1. Developmental Biology
Introduction

2. Developmental Biology vs Embryology
observational biology
experimental manipulations
Developmental Biol
expands embryological studies using molecular techniques
used genetic approaches to study model systems

3. Developmental Biology Approaches in Other Fields
Cancer Biology
Neuroscience
The answers to questions in these fields require knowing when during development particular events occur

4. Developmental Biology is Defined by the Questions Asked
Differentiation
Morphogenesis
Growth
Reproduction
Evolution
Environmental Integration

5. 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

6. 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

7. 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

8. 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

9. 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

10. 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

11. 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

12. Preformation vs Epigenesis
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

13. 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

14. 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

15. 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

16. 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

17. First Embryologists
Germ Layers (Pander)

18. Ernst von Baer’s Laws
general characters of a [genus] appear earlier during development than characters of [species]
more specific characters derive from more general characters
the embryo of a given species diverges form the adult form of lower animals rather than passing through the adult forms of lower animals
early embryos of higher animals never looks like a lower animal, but does resemble the embryo of lower animals

19. First Embryologists
Rathke’s Skull Studies

20. Lineage Tracing
Observations of pigmented cells in living Tunicate embryos (E.G. Conklin, 1905)

21. Conklin’s Drawings of Tunicate Embryogenesis: Tracing Muscle Lineage

22. Lineage Tracing in Amphibian Embryos with Vital Dyes

23. Lineage Tracing in Zebrafish with Fluorescent Dyes

24. Lineage Tracing in Xenopus with Fluorescent Dyes