Most animal testing involves invertebrates , especially Drosophila melanogaster , a fruit fly, and Caenorhabditis elegans , a nematode. These animals offer scientists many advantages over vertebrates, including their short life cycle, simple anatomy and the ease with which large numbers of individuals may be studied. Invertebrates are often cost-effective, [1] as thousands of flies or nematodes can be housed in a single room.
With the exception of some cephalopods in the European Union, invertebrate species are not protected under most animal research legislation, and therefore the total number of invertebrates used remains unknown. [2]
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Research on invertebrates is the foundation for current understanding of the genetics of animal development. C. elegans is especially valuable as the precise lineage of all the organism's 959 somatic cells is known, giving a complete picture of how this organism goes from a single cell in a fertilized egg, to an adult animal. [3] The genome of this nematode has also been fully sequenced and any one of these genes can easily be inactivated through RNA interference, by feeding the worms antisense RNA. [4] A major success in the work on C. elegans was the discovery that particular cells are programmed to die during development, leading to the discovery that programmed cell death is an active process under genetic control. [5] The simple nervous system of this nematode allows the effects of genetics on the development of nerves to be studied in detail. [6] However, the lack of an adaptive immune system and the simplicity of its organs prevent C. elegans from being used in medical research such as vaccine development. [3]
The fly D. melanogaster is the most widely used animal in genetic studies. This comes from the simplicity of breeding and housing the flies, which allows large numbers to be used in experiments. Molecular biology is relatively simple in these organisms and a huge variety of mutant and genetically modified flies have been developed. [7] Fly genetics has been vital in the study of development, the cell cycle, behavior, and neuroscience. The similarities in the basic biochemistry of all animals allows flies to be used as simple systems to investigate the genetics of conditions such as heart disease and neurodegenerative disease. [8] [9] However, like nematodes, D. melanogaster is not widely used in applied medical research, as the fly immune system differs greatly from that found in humans, [10] and diseases in flies can be very different from diseases in humans. [11]
Other uses of invertebrates include studies on social behavior.
Drosophila is a genus of flies, belonging to the family Drosophilidae, whose members are often called "small fruit flies" or pomace flies, vinegar flies, or wine flies, a reference to the characteristic of many species to linger around overripe or rotting fruit. They should not be confused with the Tephritidae, a related family, which are also called fruit flies ; tephritids feed primarily on unripe or ripe fruit, with many species being regarded as destructive agricultural pests, especially the Mediterranean fruit fly.
A model organism is a non-human species that is extensively studied to understand particular biological phenomena, with the expectation that discoveries made in the model organism will provide insight into the workings of other organisms. Model organisms are widely used to research human disease when human experimentation would be unfeasible or unethical. This strategy is made possible by the common descent of all living organisms, and the conservation of metabolic and developmental pathways and genetic material over the course of evolution.
Caenorhabditis elegans is a free-living transparent nematode about 1 mm in length that lives in temperate soil environments. It is the type species of its genus. The name is a blend of the Greek caeno- (recent), rhabditis (rod-like) and Latin elegans (elegant). In 1900, Maupas initially named it Rhabditides elegans. Osche placed it in the subgenus Caenorhabditis in 1952, and in 1955, Dougherty raised Caenorhabditis to the status of genus.
Drosophila melanogaster is a species of fly in the family Drosophilidae. The species is often referred to as the fruit fly or lesser fruit fly, or less commonly the "vinegar fly" or "pomace fly". Starting with Charles W. Woodworth's 1901 proposal of the use of this species as a model organism, D. melanogaster continues to be widely used for biological research in genetics, physiology, microbial pathogenesis, and life history evolution. As of 2017, five Nobel Prizes have been awarded to drosophilists for their work using the insect.
A genetic screen or mutagenesis screen is an experimental technique used to identify and select individuals who possess a phenotype of interest in a mutagenized population. Hence a genetic screen is a type of phenotypic screen. Genetic screens can provide important information on gene function as well as the molecular events that underlie a biological process or pathway. While genome projects have identified an extensive inventory of genes in many different organisms, genetic screens can provide valuable insight as to how those genes function.
Howard Robert Horvitz ForMemRS NAS AAA&S APS NAM is an American biologist best known for his research on the nematode worm Caenorhabditis elegans, for which he was awarded the 2002 Nobel Prize in Physiology or Medicine, together with Sydney Brenner and John E. Sulston, whose "seminal discoveries concerning the genetic regulation of organ development and programmed cell death" were "important for medical research and have shed new light on the pathogenesis of many diseases".
Under the law of dominance in genetics, an individual expressing a dominant phenotype could contain either two copies of the dominant allele or one copy of each dominant and recessive allele. By performing a test cross, one can determine whether the individual is heterozygous or homozygous dominant.
