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Developmental Biology – Biology 4361
The Anatomical Tradition
2009
A hen is only an egg’s way of making a new egg.
Samuel Butler,, 1885
The Anatomical Tradition - Overview
What is developmental biology?
How do biologists study it?
Fundamental concepts and questions
General questions
Scientific approaches
Historical
Modern
Core concepts
Fundamental Questions & Concepts
How does a fertilized egg give rise to the adult body?
How does the adult body produce yet another body?
Gametes
Life Cycle
Adult
Fundamental Questions & Concepts
Gametes
Life Cycle
Adult
gametes
1 cell
(haploid)
2 cell
types
zygote
1 cell
(diploid)
1 cell
type
embryo
multiple
cells
multiple
cell types
adult
~10
1011 cells
200+ cell
types
General Questions
(according to Gilbert)
1 cell (1 type) creates ~1014 cells (~214 types)
Yet, each cell in the zygote, embryo, and adult has identical DNA.
1. How do cells differentiate?
General Questions:
Differentiated cells are organized into complex sets of tissues
with a variety of functions.
2. How are cells organized into tissues and organs?
General Questions:
During development, all cells, tissues, and organs naturally
limit their growth.
e.g. homeostasis…
h
t i
each
h cellll d
duplication
li ti mustt b
be matched
t h d
by elimination of another cell
- “perfect waste management and recycling”1
Pathological conditions often tip this balance
- stroke/infarction
- AIDS
- cancers
3. How do cells know when to stop dividing?
1. Galluzzi et al., 2007 Cell Death and Differentiation 14:1237-1266
General Questions:
Sperm and eggs are haploid and have many other cellular
modifications that are necessary for reproduction
reproduction.
4. How are gametes formed?
General Questions:
New phenotypes have the potential to be established only
d i an organism’s
during
i ’ d
developmental
l
t l period.
i d
5. How do changes in development create new body forms?
General Questions:
During development organisms respond to the environmental
conditions to which they are exposed.
6. How is development of an organism integrated into the
larger context of its habitat?
General Questions:
1. How do cells differentiate? [Differentiation]
2 How
2.
H
are cells
ll organized
i d into
i t titissues and
d organs?
?
[Morphogenesis]
3. How do cells know when to stop dividing? [Growth]
4. How is g
gametogenesis
g
accomplished?
p
[[Reproduction]
p
]
5. How do changes in development create new
body forms? [Evolution]
6. How is development of an organism integrated
i t the
into
th larger
l
context
t t off its
it habitat?
h bit t?
[Environmental integration]
Scientific Approaches
Comparative
p
embryology
y gy ((historic))
Experimental embryology (modern)
Evolutionary embryology
T t l
Teratology
Mathematical modeling
g
Comparative Embryology
Dr. Nicole Valenzuela
Richard N Feinberg, Greg Holmes
Comparative Embryology
Hippocrates (5th century BCE) - recognized development
Aristotle (4th century BCE) - cleavage patterns
patterns, viviparity,
viviparity etc.
etc *
William Harvey (1640s) - Ex ovo omnia (“all from the egg”)
Marcello Malpighi (1672) - microscopic account of development
Origins – Preformation v. Epigenesis
Preformation – new organism contained in sperm or egg
- no cell theoryy (no
( size p
problem))
- age of Earth unknown (so not a problem)
- eliminated need for “vital force”
Homunculus
Epigenesis – new organism formed de novo (“from scratch”)
epi - “after”
genesis
i - “origin”
“ i i ”
- explained mixture of traits in hybrids
- explained
l i d bl
blending
di off ttraits
it
- embryos had structures unknown in adults
Comparative Embryology
Hippocrates (5th century BCE) - recognized development
Aristotle (4th century BCE) - cleavage patterns
patterns, viviparity,
viviparity etc.
