Frogs in research
Encyclopedia
Frogs have been used in animal tests throughout the history of biomedical science.
Eighteenth-century biologist Luigi Galvani
discovered the link between electricity
and the nervous system
through studying frog
s. The African clawed frog
or platanna, Xenopus laevis, was first widely used in laboratories in pregnancy assays in the first half of the 20th century. When human chorionic gonadotropin
, a hormone
found in substantial quantities in the urine
of pregnant women, is injected into a female X. laevis, it induces them to lay egg
s. In 1952 Robert William Briggs and Thomas Joseph King cloned a frog by somatic cell nuclear transfer
, the same technique that was later used to create Dolly the Sheep
, their experiment was the first time successful nuclear transplantation had been accomplished in metazoans.
An unexpected consequence of the use of Xenopus laevis for pregnancy tests was apparently the widespread release of a serious amphibian disease. X. laevis carries a chytrid fungus known as Batrachochytrium dendrobatidis, native to South Africa. X. laevis itself does not show symptoms from carrying this fungus, but the fungus is deadly to many amphibians outside of South Africa. Xenopus laevis frogs were exported around the world in large quantities beginning in the 1930s for use in the pregnancy test. Within a few decades, escaped populations of X. laevis were living in many countries of the world, and in the 1970s, many amphibian biologists began noting mysterious declines in frog populations in South America, Central America and Australia, the declines spreading in a pattern that suggested an infectious disease. The disease has since been identified as B. dendrobatidis. It has caused several species extinctions and is thought to be the major cause of the worldwide decline in amphibians. The chytrid fungus has recently reached North America. In 2004, Weldon et al. identified Xenopus laevis and the pregnancy test as the likely source of this worldwide calamity. ("Origin of the Amphibian Chytrid Fungus", Emerging Infectious Diseases 10(12), 2004)
Frogs are used in cloning research and other branches of embryology
because frogs are among the closest living relatives of man to lack egg shells characteristic of most other vertebrates, and therefore facilitate observations of early development. Although alternative pregnancy assays have been developed, biologists continue to use Xenopus as a model organism
in developmental biology
because it is easy to raise in captivity and has a large and easily manipulatable embryo. Recently, X. laevis is increasingly being displaced by its smaller relative X. tropicalis, which reaches its reproductive age in five months rather than one to two years (as in X. laevis), facilitating faster studies across generations. The genome sequence
of X. tropicalis is scheduled to be completed by 2015 at the latest.
Eighteenth-century biologist Luigi Galvani
Luigi Galvani
Luigi Aloisio Galvani was an Italian physician and physicist who lived and died in Bologna. In 1791, he discovered that the muscles of dead frogs legs twitched when struck by a spark...
discovered the link between electricity
Electricity
Electricity is a general term encompassing a variety of phenomena resulting from the presence and flow of electric charge. These include many easily recognizable phenomena, such as lightning, static electricity, and the flow of electrical current in an electrical wire...
and the nervous system
Nervous system
The nervous system is an organ system containing a network of specialized cells called neurons that coordinate the actions of an animal and transmit signals between different parts of its body. In most animals the nervous system consists of two parts, central and peripheral. The central nervous...
through studying frog
Frog
Frogs are amphibians in the order Anura , formerly referred to as Salientia . Most frogs are characterized by a short body, webbed digits , protruding eyes and the absence of a tail...
s. The African clawed frog
African clawed frog
The African clawed frog is a species of South African aquatic frog of the genus Xenopus. Its name is derived from the three short claws on each hind foot, which it uses to tear apart its food...
or platanna, Xenopus laevis, was first widely used in laboratories in pregnancy assays in the first half of the 20th century. When human chorionic gonadotropin
Human chorionic gonadotropin
Human chorionic gonadotropin or human chorionic gonadotrophin is a glycoprotein hormone produced during pregnancy that is made by the developing embryo after conception and later by the syncytiotrophoblast .. Some tumors make this hormone; measured elevated levels when the patient is not...
