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The zebrafish has become a favorite organism for genetic analysis of vertebrate development, but methods for generating mutants by reverse genetic approaches have been lacking. We report a method to obtain stable mutants of a gene based on knowledge of the gene sequence only. Parental fish were mutagenized with N-ethyl-N-nitrosourea; in 2679 [F.sub.1] fish, the rag1 gene was analyzed for heterozygous mutations by resequencing. In total, we found 15 mutations: 9 resulted in amino acid substitutions and 1 resulted in a premature stop codon. This truncation mutant was found to be homozygous viable and defective in V(D)J joining. Although presumably immune deficient, these homozygous rag1 mutant fish are able to reach adulthood and are fertile. As sperm samples from all 2679 [F.sub.1] fish were collected and cryopreserved, we have in principle generated a mutant library from which mutants of most zebrafish genes can be isolated., Forward genetic screens in the zebrafish have identified thousands of mutants defective in many kinds of biological processes (1, 2). Cloning of the affected genes is accelerated by both an [...]

Posttranscriptional gene silencing in Caenorhabditis elegans results from exposure to double-stranded RNA (dsRNA), a phenomenon designated as RNA interference (RNAi), or from co-suppression, in which transgenic DNA leads to silencing of both the transgene and the endogenous gene. Here we show that single-stranded RNA oligomers of antisense polarity can also be potent inducers of gene silencing. As is the case for co-suppression, antisense RNAs act independently of the RNAi genes rde-1 and rde-4 but require the mutator/RNAi gene mut-7 and a putative DEAD box RNA helicase, mut-14. Our data favor the hypothesis that gene silencing is accomplished by RNA primer extension using the mRNA as template, leading to dsRNA that is subsequently degraded., RNA interference (RNAi) in animals, co-suppression in plants, and quelling in fungi appear to be manifestations of cellular defense mechanisms against the invasion of foreign nucleic acids such as viruses [...]

Over the past two decades, the small soil nematode Caenorhabditis elegans has become established as a major model system for the study of a great variety of problems in biology and medicine. One of its most significant advantages is its simplicity, both in anatomy and in genomic organization. The entire haploid genetic content amounts to 100 million base pairs of DNA, about 1/30 the size of the human value. As a result, C. elegans has also provided a pilot system for the construction of physical maps of larger animal and plant genomes, and subsequently for the complete sequencing of those genomes. By mid-1995, approximately one-fifth of the complete DNA sequence of this animal had been determined. Caenorhabditis elegans provides a test bed not only for the development and application of mapping and sequencing technologies, but also for the interpretation and use of complete sequence information. This article reviews the progress so far toward a realizable goal--the total description of the genome of a simple animal., Caenorhabditis elegans has many attractive features as an experimental system[1]. The life cycle is simple and rapid, with a 3-day generation time, and populations can be grown with ease on [...]

The goa-1 gene encoding the alpha subunit of the heterotrimeric guanosine triphosphate-binding protein (G protein) [G.sub.o] from Caenorhabditis elegans is expressed in most neurons, and in the muscles involved in egg laying and male mating. Reduction-of-function mutations in goa-1 caused a variety of behavioral defects including hyperactive movement, premature egg laying, and male impotence. Expression of the activated [G.sub.o] alpha subunit [Gα.sub.o]) in transgenic nematodes resulted in lethargic movement, delayed egg laying, and [reduced mating efficiency. Induced expression of activated [Gα.sub.o] in adults was sufficient to cause these phenotypes, indicating that [Gα.sub.o] mediates behavior through its role in neuronal function and the functioning of specialized muscles., The heterotrimeric G protein [G.sub.o] is abundantly expressed in mammalian and insect neurons and growth cones, suggesting that it is important for both neuronal development and function (1). Although G. [...]

Genomes are databases sensitive to invasion by viruses. In recent years, a defense mechanism has been discovered, which turns out to be conserved among eukaryotes. The system can be compared to the immune system in several ways: It has specificity against foreign elements and the ability to amplify and raise a massive response against an invading nucleic acid. The latter property is beginning to be understood at the molecular level., All genomes of complex organisms are potential targets of invasion by viruses and transposable elements. Forty-five percent of the human genome consists of remnants of previous transposon/virus invasions and elements [...]