Rabbit antisera directed against a mixture of proteins solubilized from the wild-type adult Caenorhabdiis ekgans cuticle were used to isolate mutants, induced by ethyl methanesulfonate treatment, that exhibit alterations in surface antigenicity by immunofluorescence. Genetic mapping and complementation data for four such mutations define two genes, srf-2(I) and srf-3(IV). The nematode surface is antigenic in the infected host. The appearance of specific surface antigens is dynamic, with changes occurring at and between molts (4, 5). However, little is understood of the genetic mechanisms underlying surface antigen expression.The cuticle of the free-living nematode Caenorhabditis elegans has been studied by classical genetics. Mutations affecting cuticle structure include those that alter gross morphology (6-9), some of which are in collagen genes (10-13), and heterochronic mutations that cause expression of adult-specific cuticle features in larvae or vice versa (14-16). In addition, an adult-specific surface antigenic class is missing in certain C. elegans varietal strains; this marker maps to a locus designated srfl(II) (17).Little is known genetically about a characteristic feature of the nematode cuticle-i.e., its layered ultrastructural organization (e.g., ref. 18). We have isolated and analyzed several C. elegans surface antigen mutants that may have implications for understanding the layering pattern and the immune response to nematode parasites. MATERIALS AND METHODSPreparation of Immunogen and Antisera. Rabbit antisera directed against wild-type adult C. elegans cuticle proteins solubilized by SDS and 2-mercaptoethanol (2-ME) were prepared as described (19) Up to 10,000 synchronous F2 larvae were stained for immunofluorescence with L4-adsorbed antiserum and examined; only mutant larvae with alterations in surface antigenicity were expected to stain (17). Immunofluorescent Li to L4 larvae were individually picked. False positive clones were eliminated by rescreening. Only independent mutants were saved.Strains. Wild-type (strain N2) and mutant strains (6) of C. elegans var. Bristol were obtained from the Caenorhabditis elegans Genetics Center, Columbia, MO. sqt-J(scJOJ)II, sqt-J(e1350), sqt-J(sc97), sqt-1(sclOO), sqt-2(sc3)II, sqt-3(sc8)V, sqt-3(sc24), sqt-3(sc63), rol-8(scJ5)II, and rol-8(sc98) were obtained from R. S. Edgar (University of California, Santa Cruz) and were described in ref. 9. lin-JJ(n389)I was described in ref. 20. A strain containing sDf2(IV) (21) was genotypically sDf2/nTJ(IV); +/nTl(V) (22,23).Abbreviations: 2-ME, 2-mercaptoethanol; LI, L3, and L4, first, third, and fourth larval stage, respectively; EMS, ethyl methanesulfonate; PI, protease inhibitors. tTo whom reprint requests should be addressed.

Abstract. Mouse mAb M38 was used in indirect immunofluorescence experiments to detect a stagespecific antigen on the surface of the first larval stage (LI) of the free-living nematode Caenorhabditis elegans, and to detect alterations in the apparent expression of this antigen in two distinct classes of C. elegans mutants . In previously described srf-2 and srf-3 mutants (Pblitz S. M., M. T. Philipp, M. Estevez, P J. O'Brien, and K .

We have studied developmental stage-specificity and genetic specification of surface antigens in the nematode Caenorhabditis elegans. Rabbit antisera directed against the adult C. elegans cuticle were used in conjunction with antiserum adsorption experiments to obtain antibody reagents with specificity for the adult surface. Adult-specific antibodies were used to identify several varietal strains of C. elegans that display antigen-negative phenotypes as adults. Genetic mapping results using the surface antigen phenotype as a marker indicated that a single gene (designated srf-1) or cluster of genes on linkage group II determines the adult surface antigen phenotype.