hormone regulation of elasmobranch physiology chris bedore and shannon long
TRANSCRIPT
Hormone Regulation of Elasmobranch Physiology
Chris Bedore and Shannon Long
What We’ll Be Covering
• Digestion and Energy Metabolism
• Growth• Stress• Osmoregulation• Physiological Color
Change• Reproduction• Reproduction• Reproduction• Research methods
Things to Remember
DIG
ES
TIO
N A
ND
EN
ER
GY
M
ET
AB
OLIS
M
The Players• Secretin—stimulates secretion of bicarbonate-rich
pancreatic juices• Cholescystokinin (CCK)—regulates supply of bile
and pancreatic enzymes• Somatostatin (SS)—suppress production of gastric
acid, inhibit rectal gland secretion, inhibitory regulation of GH from hypothalamus
• Neuropeptide Y (NPY)—promote digestion by increasing blood flow, inhibits gastric acid secretion, pancreatic enzyme release, and gallbladder contraction, inhibit rectal gland secretion
• Bombesin/Gastrin-releasing peptide (GRP)—promote digestion by increasing blood flow, effecting acid/enzyme secretion/gut motility, inhibit rectal gland secretion
• Vasoactive intestinal polypeptide (VIP)—suppress digestion by reducing blood flow, effecting acid/enzyme secretion/gut motility, stimulates salt excretion by vasodilating the rectal gland and increasing cellular cAMP enzyme, used to regulate water and ion balance
• Tachykinins—promote digestion by increasing blood flow, effecting acid/enzyme secretion/gut motility
• Insulin—storage/conversion/uptake of energy substrate, pancreas, regulated by nutrient levels, reduction in circulating amino acid levels, no effect on ketones
• Glucagon—antagonistic to insulin• Thyroid—alter levels of enzymes in amino acid/lipid
metabolism
DIG
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TIO
N A
ND
EN
ER
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M
ET
AB
OLIS
M
GR
OW
TH
The Players
• Growth hormone (GH)—pituitary gland, regulated by GHRH, promotes somatic and skeletal growth
• Growth hormone-releasing hormone (GHRH)—regulates GH, stimulatory from hypothalmus
• Insulin-like growth factors (IGF-I)—promotes growth of vertebral column
ST
RE
SS
The Players
• Chromaffin tissue—masses of neurosecretary cells on kidney, cells secrete epinephrine and norepinephrine, response to acute stress
• Catecholamines—epinephrine and norepinephrine, promote mobilization, of energy reserves, increase blood pressure, blood flow to gut reduced, increase oxygen uptake in gills
• Hypthalamo-Pituitary-Interrenal axis (HPI axis)—mid-axis lengthwise down body, helps to regulate ions
• Corticosteroids—interrenal body, regulated by ACTH, promote nutrient movement through body, inhibit growth and energy storage, aid in retention of sodium
• Adrenocorticotropic hormone (ACTH)—regulates corticosteroids, stimulated by CRF, induces hyperglycemia
• Corticotrophin-releasing factor (CRF)—hypothalamic compound, stimulates ACTH, regulate interrenal production of 1α-OHB
• 1α-Hydroxycorticosterone (1α-OHB)—corticosteroid produced only in elasmobranchs, stimulate retention of sodium and chloride
OS
MO
RE
GU
LAT
ION
The Players• Renin-angiotensin system (RAS)—used to regulate water
and ion balance, series of biochemical steps1. convert hepatic glycoprotein angiotensinogen to
ANG I2. cleavage to ANG I by ACE makes ANG II
• Angiotensin I (ANG I)—inactive form• Renin—enzyme used to convert to ANG I, secreted by
juxtanglomerular cells of kidney• Angiotensin converting enzyme (ACE)—promotes
cleavage in ANG I to make ANG II• Angiotensin II (ANG II)—biologically active, receptors in
interrenal gland/gill/rectal gland/intestine, modulate HPI axis, stimulates 1α-OHB secretion, promotes sodium retention, influence electrolyte balance by reducing GFR and UFR, inhibits salt release from rectal gland, increase drinking rate
• C-type natriuretic peptide (CNP)—used to regulate water and ion balance, stimulates production of VIP and rise in salt secretion, expressed in heart and brain, responds to increased cardiac pressure, directly affects rectal gland epithelial cells, binds to NPR-B to increase cGMP and PKC, dilates rectal gland to cause increase in salt release
• Natriuretic peptide type-B (NPR-B)—in rectal gland epithelium
• Cyclic granosine monophosphate (cGMP)• Protein kinase C (PKC)• Arginine vasotocin (AVT)—regulates
osmoregulation, reduces diuresis
PH
YS
IOLO
GIC
AL C
OLO
R
CH
AN
GE
The Players
• Melanocyte—type of chromatophore, contains melanosome which has brown-black melanin
• α-Melanocyte-stimulating hormone (α-MSH)—regulates physiological color change, produced in neurointermediate lobe of pituitary, when removed- sharks lighten in color, when expressed- sharks darken, controlled by neural signals to hypothalamus
• Melatonin—induces skin pallor• Prolactin (PRL)—in par distalis of pituitary, in
freshwater ray, regulates physiological color change
What Goes On Inside
diverse breeding strategies in elasmos
therefore, probably diverse regulatory mechanisms
this area is largely unknown and mostly hypotheticalinformation is from hormone concentration at aspecific time in mating season and deduced
from other vert spp.
