Invertebrate Endocrinology
As You know:
► Invertebrates
are animals without a
backbone.
► The invertebrates form all of the major
divisions of the animal kingdom called
phyla, with the exception of vertebrates.
► Invertebrates include the sponges,
coelenterates, flatworms, nematodes,
annelids, arthropods, molluscs, and
echinoderms.
Hormonal System of Invertebrates
► Invertebrates
hormonal systems are rather
poorly understood in comparison with
vertebrates
► The endocrine systems of invertebrates
generally regulate the same processes that are
found in vertebrates such as development,
growth, and reproduction.
► The best understood endocrine systems are
those of insects, followed by crustaceans,
echinoderms and mollusks, although the latter
are perhaps characterized by the most diverse
hormonal systems of the invertebrate phyla.
Diversification of hormonal system of
Invertebrates
Diversified life histories of invertebrates with
characteristic events such as the formation of
larval forms, often with a succession of different
stages and/or pupation, metamorphosis, diapause
or other types of resting stages, which do not
occur in vertebrates.
2. Invertebrates represent more than 30 different
phyla within the animal kingdom. Consequently, it
is not surprising that regulation of the above
mentioned processes by their endocrine systems
is considerably more variable than in vertebrates,
which comprise only part of a single phylum, the
Chordata.
1.
The
► As
st
1
Endocrine System
you know Crustacea comprise: Crabs,
Lobster, Shrimp, Amphipods (freshwater),
Isopods (terrestrial) etc. have the first true
endocrine system
Hormones in the Lives of Crustaceans: An Overview
Ernest S. Chang, Sharon A. Chang and Eva P. Mulder
American Zoologist 2001 41(5):1090-1097
► The
crustaceans have a particularly complex
physiology due to the multiple processes that may
overlap and influence each other.
► These processes may include dramatically different
life stages (from embryo to larva to juvenile to
adult), a cyclical molt cycle that can occur many
times during the life of the crustacean, and a
reproductive cycle that may alter much of the
adult physiology.
Growth in Crustaceans
Occurs through molting = ecdysis
Stages of molting
1. Proecdysis - preparation for molting



2.
Ecdysis


3.
epidermal cells separate from the old cuticle (apolysis) and divide forming the new
exoskeleton
Calcium removed from old exoskeleton
hepatopancreas - release of energy reserves from storage (animal stops feeding)
shedding of the old exoskeleton
cuticle is soft - rapid uptake of water
Metecdysis




Mineral deposition into the new cuticle
Endocuticle formation
Feeding begins again
New tissue formation follows
►
►
4.
Increased DNA and protein synthesis
tissue replaces water
Intermolt

