For as long as there have been biomedical laboratories, animals and plants have been used for a variety of purposes, such as unravelling the mechanisms of living organisms and their diseases, producing compounds of interest or testing drugs and other substances. In the last case, animals are the obligatory step in what is known as pre-clinical testing prior to clinical trials on humans. The long historical tradition of using animals in science has made it common parlance to speak of guinea pigs, but the truth is that these animals are rarely used in modern science. Here we take a look at the species to which we owe much of today’s scientific knowledge.
Guinea pig (Cavia porcellus)
This rodent, native to the Andes, does not exist in the wild. It was domesticated in the Americas thousands of years ago as a source of meat and for ceremonial sacrifices. It was imported to Europe as a pet in the 16th century, and in the 17th century it began to be used in experiments because it was easy and quick to breed. Guinea pigs were instrumental in the study of the immune system and infectious diseases, including tuberculosis, and in 1907 they were used in the discovery of vitamin C, which they, like humans, need to get from their diet. In the middle of the 20th century, they began to be replaced by mice and rats. Today, their use is much less common, although they continue to be used for studies of allergies and respiratory diseases, nutrition, safety testing and research into the auditory system, which is very similar to ours.
House mouse (Mus musculus)
The house mouse is the most widely used animal model in laboratories today. They were first used in research in the 17th century, and in the 19th century the monk Gregor Mendel would have based his laws of genetics on them, had he not been forced to switch to pea plants after his superior complained that the animals smelled and copulated. In 1902, Lucien CuĂ©not applied Mendel’s laws to these animals, and in the same year, Harvard researchers William Ernest Castle and Clarence Cook Little began studying mouse genetics using animals bred as a hobby by Abbie Lathrop, who can be considered the mother of the laboratory mouse.
The lab mouse is not just any mouse. Thanks to Lathrop, Little created the DBA strain, the first pure line, created by cross breeding within the same family, and later the C57BL/6 strain, the most widely used in the world. Pure lines, essentially clones, allow experiments to be standardised. In 1929, Little founded The Jackson Laboratory (JAX), the first institute dedicated to breeding and selling mice for science. Today JAX maintains 13,000 strains and sells more than three million mice a year. C57BL/6 and others such as BALB/c or the immunodeficient NOD/SCID are the base strains of many of the most widely used lines. Researchers use them to create transgenic, knockout (gene-deficient) and other mutant lines (see figure).
Fancy rat (Rattus norvegicus domestica)
The lab rat is a domesticated subspecies of the brown or sewer rat. Their use in experiments began in the 19th century because they were readily available as pests. At the time, wild rats were used, but eventually they became the first domesticated animal used in laboratories. Most of today’s strains are derived from the Wistar albino rat, a variety created at the Wistar Institute in 1906. Pure lines, which are less common than in mice, have been created from this strain. Today, rodents account for 95% of all laboratory animals, with tens of millions of rats and mice used each year. Although mice are more widely used, rats are the preferred model in psychological studies and in biomedical research, where the rat’s larger organs are an advantage.
Common fruit fly (Drosophila melanogaster)
While laboratory rodents are the jack-of-all-trades of biomedicine, useful for the vast majority of research, certain animals have been adopted as ideal models for specific fields of science. Such is the case of the fruit fly, an insect of African origin first bred in the laboratory in 1901 by Charles Woodworth, who suggested its use for genetic studies to William Castle. In 1910, Thomas Hunt Morgan chose it for his studies on heredity and the effects of mutations. Although fruit flies are also used in other fields, they have been most useful in developmental and behavioural genetics. Scientists use countless mutants of these animals, which they often give names such as Ken and Barbie, Halloween or Indy.
Nematode Caenorhabditis elegans
In 1900, Ămile Maupas isolated a tiny, one-millimetre worm from the soil of Algeria that seemed destined to occupy not even a page in the history of science. But in the 1940s, the idea emerged that Caenorhabditis elegans could provide a useful model for genetic studies, and in 1963 Sydney Brenner adopted it to study neural development. The ease of breeding, handling and genetic modification of C. elegans, one of the simplest organisms with a nervous system, has made it the best known animal model: 959 cells, 302 of them neurons, whose entire map of connections or connectome is known; it was also the first multicellular organism whose entire genome was sequenced. The wealth of knowledge about this worm has extended its use to many fields of research, including molecular and cellular mechanisms, disease, ageing and others.
Arabidopsis thaliana
If the mouse is the king of animal models in biomedicine, Arabidopsis thaliana reigns supreme in plant biology. This small plant of the mustard family was first described by Johannes Thal in 1577. Native to Eurasia and Africa, it is widespread throughout the world and is considered a weed that grows in ditches and seems to be of little interest apart from the fact that it is edible. The first mutant varieties were observed in the 19th century, but it was not until 1943 that Friedrich Laibach proposed it as a model organism. By the 1980s its use had become widespread, including numerous inbred lines, for studies in genetics, evolution, development, plant cell and molecular biology, and others.
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