[
Worm Breeder's Gazette,
2001]
RNAi is being used routinely to determine loss-of-function phenotypes and recently large-scale RNAi analyses have been reported (1,2,3). Although there is no question about the value of this approach in functional genomics, there has been little opportunity to evaluate reproducibility of these results. We are engaged in RNAi analysis of a set of 762 genes that are differentially expressed in the germline as compared to the soma (4 -- "Germline"), and have reached a point in our analysis that allows us to look at the issue of reproducibility. We have compared the RNAi results of genes in our set that were also analyzed by either Fraser et al. (1 -- Chromosome 1 set "C1") or Gonczy et al. (2 -- Chromosome 3 set "C3"). In making the comparison we have taken into account the different operational definition of "embryonic lethal" used by the three groups. In the C3 study, lethal was scored only if there were fewer than 10 surviving larva on the test plate, or roughly 90% lethal. In our screen and the C1 screen the percent survival was determined for each test. To minimize the contribution of false positives from our set, in our comparison with the C1 set we defined our genes as "embryonic lethal" if at least 30% of the embryos did not hatch, but included all lethals defined by Fraser et al. (> 10%). For our comparison with the C3 set, we used a more restrictive definition of "embryonic lethal" that required that 90% of the embryos did not hatch. (This means that in Table 1, five genes from our screen that gave lethality between 30-90% were included in the not lethal category; one of these was scored as lethal by Gonczy et al.). We have analyzed 149 genes from the germline set that overlap with the C1 set and 132 genes that overlap with the C3 set. The table below shows the number of genes scored as embryonic lethal (EL) or not embryonic lethal (NL) in each study. (Note that these comparisons do not include data from our published collection of ovary-expressed cDNAs.) Table 1. Comparing RNAi analysis of the same genes in different studies. Germline Chromosome 1 Germline Chromosome 3 NL (117) EL (32) NL (97) EL (35) NL (104) 100 4 NL (89) 87 2 EL (45) 17 28 EL (43) 10 33 Overall, the degree of reproducibility is high. The concordance between our results and the published results was 86% with C1 (128/149 genes) and 90% with C3 (120/132). However, we scored a larger number of genes as giving rise to embryonic lethal phenotypes than the other studies did. What does this mean? One possibility is that we are generating a large number of false positives (God forbid!). The other interpretation is that there is a fairly high frequency of false negatives in each screen (4-8% in our screen (2/45; 4/49); 22% in the C3 screen (10/45); and 35% (17/49) in the C1 screen). It is no surprise that the different methods used by the three groups resulted in slightly different outcomes and we can only speculate on which methodological variation contributed most. In comparing our methods to those used in the C3 study we note that our two groups used different primer pairs for each gene; that we tested genes individually while they tested genes in pairs; and that the operational definition of "embryonic lethal" differed. Considering the latter two differences, we speculate that even with pools of two, the competition noted by Gonczy et al. in dsRNA pools could reduce levels of lethality below the 90% cutoff. The major difference between our approach and the C1 approach is feeding vs. injection, raising the possibility that for some genes feeding may be a less effective means of administering dsRNA. Whatever the basis for the difference, these comparisons indicate that genes scored as "non-lethal" in any single study may show an embryonic lethal RNAi phenotype when reanalyzed. It therefore seems useful to have more than one pass at analyzing C. elegans genes via RNAi. We are indebted to P. Gonczy for very useful comments. Fraser, A. G., Kamath, R. S., Zipperlen, P., Martinez-Campos, M., Sohrmann, M. and Ahringer, J. (2000). Functional genomic analysis of C. elegans chromosome I by systematic RNA interference. Nature 408 , 325-330. Gonczy, P., Echeverri, G., Oegema, K., Coulson, A., Jones, S. J., Copley, R. R., Duperon, J., Oegema, J., Brehm, M., Cassin, E. et al. (2000). Functional genomic analysis of cell division in C. elegans using RNAi of genes on chromosome III. Nature 408 , 331-336. Piano, F., Schetter, A. J., Mangone, M., Stein, L. and Kemphues, K. J. (2000). RNAi analysis of genes expressed in the ovary of Caenorhabditis elegans. Curr Biol 10 , 1619-1622. Reinke, V., Smith, H. E., Nance, J., Wang, J., Van Doren, C., Begley, R., Jones, S. J., Davis, E. B., Scherer, S., Ward, S. et al. (2000). A global profile of germline gene expression in C. elegans. Mol Cell 6 , 605-616.
