Invertebrate hormones
Physiological systems in insects:Marc J.Klowden.Secondedition, ISBN: 978-0-12-369493-5.
Insect Endocrinology:LawrenceI. Gilbert.First edition2012, ISBN: 978-0-12-384749-2.
Bi1100 Hormones – Cellular and Molecular Mechanisms
The most developed endocrine system among invertebrates can be found in
crustaceans and insects.
Differences:
▪ unlike vertebrates, invertebrates have many neurohormones
▪ invertebrates produce few classical hormones
Similarities:
▪ both groups synthesize many peptide hormones
▪ the same structural types of hormones
▪ similar hormones can have similar function (hormones can also affect
individuals in another animal group)
Hormones of invertebrates and vertebrates
Nerves - neurotransmitters
Neurosecretory cells - neurohormones
Endocrine glands - clasical hormones
1) Steroid hormones (ecdysteroids - ecdysone, 20-hydroxyecdysone,
makisteron A etc.)
2) Sesquiterpenes / terpenoids (juvenile hormones)
3) Peptide hormones (MIH, RPCH, AKH)
4) Biogenic amines (octopamine, tyramine, serotonin)
5) Eicosanoids (prostaglandins and others)
Modulation of activity: synthesis, secretion, degradation, number and specificity
of receptors
Groups of invertebrate hormones
Endocrine system of crustaceans
Endocrine system of crustaceans
1) Neurosecretory complex of the eye:
▪ X-organ (neurosecretory cells) >
axonal transport > sinus gland
(neurohemal) > hemolymph
2) Suboesophageal-postcommissural
system:
▪ suboesophageal ganglion > axons
> postcommissural organ
(neurohemal) > hemolymph
3) Pericardial system:
▪ pericardium > pericardial organ
(neurohemal)
4) Paired Y-organ
▪ 20-hydroxyecdysone
5) Androgenic gland
▪ males
▪ Y-organ: 20-hydroxyecdysone (the same function as in insects)
▪ X-organ: moult inhibiting hormone (MIH) > inhibition of Y-organ
androgen gland inhibiting hormone > inhibition of
spermatogenesis and development of male characteristics
▪ X-organ + postcommissural system: chromatophorotropins (e.g. red
pigment-concentrating hormone belonging to RPCH/AKH family > pigment
relocation in omatidia, ovarian maturation, vitellogenesis and other functions)
Endocrine system of crustaceans
Endocrine system of insects
Endocrine system of insects
1) Retrocerebral complex
▪ neurosecretory brain cells, corpora cardiaca,
corpora allata
▪ sometimes connected with prothoracic gland
forming the so-called ring gland
(Weismann‘s ring)
▪ monopolar neurons produce hormones in
their bodies > association with proteins >
axonal transport > formation of membranebound
secretory granules > exocytosis
(synaptoids) > release at the site of synthesis
or in neurohemal organs
2) Prothoracic gland (PG)
▪ paired, located in prothorax and head
▪ usually not in adult stages
3) Neurosecretory cells of other ganglia
4) Intestinal endocrine cells
5) Epitracheal cells (ecdysis triggering hormone)
Endocrine system of insects
- brain dissection in Galleria mellonella
Endocrine system of insectsEndocrine system of insects
- brain dissection in Galleria mellonella
Corpus cardiacum (corpora cardiaca)
▪ main neurohemal organ derived from ectoderm
▪ posteriorly from the brain, in the contact with dorsal vein
▪ axons of central (part intercerebralis) and lateral (variable location)
neurosecretory cells in the brain
▪ storage lobe (storage of neurosecretory products)
▪ glandular lobe (synthesis of hormones)
Releases and synthesises:
▪ prothoracicotropic hormone (PTTH)
▪ adipokinetic hormones (AKH)
▪ ovarian ecdysteroidogenic hormone
▪ neuroparsins
▪ myotropins
▪ pheromone biosynthesis activating neuropeptide (PBAN)
Insect neurohemal organs
Corpus allatum (corpora allata)
▪ posterior area of ​​the head near the pharynx
▪ sometimes merges with prothoracic gland and forms ring gland (Diptera,
Hemiptera)
▪ ectodermal origin
▪ cells with smooth endoplasmic reticulum (cholesterol, terpenoids)
Synthesizes:
▪ juvenile hormones (JH)
Insect neurohemal organs
Steroids:
▪ ecdysteroids (prothoracic gland, gonads, epidermis)
Terpenoids:
▪ juvenile hormones (corpora allata)
Peptides and proteins:
▪ prothoracicotropic hormone (PTTH; brain)
▪ eclosion hormone (EH; brain)
▪ pre-ecdysis triggering hormone (PETH; Inka cells)
▪ ecdysis triggering hormone (ETH; Inka cells)
▪ bursikon (brain and ventral nerve cord)
▪ pheromone biosynthesis activating neurohormone (PBAN)
▪ adipokinetic hormones (AKH; corpora cardiaca)
▪ crustacean cardioactive peptide (CCAP)
▪ and many more (hundreds of them is described)
Insect endocrine system:
Summary of the main hormones
Groups of neuropeptides by genome coding:
1) Preprohormones containing signal peptide and neuropeptide (eclosion
hormone, neuroparsins)
2) Preprohormones containing signal peptide, neuropeptide and other
structurally unrelated peptides (AKH + bombyxins)
3) Preprohormones containing signal peptide and a number of copies of the
same or a similar neuropeptide (isoforms; e.g. allatostatins)
Groups of neurohormones by function:
▪ adenotropic (glandotropic), gonadotropic, morphogenetic, chromotropic,
metabolic and homeostatic, myotropic, etotropic etc.
