Evo........
Evo........Devo
Evo - Devo: Evolution and Development
I. Background
Evo - Devo
I. Background
- Embrologists have long realized that organisms in different phyla have
different developmental "plans"
Evo - Devo
I. Background
- Embrologists have long realized that organisms in different phyla have
different developmental "plans"
- And in a phylum, there is the same developmental plan. This is not
necessarily what we might expect from random mutation and evolution... why
don't we see as many differences in early developmental traits as we see in
later developing traits?
- For instance, why do chordates have similar development, even though
cartilaginous fish and other vertebrates are separated by 400 million years of
divergent evolution?
Evo - Devo
I. Background
- Embrologists have long realized that organisms in different phyla have
different developmental "plans"
- And in a phylum, there is the same developmental plan. This is not
necessarily what we might expect from random mutation and evolution... why
don't we see as many differences in early developmental traits as we see in
later developing traits?
- For instance, why do chordates have similar development, even though
cartilaginous fish and other vertebrates are separated by 400 million years of
divergent evolution.
- Embryological development is highly conserved, while subsequently
allowing extraordinary variation....
Evo - Devo
I. Background
II. Core Processes
- Basic biological processes are CONSERVED, and the enzymes that
perform them are CONSERVED:
Evo - Devo
I. Background
II. Core Processes
- Basic biological processes are CONSERVED, and the enzymes that
perform them are CONSERVED:
DNA, RNA, protein synthesis - ALL LIFE
Evo - Devo
I. Background
II. Core Processes
- Basic biological processes are CONSERVED, and the enzymes that
perform them are CONSERVED:
DNA, RNA, protein synthesis - ALL LIFE
Membrane structure and function - ALL EUK's
Evo - Devo
I. Background
II. Core Processes
- Basic biological processes are CONSERVED, and the enzymes that
perform them are CONSERVED:
DNA, RNA, protein synthesis - ALL LIFE
Membrane structure and function - ALL EUK's
Cell junctions - ALL METAZOA
Evo - Devo
I. Background
II. Core Processes
- Basic biological processes are CONSERVED, and the enzymes that
perform them are CONSERVED:
DNA, RNA, protein synthesis - ALL LIFE
Membrane structure and function - ALL EUK's
Cell junctions - ALL METAZOA
Hox genes - ALL BILATERIA
Evo - Devo
I. Background
II. Core Processes
- Basic biological processes are CONSERVED, and the enzymes that
perform them are CONSERVED:
DNA, RNA, protein synthesis - ALL LIFE
Membrane structure and function - ALL EUK's
Cell junctions - ALL METAZOA
Hox genes - ALL BILATERIA
Limb formation - ALL LAND VERTEBRATES
Evo - Devo
I. Background
II. Core Processes
- Basic biological processes are CONSERVED, and the enzymes that
perform them are CONSERVED:
- Many enzymes are more than 50% similar in AA sequence in E. coli
and H. sapiens, though separated by 2 billion years of divergence.
- Of 548 metabolic enzymes in E. coli, 50% are present in ALL LIFE,
and only 13% are unique to bacteria.
Evo - Devo
I. Background
II. Core Processes
- Basic biological processes are CONSERVED, and the enzymes that
perform them are CONSERVED:
- Many enzymes are more than 50% similar in AA sequence in E. coli
and H. sapiens.
- Of 548 metabolic enzymes in E. coli, 50% are present in ALL LIFE,
and only 13% are unique to bacteria.
- So the variation and diversity of life is NOT due to changes in metabolic or
structural genes... we are all built out of the same stuff, that works the same
way at a cellular level.
Evo - Devo
I. Background
II. Core Processes
- Basic biological processes are CONSERVED, and the enzymes that
perform them are CONSERVED:
- Many enzymes are more than 50% similar in AA sequence in E. coli
and H. sapiens.
- Of 548 metabolic enzymes in E. coli, 50% are present in ALL LIFE,
and only 13% are unique to bacteria.
- So the variation and diversity of life is NOT due to changes in metabolic or
structural genes... we are all built out of the same stuff, that works the same
way at a cellular level.
- Variation is largely due to HOW these processes are REGULATED... 300 cell
types in humans, all descended from the zygote; all genetically the same.
Evo - Devo
I. Background
II. Core Processes
III. Weak Linkage Regulation
- Development is NOT a single process
Evo - Devo
I. Background
II. Core Processes
III. Weak Linkage Regulation
- Development is NOT a single process
- Development is a well choreographed dance of many parallel processes...
Evo - Devo
I. Background
II. Core Processes
III. Weak Linkage Regulation
- Development is NOT a single process
- Development is a well choreographed dance of many parallel processes...
- How is the parallelism maintained, ESPECIALLY as one process evolves?
Evo - Devo
I. Background
II. Core Processes
III. Weak Linkage Regulation
- Development is NOT a single process
- Development is a well choreographed dance of many parallel processes...
