Developmental Anatomy
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Preformation vs Epigenesis: A history.
Primary Germ Layers and early organs.
Karl von Baer and his laws.
Fate Mapping
Evolutionary Embryology.
Aristotle: First biologist?
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The Generation of Animals (350 BCE)
Noted Variations of life cycle themes:
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Some born of Eggs (oviparity)
Some from live birth (viviparity)
Some from eggs, but hatch in mother (ovoviviparity).
Holoblastic- whole egg divided into smaller cells
Meroblastic- half egg divides into smaller cells; rest is yolk
sac.
Cell Division differs amongst species
Ex ovo omnia- Willaim Harvey 1651
Preformation
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Belief that everything is in
egg and/or sperm in
smaller form.
Overtime, organs and
essentially the organism
grows.
Marcello Malphigi- studies
chick embryos..notes
abundance of structure in
embryo and questions
epigenesis
Predates cell theory
Epigenesis
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Embryonic parts arise
from embryonic tissue.
Newly formed organs.
Kasper Friedrich Wolff
provides evidence that
embryonic organs arise
from tissue that has no
adult counter part!
Sets the foundation for
Germ layer theory.
“Developmental Force”
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Immanuel Kant and Johann
Friedrich Blumenbach
(mid to late 1700s).
Mystical force leads to
development of embryos.
This “force” is heritable
from germ cells and highly
susceptible to change.
Mendel’s work almost a
century later…
Developmental force=
Genetics?
Using the microscope revolutionizes
development
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Christian Pander, Heinrich
Rathke, and Karl Ernst von
Baer.
Identify the three germ
layers:
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Ectoderm
Mesoderm
Endoderm
The Three Germ Layers
Triploblastic and diploblastic Organisms
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These organisms use all three germ layers.
Some organisms only use two germ layers (lack
mesoderm):
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Porifera (sponges)
Cnidarians (sea anemones, hydra, jellyfish)
Ctenophores (comb jellies)
Axes and Symmetry
Christian Pander
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Work with Chick
Embryos.
Supports epigenesis by
showing that tissues
worked together to form
organs.
Discovers tissue
interaction-Induction:
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No tissue can form organs
alone, must interact with
other tissues in order to
for organogenesis to occur.
Heinrich Rathke
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Discovered pharyngeal
arches.
In fish, these arches give
rise to gill apparatus
In humans, form jaw, ears,
vertebrate skull.
Karl Ernst von Baer
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“Father” of
Developmental Biology
Expanded Pander’s studies
of Chick Embryos.
Identifies notochord- rod
of dorsal-most mesoderm
tissue.
Notochord divides
embryo in right and left
sides, instructs ectoderm
above it to differentiate
into nerve tissue.
von Baer laws
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Rule 1:The general features
of a large group of animals
appear earlier in
development than do the
specialized features of a
smaller group.
All vertebrates have
similar structures during
development: gill arches,
notochord, primitive
kidneys.
Very similar shortly after
gastrulation.
von Baer’s laws
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Rule 2: Less General
characters are developed
from the more general, until
finally the most specialized
appear.
All vertebrates have skin,
later skin becomes
feathers for birds, scales
for reptiles, hair and nails
for mammals
von Baer’s Laws
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Rule 3: The embryo of a given species, instead of passing
through the adult stages of lower animals, departs more and
more from them.
Visceral clefts of embryonic birds/mammals do not
ressemble gill slits of adult fish.
von Baer’s Laws
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Rule 4: Therefore, the early
embryo of a higher animal is
never like a lower animal,
but only like its early
embryo.
We never pass through a
developmental stage
similar to adult fish or
birds.
Are there really similarities?
The Cell theory and Fate mapping
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Matthias Schleiden and
Theodor Schwann in 1838
formalize the Cell theory:
all living organisms are
composed of cells!
Embryologists followed
this movement and began
tracking cell movement
during development!
Two Cell types: Epithelial and Mesenchymal
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Epithelial
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Mesenchymal
Morphogenesis
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Direction and No. of cell
divisions
Cell shape changes
Cell movement
Cell growth
Cell death.
Cell Movement and association
Cadherin based
adhesion-self
association.
Different strength
of interaction
Morphogenesis
How do you fate map cells?
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Observing live embryos!
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Edwin G Conklin
Still used as primary fate
mapping technique.
Zebra Fish will allow you
to do this!
How do you fate map cells?
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Vital Dye Marking
Vital dyes stain the cells
but don’t kill them.
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Dead cells tell no
tales…unless you study
apoptosis.
How do you fate map cells?
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Radioactive/ Fluorescent
labeling
Radioactive label:
Transplant of graft from
radiolabeled embryo to
unlabeled embryo. Silver
stain!
Fluorescent labeling: Inject
fluorescent dye into cells
of embryo.
How do you fate map cells?
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Genetics!
Use cells from another
organism that contain a
easily detectable marker!
Darwin: Embryology’s biggest fan!
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Saw Embryology as support
for his theories.
“Community of embryonic
structure reveals community
of descent”
This is shown in
Homologous structures,
such as the forelimb of
human arms vs. wings of a
bird!
What would be an
analogous structure?
Evolutionary change is due to
developmental change..
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Ontogeny causes
phylogeny?
Human fingers versus Bat
wing!