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 (1934), who realized that
ligation of the head of immature insects could prevent
molting 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 ligated abdomen or an abdomen under
diapause 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 (in some insects the
corpus allatum 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 glands, which respond by releasing
molting hormone (an
ecdysteroid) 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'' 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 and
PDGF. 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 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