H1: Introduction
LINK BETWEEN DEVELOPMENT AND
EVOLUTION: CANT CHANGE STRUCTURE IF
DEVELOPMENT HASN’T CHANGED (EVO-
DEVO)!
Gastrulation= after cleavage: movement of
cells + formation of axes + formation 3 germ
layers→ main structure of body is generated
1. Approaches to study
developmental biology
A. Anatomical approaches
a) Comparative embryology: how does anatomy change during development?
b) Evolutionary embryology: how can changes of development cause evolutionary change?
c) Medical embryology and teratology: study of birth defects (genetic
malformations/syndromes, disruptions by teratogens)
d) Mathematical modelling: description of development by mathematical equations (growth,
patterning)
VON BAER’S LAWS OF VERTEBRATE EMBRYOLOGY:
1) General features of large group of animals appear earlier in development than specialised
features.
2) Less general characters develop from more general, until finally the most specialised
appear.
3) Embryo of given species, instead of passing through the adult stages of lower animals,
depart more and more from them
4) Early embryo of ‘higher’ animal is never like ‘lower’ animal, but only like its early embryo.
EARLY EMBRYO’S AT CERTAIN STAGE RESEMBLE EACHOTHER VERY MUCH!
Fate mapping of embryos
Fate map= map that indicates which portions of embryo will give rise to which larval/adult structures
(destinies), made by tracing cell lineages
➔ observation of living embryos (natural dye) + vital dye marking + genetic marking (quail and
chick cells) + radioactive labelling/ fluorescent dyes
Cell lineage studies reveal: Cellular basis of morphogenesis
Cells constantly change during Direction + number of cell divisions
embryogenesis Cell shape changes
Cells do NOT remain in one place + keep Cell migration
same shape Cell growth
2 major cell types in embryo: Cell death
- epithelial cells (tightly, forms layers) Changes in cell surface/ matrix
- mesenchymal cells (less properties
interconnected)
1
,Main patterns of cleavage
Holoblastic cleavage= complete cleavage, blastomeres completely separate from eachother → cells
with not a lot of yolk
Types of cell movement during gastrulation
Invagination Infolding of sheet of cells Sea-urchin endoderm
Involution Movement of cells against Amphibian mesoderm
inner surface of remaining
external cells
Ingression Migration of individual Sea-urchin mesoderm
cells to interior + neuroblast
Drosophila
Delamination Splitting of one cellular Hypoblast in birds en
sheet of cells into 2 mammals
Epiboly Movement of epithelial Ectoderm in sea-
cells spreading as unit → urchin, tunicates,
surround deeper layers of amphibia
embryo
➔ Complementary to
involution
Evolutionary embryology
Darwin: “Community of embryonic structure reveals community of descent”
Homologous structures= structures with similar function, same descent
Analogous structures= structures with a similar function, but different descent
CHOANOFLAGELLATES WERE THE COMMON ANCESTOR OF ALL ANIMALS → can live in colonies
(rosettes) or single cells: rosetteless protein important for cell-cell adhesion
2
,Production extra-embryonal tissues
a) Amnion: water sack
b) Allantois: excretion
c) Chorion: gas exchange
d) Yolk sack: food
➔ Avoids evaporation: allows development on land
➔ IMPORTANT EVOLUTIONARY INNOVATION TO GENERATE REPTILES!
Transitional states in animal evolution
a) Lancelet: rudimentary notochord + nerve
chord structures → invertebrate chordate
b) Archaeopteryx: reptilian skeleton + avian
feathered wings
c) Tiktaalik roseae: fish fins + amphibian
forelibs
d) Hydra: 2 main epithelial layers with few cells
in between → said to be diploblastic instead
of triploblastic
B. Experimental approaches
a) Environmental developmental biology
Phenotypic plasticity: phenotypic variation to environmental differences
Environmental sex Echiuroid worms: male sex is determined by population
determination density on bottom of sea (factor produced by female)
Turtles, alligators: T of incubation determines sex
Seasonal variation European map butterfly: photoperiod/T (production of
ecdysis hormone)
Caterpillar of Nemoria arizonaria: food affects
phenotype
Protection against UV Sea urchin embryos: eat algae containing mycosporine
radiation → incorporated in eggs (natural sunscreen)
Amphibian egg hatching: higher hatching success when
UV-B blocking filter is present
Phase polyphenism Schistocerca gregaria: higher population density →
become gregarious
➔ 1 genome, 2 extreme phenotypes
Thalidomide= taken by pregnant mothers to relieve morning sickness → causes lack of
proper limb development (phocomelia)
➔ Time window when different defects can occur!
