Worm Breeder's Gazette 12(4): 63 (October 1, 1992)

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.

Genetic Characterization of srf Heterochronic Mutants Reveals a Relationship with ts Dauer-Constitutive Mutants.

David G. Grenache, Samuel M. Politz

Department of Biology and Biotechnology, Worcester Polytechnic Institute, Worcester, MA

Seven independent srf mutants that express an L1 -specificcuticle antigen at inappropriate stages (referred to as srf heterochronic mutants for convenience) have been characterized genetically. In immunofluorescence tests, L1 -specificmonoclonal antibody M37 binds to the surface of live wild-type L1 'sand heterochronic srf mutant L1 -L4larval stages but not to adults. The expression of an antigenic O-linked glycoprotein is altered in these mutants [Hemmer, et al, J. Cell Biol. 5, 1237-1247 (1991)].

Five of the mutations show linkage to chromosome II visible markers, and three of these map near dpy-10 in three-factor crosses with dpy-10 and unc-4 .Four of these, yj15 , yj41 , yj43 and yj5 fail to complement the reference mutation yj13 ,suggesting that they are all alleles of the same gene, now referred to as srf-6 .These five mutants show no distinct phenotype besides the srf heterochronic phenotype.

In contrast, the remaining two mutations show linkage to dpy-1 III and have a temperature-sensitive dauer-constitutive (daf-c) phenotype in addition to the srf heterochronic phenotype. Like other known daf-c mutants, yj11 and yj12 grow normally at 16°, but form dauers when grown at 25°. yj11 fails to complement daf-7 III for the daf-c phenotype (Patrice Albert and Don Riddle, personal communication). Based on these results, we tested the reference allele of each of the previously characterized daf-c genes daf-1 , daf-2 , daf-4 , daf-7 , daf-8 , daf-11 ,and daf-14 for the srf heterochronic phenotype. Mutant stocks were grown at the permissive temperature, 16°, to prevent constitutive dauer formation and permit examination of all other post-embryonic stages. Surprisingly, in immunofluorescence tests, all of these daf-c mutants, with the exception of daf-2 ( e1370 ),bound monoclonal antibody M37 at larval stages L1 -L4but not as adults, just as the srf-6 mutants did.

These experiments suggest that the pathways for dauer formation and temporal control of surface marker expression have some steps in common. Interestingly, the temperature-sensitive period for dauer formation brackets the L1 molt [Swanson and Riddle, Dev. Biol 86, 27-40 (1981)], the same time at which switching of L1 -specificsurface marker expression appears to occur.

However, none of the five srf-6 alleles shows a ts daf-c phenotype, suggesting that the srf phenotype can be altered without affecting dauer formation. Conversely, daf-2 ( e1370 )mutants only bind M37 at the L1 stage, indicating that at least one daf-c gene can be altered without affecting surface marker expression. Lastly, the daf-c mutants show the srf heterochronic phenotype when grown at 16°, even though the daf-c phenotype is not expressed at this temperature.

The daf-c genes have been proposed to be involved in a signal transduction process that evaluates environmental signals and leads to dauer formation under appropriate conditions; indeed, daf-1 encodes a putative receptor transmembrane serine/threonine protein kinase [Georgi, Albert, and Riddle, Cell 61, 635-645 (1990)]. The evidence described above suggests that these same daf-c genes are also involved in a distinct process, timing of stage-specific surface marker expression.

Literature Cited:

Hemmer, et al, J. Cell Biol. 5, 1237-1247 (1991).

Patrice Albert and Don Riddle, personal communication.

Swanson and Riddle, Dev. Biol 86, 27-40 (1981).

Georgi, Albert, and Riddle, Cell 61, 635-645 (1990).