, a hormone
Hormone
A hormone is a chemical released by a cell or a gland in one part of the body that sends out messages that affect cells in other parts of the organism. Only a small amount of hormone is required to alter cell metabolism. In essence, it is a chemical messenger that transports a signal from one...
found in substantial quantities in the urine
Urine
Urine is a typically sterile liquid by-product of the body that is secreted by the kidneys through a process called urination and excreted through the urethra. Cellular metabolism generates numerous by-products, many rich in nitrogen, that require elimination from the bloodstream...
of pregnant women, is injected into a female X. laevis, it induces them to lay egg
Egg (biology)
An egg is an organic vessel in which an embryo first begins to develop. In most birds, reptiles, insects, molluscs, fish, and monotremes, an egg is the zygote, resulting from fertilization of the ovum, which is expelled from the body and permitted to develop outside the body until the developing...
s. In 1952 Robert William Briggs and Thomas Joseph King cloned a frog by somatic cell nuclear transfer
Somatic cell nuclear transfer
In genetics and developmental biology, somatic-cell nuclear transfer is a laboratory technique for creating a clonal embryo, using an ovum with a donor nucleus . It can be used in embryonic stem cell research, or, potentially, in regenerative medicine where it is sometimes referred to as...
, the same technique that was later used to create Dolly the Sheep
Dolly the Sheep
Dolly was a female domestic sheep, and the first mammal to be cloned from an adult somatic cell, using the process of nuclear transfer. She was cloned by Ian Wilmut, Keith Campbell and colleagues at the Roslin Institute near Edinburgh in Scotland...
, their experiment was the first time successful nuclear transplantation had been accomplished in metazoans.
An unexpected consequence of the use of Xenopus laevis for pregnancy tests was apparently the widespread release of a serious amphibian disease. X. laevis carries a chytrid fungus known as Batrachochytrium dendrobatidis, native to South Africa. X. laevis itself does not show symptoms from carrying this fungus, but the fungus is deadly to many amphibians outside of South Africa. Xenopus laevis frogs were exported around the world in large quantities beginning in the 1930s for use in the pregnancy test. Within a few decades, escaped populations of X. laevis were living in many countries of the world, and in the 1970s, many amphibian biologists began noting mysterious declines in frog populations in South America, Central America and Australia, the declines spreading in a pattern that suggested an infectious disease. The disease has since been identified as B. dendrobatidis. It has caused several species extinctions and is thought to be the major cause of the worldwide decline in amphibians. The chytrid fungus has recently reached North America. In 2004, Weldon et al. identified Xenopus laevis and the pregnancy test as the likely source of this worldwide calamity. ("Origin of the Amphibian Chytrid Fungus", Emerging Infectious Diseases 10(12), 2004)
Frogs are used in cloning research and other branches of embryology
Embryology
Embryology is a science which is about the development of an embryo from the fertilization of the ovum to the fetus stage...
because frogs are among the closest living relatives of man to lack egg shells characteristic of most other vertebrates, and therefore facilitate observations of early development. Although alternative pregnancy assays have been developed, biologists continue to use Xenopus as a model organism
Model organism
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 organism model will provide insight into the workings of other organisms. Model organisms are in vivo models and are widely used to...
in developmental biology
Developmental biology
Developmental biology is the study of the process by which organisms grow and develop. Modern developmental biology studies the genetic control of cell growth, differentiation and "morphogenesis", which is the process that gives rise to tissues, organs and anatomy.- Related fields of study...
because it is easy to raise in captivity and has a large and easily manipulatable embryo. Recently, X. laevis is increasingly being displaced by its smaller relative X. tropicalis, which reaches its reproductive age in five months rather than one to two years (as in X. laevis), facilitating faster studies across generations. The genome sequence
Genome project
Genome projects are scientific endeavours that ultimately aim to determine the complete genome sequence of an organism and to annotate protein-coding genes and other important genome-encoded features...
of X. tropicalis is scheduled to be completed by 2015 at the latest.