[
Worm Breeder's Gazette,
1986]
The
hsp70A gene (referred to previously as the
hsp70 class A gene) is both a heat inducible and a developmentally expressed
hsp70 gene. Sequencing of the
hsp70A gene has been completed in an effort to determine the similarities to a Drosophila heat inducible
hsp70 gene ( Ingolia, et. al., Cell 21, 669 (1980)) and to a developmentally expressed, or cognate,
hsp70 gene (
hsc4; M. Slater and E.A. Craig, pers. commun.) which is also induced upon heat shock. We have found: (1) At the 5' region of the
hsp70A gene, there are three heat shock elements (HSE; Pelham, Cell 30, 517 (1982)). (2) Within the transcribed region, there are a total of three introns (IS1, 49 bp; IS2 194 bp; IS3, 55 bp). (3) At the 3' end of the gene, there appears to be a second, overlapping gene which has transcription and translation starts before the polyA addition site for the
hsp70A gene. (4) The
hsp70A amino acid sequence exhibits more homology with the
hsc4 protein (79%) than with the heat inducible protein (71%). (5) There is more homology of the carboxy terminus of the
hsp70A amino acid sequence with the
hsc4 amino acid sequence than with the heat inducible
hsp70 amino acid sequence. The carboxy terminus appears to 'define' the type of function for each
hsp70 gene. The
hsp70A gene is expressed at high levels during development and its expression is increased two to six fold higher upon heat shock. The
hsp70A mRNA appears to be the major
hsp70 mRNA during both development and heat shock (T. Snutch, Ph.D. Thesis, Simon Fraser University, 1984). The
hsc4 gene is also expressed at high levels during development and its expression is increased two fold upon heat shock. It is also the major
hsp70 mRNA during development and during heat shock (Palter, et. al., MCB 6, 1187 (1986)). Based upon the amino acid homologies and the similarities in expression, we believe that the
hsp70A gene is analogous to the
hsc4 gene from Drosophila. We predict that mutations of the
hsp70A gene will be one of two types. The first could be lethal due to the lack of an essential
hsp70 protein. The second could be 'temperature sensitive'. That is, a mutation with no effects at low temperatures because the function of the
hsp70A gene would be compensated for by other genes but lethal at higher temperatures when the
hsp70A gene function cannot be compensated for. The
hsp70A gene has been mapped to the right arm of LGIV approximately 0.1 mu to the left of
dpy-4 ( Snutch, et. al., submitted) using RFLDs. A search for mutations in this area will be done to define alleles of
hsp70A.
[
Worm Breeder's Gazette,
1988]
lin-3 is a gene necessary for the Vulval Precursor Cells (VPCs; a.k. a. P(3-8).p) to form the vulva in response to a graded inductive signal from the anchor cell. In hermaphrodites carrying Vulvaless ( Vul) alleles of
lin-3, induction of the VPCs is lowered or absent such that the vulva can not form and the animal is unable to lay eggs. We are interested in
lin-3 because epistasis tests between Vulvaless and Multivulva mutations affecting vulval development indicate that
lin-3 acts early in the pathway of vulval development. In addition, other alleles of
lin-3 have lethal and sterile phenotypes, indicating that
lin-3 has functions other than vulval induction. A F1 screen for new
lin-3 alleles was carried out to determine its null phenotype.
