Worm Breeder's Gazette 11(5): 76
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.
lin-4 is a heterochronic gene that controls the timing of a number of developmental events in C. elegans. The lin-4 allele (e912) causes a retarded phenotype that is virtually identical to that caused by lin-14(sd) mutations. Genetic epistasis experiments have suggested that lin-4 acts upstream of lin-14 in the heterochronic regulatory pathway. Gary Ruvkun's laboratory has shown that the temporal gradient of lin-14 protein, high to low from early to later in development, is disrupted in lin-4(e912) animals. In lin-4(e912) animals, the level of lin-14 protein remains high throughout development causing the reiteration of early cell fates. These data suggest that lin-4 is, at least in part, responsible for generating the temporal gradient of lin-14 activity. In order to further understand the role of lin-4 in the temporal control of development we have begun to isolate new alleles of this gene. The original lin-4(e912) allele was generated by [32P] decay over 10 years ago. Because no new alleles of lin-4 have been identified in numerous general screens for egl or vul animals (where they would have been expected to turn up) we wanted to establish the null phenotype of lin-4 prior to screening for point mutations in this gene. Unfortunately, no deficiencies existed that covered the lin-4 region of chromosome II. Therefore our first non-complementation screen was aimed at isolating a deficiency of the lin-4 locus. Wild type N2 males were mutagenized with gamma rays, mated by lin-4(e912) dpy-10/mnc1; 79ts) hermaphrodites and the F1 hermaphrodite progeny were screened at 20 C for non-dpy lin-4 like animals. Out of 7,000 F1 hermaphrodites screened, one lin-4 deletion mutant (maDf4) was identified. maDf4 is homozygous inviable and fails to complement lin-4, bli-2, analysis using a dissecting microscope, the phenotype of lin-4(e912) Df4 animals is indistinguishable from that of lin-4( e912)/lin-4(e912) animals (with the exception of an enhanced sterility of lin-4(e912) Df4 animals). These data suggest that the original lin-4(e912) allele is not a gain-of-function allele and indicates that lin-4(e912)/null is fertile and viable. Since lin- 4(e912)/maDf4 is not significantly different from lin-4(e912)/lin-4( e912), lin-4(e912) is probably a null allele. However, maDf4 does not delete spe-3, a gene that maps only 0.1 mu to the right of lin-4 and thus we are not yet certain that maDf4 completely deletes lin-4. Now that we have a lin-4 clone it will be possible to test this directly ( see Lee, Feinbaum and Ambros, this WBG). Encouraged that we knew the expected phenotype of lin-4(e912)/lin-4 null we have initiated a new series of non-complementation screens to identify EMS induced lin-4 alleles. A non-complementation screen identical to the one outlined above, except that the males were treated with EMS instead of gamma rays, was undertaken. Out of 8,000 F1 hermaphrodites screened we have identified 1 new lin-4 allele ( ma161). ma161 looks phenotypically similar to e912 but Southern blot analysis with our lin-4 clone has confirmed that it is in fact a new allele of lin-4. We intend to continue isolating new lin-4 alleles utilizing this non-complementation strategy.