thoughts of dysgenesis etc. 
In propagating a Tc1 excision activated mut-6 
192::Tc1) line these are some of the numbers we 
have observed ( wild / total progeny 
6/59, 2/20, 5/93 and 4/26.