lin-3(
e1417); 90) males were mated to EMS-mutagenized
unc-24(
e138) 38)
dpy-20(
e1282) hermaphrodites and the F1 cross progeny were screened for egg-laying defective worms. Since
e1417/Df is viable, null alleles could be recovered in this screen. Three early larval lethal alleles (
sy51,
sy52,
sy53) of
lin-3 were found among 10,000 F1 progeny. A similar F1 screen by Chip Ferguson ( Genetics 110:17-72 1985) of 20,000
e1417/? F1 generated the lethal allele
n1059 and the sterile/larval lethal allele
n1058. Because larval lethal alleles are recovered more commonly than Vulvaless alleles in these screens, we believe that larval lethality is the null phenotype. Denise Clark et al. at Simon Fraser, in their analysis of lethals on LG IV, identified two late larval mutations,
s751 and
s1263, allelic to
lin-3. In agreement with the hypothesis that the null phenotype of
lin-3 is early larval lethal, they showed that the phenotype of
s751/Df and
s1263/Df is also early larval lethal ( Genetics 119: 345-353 1988). We are pursuing two approaches to clone
lin-3. Our first approach is to generate transposon-induced alleles of
lin-3. So far, one putative Tc-induced allele,
sy91, was detected by mating
lin-3(
e1417); 90) males to RW7096 [
mut-6 lin-3(+) 192::Tc1) ] hermaphrodites and picking nonUnc egg- laying defective F1. In contrast to the alleles found in the EMS F1 screens, this allele confers a Vul phenotype.
sy91 is currently being backcrossed to see if a new Tc band can be correlated with the Vul phenotype. Our second approach is to map
lin-3 with respect to cloned DNA in an attempt to define a region of DNA that must contain
lin-3. We have been mapping
lin-3 to sP5, an RFLP on the right end of the contig L122, to determine whether L122 extends far enough to cover lin- 3. 22 Vul nonDpy recombinants were picked from
lin-3(
e1417) 362) /BO heterozygotes. All the recombinants possessed the N2 version of sP5. Therefore sP5 is probably to the left of, or close and to the right of,
lin-3. We are currently examining recombinants in the
mec-3 to
lin-3 interval to determine the map order.
[
Worm Breeder's Gazette,
1994]
Correlatina the Phvsical and Genetic MaDs on Chromosome III (Left) - A First step Diana Collins, Helen 1. Stewart and David L. Baillie, Institute of Molecular Biology and Biochemistry, Simon Fraser University, Burnaby, BC As reported in the June 1994 issue of the WBG, the sequencing consortium is rapidly completing the sequence of chromosome III. Concurrently, our lab has been generating a large number of new mutations in the region covered by the free duplication sDp3 (approximately 75% of chromosome III, leftl (1). These mutations include EMS induced point mutations in essential genes and small, UV/Gamma induced deletions (see H. Stewart et al, this issue). In collaboration with the C. elegans genome sequencing consortium, specifically the St. Louis lab, our lab has begun the task of correlating the genetic and physical maps on the left arm of chromosome III. As a first step toward this goal, I have been micro injecting cosmid DNA received from St. Louis (my thanks to P. Latreille) into N2 hermaphrodites to create stable transgenic strains carrying specific sequenced cosmids. It is our intention to use these transgenic strains to cross these cosmids into various mutant strains and observe if the DNA is able to rescue the mutant phenotype. In this manner we will be able to place a large number of genetic markers on the physical map. Germline transformation is performed as per Mello et al. (1991), with cosmid DNA normally being injected at an approximate concentration of 20 ng/ul Prior to injection, cosmid DNA is mixed with the plasmid pCes 1943 to form an injection mixture having a total DNA concentration of approximately 100 ng/ul . pCes 1943 is derived from the plasmid pRF4 (2). It contains the dominant
rol-6(sulO06) allele (3), and has been modified to contain a kanR cassette. Transformant strains which stabily give
rol-6 progeny are PCR tested to confirm the presence of cosmid DNA. It has been my observation that approximately one stable
rol-6 transformant in four does not contain cosmid DNA. So far I have produced transgenic strains from 22 cosmids: C06E8, C06G4, C14B9 C18H2, C29E4, C30C5, D2007, F08F8, FllH8, F31E3, F37C12, F44B9, K06H7, K07D8, R151, R13A5, T04A6, T20B12, T20H4, T21 D11, ZK652, and ZK688. Although there are a few cosmids left of
