PTTH
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Prothoracicotropic hormone (PTTH) was the first insect
hormone A hormone (from the Ancient Greek, Greek participle , "setting in motion") is a class of cell signaling, signaling molecules in multicellular organisms that are sent to distant organs or tissues by complex biological processes to regulate physio ...
to be discovered. It was originally described simply as "brain hormone" by early workers such as Stefan Kopeć (1922) and
Vincent Wigglesworth Sir Vincent Brian Wigglesworth CBE FRS (17 April 1899 – 11 February 1994) was a British entomologist who made significant contributions to the field of insect physiology. He established the field in a textbook which was updated in a number o ...
(1934), who realized that
ligation Ligation may refer to: * Ligation (molecular biology), the covalent linking of two ends of DNA or RNA molecules * Chemical ligation, the chemoselective condensation of unprotected peptides * In medicine, the making of a ligature (tie) * Tubal liga ...
of the head of immature insects could prevent
molting In biology, moulting (British English), or molting (American English), also known as sloughing, shedding, or in many invertebrates, ecdysis, is a process by which an animal casts off parts of its body to serve some beneficial purpose, either at ...
or
pupation A pupa (; : 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 life cycle, the stages th ...
of the body region excluded from the head if the ligation was performed before a critical age in the lifestage was reached. After a certain point the ligation had no effect and both sections of the insect would molt or pupate. However, implantation of a
conspecific Biological specificity is the tendency of a characteristic such as a behavior or a biochemical variation to occur in a particular species. Biochemist Linus Pauling stated that "Biological specificity is the set of characteristics of living organism ...
brain to a
sessile Sessility, or sessile, may refer to: * Sessility (motility), organisms which are not able to move about * Sessility (botany), flowers or leaves that grow directly from the stem or peduncle of a plant * Sessility (medicine), tumors and polyps that ...
ligated abdomen or an abdomen under
diapause In animal dormancy, diapause is the delay in development in response to regular and recurring periods of adverse environmental conditions.Tauber, M.J., Tauber, C.A., Masaki, S. (1986) ''Seasonal Adaptations of Insects''. Oxford University Press It ...
would induce molting or pupation. Thus, the brain was originally thought to be the source of the hormone that induces molting in insects. Later it was established that the
insect brain The supraesophageal ganglion (also "supraoesophageal ganglion", "arthropod brain" or "microbrain") is the first part of the arthropod, especially insect, central nervous system. It receives and processes information from the first, second, and t ...
produces a number of hormones, but the hormone which was the cause of the observations made by Kopeć and Wigglesworth was prothoracicotropic hormone. PTTH is secreted by a neurohemal organ, the
corpus cardiacum Corpus (plural ''corpora'') is Latin for "body". It may refer to: Linguistics * Text corpus, in linguistics, a large and structured set of texts * Speech corpus, in linguistics, a large set of speech audio files * Corpus linguistics, a branch of ...
(in some insects the
corpus allatum In insect physiology and anatomy, the corpus allatum (plural: corpora allata) is an endocrine gland that generates juvenile hormone; as such, it plays a crucial role in metamorphosis. Surgical removal of the corpora allata (an allatectomy) can caus ...
secretes PTTH) which is actually a discrete structure posterior to the brain. PTTH is released in response to environmental stimuli and as its name implies PTTH acts on the
prothoracic gland The prothoracic glands are either of a pair of endocrine glands located in the prothorax of certain insects that regulate molting. They have an ectodermal origin and secrete ecdysteroids, such as ecdysone Ecdysone is a prohormone of the major in ...
s, which respond by releasing
molting hormone Ecdysone is a prohormone of the major insect molting hormone 20-hydroxyecdysone, secreted from the prothoracic glands. It is of steroidal structure. Insect molting hormones (ecdysone and its homologues) are generally called ecdysteroids. Ecdys ...
(an
ecdysteroid Ecdysteroids are arthropod steroid hormones that are mainly responsible for molting (ecdysis), development and, to a lesser extent, reproduction; examples of ecdysteroids include ecdysone, 20-hydroxyecdysone (ecdysterone), turkesterone and 2- ...
) into the
haemolymph Hemolymph, or haemolymph, is a fluid, similar to the blood in invertebrates, that circulates in the inside of the arthropod's body, remaining in direct contact with the animal's tissues. It is composed of a fluid plasma in which hemolymph ce ...
. Molting hormone stimulates the molting process. PTTH was first purified and identified from the silkworm ''
Bombyx mori ''Bombyx mori'', commonly known as the domestic silk moth, is a moth species belonging to the family Bombycidae. It is the closest relative of '' Bombyx mandarina'', the wild silk moth. Silkworms are the larvae of silk moths. The silkworm is of ...
'' by Hiroshi Kataoka and colleagues with his menters Hironori Ishizaki and Akinori Suzuki in 1990. PTTH adopts the fold unique to the structural superfamily of the
growth factors A growth factor is a naturally occurring substance capable of stimulating cell proliferation, wound healing, and occasionally cellular differentiation. Usually it is a secreted protein or a steroid hormone. Growth factors are important for regu ...
, such as NGF,
TGF-β Transforming growth factor beta (TGF-β) is a multifunctional cytokine belonging to the transforming growth factor superfamily that includes three different mammalian isoforms (TGF-β 1 to 3, HGNC symbols TGFB1, TGFB2, TGFB3) and many other ...
and
PDGF Platelet-derived growth factor (PDGF) is one among numerous growth factors that regulate cell growth and division. In particular, PDGF plays a significant role in blood vessel formation, the growth of blood vessels from already-existing blood ...
. The
receptor Receptor may refer to: * Sensory receptor, in physiology, any neurite structure that, on receiving environmental stimuli, produces an informative nerve impulse *Receptor (biochemistry), in biochemistry, a protein molecule that receives and respond ...
of PTTH on the prothoracic glands is a
tyrosine kinase A tyrosine kinase is an enzyme that can transfer a phosphate group from ATP to the tyrosine residues of specific proteins inside a cell. It functions as an "on" or "off" switch in many cellular functions. Tyrosine kinases belong to a larger cla ...
Torso.{{Cite journal , last1=Rewitz , first1=Kim F. , last2=Yamanaka , first2=Naoki , last3=Gilbert , first3=Lawrence I. , last4=O’Connor , first4=Michael B. , date=2009-12-04 , title=The Insect Neuropeptide PTTH Activates Receptor Tyrosine Kinase Torso to Initiate Metamorphosis , url=https://www.science.org/doi/10.1126/science.1176450 , journal=Science , language=en , volume=326 , issue=5958 , pages=1403–1405 , doi=10.1126/science.1176450 , pmid=19965758 , bibcode=2009Sci...326.1403R , issn=0036-8075, url-access=subscription


References

Insect hormones