developmental biology – biology 4361pschoff/documents/theanatomicaltradition09.pdf · germ layers...
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Developmental Biology – Biology 4361
The Anatomical TraditionThe 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
How do biologists study it?
Fundamental concepts and questions
General questions
Scientific approachesHistoricalModern
Core concepts
Modern
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 zygote embryo adult
1 cell 1 cell multiple ~1011 cells
gametes zygote embryo adult
(haploid) (diploid) cells 10 cells
2 cell 1 cell multiple 200+ cell2 celltypes
1 celltype
multiplecell types
200+ celltypes
General Questions(according to Gilbert)(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 tissuesDifferentiated cells are organized into complex sets of tissueswith 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.h t i h ll d li ti t b t h de.g. homeostasis… each cell duplication must be matched 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 cellularmodifications that are necessary for reproductionmodifications that are necessary for reproduction.
4. How are gametes formed?
General Questions:
New phenotypes have the potential to be established onlyd i i ’ d l t l i dduring an organism’s developmental period.
5. How do changes in development create new body forms?
General Questions:
During development organisms respond to the environmentalconditions to which they are exposed.
6. How is development of an organism integrated into the larger context of its habitat?
General Questions:
2 H ll i d i t ti d ?
1. How do cells differentiate? [Differentiation]
2. How are cells organized into tissues and organs? [Morphogenesis]
3. How do cells know when to stop dividing? [Growth]
4. How is gametogenesis accomplished? [Reproduction]g g p [ p ]
5. How do changes in development create new body forms? [Evolution]body forms? [Evolution]
6. How is development of an organism integrated i t th l t t f it h bit t?into the larger context of its habitat? [Environmental integration]
Scientific Approaches
Comparative embryology (historic)p y gy ( )
Experimental embryology (modern)
Evolutionary embryology
T t lTeratology
Mathematical modelingg
Comparative Embryology
Richard N Feinberg, Greg HolmesDr. Nicole Valenzuela
Comparative EmbryologyHippocrates (5th century BCE) - recognized development
Aristotle (4th century BCE) - cleavage patterns viviparity etc *Aristotle (4 century BCE) - cleavage patterns, viviparity, 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 theory (no size problem)y ( p )- age of Earth unknown (so not a problem)- eliminated need for “vital force”
Homunculus
Epigenesis – new organism formed de novo (“from scratch”)epi - “after”
i “ i i ”
l i d bl di f t it- explained mixture of traits in hybrids
genesis - “origin”
- explained blending of traits- embryos had structures unknown in adults
Comparative EmbryologyHippocrates (5th century BCE) - recognized development
Aristotle (4th century BCE) - cleavage patterns viviparity etc *Aristotle (4 century BCE) - cleavage patterns, viviparity, 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 origingerm – initiates development or serves as an originecto- outside, external
d i id i t l ithiendo- inside, internal, withinmeso- middle, intermediated ki i-derm skin, covering
-blast immature form
Germ LayersDiploblastic organisms (cnidaria, ctenophores, porifera)
- 2 germ layers (lack true middle layer)
Triploblastic organisms (vertebrates, echinoderms, etc) - 3 germ layers
Germ LayersDiploblastic 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
Mesoderm middle layer; forms blood, heart, kidneys, gonads, bones, muscles, connective tissues-
Endoderm inner layer; forms inside of digestive tract, associated organs-
TriploblastsTriploblasts
DiploblastsDiploblasts
Comparative EmbryologyHippocrates (5th century BCE) - recognized development
Aristotle (4th century BCE) - cleavage patterns viviparity etc *Aristotle (4 century BCE) - cleavage patterns, viviparity, 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 appearuntil finally the most specialized appear.
3. The embryos of a given species, instead of passingthrough the adult stages of lower animals departsthrough the adult stages of lower animals, departs more and more from them.
4. Therefore, the early embryo of a higher animal is neverlike a lower animal, but only like its early embryo.
B ’ k k d th t iti f i lvon Baer’s work marked the transition from mainlyobservational to experimental embryology.
Scientific Approaches
Comparative embryology (historic)
Experimental embryology (modern techniques)Embryo manipulationCell lineage
Evolutionary embryology
Cell lineageFate mapping
Evolutionary embryology
Teratology
Mathematical modeling
Experimental Embryology TechniquesIsolation – remove and grow part of embryo by itself
(no communication, signals, regulation from outside)
Removal – a portion of the embryo is removedWh t h t th i i b ?What happens to the remaining embryo?Is there a gap? Are organs or tissues missing?
Transplantation – portion removed, transplanted to another embryo
h t h i diff theterospecific - different specieshomospecific - same species
heterotopic - different place (same embryo)heterochronic - different age
Tracing Cell Lineage
C. elegansg
invariant cell lineages- 959 cells; each lineage known
Constructing Fate Maps
zygote 8-cellyg
Fate Mapping
Fate Mapping Techniques
Heterospecifictransplantation
Scientific Approaches
Comparative embryology (historic)p y gy ( )
Experimental embryology (modern)
Evolutionary embryology
Teratology
Mathematical modelingg
Evolutionary Embryology
Homologousstructures?
Analogousstructures?structures?
Homologous Structures
Evolutionary Embryology
jointed legs etc
barnacle (arthropod)barnacle larvaelegs, etc.
notochord,nerve cord
sea squirt (chordate)sea squirt larvae
Evolutionary Developmental Biology
PeripatusPeripatus
Distal-lessgene
Scientific Approaches
Comparative embryology (historic)p y gy ( )
Experimental embryology (modern)
Evolutionary embryology
Teratology/medical embryology
Mathematical modelingg
Medical Embryology & Teratology
Mathematical Embryology
Mathematical Embryology
Mort Henick