mec-14 which I have not been able to successfully inject (due to problems with DNA availability or possible dosage effects), these transgenic strains represent a reasonably continuous stretch of DNA approximately 654 000 bp long. Preliminary crosses between lethal bearing strains and cosmid-containing transformants have yet to reveal a cosmid rescue. However, as our newly generated mutations are further mapped with respect to previously generated physical markers, the task of choosing cosmids which are likely to rescue particular mutants will become easier. In the meantime we are making these transformant strains available to the C. elegans community. If you would like us to send you any of these strains please contact me at: dcollins@darwin.mbb.sfu.ca This research is being funded by a grant from the Canadian Genome and Associated Technologies (CGAT). 1) Collin, D H Stewart and D. L. Baillie 119941 WBG Vol 13 No 2 66 2) Mollo, C, J Kramer, D Stinchcomb, and V Ambros 119911 EMB0 J Vol 10 3959-3970 3) Kramer J M, E Fronch, E Park, and J Johnson 119901 Mol Coll 8iol Vol 10 2081-2089
[
Worm Breeder's Gazette,
1977]
A small free-living soil nematode is receiving close scrutiny from a growing number of biological researchers. Some of these investigators believe that Caenorhabditis me the E. coli or at least the bacteriophage T4 of the animal world. C. elegans is a small transparent worm about a millimeter in length. Its genes are carried on five autosomes and a sex chromosome (X), and it has a genome size about 20 times that of E. coli. It generally reproduces as a self-fertilizing hermaphrodite (XX), but occasional males (XO), which arise by nondisjunction, permit sexual reproduction as well. The worm's prime virtues for research are its short life cycle (3 days) , ease of cultivation on E. coli as a food source, simple anatomy ( 810 somatic nuclei) and convenience for genetic analysis. Building upon the pioneering work of Dougherty (1), Nigon (2), and especially Brenner (3), who first described the animal's genetics, there are now more than a dozen laboratories in Canada, France, Germany, India, Japan, the United Kingdom, and the United States that are investing heavily in studies of this organism. From April 13 to April 16, researchers from these laboratories gathered for the first time to assess the status of their investment at a conference in Woods Hole, Massachusetts, supported in part by a grant from the National Institute of Aging, NIH. Many investigators initially turned to C. elegans in the hope of understanding its behavior in terms of its simple nervous system. The status of this work was a major topic at the meeting. C. elegans contains only 256 neurons, and a complete anatomical description of the nervous system at the electron microscope level is virtually at hand. Previous work had allowed detailed reconstruction of the head anterior sensory neuroanatomy, the ventral nerve cord, and the associated dorsal cord composed of processes from cells in the ventral cord (4). At the meeting, John White (MRC Cambridge) described reconstruction of the complex nerve ring that surrounds the pharynx and presumably plays the major role in processing sensory inputs to produce motor outputs. D. Hall (Albert Einstein College of Medicine) presented a reconstruction of the tail ganglia carried out in R. Russell's laboratory at Caltech. As a result of these studies, a complete wiring diagram for the whole nervous system of the animal is now within reach. Due to its small size, the system's function cannot yet be approached directly by standard electrophysiological techniques, and must await technical advances in electrode technology or in optical methods using potential-sensitive dyes. Meanwhile, however, Tony Stretton (University of Wisconsin) has shown that the anatomy of the related nematode Ascaris, which is sufficiently large for conventional electrophysiological studies, is virtually identical to that of C. elegans at least in the ventral cord. John Walrond from Stretton's laboratory presented evidence on which of the seven types of motor neurons in the ventral cord are inhibitory and which stimulatory. As a taste of things to come, R. Russell (now at University of Pittsburgh) presented a model to account for control of movement in C. elegans based on its ventral cord circuitry. More complete and detailed nervous system models should become possible as more functional features of the anatomy become understood. Another approach to obtaining such functional information is the investigation in several laboratories of nematode neurotransmitters. Earlier work by J. Sulston (MRC, Cambridge) localized three catecholamine-containing neurons, but mutants that did not produce catecholamines