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

What goes on as an embryo develops from a single, pluripotent cell into a complete organism?

Majority of dev systems are multicellularSingle-celled systems used to study cellular

differentiation

Differentiation Morphogenesis Growth Reproduction Evolution Environmental Integration

Developmental Biology is Defined by the Questions Asked

Cell movements & tissue reorganizationsHow 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 divisionAllometric growth - varying rates of mitosis in

regions of the embryoIsometric growth- equal rates of mitosis throughout

embryo

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

The germ plasmGametogenesis - 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 embryoWhat 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

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

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

Early “Embryologists”

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

Preformation vs Epigenesis

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

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

Preformation vs Epigenesis

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

The First Embryologists ca1820

First Embryologists

Germ Layers (Pander)

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

Ernst von Baer’s Laws

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