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Invertebrate Endocrinology
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Invertebrate Endocrinology

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    1. Invertebrate Endocrinology

    2. 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.

    3. 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. Hormonal System of Invertebrates

    4. 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. 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.

    5. The 1st Endocrine System As you know Crustacea comprise: Crabs, Lobster, Shrimp, Amphipods (freshwater), Isopods (terrestrial) etc. have the first true endocrine system

    6. 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.

    7. Growth in Crustaceans Occurs through molting = ecdysis Stages of molting Proecdysis - preparation for molting 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) Ecdysis 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 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

    8. Crustacean Hormones have multifunctional nature: Ecdysteroids may serve: During embryonic development as morphogens or promote protective membranes From larval to adult life they then function as molting hormones. In adults, they may act as gonadotropins. 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). MF (Methyl farnesoate) may also function as a developmental hormone in larvae and as a gonadotropin in adults. These examples illustrate the amazing economy of naturea single hormone that can mediate different functions at different life stages.

    9. 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

    11. 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.

    12. 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

    13. Molt Inhibiting Hormone Produced in the eyestalks Removal of eyestalks results in initiation of the processes seen during proecdysis epidermal cells - cells divide form new cuticle Calcium is 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

    14. CRUSTACEAN HYPERGLYCEMIC HORMONE (CHH) NEUROPEPTIDE FAMILY They are synthesized and stored in the x-organ/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)

    15. Regulates release of glucose from hepatopancreas metabolic hormone glycogen (storage) glucose (energy metabolism) Very 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

    16. 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

    17. 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.

    18. Juvenile Hormone

    19. 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

    20. 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

    21. Vitellogenesis Inhibiting Hormone (VIH) Vitellogenesis - production of yolk proteins VIH inhibits egg development

    22. Molluscs Mollusks are the most diverse of the invertebrate phyla, being second to the insects in number of identified species. They comprise: Bivalvia - clams, oysters, mussels Cephalopoda - octopus, squid Gastropoda - snails, slugs Prosobranchs - Crepidula Opisthobranchs - Sea Hare Aplysia Pulmonates - Snails Stylommatophora - terrestrial - land snails - Helix Basommatophora - aquatic snails Lymnea

    23. 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

    24. Endocrine disruption in invertebrates

    25. 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

    26. 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.

    27. Endocrine Disruptors Certain compounds are likely to act as endocrine disruptors not only by a direct binding to receptorsacting 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.

    28. 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.

    29. 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.

    30. 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 TBT-sensitive groups

    31. 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 ball-shaped 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.

    32. 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.

    33. The issue of ED in invertebrates has found an increasing scientific interest although only a limited number of confirmed cases have been reported.