etc *
William Harvey (1640s) - Ex ovo omnia (“all from the egg”)
Marcello Malpighi (1672) - microscopic account of development
Kaspar Friedrich Wolff (1733-1794) - differentiated tissues arise
from undifferentiated cells
Christian Pander (c. 1817) - germ layers, induction
Germ Layers
Germ layer – region of cells that give rise to all tissues and organs
germ – initiates development or serves as an origin
ecto- outside, external
endod inside,
i id iinternal,
t
l within
ithi
meso- middle, intermediate
-derm
d
skin,
ki covering
i
-blast immature form
Germ Layers
Diploblastic organisms (cnidaria, ctenophores, porifera)
- 2 germ layers (lack true middle layer)
Triploblastic organisms (vertebrates, echinoderms, etc)
- 3 germ layers
Germ Layers
Diploblastic organisms (cnidaria, ctenophores, porifera)
- 2 germ layers (lack true middle layer)
Triploblastic organisms (vertebrates, echinoderms, etc)
- 3 germ layers
Ectoderm
- outer layer; forms epidermis, brain, CNS
middle layer; forms blood, heart, kidneys,
Mesoderm gonads, bones, muscles, connective tissues
inner layer; forms inside of digestive tract,
Endoderm associated organs
Triploblasts
Diploblasts
Comparative Embryology
Hippocrates (5th century BCE) - recognized development
Aristotle (4th century BCE) - cleavage patterns
patterns, viviparity,
viviparity etc.
etc *
William Harvey (1640s) - Ex ovo omnia (“all from the egg”)
Marcello Malpighi (1672) - microscopic account of development
Kaspar Friedrich Wolff (1733-1794) - differentiated tissues arise
from undifferentiated cells
Christian Pander (c. 1817) - germ layers, induction
Karl Ernst von Baer (1820’s) - described blastula, notochord,
mammalian egg
von Baer’s Laws
1. General features of a large group of animals appear earlier
in development than do the specialized features of a
smaller group.
2. Less general characters develop from the more general,
until finally the most specialized appear
appear.
3. The embryos of a given species, instead of passing
through the adult stages of lower animals
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.
von Baer’s
B ’ work
k marked
k d th
the ttransition
iti ffrom mainly
i l
observational to experimental embryology.
Scientific Approaches
Comparative embryology (historic)
Experimental embryology (modern techniques)
Embryo manipulation
Cell lineage
Fate mapping
Evolutionary embryology
Teratology
Mathematical modeling
Experimental Embryology Techniques
Isolation – remove and grow part of embryo by itself
(no communication, signals, regulation from outside)
Removal – a portion of the embryo is removed
Wh t happens
What
h
t the
to
th remaining
i i embryo?
b ?
Is there a gap? Are organs or tissues missing?
Transplantation – portion removed,
transplanted to another embryo
homospecific - same species
heterospecific - different species
h t
heterochronic
h i - different
diff
t age
heterotopic - different place (same embryo)
Tracing Cell Lineage
C. elegans
g
invariant cell lineages
- 959 cells; each lineage known
Constructing Fate Maps
zygote
yg
8-cell
Fate Mapping
Fate Mapping Techniques
Heterospecific
transplantation
Scientific Approaches
Comparative
p
embryology
y gy ((historic))
Experimental embryology (modern)
Evolutionary embryology
Teratology
Mathematical modeling
g
Evolutionary Embryology
Homologous
structures?
Analogous
structures?
Homologous Structures
Evolutionary Embryology
jointed
legs etc
legs,
etc.
barnacle larvae
barnacle (arthropod)
sea squirt larvae
sea squirt (chordate)
notochord,
nerve cord
Evolutionary Developmental Biology
Peripatus
Distal-less
gene
Scientific Approaches
Comparative
p
embryology
y gy ((historic))
Experimental embryology (modern)
Evolutionary embryology
Teratology/medical embryology
Mathematical modeling
g
Medical Embryology & Teratology
Mathematical Embryology
Mathematical Embryology
Mort Henick