Worm Breeder's Gazette 16(1): 54 (October 1, 1999)
Department of Genetics, University of Washington, Seattle, WA 98195
C. briggsae, a sister species of C. elegans, is capable of growth at higher temperatures, and does not form dauers at high temperatures in the absence of exogenous dauer pheromone. We would like to understand the genetic mechanisms underlying this difference. To this end, we have been isolating dauer formation mutants in C. briggsae.
sa973 was isolated as a Daf-c mutation in C. briggsae G16 (AF16) background. It forms ~50% dauers at 25° and forms 100% dauers at 27û. In addition, the mutant is Sma (small) and Mab (male abnormal — spicule is deformed. Ray abnormalities were not clear). The Sma phenotype is temperature-sensitive. The mutant is Sma at 25° but wild-type at 22°. The temperature sensitive period is between the L1 and the adult.
This combination of phenotypes (Daf-c, Sma, Mab) is seen only in daf-4 mutants in C. elegans. Thus, we tested for rescue of the sa973 mutation with a genomic clone of C. elegans daf-4 (provided by G. Ruvkun lab). Two transgenic arrays were made by coinjection of the daf-4 clone with myo-2::gfp, which seems to be a usable transformation marker for C. briggsae. At 25°, the transgenes rescued the Sma phenotype completely. However, no rescue of the Daf-c phenotype was observed at 27°.
This discrepancy may result from several causes, including lack of C.e. DAF-4 expression at the right level in the appropriate tissues for dauer regulation, or inability of the C. elegans DAF-4 to function at 27°. Alternatively, the mutation may affect some other unknown component of the dauer/body size regulation pathway, and the rescue is spurious or not by direct complementation.
We also isolated a cilium structure mutation in C. briggsae, sa934. In C. elegans, the cilium structure mutations comprise a class of >40 genes which affect dauer formation (Daf-d or dauer formation defective) and filling of amphid neurons by fluorescent dyes (Dyf ). Paradoxically, in addition to the Daf-d phenotype at lower temperatures (up to ~25°), all tested C. elegans cilium structure mutants are Daf-c at 27°. sa934, is Dyf and Daf-d. Unlike C. elegans cilium structure mutants, sa934 did not form any dauers at 27° and 29°.