b) Developmental dynamics of cell specification
Commitment of cell fate in 2 stages:
specification (labile stage) + determination (fixed
fate)
DEVELOPMENT USES MIXTURE OF CONDITIONAL AND
AUTONOMOUS SPECIFICATION (DEPENDS ON FATE)
3
, Autonomous Specification: differential acquisition of cytoplasmic molecules present
specification in egg
Results in mosaic development: cells cannot change fate if blastomere
is lost (isolation of trophoblast → only forms trophoblast)
CELLS HAVE ALREADY GAINED THEIR FATE
➔ Most invertebrates
Conditional Specification: interaction among cells (position of cells relative to
specification eachother are key)
Regulative developments: acquire different functions as result of
interactions with neighbouring cells → develops differently in other
environment
Existence of identical twins
➔ Vertebrates + few invertebrates
Syncytial Specification: cytoplasmic morphogens + concentration gradients
specification After cellularisation: autonomous + conditional specification
➔ Most insect classes
Germ plasm theory (August Weismann)= different cell types might be generated because
they lost determinants so they stay totipotent → only muscle determinants need to be
detained in order to form muscle!
➔ JUST A THEORY!
C. Genetic approaches
2. Main things to know
Neural tube= ectoderm above notochord → becomes nervous system
Somites= mesodermal masses on either side of notochord → form vertebrae + ribs + skeletal muscles
Neural crest= critical in making gut neurons
3. Development of Drosophila melanogaster
Syncytial blastoderm= dividing nuclei move to periphery (arranged in ordered
way), multiple nuclei in cell with 1 cytoplasm → 14th cycle: cellular boundaries
are being made
➔ Gradients in cytoplasm are sensed by nuclei in different manner!
1. Oocyte: maternal mRNA deposited in genital chamber → anterior
localisation of Bicoid mRNA + posterior localisation of Nanos mRNA
2. Fertilisation: formation syncytial blastoderm + production proteins →
formation Bicoid-Nanos gradient
3. Define A-P axis
➔ Example of syncytial specification!
How to test hypotheses in experimental embryology?
1) Defect experiment: observe development when portion of embryo is destroyed
2) Isolation experiment: remove part of embryo + observe both parts
3) Recombination experiment: replace original part of embryo by other part of same embryo
4) Transplantation experiment: portion of embryo is replaced by part of other embryo
➔ Control experiments are important!
Driesch’s pressure-plate experiment= put pressure on embryo so 3rd equatorial division becomes
medial → alter distribution of nuclei (saw normal development)
4
LINK BETWEEN DEVELOPMENT AND
EVOLUTION: CANT CHANGE STRUCTURE IF
DEVELOPMENT HASN’T CHANGED (EVO-
DEVO)!
Gastrulation= after cleavage: movement of
cells + formation of axes + formation 3 germ
layers→ main structure of body is generated
1. Approaches to study
developmental biology
A. Anatomical approaches
a) Comparative embryology: how does anatomy change during development?
b) Evolutionary embryology: how can changes of development cause evolutionary change?
c) Medical embryology and teratology: study of birth defects (genetic
malformations/syndromes, disruptions by teratogens)
d) Mathematical modelling: description of development by mathematical equations (growth,
patterning)
VON BAER’S LAWS OF VERTEBRATE EMBRYOLOGY:
1) General features of large group of animals appear earlier in development than specialised
features.
2) Less general characters develop from more general, until finally the most specialised
appear.
3) Embryo of given species, instead of passing through the adult stages of lower animals,
depart more and more from them
4) Early embryo of ‘higher’ animal is never like ‘lower’ animal, but only like its early embryo.
EARLY EMBRYO’S AT CERTAIN STAGE RESEMBLE EACHOTHER VERY MUCH!
Fate mapping of embryos
Fate map= map that indicates which portions of embryo will give rise to which larval/adult structures
(destinies), made by tracing cell lineages
➔ observation of living embryos (natural dye) + vital dye marking + genetic marking (quail and
chick cells) + radioactive labelling/ fluorescent dyes
Cell lineage studies reveal: Cellular basis of morphogenesis
Cells constantly change during Direction + number of cell divisions
embryogenesis Cell shape changes
Cells do NOT remain in one place + keep Cell migration
same shape Cell growth
2 major cell types in embryo: Cell death
- epithelial cells (tightly, forms layers) Changes in cell surface/ matrix
- mesenchymal cells (less properties
interconnected)
1
,Main patterns of cleavage
Holoblastic cleavage= complete cleavage, blastomeres completely separate from eachother → cells
with not a lot of yolk
Types of cell movement during gastrulation
Invagination Infolding of sheet of cells Sea-urchin endoderm
Involution Movement of cells against Amphibian mesoderm
inner surface of remaining
external cells
Ingression Migration of individual Sea-urchin mesoderm
cells to interior + neuroblast
Drosophila
Delamination Splitting of one cellular Hypoblast in birds en
sheet of cells into 2 mammals
Epiboly Movement of epithelial Ectoderm in sea-
cells spreading as unit → urchin, tunicates,
surround deeper layers of amphibia
embryo
➔ Complementary to
involution
Evolutionary embryology
Darwin: “Community of embryonic structure reveals community of descent”
Homologous structures= structures with similar function, same descent
Analogous structures= structures with a similar function, but different descent
CHOANOFLAGELLATES WERE THE COMMON ANCESTOR OF ALL ANIMALS → can live in colonies
(rosettes) or single cells: rosetteless protein important for cell-cell adhesion
2
,Production extra-embryonal tissues
a) Amnion: water sack
b) Allantois: excretion
c) Chorion: gas exchange
d) Yolk sack: food
➔ Avoids evaporation: allows development on land
➔ IMPORTANT EVOLUTIONARY INNOVATION TO GENERATE REPTILES!
