An imaginal disc is one of the parts of a

holometabolous Holometabolism, also called complete metamorphosis, is a form of insect development which includes four life stages: egg, larva, pupa, and imago (or adult). Holometabolism is a synapomorphic trait of all insects in the superorder Endopterygot ...

insect Insects (from Latin ') are pancrustacean hexapod invertebrates of the class Insecta. They are the largest group within the arthropod phylum. Insects have a chitinous exoskeleton, a three-part body ( head, thorax and abdomen), three pairs ...

larva A larva (; plural larvae ) is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle. The ...

that will become a portion of the outside of the adult insect during the

pupal transformation A pupa ( la, pupa, "doll"; plural: ''pupae'') is the life stage of some insects undergoing transformation between immature and mature stages. Insects that go through a pupal stage are holometabolous: they go through four distinct stages in their ...

. Contained within the body of the larva, there are pairs of discs that will form, for instance, the

wing A wing is a type of fin that produces lift while moving through air or some other fluid. Accordingly, wings have streamlined cross-sections that are subject to aerodynamic forces and act as airfoils. A wing's aerodynamic efficiency is expres ...

s or

leg A leg is a weight-bearing and locomotive anatomical structure, usually having a columnar shape. During locomotion, legs function as "extensible struts". The combination of movements at all joints can be modeled as a single, linear element ca ...

s or antennae or other structures in the adult. The role of the imaginal disc in insect development was first elucidated by

Jan Swammerdam Jan Swammerdam (February 12, 1637 – February 17, 1680) was a Dutch biologist and microscopist. His work on insects demonstrated that the various phases during the life of an insect—egg, larva, pupa, and adult—are different forms of the ...

. During the pupal stage, many larval structures are broken down, and adult structures, including the discs, undergo rapid development. Each disc everts and elongates, with the central portion of the disc becoming the distal part of whichever appendage it is forming: the wing, leg, antenna, etc. During the larval stage, the cells in the growing disc appear undifferentiated, but their developmental fate in the adult is already determined. The experiment that demonstrates this developmental commitment is to take an imaginal disc from a third instar larva, about to undergo pupation, and subdivide it and culture it in the body of a younger larva. Discs can be continuously cultured this way for many larval generations. When such a cultured disc is eventually implanted in the body of a larva that is allowed to pupate, the disc will develop into the structure it was originally determined to become. That is, an antenna disc can be cultured this way and will, almost always, become an antenna (out of place, of course) when final development is triggered by pupation. The study of imaginal discs in the fruit fly ''

Drosophila melanogaster ''Drosophila melanogaster'' is a species of fly (the taxonomic order Diptera) 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 Ch ...

'' led to the discovery of homeotic mutations such as antennapedia, where the developmental fate of a disc could sometimes change. It is of interest to entomologists that the kinds of developmental switches that occur are very specific (leg to antenna, for instance). Study of this phenomenon led to the discovery of the

homeobox A homeobox is a DNA sequence, around 180 base pairs long, that regulates large-scale anatomical features in the early stages of embryonic development. For instance, mutations in a homeobox may change large-scale anatomical features of the full- ...

genes, and started a revolution in the understanding of development in multi-celled animals.

Imaginal cells

Imaginal cells are tissue-specific progenitors allocated in

embryogenesis An embryo is an initial stage of development of a multicellular organism. In organisms that reproduce sexually, embryonic development is the part of the life cycle that begins just after fertilization of the female egg cell by the male sperm ...

that remain quiescent during embryonic and larval life. During ''Drosophila'' metamorphosis, most larval cells die. Pupal and adult tissues form from imaginal cells. Clonal analysis and fate mapping of single, identified cells show that tracheal system remodeling at metamorphosis involves a classical imaginal cell population and a population of differentiated, functional larval tracheal cells that reenter the cell cycle and regain developmental potency. In late larvae, both populations are activated and proliferate, spread over and replace old branches, and diversify into various stalk and coiled tracheolar cells under control of fibroblast growth factor signaling. Thus, ''Drosophila'' pupal/adult tissue progenitors can arise both by early allocation of multipotent cells and late return of differentiated cells to a multipotent state, even within a single tissue.

References

External links

Web site for the book ''Imaginal Discs: The Genetic and Cellular Logic of Pattern Formation'' by Lewis I. Held, Jr.
{{DEFAULTSORT:Imaginal Disc Insect anatomy Insect developmental biology

Imaginal cells

See also

References

Further reading

External links