Worm Breeder's Gazette 11(2): 117
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.
A stable male/female strain (CB4628, or strain A) consisting of tra- 2;fem-1:xol-1 XX females and tra-2 xol-1 XX males was constructed by conventional means: in this strain sex is determined by the presence or absence of fem-1(+) on LGIV, so LGIV now behaves as a Y(dominant masculinizing) or an X (recessive feminizing). As expected, strain A consists of 50% fertile females and 50% fertile males, and hermaphrodites are never seen. A variation on strain A was constructed, consisting of tra-2; xol-1 XX females and tra-2; xol-1: eEx14 XX males. In this strain (CB4706, or strain B) sex is determined by the presence or absence of the extrachromosomal eEx14 element (from Andrew Spence) which carries a 10kb fem-1(+) fragment. Sex ratio in this strain is rather variable, owing to unstable transmission of eEx14, but has a mean of about 50% females, 50% males. A few clearly intersexual animals are seen, presumably the result of somatic loss of eEx14. Unexpectedly, strain B also segregated a few (~5%) self-fertile hermaphrodite worms. These were used to found a separate strain, CB4707 or strain C. Initially only about 1-10% of the animals in strain C were self-fertile, but with time this fraction increased. The self-fertile animals have truncated tail spikes but are not otherwise strongly masculinized. They produce broods of up to 200 progeny, consisting approximately of 20% hermaphrodites, 60% females, and 20% unhatched eggs (often misshapen). Males or strongly masculinized animals are never seen. In strain B, eEx14 is expressing full fem-1(+) function in both germ line and soma; in strain C it is expressed in the germ line but not in the soma (or at drastically lower levels). One possible explanation is that eEx14 has integrated on one of the chromosomes at a site that only permits expression in the germ line, and has disrupted a zygotic essential gene in the process, hence the dead eggs. However, the fem activity and the lethality do not segregate in a Mendelian manner. A second explanation is that 'eEx14C' has acquired a spontaneous mutation that selectively interferes with fem-1 somatic function. However, no such mutation has been found in previous work on fem-1, despite strong selections. A third explanation is that the eEx14C extrachromosomal array has become sequestered, either physically or functionally, so that it is now only transmitted or expressed in the germ line. Further molecular and cytological analysis should clarify what is going on in strain C. Two preliminary and tentative conclusions can be drawn. First, the germ-line function of fem-1 seems to be autonomous to the germ line. Second, expression from a transgene can be quite variable, and the presence of a functional gene in one tissue does not guarantee expression in all tissues. Some workers have begun to use cloned fem-1(+) as a convenient selectable marker for cotransformation experiments, but these results suggest that its behavior might be treacherous.