Endocrine Systems 內分泌系統

1. Insect Physiology Endocrine Systems內分泌系統 Wu-Chun Tu Department of Entomology National Chung Hsing University

2. Internal Communication • Two systems of internal communication • Nervous system 神經系統 • Rapid • Short-term responses • Direct action between effectors and receptors • Endocrine system 內分泌系統 • Slower • More long-term responses • Blood-borne

3. CONTENTS • Hormone in Insects • Early Experiments that Set the Stage for Current Understanding • Types of Hormones in Insects • Prothoracicotropic Hormones • Ecdysteroids • The Juvenile Hormones • Other Neuropeptides Found in Insects • Vertebrate-Type Hormones in Insects

4. What Are Hormones? • Classical definition • Hormones are chemical substances produced by specialized tissues (glands) and secreted into blood, in which they are carried to target organs. • Modern definition • Hormones are chemical substances that carry information between two or more cells at micromolar concentration or less.

5. Plasma membranes Plasmodesmata between plant cells Gap junctions between animal cells Cell junctions. Both animals and plants have cell junctions that allow molecules to pass readily between adjacent cells without crossing plasma membranes. • Animal and plant cells • Have cell junctions that directly connect the cytoplasm of adjacent cells

6. Cell-cell recognition. Two cells in an animal may communicate by interaction between molecules protruding from their surfaces. • In local signaling, animal cells • May communicate via direct contact

7. Local signaling Target cell Electrical signal along nerve cell triggers release of neurotransmitter Neurotransmitter diffuses acrosssynapse Secretory vesicle Local regulator diffuses through extracellular fluid Target cell is stimulated (b) Synaptic signaling. A nerve cell releases neurotransmitter molecules into a synapse, stimulating the target cell. (a) Paracrine signaling. A secreting cell acts on nearby target cells by discharging molecules of a local regulator (a growth factor, for example) into the extracellular fluid. • In other cases, animal cells • Communicate using local regulators

8. Long-distance signaling Blood vessel Endocrine cell Hormone travels in bloodstream to target cells Target cell (c) Hormonal signaling. Specialized endocrine cells secrete hormones into body fluids, often the blood. Hormones may reach virtually all body cells. • In long-distance signaling • Both plants and animals use hormones

9. Neurohemal organ Examples of Neurotransmitter Release 神經傳導物質 神經賀爾蒙 賀爾蒙 神經調節物質 Receptor

10. Hormone in Insects • Insect hormones affect a wide variety of physiological processes including • Embryogenesis 胚胎發育 • postembryonic development 後胚期發育 • Behavior 行為 • water balance 水分平衡 • Metabolism 代謝 • Caste determination 位階決定作用 • Polymorphism 多型性 • Mating 交配 • Reproduction 生殖 • Diapause 滯育 • Others

11. Endocrine Organs in Insects • Conventional endocrine glands 內分泌腺 (hormone synthesis and secretion) • Prothoracic glands (PGs) 前胸腺 • Corpora allata (CA) 咽喉側腺 • Corpora cardiaca (CC) 心臟內泌體 • Ovaries and testes • Neurosecretory cells (NSC) 神經內泌細胞 • Produce small neuropeptides – neurohormones • They can be found in brain (major source) and all the ganglia.

12. Endocrine Organs in Insects • Prothoracic glands (PGs) • The source of ecdysteroids 脫皮固醇 • Corpora allata (CA) • The source of juvenile hormones 青春賀爾蒙 • Corpora cardiaca (CC) • The source of neuropeptide hormones 神經肽 • Ovaries and testes 卵巢與精巢 • Ovaries: ecdysteroid 脫皮固醇 • Testes: androgen hormone of European firefly, Lampyris noctinca 雄性素

13. Endocrine Organs in Insects

14. The Innervation of the Corpora Allata and Corpus Cardiacum in the Locust

15. Neurosecretory Cells in Insect Nervous System

16. Fig. A general scheme for pathways of neuroendocrine regulation in insects.

17. Early Experiments • Bataillon (1894) – the first evidence for the existence of hormones in insects. • ligature of silkworm larvae • Kopeć (1917) – confirmation of the presence of hormones in insects. • ligature of last instar larvae of gypsy moth (next slide) • removal of the brain of gypsy moth larvae • Wigglesworth (1930s) – demonstrating that neurosecretory cells are indeed the source of the brain’s endocrine effect. • decapitation of the blood sucking bug (next slide)

