Lecture 5
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Transcript of Lecture 5
Lecture 5
• The history of comparative embryology and the 20th century dissociation between development and evolution
• Modern evolutionary developmental biology (EvoDevo)
Pre-Darwinian concept of evolution
‘Transformationism’
Human
Fish
Worm
Protozoan
Ont
ogen
y, P
hylo
geny
Karl Ernst von Baer (1792-1876): Embryologist, anti-transformationist
(and creationist)
Von Baer’s Four Principles
1) The general features of a large group of animals appear earlier than do the specialized features of a smaller group
2) Less general characters develop from the more general, until finally the most specialized appear
3) The embryo of a given species, instead of passing through the adult stages of lower animals, departs more and more from them
4) Therefore, the early embryo of a higher animal is never like a lower animal, but only like its early embryo
Trochophore type embryos
Polychaete worm Bivalve mollusc (clam) Vestimentiferan
Dipleurula type embryos
Sea urchin Brittle star Sea cucumber Sea star
Sea urchin Brittle star Sea star Acorn worm Echinoderms Hemichordate
Charles Darwin co-opted von Baer’s comparative embryology as evidence for evolution
Ernst Haeckel (1834-1919): Naturalist, Philosopher, Transformationist
Biogenetic law: “Ontogeny recapitulates phylogeny”
The 20th century divorce and reconciliation between embryology and evolutionary biology
• Divorce:– The late-19th century rise of Entwicklungsmechanik
arose in part in reaction to Haeckel– The nucleus-cytoplasm controversy in embryology gave
birth to genetics as a distinct field removed from embryology
– Embryologists remained fixated on cell signaling and cytoplasm
– The Modern Synthesis (of genetics and Darwinian evolutionary biology) considered embryology to be irrelevant
Figure 4.1 E. B. Wilson (1856–1939) (A) and Thomas Hunt Morgan (1866–1945) (B)
Figure 4.2 Theodor Boveri (1862–1915) (A) and Nettie M. Stevens (1861–1912) (B)
Figure 4.3 Frank Lillie (A), Hans Spemann (left) and Ross Harrison (right) (B), Ernest E. Just (C).
The 20th century divorce and reconciliation between embryology and evolutionary biology
• Reconciliation– The developmental genetics pioneered by C.H.
Waddington and others– The writings of Stephen J. Gould and others in
the 1970s– The discovery of Hox genes in the 1980s– Revival of EvoDevo in the late 20th century
Figure 4.4 Salome Gluecksohn-Schoenheimer (Now S. Gluecksohn-Waelsch) (A),and Conrad Hal Waddington (B).
Developmental reaction normCanalizationGenetic assimilation of environmentally-induced characters(see also: Richard Goldschmidt, I. Schmalhausen)
Brachyury mutant
Developmental reaction norm
Figure 3 Temperature shocking Aglais urticae produces phenocopies of geographic variants. (A) Usual central European variant; (B) heat-shock phenocopy resembling Sardinian form; (C) a Sardinian form of the species. (After Goldschmidt 1938.)
Canalization
Phenotype (reaction norm)
Genetic or environmental change
Genetic assimilation
Stephen J. Gould
Developmental heterochronies and the importance of gene regulation
Ed Lewis, Christianne Nusslein-Volhard, and Eric Wieschaus
Discoveries of developmental regulatory genes
..
Bithorax mutant
Scenario of insect evolution proposed by Ed Lewis based on homeotic mutations like bithorax
Discovery of the Homeobox (Hox) in1984
Modern evolutionary developmental biology (EvoDevo)
• What is the structure of the tree of life?
Figure 23.1(1) Relationships among Phyla
Modern evolutionary developmental biology (EvoDevo)
• What is the structure of the tree of life?• How do differences and similarities among
organisms correlate with developmental genetics?
…ACGTGATAACCGTCGATGTGGTCTGAGCATCAATGCATATTACTGAC……TGCACTATTGGCAGCTACACCAGACTCGTAGTTACGTATAATGACTG…
GAGCAUCAAUGCAUAUUACUGAC…
DNA:
RNA:
M H I T D… Protein:
Structural InformationRegulatory Information
Amino Acid Codons
Transcription
Translation
…ACGTGATAACCGTCGATGTGGTCTGAGCATCAATGCATATTACTGAC……TGCACTATTGGCAGCTACACCAGACTCGTAGTTACGTATAATGACTG…DNA:
Structural InformationRegulatory Information
* * *
*Potential targets of evolutionary mutation
Modern evolutionary developmental biology (EvoDevo)
• What is the structure of the tree of life?– Phylogeny reconstruction
• Molecular distances• Character matrices (anatomy, gene expression, etc.)