showed no demonstrable alteration in behavior (5). C. Johnson (University of Wisconsin) reported that in Ascaris acetylcholine appears to function as an excitatory transmitter, on grounds that it is synthesized in excitatory but not in inhibitory motor neurons. Johnson also reported on work carried out in R. Russell's laboratory at Caltech on the identification of a C. elegans mutant defective in acetylcholinesterase and another defective in choline acetyltransferase (the latter isolated in the laboratory of D. Hirsh, University of Colorado, as resistant to the drug trichlorofon). Jim Lewis (Columbia University) reported on the properties of putative acetylcholine receptor mutants isolated as resistant to the acetylcholine analog levamisole. R. Horvitz (MRC, Cambridge) reported on the behavior of mutants that fail to accumulate serotonin normally in certain neurons. The combination of biochemical, genetic, anatomical, and physiological approaches being taken by these researchers seems certain to provide insight into the processing of neuronal signals in C. elegans, and eventually could lead to an understanding of the animal's behavior at the level of its neuroanatomy and neurophysiology. Recently many investigators have recognized the potential of C. elegans for the study of development. The major portion of the meeting was devoted to description of the worm's development at the cellular level, and to studies of mutations that perturb it. The adult animal has only 810 somatic nuclei in six major cell types ( hypodermis, muscle, neurons, gut, gonadal sheath, and coelomocytes), and its anatomy at the cellular level is virtually invariant. A current major effort in the descriptive work has been the determination of cell lineages, and an important result of the meeting was the prospect that the complete cell lineage of C. elegans soon will be established from the zygote to the adult animal. Upon hatching from the egg, the juvenile or first-stage larva has only 540 somatic cells. During larval development, about 200 post- embryonic cells arise from division of a few blast cells present at hatching. J. Sulston and R. Horvitz (MRC, Cambridge) had previously traced in detail the origins of these post-embryonic cells (6). Their lineage studies revealed a remarkable reproducibility from one animal to another in times of cell division, paths of cell migrations, cell deaths, and ultimate differentiated cell fates. In experiments reminiscent of Boveri's classical observations on Ascaris embryogenesis, E. Schierenberg and other workers in G. von Ehrenstein's laboratory (Gottingen) now have established cell lineage in the egg up to the 186-cell embryo. Their studies, carried out with the light microscope using differential interference contrast optics and time lapse video recording reveal that characteristic rates of cell division are maintained in different subclones, regardless of cell migrations. The Gottingen group also has made detailed reconstructions of a 294-cell and 540-cell embryo from electron micrographs of serial sections. Surprisingly, the 540-cell stage is reached quite early in embryogenesis, about midway between fertilization and hatching and prior to most of the cell growth and differentiation that takes place before hatching, indicating that cell division and migration precede differentiation per se. Nevertheless, from the correspondence between the positions of cells in the 540-cell embryo and first stage larva, von Ehrenstein has been able to identify most of the embryonic cells with regard to their future fates. There is optimism that the remaining gap, between the 186-cell and the 540- cell stages can be filled by a combination of light and electron microscopy, to provide for the first time a complete description at the cellular level of the development of an animal from the egg to adulthood. The post-embryonic lineage of the gonad somatic cells, not investigated by Sulston and Horvitz, now has been determined by J. Kimble (University of Colorado). The gonad arises during larval development from a 4-celled precursor structure in both the hermaphrodite and the male. In the hermaphrodite the two somatic cells of the precursor give rise to a total of 142 cells, which form the gonadal sheath, spermatheca, and uterus. In the male a similar lineage produces about 50 cells to form the spermatheca and vas deferens. As in other tissues, the lineages are invariant in their significant features. The lineage in another single organ, the intestine, has been followed by K. Lew working in S. Ward's laboratory (Harvard