As skeleton and tissue growth nears completion metabolism is shifted to storage of energy
reserves into the hepatopancreas
Regulation of many processes is involved
► Metabolism
► Water /mineral balance
► Molting process
Crustacean Hormones have multifunctional
nature:
Ecdysteroids may serve:
1. During embryonic development as morphogens or promote
protective membranes
2. From larval to adult life they then function as molting
hormones.
3. In adults, they may act as gonadotropins.
2. Members of the CHH (Crustacean Hyperglycemic Hormone)
family of neuropeptides appear to be present from embryos to
adults and a single peptide can have multiple functions (acting
as a molt-inhibiting hormone and as a hyperglycemic hormone).
3. MF (Methyl farnesoate) may also function as a developmental
hormone in larvae and as a gonadotropin in adults.
1.
►
These examples illustrate the amazing economy of nature—a
single hormone that can mediate different functions at different
life stages.
Ecdysteroids
The steroid arthropod molting hormone was first isolated
from insects and it was called ecdysone.
► The structure of the more active and most predominant
form of the hormone was subsequently determined to be
20-hydroxyecdysone (20E).
► It is now apparent that ecdysone and 20E are the two
most predominant members of a family of steroids that
possess molting hormone activity.
► Members of this hormone family are collectively called the
ecdysteroids.
► Ecdysteroids are secreted by the Y- organ
►
► Cholesterol
is not synthesized in arthropods they cannot make it. But a very important
hormone in the arthropods is:
 Ecdysone - the molting hormone. It is similar to the
steroid hormones found in vertebrates: Estradiol and
testosterone.
 How do they make it then ? They obtain cholesterol
from their diet and modify it into ecdysone.
► Steroid
hormones are not as common ecdysone is one of the few sterol derived
hormones in invertebrates.
► The actual production of ecdysone is regulated
by peptide hormones.
Role of Ecdysone
► Embryonic
ecdysteroids may mediate the
formation of the various embryonic
envelopes that surround the embryo during
development
And/or
► They may be involved in early
morphogenesis as described for insects
► Ecdysteroids may also play a gonadotropic
role in crustaceans
Molt Inhibiting Hormone
►
Produced in the eyestalks
 Removal of eyestalks results in initiation of the processes seen
during proecdysis
► epidermal
► Calcium is
cells - cells divide form new cuticle
removed from old exoskeleton - becomes soft - able to be
broken
► Hepatopancreas (storage organ) - mobilizaton of reserves
►
Inhibiting effect on the Y-organ (endocrine gland)
 If you remove the Y-organ - you remove the source of the molting
hormone = ecdysone.
 Removal only has an effect when it is done during the intermolt
period, not during proecdysis.
► During
proecdysis the ecdysone is already there - it has already been
produced. Therefore removal will have no effect.
 Implanting Y-organs will during the intermolt period will induce the
processes seen during proecdysis
CRUSTACEAN HYPERGLYCEMIC HORMONE (CHH)
NEUROPEPTIDE FAMILY
► They
are synthesized and stored in the xorgan/sinus gland and the subesophageal
ganglion
► There are two forms:
 CHH-A (which has both hyperglycemic and
molt-inhibiting hormone activity);
 CHH-B (which has hyperglycemic activity only)
► Regulates
release of glucose from hepatopancreas
 metabolic hormone
► glycogen
► Very
(storage) Þ glucose (energy metabolism)
large peptide - 72 amino acid
 No sequence homology to known peptides
 May be up to 4 related peptides
 Also may be related to VIH and MIH
► Release
is affected by:
 Daily cycle - small peak in the morning and large peak at
night
 Starvation, stress (lack of O2), temperature elevation
► Short
term increase CHH production/release
► Long term decrease
Mandibular Glands
► Secrete
JH-like compounds - morphogens
 methyl farnesoate
 farnesoic acid
► Responsible
for juvenile characteristics
► Presence results in retention of juvenile
characterisitcs
► However actions are not totally clear
Methyl farnesoate (MF)
► It
is related to the insect juvenile hormone.
► MF is secreted by the mandibular organ
► There is some evidence that MF may have a
role in larval development by acting as a
hormone that retards development (a
juvenilizing factor)
► In adults, MF may function in a
reproductive capacity.
Juvenile Hormone
Crustacean Cardioactive Peptide (CCAP)
► Hormone
that causes acceleration of heartbeat
 amplitude and frequency increase
► Production
site – The neurosecretory cells (NSC)
in thoracic ganglion
► Release site - pericardial organ = neurohemal
organ - near heart
► Target - neurons that innervate the heart (large
cardiac ganglion cells)
► No structural homology to any known peptide
Androgenic hormone
► Androgenic
glands - endocrine glands in
male crustaceans
► Responsible for masculine characteristics act on:
 Gonads - spermatogenesis in the testes
 Epidermis - secondary male characteristics
►specialized
appendages
►i.e. large claws
Vitellogenesis Inhibiting Hormone
(VIH)
► Vitellogenesis
- production of yolk proteins
► VIH inhibits egg development
Molluscs
Mollusks are the most diverse of the invertebrate phyla,
being second to the insects in number of identified
species.
► They comprise:
1. Bivalvia - clams, oysters, mussels
2. Cephalopoda - octopus, squid
3. Gastropoda - snails, slugs
►