Transitional states in animal evolution
a) Lancelet: rudimentary notochord + nerve
chord structures → invertebrate chordate
b) Archaeopteryx: reptilian skeleton + avian
feathered wings
c) Tiktaalik roseae: fish fins + amphibian
forelibs
d) Hydra: 2 main epithelial layers with few cells
in between → said to be diploblastic instead
of triploblastic
B. Experimental approaches
a) Environmental developmental biology
Phenotypic plasticity: phenotypic variation to environmental differences
Environmental sex Echiuroid worms: male sex is determined by population
determination density on bottom of sea (factor produced by female)
Turtles, alligators: T of incubation determines sex
Seasonal variation European map butterfly: photoperiod/T (production of
ecdysis hormone)
Caterpillar of Nemoria arizonaria: food affects
phenotype
Protection against UV Sea urchin embryos: eat algae containing mycosporine
radiation → incorporated in eggs (natural sunscreen)
Amphibian egg hatching: higher hatching success when
UV-B blocking filter is present
Phase polyphenism Schistocerca gregaria: higher population density →
become gregarious
➔ 1 genome, 2 extreme phenotypes
Thalidomide= taken by pregnant mothers to relieve morning sickness → causes lack of
proper limb development (phocomelia)
➔ Time window when different defects can occur!
b) Developmental dynamics of cell specification
Commitment of cell fate in 2 stages:
specification (labile stage) + determination (fixed
fate)
DEVELOPMENT USES MIXTURE OF CONDITIONAL AND
AUTONOMOUS SPECIFICATION (DEPENDS ON FATE)
3
, Autonomous Specification: differential acquisition of cytoplasmic molecules present
specification in egg
Results in mosaic development: cells cannot change fate if blastomere
is lost (isolation of trophoblast → only forms trophoblast)
CELLS HAVE ALREADY GAINED THEIR FATE
➔ Most invertebrates
Conditional Specification: interaction among cells (position of cells relative to
specification eachother are key)
Regulative developments: acquire different functions as result of
interactions with neighbouring cells → develops differently in other
environment
Existence of identical twins
➔ Vertebrates + few invertebrates
Syncytial Specification: cytoplasmic morphogens + concentration gradients
specification After cellularisation: autonomous + conditional specification
➔ Most insect classes
Germ plasm theory (August Weismann)= different cell types might be generated because
they lost determinants so they stay totipotent → only muscle determinants need to be
detained in order to form muscle!
➔ JUST A THEORY!
C. Genetic approaches
2. Main things to know
Neural tube= ectoderm above notochord → becomes nervous system
Somites= mesodermal masses on either side of notochord → form vertebrae + ribs + skeletal muscles
Neural crest= critical in making gut neurons
3. Development of Drosophila melanogaster
Syncytial blastoderm= dividing nuclei move to periphery (arranged in ordered
way), multiple nuclei in cell with 1 cytoplasm → 14th cycle: cellular boundaries
are being made
➔ Gradients in cytoplasm are sensed by nuclei in different manner!
1. Oocyte: maternal mRNA deposited in genital chamber → anterior
localisation of Bicoid mRNA + posterior localisation of Nanos mRNA
2. Fertilisation: formation syncytial blastoderm + production proteins →
formation Bicoid-Nanos gradient
3. Define A-P axis
➔ Example of syncytial specification!
How to test hypotheses in experimental embryology?
1) Defect experiment: observe development when portion of embryo is destroyed
2) Isolation experiment: remove part of embryo + observe both parts
3) Recombination experiment: replace original part of embryo by other part of same embryo
4) Transplantation experiment: portion of embryo is replaced by part of other embryo
➔ Control experiments are important!
Driesch’s pressure-plate experiment= put pressure on embryo so 3rd equatorial division becomes
medial → alter distribution of nuclei (saw normal development)
4