Medical School), taking advantage of a mutant discovered by P. Babu (Tata Institute, Bombay; 7) in which gut cells fluoresce due to a defect in tryptophan catacolism. Lew has traced the lineage of the gut cells, which begin to fluoresce during embryogenesis, from a single precursor cell in the 8-cell embryo through the 20-cell juvenile gut to the adult 32-cell gut. He also has found aberrations in the lineage pattern in certain embryonic lethal mutants. On a related project, P. Siddiqui in P. Babu's laboratory reported that X irradiation of embryos heterozygous for such a fluorescence mutation gave rise to adults with fluorescent patches in the gut, suggesting an approach to the study of somatic crossing over in C. elegans.The factors responsible for lineage patterns are being investigated using a laser to selectively destroy certain cells, or using mutations that alter lineage. The preliminary results so far reported suggest that whereas there are some inductive or positional effects of cell differentiation, much of the developmental process is cell-autonomous. Two examples of nonautonomy were reported by J. White (MRC, Cambridge). Neuroblast cells that in a particular mutant fail to migrate to the normal position fail to differentiate completely into nerve cells. Also, if gonad development is prevented by laser ablation of the precursor cells, then the hypodermal cells that normally proliferate to form the vulva fail to do so, By contrast, other studies revealed a remarkable degree of cell autonomy. D. Albertson (MRC, Cambridge) reported on the behavior of certain blast cells that normally undergo a migration followed by a pattern of division to form 6 neurons and a hypodermal cell. In a particular mutant strain the blast cells undergo up to three abortive attempts at division to yield a polyploid cell, which differentiates to display cellular features of both hypodermal and nerve cells. R. Horvitz (MRC, Cambridge) reported on current progress in the genetic dissection of lineage patterns. He has isolated a large number of mutants that are defective in vulva formation and hence cannot lay eggs. These mutants so far define 15 different genes in which defects appear to directly affect the vulval lineage pattern, by preventing either divisions or normal migrations of precursor cells. Two laboratories are investigating differentiation of sperm, which are amoeboid cells in C. elegans. A large number of temperature- sensitive sperm-defective mutants have been isolated by D. Hirsh ( University of Colorado; 8), and S. Ward (Harvard Medical School), and analysis of these mutants is proceeding. At non-permissive temperature, some mutants appear to be blocked early in spermatogenesis and form no sperm, whereas others produce normal numbers of inactive sperm. All the mutants can lay viable eggs when mated with normal males. Ward reported that male sperm migrate rapidly to the hermaphrodite spermatheca following copulation and effectively supplant the endogenous sperm. Sperm may be required for some step in oogenesis, because some sperm-defective mutants fail to produce oocytes alone, but will do so when mated to males. The abundance of mutants and the prospects for isolating sperm in quantity make this system promising for studying the genetic control of a cellular differentiation pathway. Development of the male is virtually identical to that of the hermaphrodite until some hours after hatching, when a few of the post- embryonic cell lines display a male-specific pattern of division, migration, and differentiation. Intersex and transformer mutants defective in genes that control these processes were described by M. Klass (University of Colorado), Ward, and J. Brun (Lyon, France). These mutants should prove useful in determining how the male developmental pattern is superimposed upon that of the hermaphrodite. A special feature of the C. elegans life cycle has been studied by D. Riddle (University of Missouri). Normally, the young hatched larva progresses through a series of four molts to adulthood. In the absence of food, however, the second molt produces a special form, the dauer larva, which has an altered cuticle and can withstand adverse conditions (e.g., 4% SDS) and no food for periods up to 60 days. When presented with food, the dauer larva molts and continues the normal progress toward adulthood. Riddle has identified 7 genes whose functions are involved in the choice between the regular and the dauer developmental pathways. Mutants defective in these genes are constitutive dauer formers which enter the dauer