Worm Breeder's Gazette 7(2): 64
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.
We are interested to know whether hybrid dysgenesis exists in nematodes. One approach is to study progeny populations of hybrids whose mother belongs to a laboratory, while their father to a wild ( recently isolated) strain of the same species. In the last issue (WBG 7, (1:)48-49) a newly isolated strain of (then called as 'var. Gujarat' but we call it Guj-16/Szeged/) was reported by us and was taxonomically determined as C. briggsae by I. Andrassy. Guj-16 males have been used as fathers and the Zuckerman (Boulder) hermaphrodites as mothers of such hybrids needed in our recent studies. F1 hybrids were selected either as dauer larvae from DRIF (WBG 6, ( 1:)25) containing media or simply as NonUnc hermaphrodites. (The Zuckerman's self-progeny are dauer defectives and Uncs,) We were looking for levamisole resistant (lev) mutants first. The idea behind that was to find mendelian mutations - independent of the genetic background - by using the advantages of the selective procedure. We also supposed the target size - 13 non-clustered lev gene was found in C. elegans (Lewis, 1980) large enough to find spontaneous or hybrid dysgenesis mutants even if their distribution in the genome is not be random. In preliminary control experiments when progeny populations of 200 Guj-16 hermaphrodites were scored on levamisole plates there were no resistant animals. In two run of 'pilot' experiments (differring from each other in some details but based upon Brenner's scheme) we scored progeny populations of 144 F1s and found four independent lev mutants. One of them is a remarkable twitcher (hdg-3 or twi-3). All four mutants are kept in both original and outcrossed strains. Although we do not know whether our mutants confine one or more cistrons, we might conclude that the forward mutation rate was not lower than 10+E-5 - 10+E-4, which significantly exceeds the spontaneous rate. We were afraid that the wild strain harbored these mutations, but it was not the case. However, the Zuckerman strain harbors several mutations like unc, che, daf (defective), so the possibility of mutator activity in this strain cannot be ruled out, (Emmons, personal communication.) We have to study this strain carefully. We have not observed spontaneous the parental strains so far, but we isolated several twitchers from both strains by using EMS. Mutants affecting size, shape and movement are too difficult to analyze. Considerable time was spent in both Columbia and Szeged cleaning up putative dpys, lons, etc. None of them bred purely and some proved sterile. These phenotypes might be consequences either of interacting polygenes or of unstable mutations or both. The only morphological mutants which could be kept, outcrossed and handled were the blisters. Their frequency however, was suspiciously high and we cannot be ruled out that this mutation together with its epistatic suppressor had not been present in either of the parental strains. ( In fact we have not found spontaneous bli mutants in any of the parental strains so far.) These bli's can be characterized by low penetrance and extremely high expressivity. The high spontaneous mutation rate (even in a laboratory strain) itself might be interesting when looking for transposons in the nematode genome. The question arises whether our mutants were generated by hybrid dysgenesis. To answer this question further experiments have to be accomplished (involving determination of the spontaneous mutation rates of the parental strains; comparison reciprocal hybrid populations as well as F2s and F3s, etc.). We are going to study other phenomena (like different kinds of hybrid sterility) which accompany hybrid dysgenesis in other organisms. The project is continued in Szeged and we want to extend our studies to other strains as well. Therefore, any new nematode strains would be welcome and gratefully appreciated.