Worm Breeder's Gazette 14(2): 24 (February 1, 1996)

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.

mut-7, a new mutator allele isolated in a non-mutator strain

Rene F. Ketting, Miriam Th. Smits, Ronald H.A. Plasterk

The Netherlands Cancer Institute, Division of Molecular Biology, Plesmanlaan 121, 1066 CX Amsterdam, The Netherlands.

We have obtained a new mutator (activator of transposition) in a line of primarily Bristol N2 background, using EMS as a mutagen. This new mutator locus, called mut-7, is located on chromosome III and activates Tc1, Tc3, Tc4 and Tc5 in the germ line. Somatic transposition activity does not seem to be affected.

The method we used to detect mutators was in principle the same as the one used by John Collins (1). However, instead of searching for an elevated transposition frequency, we set out to find mutators in a background that had no transposition activity at all. The unc-54(r323::Tc1) allele used in this screen is derived from TR674 (a high hopper strain) that was backcrossed 10 times with Bristol N2, after which the unc-54(r323::Tc1) allele did not revert anymore. Judged from a southern blot this strain only has about 4 extra Tc1 copies compared to the 30 of Bristol N2.

Worms were mutagenised, cloned out, and checked for the occurrence of non-Unc progeny. Among 1000 mutagenised animals one line was found in which Tc1 could excise. The excision frequency from the unc-54 locus is similar to that of TR674, a mut-2 strain. Not only Tc1 excision but also integration frequencies are raised: spontaneous, revertible unc-22 mutations can be identified. Also other transposons (Tc3, 4 and 5) proved to be activated, as scored by reversion of the respective transposon insertion alleles of unc-22 (kindly provided by John Collins). Southern blot experiments show that upon culturing, new alleles of Tc1 and Tc3 arise. Activation of transposition seems to be specific for the germ-line, since no elevation of somatic transposition activity could be detected using a PCR assay. Crosses with Bristol N2 show the mutation to be a single locus in the centre of chromosome III; it will be named mut-7. Further mapping studies are now in progress to clone the mut-7 locus.

It may be interesting to note that the mut-7 allele also confers a Him-phenotype, just like mut-2 and the other EMS induced mutators found by John Collins.

The fact that this new high hopper line has a Bristol background makes it a much healthier strain than the mut-2 strains. For example, lines with mut-7 can readily be injected to generate transgenic lines, unlike in our hands other high hopper strains. This, combined with the fact that there are only a few extra transposons compared with Bristol N2, makes that these lines are very useful for transposon tagging experiments. Together with the ongoing sequencing project, this should make it possible to quickly identify new mutations.

1. J. Collins, B. Saari and P. Anderson (1987). Nature 238: 726-728