▪ usually pleiotropic effect
Insect endocrine system:
General characteristics of neuropeptides
Insect metamorphosis
terpenoids
peptide
steroids
Insect metamorphosis
▪ the first insect hormone that was discovered
▪ insulin-like peptide (homodimer consisting of two identical amino acid chains
interconnected with disulfide bonds)
▪ synthetised by neurosecretory cells in the brain
▪ axonal transport and release in neurohemal organs (corpora cardiaca/allata)
▪ development and control of metamorphosis
▪ photoperiod (Manduca sexta), temperature (Hyalophora cecropia), nerve
stimulus (blood-sucking bug Rhodnius: blood volume is the primary stimul >
enlarged abdomen > receptor signal > PTTH synthetised in the brain)
▪ activates prothoracic gland and synthesis of ecdysteroids through cAMP, Ca2+,
calmodulin and phosphorylation of specific proteins (exact mechanism still
unknown)
Insect metamorphosis:
Prothoracicotropic hormone (PTTH)
Insect metamorphosis:
Prothoracicotropic hormone (PTTH)
Insect metamorphosis:
Prothoracicotropic hormone (PTTH)
What can one brain do? (Williams1952)
The transformation (B) was induced by the implantation of one brain into the
first pupa without the brain (A).
▪ non-polar
▪ derived from cholesterol or plant sterols (zoophagous x phytophagous:
ecdysone, makisteron A, 20-hydroxyecdysone and others)
▪ controls the metamorphosis, molting of embryos, larvae, nymphs and
reproduction of adults
Insect metamorphosis:
Ecdysteroids (molting hormones)
▪ ecdysone (E) keto group on the B ring and five OH groups
▪ 20-E (main molting hormone; six OH groups)
▪ makisterone A (24-methyl-20-hydroxyecdysone; e.g. Heteroptera,
Hymenoptera, Diptera)
▪ synthesis in larvae: prothoracic gland vs. adults: accessory glands (main
source of ecdysteroids), epithelial cells and ovarian follicles
▪ regulated by PTTH, ovarian ecdysteroidogenic hormone, prothoracicostatin
described in some insect species, excretion by Malpighian tubes
▪ transported in hemolymph by carriers or freely (↑OH > sufficiently soluble)
▪ conversion of E to 20-E in target tissues (epidermis, fat body, intestine,
ovaries…)
▪ nuclear receptors (ecdysteroid receptor); non-covalent dimers EcR/USP
(ultraspiracle protein, RXR homolog)
Insect metamorphosis:
Ecdysteroids – synthesis and release
makisteron Aecdysone
Metamorphosis:
▪ ecdysteroids control the expression of hundreds of genes (e.g. DOPA
decarboxylase), circadian fluctuations of E are related to PTTH level
▪ in larvae, the titer increases before apolysis of old cuticle
▪ larva-imago: Hemimetabola - large dose of ecdysteroids neccessary
Lepidoptera - often two doses of ecdysteroids
E : 20-E = 1 : 1 > reprogaming of larval development and behavior change
E : 20-E = 1 : 5 > triggers larval molting and transformation into pupa
▪ delayed secretion during the diapause
Insect metamorphosis:
Ecdysteroids – function
Reproduction:
▪ synthetised also in ovaries and stored conjugated in eggs > embryonic molts
▪ increase vitellogenin synthesis in the fat body and its secretion into the
hemolymph (20-E; Diptera)
▪ stimulation of meiosis, maturation of oocytes and oviposition
▪ spermatogenesis and formation of spermatophore
Metabolism and diapause:
▪ stimulation of proteosynthesis, etc.