Prosobranchs - Crepidula
Opisthobranchs - Sea Hare Aplysia
Pulmonates - Snails


Stylommatophora - terrestrial - land snails - Helix
Basommatophora - aquatic snails – Lymnea
►
►
►
►
►
►
The endocrine systems of the various classes of mollusks and even
of major groups of gastropods – prosobranchs, opisthobranchs, and
pulmonates – differ considerably, reflecting extreme differences in
morphology and life histories.
This can be exemplified by the use of vertebrate-type steroids,
which do occur and play a functional role in prosobranchs. In
contrast, there is no indication for pulmonates using steroids.
Recently, the first estrogen receptor sequence for an opisthobranch
mollusk, the sea hare Aplysia californica, was published.
Estrogen and androgen receptors occur in a number of marine and
freshwater prosobranchs
The prosobranch mollusks and the echinoderms use at least partially
or even totally comparable hormones as vertebrates so that
vertebrate-type sex steroids are produced in these groups and play
a functional role.
Nevertheless, firm evidence of the role of these steroids in the
endocrine system of invertebrates is still lacking for most phyla
Endocrine disruption
in invertebrates
►
►
►
►
The hormonal regulation of biological functions is a
common characteristic for all animal phyla, including
invertebrates.
Invertebrates constitute more than 95% of all known
species in the animal kingdom,
They play a very important part of the global biodiversity
with key species for the structure and function of aquatic
and terrestrial ecosystems.
The endocrine systems of invertebrates have not been
documented in the same detail as vertebrates, nor have
responses of invertebrate endocrine systems to
suspected endocrine active substances (EASs) been
studied with comparable intensity
Endocrine Disruptors
► Our
ignorance of invertebrate endocrinology
is one of the main reasons for the
unsatisfactory progress that has been made
regarding endocrine disruptors (ED) in
invertebrates.
► Endocrine disruptors (ED) are chemicals
that have been purposely synthesized to
disrupt the endocrine system of a number of
insects to aid their control.
Endocrine Disruptors
► Certain
compounds are likely to act as endocrine
disruptors not only by a direct binding to
receptors—acting as hormone-mimics (agonists)
or as “antihormones” (antagonists)—but also
indirectly by modulating endogenous hormone
levels by interfering with biochemical processes
associated with the production, availability, or
metabolism of hormones or also by the modulation
of receptors.
► Therefore, it is likely that the various endocrine
systems in invertebrates are subject to modulation
by an unforeseeable number of exogenous
compounds.
EVIDENCE FOR ENDOCRINE
DISRUPTION IN INVERTEBRATES
► The
issue of ED in invertebrates has found
an increasing scientific interest although
only a limited number of confirmed cases
have been reported.
► These are dominated by the antifouling
biocide tributyltin (TBT) and its effects on
prosobranch snails and by insect growth
regulators (IGRs) which were designed as
EASs for use in insect pest control.
Insect Growth Regulators
►
Insect growth regulators (IGRs) represent third
generation insecticides and were developed to
intentionally interact with the hormonal system of these
arthropods, acting as ecdysone agonists, antagonists or
juvenile hormone analogs
► Ecdysteroid
antagonists prevent normal diapause
induction, and induce an early termination of diapause
or a precocious metamorphosis, while juvenile hormone
(JH) analogs, interfere with egg hatching, larval
development, larval-pupal molts, and ecdysis and reduce
the fertility and longevity of exposed specimens.
Tributyltin (TBT)
► The
effects of TBT on prosobranch snails are one
of the most complete examples of an EAS impact
on aquatic invertebrates.
► TBT induced malformations in gastropods TBT
compounds are mainly used as biocides in
antifouling paints, but also in other formulations.
► TBT caused pollution of coastal waters
► They induce a variety of malformations in aquatic
animals with mollusks as one of the most TBTsensitive groups
Effects of TBT on Crassostrea gigas mollusks
► The
first adverse effects of TBT on mollusks
were observed in Crassostrea gigas at the
Bay of Arcachon, one of the European
centers of oyster aquaculture, with ballshaped shell deformations in adults and a
decline of annual spatfall [11].
► These effects led to a break-down of local
oyster production with marked economic
consequences.
► One
of the most important lessons to be learned
from the "TBT story" and its effects in mollusks is
that EDCs may impact different levels of biological
integrations from molecules to communities
affecting also the survival of populations in the
field.
► Furthermore, the case history of TBT provides
evidence for vertebrate-type steroids playing an
important functional role in a number of
invertebrate groups, including prosobranchs.
► The
issue of ED in invertebrates has found
an increasing scientific interest although
only a limited number of confirmed cases
have been reported.