Endocrinology, lecture on Comparative Endocrinology
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
Syllabus
