Worm Breeder's Gazette 12(3): 101 (June 15, 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.

mec-8 :Phenotypic and Suppressor Analysis of a Gene Involved in Embryonic Development and Sensory Neuron Development and Function

Erik A. Lundquist, Claire M. Kari, Robert K. Herman

University of Minnesota-St. Paul, St. Paul, MN 55108

Homozygous mec-8 I mutants are defective in the touch response (Chalfie and Au, 1989, Science 243: 1027-1033), or mechanosensation (the Mec phenotype); exhibit fasciculation defects in chemosensory neuron processes (Perkins et al., 1986, Dev. Biol. 117: 456487), which affect the ability of the neurons to fill with fluorescent dyes (the Dyf phenotype); and are viable and fertile. Most mec-8 animals are non-Unc, but a few animals in each brood display an uncoordination.

Based upon the proportion, relative to N2 ,of phasmid neurons filling with the dye DiO, the eight mec-8 alleles can be placed in a series of severity. The least severe alleles are u218 , e398 and u303 ,showing filling from 17% to 5% of N2 .The most severe alleles are rh170 and u456 ,with filling of 1% and 0% respectively. The phasmid Dyf phenotypes of u218 , e398 and u303 over a deficiency ( mnDf111 ) are more severe than the homozygous phenotypes, whereas the phenotypes of rh170 and u456 over mnDf111 are similar to those of the homozygous alleles. Thus, rh170 and u456 show characteristics of null alleles, but the null phenotype of mec-8 is still unknown.

In addition, mec-8 mutations display a synthetic lethal phenotype with viable unc-52 mutations; mec-8 ; unc-52 (viable)animals arrest at the two-fold stage of elongation, show lumps and constrictions in the hypodermis, and are paralyzed (the Pat phenotype). This interaction is gene-specific and allele-non-specific. The Pat phenotype is characteristic of defects in the body wall musculature (B. Williams and R. Waterston, pers.comm.). unc-52 is involved in the attachment of body wall muscle cells to the basement membrane, and unc-52 encodes a probable component of the basement membrane (T. Rogalski and D. Moerman, pers.comm.). Viable unc-52 alleles display a progressive paralysis posterior to the pharynx, and lethal unc-52 alleles show a Pat phenotype (B. Williams and R. Waterston, pers.comm). Thus, a mec-8 mutation enhances the attachment defect of an unc-52 mutation, suggesting that mec-8 plays a role in muscle cell attachment.

We sought to isolate suppressors of mec-8 to identify interacting loci that may be involved in cell adhesion. mec-8 ( u218 ); unc-52 ( e669s u250)(ts alleles of each locus) are viable at 15°C and lethal at 25°C. We have used this observation to isolate suppressors of the synthetic lethality of mec-8 ; unc-52 . mec-8 ( u218 ); unc-52 ( e669s u250)animals were mutagenized, grown at 15° C for at least two generations and switched to 25°C. Surviving animals were isolated for study. By this method, 17 suppressors were isolated. They were grouped into three classes, all of which suppress the synthetic lethality: class I (4) suppress the individual phenotypes of mec-8 and unc-52 (are non-Mec, non-Dyf and nonUnc), class II (7) suppress only the unc-52 phenotype (are Mec, Dyf and non-Unc), and Class III (6) suppress only the lethality. We have chosen the class I suppressors for further study. Based upon suppression of unc-52 ,these four mutants fall into two complementation groups: mn415 , mn417 and mn433 are allelic and map to the right arm of LGI, near unc-101 ( mn415 complements unc-101 ). mn416 defines another locus and maps to LGII, probably on the left arm. In a mec-8 ; unc-52 background, suppressed animals are very slow and slightly uncoordinated, but not paralyzed. mn415 and mn417 in an unc-52 (+)background show no visible phenotype, although mec-8 is still suppressed in this background.

Experiments to clone mec-8 are under way. mec-8 maps 0.3 map unit to the right of unc-29 and very close but to the left of hP6 ,a Tc 1 dimorphism (Starr et al. 1989, Genome 3 2, no. 3, 365-372); 1/27 crossovers between unc-29 and hP6 was also between mec-8 and hP6 .The region spanning unc-29 and hP6 is included in the physical map, and we will attempt to identify a cosmid clone from this region that rescues the mec-8 phenotype.

Literature Cited:

Chalfie and Au, 1989, Science 243: 1027-1033

Perkins et al., 1986, Dev. Biol. 117: 456487

Starr et al. 1989, Genome 3 2, no. 3, 365-372