- How is the parallelism maintained, ESPECIALLY as one process evolves?
- Because they may be triggered by the same (or subsets of the same)
REGULATORS... these are transcription factors that can turn suites of
metabolic/structural genes on and off.
Evo - Devo
I. Background
II. Core Processes
III. Weak Linkage Regulation
- Development is NOT a single process
- Development is a well choreographed dance of many parallel processes...
- How is the parallelism maintained, ESPECIALLY as one process evolves?
- Because they may be triggered by the same (or subsets of the same)
REGULATORS... these are transcription factors that can turn suites of
metabolic/structural genes on and off. And transcription factors can interact.
Evo - Devo
I. Background
II. Core Processes
III. Weak Linkage Regulation
- Best (and most fundamental)
examples are HOX genes. These
are 'homeotic genes' that produce
a variety of transcription factors.
The production and localization of
these transcription factors are
CRITICAL in determining the
'compartments' of bilaterally
symmetrical animals.
Evo - Devo
I. Background
II. Core Processes
III. Weak Linkage Regulation
- Duplication of hox genes
can lead to differential
regulation in different
segments, and different
phenotypes in different
segments.
inhibition of limb
development
Evo - Devo
I. Background
II. Core Processes
III. Weak Linkage Regulation
- Duplication of hox genes
can lead to differential
regulation in different
segments, and different
phenotypes in different
segments.
Each gene produces a DNA
binding protein that turns on a
set of genes... different hox
genes produce different
binding proteins, that
stimulate different sets of
genes...that are ALL regulated
by THIS transcription factor
(linked regulation coordinated response).
Evo - Devo
I. Background
II. Core Processes
III. Weak Linkage Regulation
- Effects can be profound
antennaepedia
Evo - Devo
I. Background
II. Core Processes
III. Weak Linkage Regulation
- Effects can be profound
- But they demonstrate the 'modularity' of
the developmental plan - only single units
are affected.
Bithorax
Evo - Devo
I. Background
II. Core Processes
III. Weak Linkage Regulation
- Effects can be profound
- But they demonstrate the 'modularity' of
the developmental plan - only single units
are affected.
- 'Master Switches'
that initiate
downstream cascades
that can be very
different... like
compound or
vertebrate eyes.
Evo - Devo
I. Background
II. Core Processes
III. Weak Linkage Regulation
- and they are still integrated with the rest of the
organism
For example, the length of a breed's snout
correlated directly with the number of repeats in a
gene called Runx-2. Runx-2's tandem repeat
consists of two different three-base sequences,
randomly ordered along the length of the repeat. If
there's more of one threesome relative to the other,
that breed's muzzle tends to be longer and
straighter. Fonden and Garner. 2004. PNAS
Evo - Devo
I. Background
II. Core Processes
III. Weak Linkage Regulation
- Types of Regulation
Enhancer - upstream activation
sequence. Binding site for
transcription factor.
Mutation here is cis-regulation
(within the operational "cistron")
Evo - Devo
I. Background
II. Core Processes
mutation in the
transcription factor gene is
called trans-regulation
III. Weak Linkage Regulation
- Types of Regulation
Enhancer - upstream activation
sequence. Binding site for
transcription factor.
Mutation here is cis-regulation
(within the operational "cistron")
Evo - Devo
I. Background
II. Core Processes
mutation in the
transcription factor gene is
called trans-regulation
III. Weak Linkage Regulation
- Types of Regulation
Enhancer - upstream activation
sequence. Binding site for
transcription factor.
Mutation here is cis-regulation
(within the operational "cistron")
Each type modulates
activity about 50% of the
time...
Evo - Devo
I. Background
II. Core Processes
III. Weak Linkage Regulation
- NOVELTY
Mutations may make an enhancer
available to a different transcription
factor... and now that gene is 'on' in a
new tissue and can be used for a new
function. Crystallins are heat-shock
proteins and mitochondrial enzymes;
but when they are expressed in the
eye, they are used as transparent
structural proteins in a completely
different process.
And of course, how
they are arranged in
lenses vary.
Evo - Devo
I. Background
II. Core Processes
III. Weak Linkage Regulation
- NOVELTY
OR, an entirely new binding site can
evolve - they are typically quite short
(6-10 bases) so they will arise
frequently by random
mutation...selection can then favor new
regulatory pathways....
KEEP THE OLD, but GAIN NEW
(sound familiar???)
- Prud'homme et al. 2006. Repeated morphological evolution through cisregulatory changes in a pleiotropic gene Nature 440:1050-1053.
a–c, The wing spots on
male flies of the
Drosophila genus.
Drosophila tristis (a)
and D. elegans (b)
have wing spots that
have arisen during
convergent evolution.
Drosophila gunungcola
(c) instead evolved
from a spotted
ancestor. d, Males
wave their wings to
display the spots during
elaborate courtship
dances. (Photographs
courtesy of B.