well studied in only a few species (ex: D. sabina, S. tiburo)
Reproductive Endocrinology- Overview
Brain-Pituitary-Gonad (BPG) axis: primary endocrine regulation, initiated by env. stimuli
Reproductive Endocrinology- Overview
gonadal steroids:regulate gametogenesis, modulate reproductivebehavior, modulate development and function of2⁰ sex characteristics
influence production of GnRH and GTH (neg. feedback)steroid binding sites in hypothalamus
potential to alter production of relaxin, calcitonin,thyroid
most cycle throughout mating season
Reproductive Endocrinology- Overview
Reproductive Endocrinology- Anatomy
Reproductive Endocrinology- Anatomy
Gonadotropin-releasing hormone:
many forms (7?), therefore many functionsdfGnRH, sGnRH, cIIGnRH, mGnRH
GnRH and GnRH-BPs present in systemic circulationdirect action on gonads?
different forms present in different parts of the brain
GnRH
Hypothalamus/Forebrain: regulate GTH
Pituitary/Forebrain: regulate pituitary/gonads, conveyenv. info to initiate BPG
GnRH
Terminal nerve: regulate repro. processes?!
GnRH
Midbrain/Hindbrain: regulate sensory sensitivity duringreproduction (ie-e-reception)? clasper movement
GnRH
gonadotropin hormone
pituitary gland
partially regulate steroidogenesis, gametogenesis(systemic GnRH)
response to GTH may depend on env. stimuli (H2O temp,photoperiod) and reproductive stage
2 types found so far in elasmossimilar structure to FSH, LH in tetrapods?*future research*
GTH
3 major gonadal steroids:
17β-estradiol (estrogen)- E2
Progesterone- P4
Testosterone- T
Female Steroids-Gonadal
Female Steroids-Gonadal
E2
Female Steroids-Gonadal
2 peaks1. pre-ovuation/follicle development stimulate vitellogenesis regulate development of oviducal gland
2. late gestation (Squalus acanthias) regulate vitellogenesis regulate secretion of histotroph (Dasyatis sabina)
P4
Female Steroids-Gonadal
suppress vitellogenesis (opposes E2)
viviparous: peaks close to ovulation↓ late gestation-permits next follicles to develop
(S. acanthias)
oviparous: regulate timing of oviposition (↑=oviposit)
T and DHT (androgens)
Female Steroids-Gonadal
↑ during follicle development
precursor to E2 synthesis
modulate copulatory behavior
sperm storage (T)
regulate oviposition?
*future research- distribution of receptors*
Female Steroids-Other
Relaxin (Rlx)
Female Steroids-Other
found in ovary of several species
implant and removal experiments-↑ cervical area- prep for parturition
probably aids pupping and oviposition
maintains uterus during gestation (↓ contractions)
Sphyrna tiburo- participates in ova release?
