Interstrain crosses enhance excision of Tc1 transposable elements in Caenorhabditis elegans

We report here an unusual activation of the Tc1 transposable element system in Caenorhabditis elegans. Germline Tc1 activity, as measured by reversion of unc-22::Tc1 alleles, is elevated 50- to 100-fold by certain crosses. For example, unc-22::Tc1 reversion is 1 x 10(-3) in a mut-6 IV strain and less than 1 x 10(-6) in a non-mutator strain, but in the unc-22::Tc1 progeny of a cross between mut-6 hermaphrodites and non-mutator males, reversion is 10(-1). The reciprocal cross does not induce this enhancement of reversion. Results similar to those for mut-6 were obtained using a mut-5 II strain. The mutator hermaphrodite by nonmutator male cross per se is not required for the enhancement of reversion, as mut-5 hermaphrodites x mut-6/+ males also induce unc-22 revertants at an elevated frequency. This reversion enhancement appears to depend on a maternal component inherited from a mutator strain, suggesting that the regulation of Tc1 activity may be complex.