pathway even in the presence of food. Some of these mutants have defects in sensory neuronal anatomy. Mutant analysis indicates that a larger number of genes probably is essential for recovery of the dauer larva and return to the standard developmental pathway. Brenner had estimated earlier that C. elegans carries about 2000 genes (3), somewhat fewer than Drosophila. If so, then more than 10% of them already have been identified. R. Horvitz (MRC, Cambridge) has undertaken the task of collating mapping data from different laboratories, and reported that over 200 genes have been identified and mapped with various degrees of precision. This number promises to increase rapidly, because investigators in the laboratories of R. Herman (University of Minnesota), D. Baillie (Simon Fraser University) , and W. Wood (Caltech) are embarking on exhaustive studies of lethals in defined regions of the genome. This work will be aided greatly by the availability of chromosomal duplications, deficiencies, and translocations, some of which already have been isolated and characterized in Herman's laboratory for use as crossover suppressors and balancers for lethals. Herman also reported on the isolation of stable tetraploid strains and on the instability of triploids generated by crosses to diploids. These studies incidentally provide information on the sex-determining mechanism in C. elegans, which as in Drosophila depends upon the balance between the numbers of sex chromosomes and autosomes. Promising studies also were reported on molecular genetic analysis of genes for muscle proteins. A large number of mutants defective in myosin, paramyosin (Q protein of the thick filaments) and other muscle components previously had been reported by R. Waterston and H. Epstein while working in Brenner's laboratory (9). At the meeting, Epstein (Stanford University) reported on the anatomical and biochemical properties of C. elegans muscle. At least 6 genes have been identified as being involved in muscle development. Of these, 2 appear to be the structural genes for myosin and paramyosin. Epstein reported that at least 2 different myosins exist in the nematode, one in the body wall muscle and another in the pharynx. The identified myosin gene controls the structure of the body wall muscle myosin. Some 30 alleles of this gene have been found, including a small internal deletion. S. MacCleod (MRC, Cambridge) reported on biochemical mapping of the mutational alterations in defective myosins by chemical cleavage and peptide analysis. Myosin and paramyosin mutations also have provided possible genetic access to the translational apparatus of C. elegans. R. Waterston ( Washington University) has shown that revertants of certain myosin mutations carry a second site suppressor that suppresses chain- terminating mutations in the myosin and paramyosin genes and certain alleles in genes with other diverse functions. This suppressor mutation is a promising candidate for the first tRNA nonsense suppressor to be described in a metazoan organism. C. elegans also is well suited to studies on the phenomenon of aging, in view of its short life cycle and the existence of a non- aging developmental variant, the dauer larva (10). M. Klass ( University of Colorado) reported on the effects of nutrition and other parameters on life span, and D. Mitchell (Boston Research Institute) presented evidence for entrainment of increased life span by prolonged cultivation under semi-starved conditions. However, attempts to find mutations that directly alter the life span so far have failed, and progress in this general area has been minimal. In a panel discussion following the session on aging the participants agreed that C. elegans has many potential advantages as an aging model, but that fruitful approaches exploiting genetics have yet to be developed. Many other studies were presented in addition to those mentioned. In this brief summary we have attempted only to highlight what in our opinions were the major themes of a rich and exciting meeting. The group of investigators who gathered at Woods Hole is taking a somewhat unusual holistic and cooperative approach to understanding the biology of a single organism. The meeting was invaluable in bringing together senior researchers and students with backgrounds in molecular, cellular, developmental, and neurobiology, in fostering the spirit of cooperative and integrated inquiry, and in generating a mutual enthusiasm that will help to make C. elegans an important model organism for intensive biological study during the next few years.