Prud'homme and S.
Carroll.)
- Prud'homme et al. 2006. Repeated morphological evolution through cisregulatory changes in a pleiotropic gene Nature 440:1050-1053.
yellow gene
enzyme for pigment
production
"spotted wing"
In their previous research, they
found that spotted members of
both spotted clades had same cis
regulatory element (CRE). So,
they hypothesized that all
members of the clade were
descended from a spotted
ancestor (99% chance ancestor
was spotted - fig.)
- Prud'homme et al. 2006. Repeated morphological evolution through cisregulatory changes in a pleiotropic gene Nature 440:1050-1053.
yellow gene
LOSS of the spot within this clade
(an example of convergent
evolution AND reversion) occurred
by different mutations in same
CRE.
- Prud'homme et al. 2006. Repeated morphological evolution through cisregulatory changes in a pleiotropic gene Nature 440:1050-1053.
yellow gene
LOSS of the spot within this clade
(an example of convergent
evolution AND reversion) occurred
by different mutations in same
CRE.
Importantly, yellow is still on
elsewhere. This is a pleiotropic
gene that has many effects.
- Prud'homme et al. 2006. Repeated morphological evolution through cisregulatory changes in a pleiotropic gene Nature 440:1050-1053.
yellow gene
LOSS of the spot within this clade
(an example of convergent
evolution AND reversion) occurred
by different mutations in same
CRE.
Importantly, yellow is still on
elsewhere. This is a pleiotropic
gene that has many effects.
Shutting it "off" by a mutation in the
gene would cripple it's activity
throughout the organism. Here,
through cis regulation, it's
expression is modulated in only
one tissue (wing).
- Prud'homme et al. 2006. Repeated morphological evolution through cisregulatory changes in a pleiotropic gene Nature 440:1050-1053.
yellow gene
spotted wing
In D. tristis, the yellow gene is
enhanced by a completely different,
independently evolved CRE.
- Prud'homme et al. 2006. Repeated morphological evolution through cisregulatory changes in a pleiotropic gene Nature 440:1050-1053.
Two gains and two losses are due
to independent changes in the
regulation of the yellow gene.
The developmental 'scaffold' for
forming spots exists... subsequent
evolution of enhancement can form
a new anatomical trait, which can
be rapidly selected for by sexual
selection.
Evo - Devo
I. Background
II. Core Processes
III. Weak Linkage Regulation
- HETEROCHRONY
- paedomorphism
- peramorphism
- allometry
All simply changes in the developmental rates of different structures or
processes.
Allometry in horn length relative to body size in Beetles
Scarabaeidae: Onthophagus
Evolution of legs from fins
Evolution of legs from fins
Evo - Devo
I. Background
II. Core Processes
III. Weak Linkage Regulation
IV. Exploratory Behavior
Evo - Devo
I. Background
II. Core Processes
III. Weak Linkage Regulation
IV. Exploratory Behavior
- environmental cues affect cell activity - production of growth factors
Evo - Devo
I. Background
II. Core Processes
III. Weak Linkage Regulation
IV. Exploratory Behavior
- environmental cues affect cell activity - production of growth factors
- hypoxia - stimulates cell to produce endothelial growth factor
Evo - Devo
I. Background
II. Core Processes
III. Weak Linkage Regulation
IV. Exploratory Behavior
- environmental cues affect cell activity - production of growth factors
- hypoxia - stimulates cell to produce endothelial growth factor
- neighboring vascular tissue grows towards the source of growth factor
Evo - Devo
I. Background
II. Core Processes
III. Weak Linkage Regulation
IV. Exploratory Behavior
- environmental cues affect cell activity - production of growth factors
- hypoxia - stimulates cell to produce endothelial growth factor
- neighboring vascular tissue grows towards the source of growth factor
- and BINGO... now you have vascular tissue and hypoxia is corrected
Evo - Devo
I. Background
II. Core Processes
III. Weak Linkage Regulation
IV. Exploratory Behavior
- environmental cues affect cell activity - production of growth factors
- hypoxia - stimulates cell to produce endothelial growth factor
- neighboring vascular tissue grows towards the source of growth factor
- and BINGO... now you have vascular tissue and hypoxia is corrected
- Nerves and vessels grow in response to local signals... the pattern is not
hardwired.
Evo - Devo
I. Background
II. Core Processes
III. Weak Linkage Regulation
IV. Exploratory Behavior
- environmental cues affect cell activity - production of growth factors
- hypoxia - stimulates cell to produce endothelial growth factor
- neighboring vascular tissue grows towards the source of growth factor
- and BINGO... now you have vascular tissue and hypoxia is corrected
- Nerves and vessels grow in response to local signals... the pattern is not
hardwired.
- So, if bone growth changes, muscles cell growth responds, and correct
ennervation and vascularization occurs on this new platform.