Developmental Biology Introduction

Developmental Biology vs 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 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

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 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

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