18. Types of Hormones in Insects • Steroid hormone • ecdysteroids • Sesquiterpenes • juvenile hormones • Peptide hormones • prothoracicotropic hormone (PTTH) • many others • Biogenic amines • octopamine • serotonin

19. Factors that Affect the Activity of Hormones Circulating titer of hormone

20. Modes of Actions • Non-polar hormones (next slide) • Hormones are able to enter the cell and bind to cytosolic and nuclear receptors. • e.g. juvenile hormones, ecdysteroids • Polar hormones (next slide) • Hormones can not pass through the cell membrane. • Via the synthesis of second messenger molecules that carry the message inside the cell. • e.g. peptide hormones

21. G-protein-linked receptors Relay protein

22. Signal-binding sitea Signalmolecule Signal molecule Helix in the Membrane Tyr Tyr Tyr Tyr Tyrosines Tyr Tyr Tyr Tyr Tyr Tyr Tyr Tyr Receptor tyrosinekinase proteins(inactive monomers) Dimer CYTOPLASM Activatedrelay proteins Tyr Tyr Cellularresponse 1 Tyr Tyr Tyr Tyr P P Tyr P Tyr Tyr Tyr Tyr P Tyr Tyr Tyr P P P Tyr Tyr Tyr Tyr Tyr P Tyr Tyr Tyr Cellularresponse 2 P P P Tyr Tyr P 6 ATP 6 ADP Activated tyrosine- kinase regions (unphosphorylated dimer) Fully activated receptor tyrosine-kinase (phosphorylated dimer) Inactiverelay proteins Receptor tyrosine kinases

23. First messenger (signal molecule such as epinephrine) Adenylyl cyclase G protein GTP G-protein-linked receptor ATP cAMP Protein kinase A Cellular responses • Many G-proteins • Trigger the formation of cAMP, which then acts as a second messenger in cellular pathways

24. EXTRACELLULAR FLUID Plasma membrane Ca2+pump ATP Mitochondrion Nucleus CYTOSOL Ca2+pump Endoplasmic reticulum (ER) ATP Ca2+pump Key High [Ca2+] Low [Ca2+] • Calcium is an important second messenger • Because cells are able to regulate its concentration in the cytosol

25. 6 3 2 1 5 4 A signal molecule binds to a receptor, leading to activation of phospholipase C. DAG functions as a second messenger in other pathways. Phospholipase C cleaves a plasma membrane phospholipid called PIP2 into DAG and IP3. EXTRA- CELLULAR FLUID Signal molecule (first messenger) G protein DAG GTP PIP2 G-protein-linked receptor Phospholipase C IP3 (second messenger) IP3-gated calcium channel Endoplasmic reticulum (ER) Various proteins activated Cellularresponse Ca2+ Ca2+ (second messenger) The calcium ions activate the next protein in one or more signaling pathways. IP3 quickly diffuses through the cytosol and binds to an IP3– gated calcium channel in the ER membrane, causing it to open. Calcium ions flow out of the ER (down their con- centration gradient), raising the Ca2+ level in the cytosol.

26. Signal molecule A relay molecule activates protein kinase 1. Receptor Activated relay molecule 4 1 3 5 2 Inactive protein kinase 1 Active protein kinase 1 transfers a phosphate from ATP to an inactive molecule of protein kinase 2, thus activating this second kinase. Active protein kinase 1 Active protein kinase 2 then catalyzes the phos- phorylation (and activation) of protein kinase 3. Inactive protein kinase 2 ATP Phosphorylation cascade P ADP Active protein kinase 2 PP P i Enzymes called protein phosphatases (PP) catalyze the removal of the phosphate groups from the proteins, making them inactive and available for reuse. Inactive protein kinase 3 Finally, active protein kinase 3 phosphorylates a protein (pink) that brings about the cell’s response to the signal. ATP P ADP Active protein kinase 3 PP P i Inactive protein ATP P ADP Active protein Cellular response PP P  i • A phosphorylation cascade

27. Nitric Oxide as A Second Messenger Central nervous system Malpighian tubules Compound eye develop Activation of cGMP-dependent enzymes Permeability of membrane channels

