Download Evo-Devo: The merging of Evolutionary and Developmental Biology

Evo-Devo: The merging of Evolutionary and
Developmental Biology
Eddy M. De Robertis
HHMI/UCLA, USA
1) Cell differentiation self-regulates during animal development.
2) Conserved ancestral gene networks control development of the
Antero-Posterior (A-P) and Dorso-Ventral (D-V) embryonic axes.
3) Evolution has been channeled by an ancestral “primeval
genome” tool-kit shared by all animals.
Slide 1
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The early embryo is a self-regulating field
In 1901 Hans Spemann
used baby hair ligature
to induce twins
Slide 3
Self-regulating morphogenetic fields:
Ross Harrison, 1918
Ross Harrison
Slide 4
The Organizer experiment - 1924
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Embryonic induction: tissue differentiations
are directed by neighboring cells
The discovery of embryonic induction represented the apogee of
developmental biology, for which Spemann received the Nobel Prize in
1935. After that, the genetics of Thomas H. Morgan became the preeminent science for the most of the 20th century.
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Thomas H. Morgan
Bithorax, a four-winged Drosophila mutant.
Bridges and Morgan, 1923
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Edward B. Lewis
Homeotic genes specify A-P segment identity in Drosophila.
Colinearity between their order in DNA and in the body.
Slide 8
Homeobox DNA encodes a DNA-binding protein
domain of 60 amino acids called the Homeodomain.
Walter Gehring
Matthew Scott
“A Xenopus laevis gene was cloned on the basis of
cross-homology to a region conserved between
several Drosophila homeotic genes… This gene
could perhaps represent the first developmentcontrolling gene identified in vertebrates.”
Carrasco, McGinnis, Gehring and De Robertis, Cell
1984
Slide 9
Hox complexes are conserved between Drosophila and mammals
(from De Robertis, Oliver and Wright, Scientific American, 1990)
Slide 10
Evo-Devo: the A-P Hox patterning system was
conserved
Hox-C6, the first vertebrate Hox
gene cloned.
De Robertis, Cell 2008
Slide 11
Evo-Devo: the common urbilaterian ancestor had a Hox
complex with least seven Hox genes.
Ur = Primeval
Bilateria = all bilateral animals (30 phyla)
De Robertis & Sasai, Nature 1996
Slide 12
In October 1991, a meeting on “Evolution
and Development” was held in Crete in
honor of F. Jacob's retirement
F. Jacob
Slide 13
S. J. Gould
Etienne Geoffroy Saint-Hilaire’s lobster - 1822
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Chordin is a BMP antagonist required for
Spemann organizer function
BMP = Bone Morphogenetic Protein
Slide 16
Chordin/BMP pathway: a network of interacting extracellular proteins
BMP4
Slide 17
The Chordin/BMP network patterns D-V differentiation in
vertebrates, Drosophila, and many other animals.
De Robertis, Cell 2008
Slide 18
Evo-Devo: Urbilateria used the Chordin/BMP/Tolloid pathway
for D-V cell differentiations
One common gene tool-kit
Slide 19
Owl
Insect
Coquille Saint-Jacques
Sepia
Walter Gehring
Slide 20
Expression of mouse Pax6 induces ectopic eyes in Drosophila
Eyes evolved only once.
Slide 21
Musca
Hypothetical
Cajal and Sanchez, 1915
The ancestral eye was complex.
Mammalian retina
Slide 22
Evo-Devo: Urbilateria had complex neural circuits
One common gene tool-kit
Slide 23
Genomes contain the record of our evolutionary history
5 Wnts
7 Wnts
13 Wnts in
humans
12 Wnt families in Sea Anemone
Gene deletions were common during evolution
Slide 24
Developmental control networks placed evolutionary constraints
on the animal anatomies that evolved by natural selection
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Future directions in Evo-Devo:
1) Reconstruct the ancestral animal genomic tool-kit.
2) Retrace the genetic mutations, duplications and deletions that
actually caused adaptations in the course of evolution. How
has the obligatory use of ancient developmental gene
networks channeled these outcomes?
3) Establish how cells integrate positional information within
fields of cells to decide when to divide, differentiate or die.
Slide 26
In sum, animals evolved through variations in
ancestral gene networks hard-wired in our DNA.
Slide 27