▪ in relation to the above mentioned functions
Insect metamorphosis:
Ecdysteroids – function
Insect metamorphosis:
Juvenile hormones (JH)
▪ formerly known as neotenin
▪ structurally terpenoids (sesquiterpenes, derivatives of farnesol): methyl ester
group + epoxy group
▪ non-polar (enter cells and bind to nuclear receptors)
▪ JH-I, JH-II, JH-III, JH-0, 4-methyl-JH-I, juvenile hormone acid, methyl
farnesoate (their use is species specific)
Insect metamorphosis:
Juvenile hormones (JH)
▪ produced in corpora allata
▪ cholesterol synthesis-like biosynthesis
▪ not stored, released into the hemolymph immediately after synthesis (the
mechanism is not yet known)
▪ lipophorine juvenile hormone binding/carrier protein (JHBP/JHCP)
▪ regulated by allatostatin, allatotropin, negative feedback loop
▪ degradation by specific enzymes (JH esterases and epoxide hydrolases),
excretion by Malphigian tubes
▪ mode of action is assumed similar to steroid hormones
▪ receptors for JH in target cells have not yet been precisely identified
(intracellular proteins methoprene-tolerant / germ cell expressed)
Insect metamorphosis:
Juvenile hormones (JH) – function
Metamorphosis:
▪ embryogenesis, larval molting, metamorphosis, ending of larval and adult
diapause
▪ JH protects larval brain from reprograming and thus the onset of
metamorphosis, keeps the insect in the larval stage
▪ presence of JH at critical time points in the development or reaching the
threshold concentration
▪ critical body size > JH titer reduction
Insect metamorphosis:
Juvenile hormones (JH) – function
Reproduction:
▪ inhibitory during the larval stage, stimulates gene expression in adults
▪ synthesis of vitellogenins, development of ovaries and oocytes
▪ stimulation of the accessory glands in adult males to growth and secrete
▪ pheromone production in males and reproductive behavior of both sexes
▪ aging (D. melanogaster)
Polymorphism:
▪ social-caste: higher titer drives development of dominant individuals (queen
bees)
▪ phase: solitary vs. gregarious locusts (different color or size of ovaries);
development of parthenogenetic female aphids
↓ JH
gregarious
↑ JH
solitary
Insect metamorphosis:
Juvenile hormones (JH) – function
▪ synthesis of vitellogenins in Aedes aegypti
▪ polar peptides, homologues of cardioactive peptides (CAPs)
▪ synthesis in endocrine epitracheal glands close to spiracles (Inka cells)
▪ etotropic effect, acts directly on the CNS
▪ coordinate the molting and abandoning of the old cuticle
Ecdysis triggerign hormone (ETH)
Pre-ecdysis triggering hormone (PETH)
Eclosion hormone
▪ polar peptide
▪ synthesis in the brain and abdominal ganglia; in part secreted in hindgut
▪ its synthesis is induced by ecdysteroids
▪ acts in the CNS through cGMP
▪ supports the secretion of ETH, PETH, bursicon and others
▪ mediates positive feedback during ecdysis
▪ stimulates molting, hatching (eclosion) and supporting behaviour
Bursicon
▪ large polar protein (approx. 30 kDa)
▪ produced by ganglia and stored in corpora cardiaca
▪ acts on the cuticle and epidermis
▪ wing formation, coloring and hardening of the new cuticle
▪ hatching of adult Glossina morsitans morsitans (tse-tse)
Eclosion hormone (EH)
Bursicon
Hormones regulating metabolism
Adipokinetic hormones (AKH)
▪ RPCH/AKH family of peptide hormones
▪ homologs of vertebrate glucagon
▪ mediate stress reactions, activate metabolism for energy release (inhibit
synthesis), stimulate flight, movement and immune response
Synthesis and transport:
▪ okta- to decapeptides
▪ glandular lobe of corpora cardiaca, in part neurosecretory brain cells
▪ stored in the storage lobe of corpora cardiaca
▪ specific mRNA > prepro-AKH (signal peptide + AKH sequence + sequence of
another peptide)
Adipokinetic hormones (AKH)
Regulation:
▪ stimulated by movement and stress conditions (e.g. infection with pathogen)
▪ level of metabolites and negative feedback (high lipids > ↓ / low trehalose > ↑)
▪ regulated and degraded by membrane-bound endopeptidases
Effect:
▪ specific AKHR (e.g. fat body) > cAMP > Ca2+ > PKC > TAG > DAG
activated lipases
Adipokinetic hormones (AKH)
▪ activation of glycogen phosphorylase and fat metabolism, stimulation of
trehalose release (hypertrehalosemic hormones) from the fat body > switch
from carbohydrate metabolism to lipid metabolism
▪ increased heart activity and muscle contraction
▪ support immune response, stimulate antioxidant reactions
▪ inhibition of lipid, protein and RNA synthesis
▪ inhibition of oocyte maturation
Insulin-like peptides (ILP)
▪ evolutionarily conserved (structure with disulfide bonds)
▪ neurosecretory cells in the brain and other ganglia
▪ linked to receptor with tyrosine kinase activity > phosphorylation of
receptor substrate > signal via PI3K and other pathways
▪ metabolism, growth, immunity, reproduction, aging etc.
▪ glycogen and lipid metabolism (AKH antagonist)
IPCs - DILP-producing cells
DILP - Drosophila insulin-like peptide
Diuretic (DH) and antidiuretic (ADH) hormones
Diuretic hormones:
▪ corpora cardiaca, suboesophageal and thoracic ganglia
▪ stimulate diuresis in Malpighian tubules:
1) homologs of corticotropin releasing factor (CRF; vertebrate
neuropeptide family) stimulating Na/K transport in Malpighian tubules
via cAMP
2) calcitonin-like (CT-like) peptides
3) myokinins acting via Ca2+ and changing the channel throughput for Cl(Na,
K)
▪ they are also involved in meconium excretion after adult hatching
Antidiuretic hormones:
▪ abdominal nerves
▪ stimulate the reabsorption of water from the intestine into the hemolymph
▪ e.g. neuroparsin (antigonadotropin, antidiuretic activity, increases the
concentration of lipids and trehalose in the hemolymph)
Diapause hormones
▪ peptide structurally similar to PBAN (pheromone biosynthesis activating
neuropeptide) produced in female suboesophageal ganglion and transported
to ovaries
▪ moreover, pheromonotropic and myotropic effect
▪ stimulation of embryonic diapause by supporting glycogen storage in oocytes
and activation of trehalase
Diapause hormones
▪ diapause is also controlled by PTTH, ecdysteroids and JH
▪ diapause mechanisms are connected to molecular clock mechanisms
Gonadotropic hormones
▪ ovarian and testes development, vitellogenesis, transport of storage
molecules from the fat body to the ovaries and others
▪ key role of ecdysteroids and juvenile hormones, involvement of
neuropeptides
1) Stimulatory:
▪ prothoracicotropic hormone (PTTH)
▪ ovary maturing parsin (OMP) – stimulates synthesis of ecdysteroids and Vg
▪ folicle cell tropic hormone (FTCH) – synthesis of ecdysteroids in ovaries
▪ egg development neurohormone / ovarian ecdysteroidogenic hormone
(EDNH / OEH) - alternates PTTH in adults, produced in brain and stored in
corpora cardiaca
2) Inhibitory:
▪ neuroparsin – inhibits corpora allata and the production of juvenile hormones
▪ oostatic hormones and trypsin-modulating oostatic factor (folliclostatins) –
inhibits production of ecdysteroids, JH and EDNH
Tyramine and octopamine
▪ equivalents of adrenaline and noradrenalin in vertebrates
▪ the only non-peptidic hormones found only in invertebrates
▪ autocrine in prothoracic glands (interacts with PTTH)
▪ flight-or-fight response, energetic metabolism, muscle contraction, learning
and memory in bees, sensory neuron sensitivity (synaptic plasticity)
Biogenic amines of insects
Serotonin (5-hydroxytryptamine)
▪ mainly neurotransmitter
▪ present for instance in the CNS and
crustacean gonads
▪ stimulates reproduction (probably via
gonads-stimulating hormone, but the
exact mechanism is unknown)
Biogenic amines of insects