Thyroid (T3 and T4)
Female Steroids-Other
interacts with BPG axis, role unknown
↑ during ovulation and gestation (D. sabina)associated with > metabolic costs at this time?S. tiburo highest levels- placental formation
Thyroid (T3 and T4)
Female Steroids-Other
embryo- passed to young through yolk (McComb et al. 2005)regulate rate of development> concentration found in yolk from populations with:
larger birth sizefaster rate of developmentgreater size at maturityhigher maternal investment
Calcitonin (CT)
Female Steroids-Other
produced in ultimobranchial glandmuscles between pharynx and pericardial cavity
↑ in response to E2 binding on gland
maternal gill: ir-cellsregulate Ca2+ homeostasis during gestation?mechanism/role unclear
Calcitonin (CT)
Female Steroids-Other
S. tiburo: peaks during yolk dependent stageasstd w/digestion of yolk? ir-cells in duodenum &pancreas of early embyros
Calcitonin (CT)
Female Steroids-Other
D. sabina: peaks during histotroph productionno ir-cells in embryo, therefore not involved inembryo nutrition
Male Steroids-Gonadalmostly produced in Sertoli cells (in testes)
Leydig cells: supplements gonad steroids for regulatingstages of spermatogenesis (epididymis and ductus deferens)
trends differ among spp, but all regulate aspects of repro.
Male Steroids-Gonadal4 major gonadal steroids:
Testosterone (T)
Dihydrotestosterone (DHT)
Progesterone (P4)
17β-estradiol (E2)
Male Steroids-Gonadal
T and DHT (androgens)
Male Steroids-Gonadal
↑ middle to late spermatogenesis= peak GSI (high # spermatocytes in testes)
influence development of spermatogonia and repro. ducts
routes of hormone transfer between testes and urogenitalsystem:
systemic circulation, binding sites in spermatozoa,enzymes in semen
T and DHT (androgens)
Male Steroids-Gonadal
claspers/cartilage: calcification due to androgens?
indirect evidence, but no direct evidencecoincides with androgen peakenlarged S. tiburo cephalofoil during malepubertal development
but- implant/removal experiments showed norelationship
mediated through GH and IGF-1 (after E2 peak)?*future studies*
T and DHT (androgens)
Male Steroids-Gonadal
E2
Male Steroids-Gonadal
unsure of role in males- some spp show cycling patterns (D.sabina), irregular variations in others (S. tiburo)
D. sabina:receptors in epididymis and seminal vesicles
maintain repro. tract function?
peak early-middle spermatogenesisregulate early spermatogenesis?
*future studies*
P4
Male Steroids-Gonadal
cycle mirrors androgens (S. tiburo)substrate for androgen synthesis?
but- pubertal S. tiburo & D. .sabina:peak precedes androgen peak
regulate spermiogenesis and/or spermiation?
Relaxin (Rlx)
Male Steroids-Other
produced by gonads
other verts: regulate male fertility
S. tiburo:↑ during late spermatogenesis and copulatory period
[relaxinsemen]=1000x [relaxinblood]
facilitate insemination through contractability ofrepro tract of postmated female?
Male Steroids-Other
seasonal cycling
peak spring and fall
aid in ↑ metabolic needs during migration?
*future studies*
Thyroid (T3 and T4)
Gonadal Steroid & Development
*effect of steroid hormones on development needs moreresearch!*
E2, P4, T transferred from female to yolkE2, T probably utilized during development
BPG axis activated during maturationsteroidogenesis
stage specific increases of hormones (S. tiburo), butroles unclear
Hormones and Behavior
androgens peak in males during copulatory period in somespecies (ex: D. sabina)
may influence certain behaviors- aggressionex: protracted mating period/aggression D. sabina
may also affect sensory sensitivitiesex: electroreception in D. sabina
Dasyatis sabina
Tricas et al., 2000spermatogenesis:
production and development of spermatozoa
spermiogenesis: last stage; produces mature spermatozoa
spermiation: release of spermatozoa from Sertoli cells
spermatogonium → spermatocytes → spermatids →spermatozoa
Dasyatis sabina
Tricas et al., 2000
male steroid hormones:
4 phases:1. androgen suppression
2. PAI, peak E2, P4
3. androgen decrease
4. SAI
Dasyatis sabina
phase 1:
androgen suppressionbetween mating seasons
Dasyatis sabina
phase 2:
primary androgen increase
E2, P4 increases
maximum spermatocyte development (max GSI)
Dasyatis sabina
phase 3:
androgen decrease following maximum testisgrowth and spermatocyte development
E2 and P4 also decrease
Dasyatis sabina
phase 4:
secondary androgen increase
peak sperm maturation
copulatory period
Dasyatis sabina
Female hormones
androgens
small, brief peaks winter, spring
aggression during matingperiod?
