Evo-Devo: The merging of Evolutionary and Developmental Biology
Eddy M. De RobertisHHMI/UCLA, USA
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.
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The early embryo is a self-regulating field
In 1901 Hans Spemann used baby hair ligature to induce twins
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Self-regulating morphogenetic fields: Ross Harrison, 1918
Ross Harrison
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The Organizer experiment - 1924
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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 pre-eminent science for the most of the 20thcentury.
Embryonic induction: tissue differentiations are directed by neighboring cells
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Thomas H. Morgan
Bithorax, a four-wingedDrosophilamutant. Bridges and Morgan, 1923
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Homeotic genes specify A-P segment identity inDrosophila. Colinearity between their order in DNA and in the body.
Edward B. Lewis
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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 development-controlling gene identified in vertebrates.”Carrasco, McGinnis, Gehring and De Robertis, Cell 1984
Homeobox DNA encodes a DNA-binding protein domain of 60 amino acids called the Homeodomain.
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Hox complexes are conserved betweenDrosophilaand mammals(from De Robertis, Oliver and Wright, Scientific American, 1990)
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Evo-Devo: the A-P Hox patterning system was conserved
Hox-C6, the first vertebrate Hox gene cloned.
De Robertis, Cell 2008
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De Robertis & Sasai, Nature 1996
Evo-Devo: the common urbilaterian ancestor had a Hox complex with least seven Hox genes.
Ur = PrimevalBilateria = all bilateral animals (30 phyla)
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F. Jacob
In October 1991, a meeting on “Evolution and Development” was held in Crete in honor of F. Jacob's retirement
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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
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Chordin/BMP pathway: a network of interacting extracellular proteins
BMP4
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De Robertis, Cell 2008
The Chordin/BMP network patterns D-V differentiation in vertebrates,Drosophila, and many other animals.
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Evo-Devo:Urbilateriaused the Chordin/BMP/Tolloid pathway for D-V cell differentiations
One common gene tool-kit
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Owl
Coquille Saint-Jacques
Sepia
Insect
Walter Gehring
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Expression of mouse Pax6 induces ectopic eyes inDrosophila
Eyes evolved only once.
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Musca Hypothetical Mammalian retina
Cajal and Sanchez, 1915 The ancestral eye was complex.
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Evo-Devo:Urbilateriahad complex neural circuits
One common gene tool-kit
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13 Wnts in humans
12 Wnt families in Sea Anemone
5 Wnts
7 Wnts
Genomes contain the record of our evolutionary history
Gene deletions were common during evolution
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Developmental control networks placed evolutionary constraints on the animal anatomies that evolved by natural selection
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Future directions in Evo-Devo:Reconstruct the ancestral animal genomic tool-kit.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?Establish how cells integrate positional information within fields of cells to decide when to divide, differentiate or die.
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In sum, animals evolved through variations in ancestral gene networks hard-wired in our DNA.
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