28. Prothoracicotropic Hormone (PTTH) • The first insect hormone to be discovered. • PTTH acts on the prothoracic glands (PTGs) to regulate the synthesis of ecdysteroids. • Williams (late 1940s - early 1950s) demonstrated the relationship of PTTH and PGs. • Implanted both the PGs and a brain into a diapausing pupa • Parabiosis (next slide) • Bollenbacher (1979) developed a more direct assay for PTTH. • Using the criterion of ecdysone production by a pair of PGs in vitro. (next slide)

29. The Amino Acid Structure of PTTH In Bombyx mori 224-amino-acid precursor ; 109-amino-acid functional

30. Groups of PTTH Big PTTH : 14-29 kDa True PTTH Small PTTH : 3-7 kDa Bombyxin : receptor in some ovaries of lepidopterans — involved in ovarian development — utilization of carbohydrate during egg maturation

31. Sources of PTTH • The main sites of production are the neurosecretory cells (NSCs) in the brain. (next slide) • PTTH activity has also been identified in the subesophageal ganglion and the ganglia of the ventral nerve cord.

32. Control of PTTH Release and Its Mode of Action • Control of PTTH release • environmental stimuli such as photoperiod, temperature • nervous stimuli such as stretch receptors • Mode of action • Via a second messenger, cAMP

33. Ecdysteroids • Hachlow (1931) showed an organ in the thorax was also necessary for molting and metamorphosis; Fukuda (1940) demonstrated that this particular organ was the prothoracic gland. • Ecdysone was the first insect hormone to be structurally identified. • Butenandt and Karlson purified 25 mg of the hormone starting with approximately 500 kg of B. mori pupae. • Two major forms of ecdysteroids • α-ecdysone: ecdysone • β -ecdysone: 20-hydroxyecdysone

34. The Calliphora Bioassay Developed by Fraenkel (1934)

35. Precursor and Synthesis of Ecdysteroids • The precursors for ecdysteroid synthesis are sterols, such as cholesterols. (campesterol; sitosterol; stigmasterol) • Insects cannot synthesize cholesterols and require cholesterol in their diets. • The primary site of ecdysteroid synthesis is the prothoracic gland; the major product is ecdysone. • Ecdysone (inactive form) is converted to 20-hydroxyecdysone (active form) by target tissues.

36. Some Common Ecdysteroids embryos 28 Honeybee Hemipterans Dipterans embryos

37. Synthesis of the Various Ecdysteroids from Cholesterol in Some Lepidopterans Carrier proteins

38. Prothoracic Glands (PG) The ring gland of higher dipterans. 環 腺

39. A. Blattaria B. Hemiptera C. Lepidoptera D. Hymemoptera Prothoracic Glands (PG)

40. Prothoracic gland degeneration PTG exposure to ecdysteroids in the absence of JH Ecdysteroids acting alone trigger apoptosis by the PTG cells Adult pterygote insects Apterygote insects retain active PTG

41. Other Sources of Ecdysteroids • Ovaries • Incorporated into the eggs for later use during embryogenesis (follicle cells) • Stimulate fat body to activate the synthesis of yolk proteins. • Testes • Sheaths cells produce • Epidermal cells • During certain developmental stages Neurohormones : Ovarian ecdysiotropic hormones Testes ecdysiotropin

42. Mode of Action of Ecdysteroids

43. Chromosome Puffs in Drosophila Polytene Chromosomes Early puffs : hormone directly Late puffs Puffing patterns are correlated with the development stage

44. Hormone receptor complex receptor ultraspiracle gene EcR Isoforms in different cells Morphogenesis of salivary gland Fig. A model originally proposed by Ashburner (1974) for the action of ecdysteroids in the Drosophila salivary gland.

45. Juvenile Hormones (JHs) • First described by Wigglesworth as an “inhibitory hormone” that prevented the metamorphosis of the Rhodnius prolixus. • JH is synthesized in and released from the corpus allatum (CA) • JHs belong to sesquiterpenes • JHs have multiple effects during the life of an insect, especially involvement in • Metamorphosis • Diapause • Reproduction • Metabolism

46. Endocrine Organs in Insects

47. The Location and Structure of the Corpus Allatum • A mosquito • A cockroach • A hemipteran

48. Six Major Members of the JHs 19 18 19 17 17 16; dipterans, ticks 2 epoxide group

49. Examples of Hydroxy Juvenile Hormones(produced by the CA of locusts and cockroaches) This hydroxylation may result in molecules with greater biological activity, just as 20-hydroxyecdysone is more active than ecdysone

50. Initial Steps in the Synthesis of Common Juvenile Hormones