Endocrinology, lecture on Comparative Endocrinology
USD Department of Biology
Endocrine Glands
2nd Messengers
Nuclear Receptors
Genetic Regulation
Hormone Synthesis
Receptor Regulation
Hypothalamo-Hypophysial Communication
Tropic Hormones
Neurohypophysial Nonapeptides
Thyroid Axis
Adrenal Axis
Adrenal Medulla
Osmo-Pressure Balance
Reproductive Endocrinology
Somatic Axis
Growth Factors
Immune System
Ca++, PO4 Homeostasis
Pancreatic Hormones
GI Hormones
Guts 'n Brains
Brain Hormones
Figures for Endocrionology
text:Vertebrate Endocrinology4th Edition - David O. Norris:
Read pages 20-27, 169-186 for this lecture
acronyms    end
XXX. Evolution of Endocrine Function 		

	A. Most endocrine functions, structures, & molecules are highly conserved

		1. remarkably similar between species

			a. biochemicals with important functions
			   do not change much over evolutionary time

				i. change usually leads to a loss of fitness (and death)

				ii. unicellular organisms (like bacteria, fungi, protozoa) have some
				    of the same hormones seen in humans: insulin, somatostatin,
				   CG, glucagon, calcitonin, TSH, CCK, ACTH, & b-endorphin

		2. strikingly similar within a group or family of molecules

			a. families of genes may code for molecules
			   with high degrees of homology

				i. often with related function

	B. Repetitive DNA ® Variant Repetition

		1. some portions of DNA are highly repetitive

		2. mutations in individual portions of repetitive sequences
		   may result in variants

		3. variants may initially have no function

			a. the original gene (+ hormone) retain the original function

		4. variants of hormones when matched with variants of receptors
		   stimulate 2nd messenger activation

			1. hormone + receptor evolution must occur together

				a. results in related hormone + receptor families

		5. when variant 2nd messenger activation is localized in a cell type
		   a new function or regulatory control the changes are adaptive

			a. target tissue is formed
			   - new target tissue may be the only change

		6. adaptive changes increase fitness

			a. increased fitness may result in reproductive advantage

				i. reproductive advantage yields changes in the
				   frequency of the population with variant genes

	C. Evolution of glycoprotein hormones						               

		1. LH, TSH, FSH & CG are derived entirely from one ancesteral gene

			a. duplicated (variant repetition) early in evolution

				i. a and b chains

					(1) a subunit is similar for all glycoproteins

					(2) b subunit is different and confers
					    biological activity (when a and b are together)

						(a) b chain changed over evolutionary time

		2. cyclostomes have 1 gonadotropin (GTH),
		   i.e. 1 glycoprotein hormone, LH like

			a. a & b chains already present (genes already diverged)

			b. ovulation/oviposition is an important function

		3. a subunit remains independent, with few mutations during evolution

		4. ancient teleost (bony) fishes have b-gonadotropin subunit,
		   but also b-TSH

			a. cellular evolution of gonadotropes and thyrotropes

		5. during the evolution of modern teleosts
		   and terrestrial vertebrates (amphibians)

			a. b-TSH gave rise to b-FSH

				i. follicular development, ovulation, oviposition
				   become separate events

		6. evolution of placental function
		   made a chrorinic gonadotropin adaptive

			a. b-CG is derived from b-LH

	D. Multiplicity of forms: GnRH

		1. decapeptide with 14 known forms

			a. lGnRH1, lGnRH2, lGnRH3, dfGnRH, cfGnRH, sGnRH1,
				 sGnRH2, sbGnRH, cGnRH1, cGnRH2, mGnRH

				i. named for discovery in lamprey, dogfish, catfish, salmon,
				   sea bream, chicken, and mammals

				ii. all vertebrates have cGnRH2  (may be ancestral)

		2. develop in neural ridge that gives rise to olfactory epithelium

			a. migration from olfactory bulb to POA

		3. also develop form posterior hypothalamic neural ridge

			a. multiple forms follow from multiple regions

				i. cGnRH2 found in extrahypothalamic regions

				ii. other forms are often found in ARC with terminals
				   in median eminence for stimulation of LH + FSH release

					(1) usually sGnRH1, mGnRH or cGnRH1

						(a) more than one form can cause release of LH/FSH
						    but only one is positioned to do so per species

		4. extrahypothalamic + hypothalamic cGnRH2 functions
		   as a neuromodulator

			a. GnRH made in VMN and released in the midbrain central grey
			   stimulates sexual behavior

				i. multiple forms follow the need for coordination
				   of multiple related functions