Developmental Biology
Introduction
Developmental Biology vs
Embryology
Embryology
– observational biology
– experimental manipulations
Developmental Biol
– expands embryological studies using molecular
techniques
– used genetic approaches to study model
systems
Developmental Biology
Approaches in Other Fields
Cancer Biology
Neuroscience
The answers to questions in these fields
require knowing when during development
particular events occur
Developmental Biology is
Defined by the Questions Asked
 Differentiation
 Morphogenesis
 Growth
 Reproduction
 Evolution
 Environmental
Integration
Developmental Biology is
Defined by the Questions Asked
Differentiation
 Morphogenesis
 Growth
 Reproduction
 Evolution
 Environmental
Integration
What goes on as an embryo
develops from a single,
pluripotent cell into a
complete organism?
Majority of dev systems are
multicellular
Single-celled systems used to
study cellular
differentiation
Developmental Biology is
Defined by the Questions Asked
 Differentiation
Morphogenesis
 Growth
 Reproduction
 Evolution
 Environmental
Integration
Cell movements & tissue
reorganizations
How do differentiated cells
move and reorganize
during development to
generate functional
organisms?
Major point of study for
classical embryology
Developmental Biology is
Defined by the Questions Asked
 Differentiation
 Morphogenesis
Growth
 Reproduction
 Evolution
 Environmental
Integration
What are the limiting factors
for cell division
Allometric growth - varying
rates of mitosis in regions
of the embryo
Isometric growth- equal rates
of mitosis throughout
embryo
Developmental Biology is
Defined by the Questions Asked
 Differentiation
 Morphogenesis
 Growth
Reproduction
 Evolution
 Environmental
Integration
The germ plasm
Gametogenesis - formation
and maintenance of
pluripotent, haploid germ
cells (gametes)
Recognition & interaction of
gametes at fertilization
Developmental Biology is
Defined by the Questions Asked
 Differentiation
 Morphogenesis
 Growth
 Reproduction
Evolution
 Environmental
Integration
Survivability of evolutionary
mutations is limited by
restraints of
embryogenesis
Evolutionary changes must
be small changes for the
embryo
What are the evolutionary
relationships between
groups of organisms
Developmental Biology is
Defined by the Questions Asked
 Differentiation
 Morphogenesis
 Growth
 Reproduction
 Evolution
Environmental
Integration
Early development of many
organisms is influenced by
environmental cues
Examples:
color/shape of butterfly
larvae (caterpillars)
diapause in invertebrates
in vernal pools
Early “Embryologists”
 Aristotle (300BC)
– credited with 1st notions on embryology
 William Harvey (mid 1600s)
– hypothesized that all animals originate from an egg
 Marconi Malpighi (late 1600s)
– drew 1st micrographs of developing chick embryos
– ignited debate between preformationist and epigenesists
Preformation vs Epigenesis
Preformation
– Embryonic structures are preformed within the
gamete (either egg or sperm)
Epigenesis
– the embryonic structures arise anew from the
interaction of substances within the gametes
Preformation vs Epigenesis
Malpighi found embryonic structures in
“unincubated” eggs
– these eggs were left in the warm sun of
southern Italy during the summer months
– So although they were unincubated, they were
not unfertilized and some embryonic
development occurred
Malpighi’s observation spurned the
preformationist
Preformationist vs Epigenesis
Unusual Hypotheses of Preformationists
– a tiny preformed being present in the gamete
• This being would also have even tinier beings within
it’s embryonic germ cells
– and those tinier beings would have tinier still beings
within their gametes
» and so on and so on
» and so on and so on
»
and so on and so on
»
and so on and so on
»
and so on and so on
Preformation vs Epigenesis
Pervasiveness of preformationist ideas
– Fertilization had never been observed
– There was as yet (1600s) no cell theory to give
a lower limit to the size a cell could have
The First Embryologists ca1820
Christian Pander
– visualized epigenesis of embryonic germ layers
Karl Ernst von Baer
– described notochord, discovered mammalian
egg, proposed 4 laws of development
Heinrich Rathke
– described pharyngeal arches, skull formation
First Embryologists
Germ Layers (Pander)
Ernst von Baer’s Laws
1. general characters of a [genus] appear earlier during
development than characters of [species]
2. more specific characters derive from more general
characters
3. the embryo of a given species diverges form the adult
form of lower animals rather than passing through the
adult forms of lower animals
4. early embryos of higher animals never looks like a
lower animal, but does resemble the embryo of lower
animals
First Embryologists
Rathke’s Skull Studies
Lineage Tracing
Observations of pigmented cells in living
Tunicate embryos (E.G. Conklin, 1905)
Conklin’s Drawings of Tunicate
Embryogenesis: Tracing Muscle Lineage
Lineage Tracing in Amphibian
Embryos with Vital Dyes
Lineage Tracing in Zebrafish
with Fluorescent Dyes
Lineage Tracing in Xenopus with
Fluorescent Dyes