Dasyatis sabina
Female hormones
E2:
1st peak- maturation of oocytes (March); synthesis and uptake of vitellogenin
2nd peak- late development, parturitiontransition yolk to histotroph? *future studies*
Dasyatis sabina
Female hormones
P4:
1st peak: near ovulation
2nd peak: parturition
Dasyatis sabina
androgens, behavior, and protracted mating period:
courtship behaviors- males follow females nose to ventchase, bite fins
females- enhance mate choice by fleeing
Immunocytochemistry, Immunohistochemistry(ICC, IHC):
ir-staining of desired hormone
ex: GnRH neurons inhypothalamus or terminal nerve
Reproductive Endocrinology- Methods
ICC, IHC:-collect tissue samples
Reproductive Endocrinology- Methods
ICC, IHC:
- section tissue
Reproductive Endocrinology- Methods
ICC, IHC:
- apply primary antibody, apply secondary antibodywith enzyme, provide substrate, then counter-stain
Reproductive Endocrinology- Methods
Reproductive Endocrinology- Methods
P. marinus GnRH neurons (top-female, bottom-male) before (left column) and after(right column) electro-stimulation
Control
Male
Female
Electro-Stimulated
Radioimmunoassay (RIA)
Reproductive Endocrinology- Methods
Radioimmunoassay (RIA)
uses radiolabeled (ex: 3H) antibody for competitive binding to hormone
calculate % bound radiolabel to determine hormoneconcentration in a sample
Reproductive Endocrinology- Methods
hormone implants
ex: Sisneros and Tricas, 2000
surgically implant hormone tablet/capsule into body
wait for it to take effect (usually a # of days)
check for changes (RIA, behavior, electrophysiology)
Reproductive Endocrinology- Methods
hormone implants
Reproductive Endocrinology- Methods
organ removal (ie pituitary, hypothalamus)
similar to hormone implant, but remove organ
wait for it to take effect
check for changes (RIA, behavioral, electrophysiology)
Reproductive Endocrinology- Methods
Conclusion/Future Research
hormone regulatory mechanisms seem to be similarto other vertebrates
many vertebrate hormones first appeared in elasmobranchs
MUCH research is needed to determine roles of manyhormones. There is less information on elasmo hormones than any other vertebrate group, despiteevolutionary role. We need to catch up!
Literature CitedChung-Davidson, Y.-W., M.B. Bryan, J. Teeter, C.N. Bedore, and W. Li. 2007. Neuroendocrine
and behavioral responses to weak electric fields in adult sea lampreys(Petromyzon marinus). Hormones and Behavior. (In Review)
Gelsleichter, J. 2004. Hormonal Regulation of Elasmobranch Physiology. Pp. 287-324 in Biologyof Sharks and Their Relatives (J.C. Carrier, J.A. Musick, and M.R. Heithaus, eds). CRC Press, Boca Raton.
Kajiura, S.M., J.P. Tyminski, J.B. Forni, and A.P. Summers. 2005. The sexually dimorphic cephalofoil of bonnethead sharks, Sphyrna tiburo. Biol. Bulletin 209: 1-5
Sisneros, J.A. and T.C. Tricas. 2000. Androgen-induced changes in the response dynamics ofampullary electrosensory primary afferent neurons. J. Neurosci. 20(22): 8586-8595.
Tricas, T.C., K.P. Maruska, and L.E.L. Rasmussen. Annual cycles of steroid hormoneproduction, gonad development, and reproductive behavior in the Atlantic stingray.Gen. Comp. Endocrin. 118: 209-225.
Trivett, M.K., T.I. Walker, D.L. Macmillan, J.G. Clement, T.J. Martin, and J.A. Danks. 2002. Parathyroid hormone-related protein (PTHrP) production sites in elasmobranchs.J. Anat. 201: 41-52.