Worm Breeder's Gazette 3(2): 24

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.

Chemical Mutagens Other than EMS

D. Riddle

The ability of a variety of compounds to induce visible mutants (unc,
dpy, etc.) has been tested.  The list of compounds includes the 
following: ICR-191, ICR-364, proflavin, 2-nitrofluorene, 9-
isothiocyanato-acridine, irehdiamine A, nitrosoguanidine (NG) and 
diethyl sulfate (DES).  DES is a very effective mutagen, while NG and 
ICR-191 are weakly mutagenic.  The other compounds listed were not 
mutagenic even at saturating concentrations or when the animals were 
grown for a generation in the presence of the compound.  
Nitrosofluorene induced some phenocopies but no true-breeding mutants. 
The possibility that the gut or the cuticle might not be permeable to 
some of these agents was recognized, so mutagenesis was also attempted 
in the presence of DMSO or Tween 80.  These agents did not seem to 
enhance mutagenesis by any of the compounds tested, but it was 
interesting to find that C.  elegans grows almost normally in 0.5% 
DMSO or in 1% Tween 80.  (However, worms will not reproduce in liquid 
medium containing 5% DMSO.)
The best treatment found for NG mutagenesis was suspension of the 
animals for one hour in pH 6.0 buffer containing 0.5 mg/ml NG.  This 
concentration of mutagen is 10-fold higher than that used for bacteria.
Visible mutants were detected at a frequency of about 1%; about 10-
fold less frequent than is found with the standard EMS treatment.  At 
lower concentrations of NG, mutagenesis is less efficient, while 
higher concentrations substantially decrease fertility.
The acridine derivitive, ICR-191, was mutagenic when the animals 
were grown in 0.1 mg/ml ICR for a generation.  Again, this 
concentration is 10-fold higher than that used for efficient bacterial 
mutagenesis, but the nematodes thrive on it.  They seem to accumulate 
the compound in their gut to produce a bright yellow coloration, but 
neither fertility nor growth rate are greatly affected.  David Baillie 
and I collected 50 ICR-induced visible mutants.  They occur at the 
relatively low frequency of 0.2%.  Most of the mutants fell into 
complementation groups previously defined by EMS-induced mutants.  
However, three new genes were detected in this study: dpy-4 (IV) has 
two ICR-induced alleles, him-4(X) has two ICR-induced alleles, and let-
13(I) has one allele.  With these exceptions the spectrum of ICR-
induced mutants does not differ from the spectrum of EMS-induced 
mutants.  EMS was tested for its ability to induce reversion of ten of 
the ICR-induced mutants.  Three of the ten were induced to revert at a 
closely-linked site by EMS.  This suggests that ICR-191 and EMS may 
induce similar types of mutations in C.  elegans.In contrast to the 
above compounds, DES (Aldrich Chemical Co.) is an extremely effective 
mutagen.  Foreward mutation frequencies comparable to those obtained 
with EMS are achieved when using 0.01 M DES.  In this procedure, 5  l 
DES are dissolved in 2 ml M9 buffer and added to a 2 ml suspension of 
worms for 2 hours at 20 C.  Under these conditions, the spectrum of 
mutants induced to revert by DES is as yet indistinguishable from that 
of EMS.  Also, similar numbers of revertants are obtained with these 
two mutagens.  Thus, the only advantages of DES are that less is used 
for a shorter time.  DES carries a warning label: skin