Cynthia Jane Kenyon is an American molecular biologist and biogerontologist known for her genetic dissection of aging in a widely used model organism, the roundworm Caenorhabditis elegans. She is the vice president of aging research at Calico Research Labs, and emeritus professor of biochemistry and biophysics at the University of California, San Francisco (UCSF).
Balancer chromosomes are a type of genetically engineered chromosome used in laboratory biology for the maintenance of recessive lethal mutations within living organisms without interference from natural selection. Since such mutations are viable only in heterozygotes, they cannot be stably maintained through successive generations and therefore continually lead to production of wild-type organisms, which can be prevented by replacing the homologous wild-type chromosome with a balancer. In this capacity, balancers are crucial for genetics research on model organisms such as Drosophila melanogaster, the common fruit fly, for which stocks cannot be archived. They can also be used in forward genetics screens to specifically identify recessive lethal mutations. For that reason, balancers are also used in other model organisms, most notably the nematode worm Caenorhabditis elegans and the mouse.
The nematode worm Caenorhabditis elegans was first studied in the laboratory by Victor Nigon and Ellsworth Dougherty in the 1940s, but came to prominence after being adopted by Sydney Brenner in 1963 as a model organism for the study of developmental biology using genetics. In 1974, Brenner published the results of his first genetic screen, which isolated hundreds of mutants with morphological and functional phenotypes, such as being uncoordinated. In the 1980s, John Sulston and co-workers identified the lineage of all 959 cells in the adult hermaphrodite, the first genes were cloned, and the physical map began to be constructed. In 1998, the worm became the first multi-cellular organism to have its genome sequenced. Notable research using C. elegans includes the discoveries of caspases, RNA interference, and microRNAs. Six scientists have won the Nobel prize for their work on C. elegans.
A behaviour mutation is a genetic mutation that alters genes that control the way in which an organism behaves, causing their behavioural patterns to change.
Jonathan Alan Hodgkin is a British biochemist, Professor of Genetics at the University of Oxford and an emeritus fellow of Keble College, Oxford.
Genetics of aging is generally concerned with life extension associated with genetic alterations, rather than with accelerated aging diseases leading to reduction in lifespan.
Caenorhabditis elegans- microbe interactions are defined as any interaction that encompasses the association with microbes that temporarily or permanently live in or on the nematode C. elegans. The microbes can engage in a commensal, mutualistic or pathogenic interaction with the host. These include bacterial, viral, unicellular eukaryotic, and fungal interactions. In nature C. elegans harbours a diverse set of microbes. In contrast, C. elegans strains that are cultivated in laboratories for research purposes have lost the natural associated microbial communities and are commonly maintained on a single bacterial strain, Escherichia coli OP50. However, E. coli OP50 does not allow for reverse genetic screens because RNAi libraries have only been generated in strain HT115. This limits the ability to study bacterial effects on host phenotypes. The host microbe interactions of C. elegans are closely studied because of their orthologs in humans. Therefore, the better we understand the host interactions of C. elegans the better we can understand the host interactions within the human body.
Worm bagging is a process by which C. elegans eggs hatch within the parent and the larvae proceed to consume and emerge from the parent.
Abby F. Dernburg is a Professor of Cell and Developmental Biology at the University of California, Berkeley, an Investigator of the Howard Hughes Medical Institute, and a Faculty Senior Scientist at Lawrence Berkeley National Laboratory.
The Drosophila quinaria species group is a speciose lineage of mushroom-feeding flies studied for their specialist ecology, their parasites, population genetics, and the evolution of immune systems. Quinaria species are part of the Drosophila subgenus.
Eileen Southgate is a British biologist who mapped the complete nervous system of the roundworm Caenorhabditis elegans, together with John White, Nichol Thomson, and Sydney Brenner. The work, done largely by hand-tracing thousands of serial section electron micrographs, was the first complete nervous system map of any animal and it helped establish C. elegans as a model organism. Among other projects carried out as a laboratory assistant at the Medical Research Council Laboratory of Molecular Biology (MRC-LMB), Southgate contributed to work on solving the structure of hemoglobin with Max Perutz and John Kendrew, and investigating the causes of sickle cell disease with Vernon Ingram.
Paul W. Sternberg is an American biologist. He does research for WormBase on C. elegans, a model organism.
Warwick Llewellyn Nicholas (1926-2010) was an Australian zoologist known as a pioneer in the field of nematology. He was a foundational member of the Australian Society for Parasitology (ASP) and in 1964, he organised the first ASP meeting. He became President of the Society in 1978, before being an elected Fellow from 1979.
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