Bioinformatics and Genomics
Multiple Sequence Alignments
Phylogenetic trees
Rennert et al., BMC Evol. Biol. 3: 4, 2003
-1
SpRunt-2
Runx Gene Evolution
!
Runx Gene Evolution
Runx Gene Evolution
Modern evolutionary developmental biology (EvoDevo)
• What is the structure of the tree of life?– Phylogeny reconstruction
• Molecular distances• Character matrices (anatomy, gene expression, etc.)
• How do differences and similarities among organisms correlate with developmental genetics?– Gene expression (esp. regulatory genes)– Gene function (changes in protein structure or gene
regulation/expression)– GRN architecture
Example: Homeobox (HOX) gene evolution
• ‘Downstream’ cis-regulatory changes in Hox target genes
• ‘Upstream’ changes in the regulation/pattern of Hox gene expression
• Changes in Hox protein structure/function• Changes in Hox gene number
Figure 23.2 Expression of Regulatory Transcription Factors in Drosophila and in Vertebrates Along the Anterior-Posterior Axis
Example: Homeobox (HOX) gene evolution
• ‘Downstream’ cis-regulatory changes in Hox target genes
• ‘Upstream’ changes in the regulation/pattern of Hox gene expression
• Changes in Hox protein structure/function• Changes in Hox gene number
Figure 23.3 Differences in Larval and Adult Morphology Due to Hox Gene Differences
Upstream changes in Hox regulation (Ubx, AbdA) Downstream changes in Hox target genes
Figure 23.4 Distal-Less Gene Expression in the Larva of the Buckeye Butterfly, Precis
Sean Carroll
Upstream changes in Hox regulation (Ubx, AbdA)
Figure 23.5(1) “Holes” in the Expression of abdA and Ubx in the Abdomenof the Larval Butterfly Precis
Sean Carroll
Upstream changes in Hox regulation (Ubx, AbdA)
Figure 23.5(2) “Holes” in the Expression of abdA and Ubx in the Abdomenof the Larval Butterfly Precis
Example: Homeobox (HOX) gene evolution
• ‘Downstream’ cis-regulatory changes in Hox target genes
• ‘Upstream’ changes in the regulation/pattern of Hox gene expression
• Changes in Hox protein structure/function• Changes in Hox gene number
Figure 23.6(1) Changes in the Ultrabithorax Protein Associated with the Insect Clade (Polyalanine repression domain: Ubx Dll)
S. Carroll; W. McGinnis
Figure 23.6(2) Changes in the Ultrabithorax Protein Associated with the Insect Clade (Polyalanine repression domain: Ubx Dll)
Example: Homeobox (HOX) gene evolution
• ‘Downstream’ cis-regulatory changes in Hox target genes
• ‘Upstream’ changes in the regulation/pattern of Hox gene expression
• Changes in Hox protein structure/function• Changes in Hox gene number
Figure 23.7(1) Hox Gene Expression and Morphological Change in Crustaceans
Figure 23.7(2) Hox Gene Expression and Morphological Change in Crustaceans
Figure 23.8 Schematic Representation of the Expression of Ubx and abdA (Green) in the Thoracic Segments of Different Types of Crustaceans
Figure 23.9 Loss of Limbs in Snakes
Example: Homeobox (HOX) gene evolution
• ‘Downstream’ cis-regulatory changes in Hox target genes
• ‘Upstream’ changes in the regulation/pattern of Hox gene expression
• Changes in Hox protein structure/function• Changes in Hox gene number
Figure 23.11 Postulated Ancestry of the Hox Genes From a Hypothetical Ancestor
“Deep Homology”
Figure 23.14 Homologous Pathways Specifying Neural Ectoderm in Protostomes (Drosophila) and Deuterostomes (Xenopus)
Figure 23.15 Homology of Signaling Pathways in the Formation of the Anterior-Posterior Axes in Drosophila and Chick Appendages
Figure 23.16 Deep Homology of the Limbs
Deep Homology from the GRN perspective
An endomesoderm GRN subcircuit conserved between sea urchins and sea stars
V. Hinman
Mechanisms for recent phenotypic divergenceFigure 23.22 Regulation of Chick Limb Apoptosis by BMPs
Mechanisms for recent phenotypic divergence
3 SEPTEMBER 2004 VOL 1462 305 SCIENCE
Evolutionary Questions
• How do organisms evolve? – Bottom up processes (changes in genes and
gene regulatory networks)
• Why do organisms evolve?– Top down processes (changes in ecology,
natural selection)