Developmental Biology – Biology 4361pschoff/documents/TheAnatomicalTradition09.pdf · Germ Layers Germ layer – region of cells that give rise to all tissues and organs germ –

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





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





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.


Comparative embryology (historic)

Experimental embryology (modern techniques)Embryo manipulationCell lineage


Cell lineageFate mapping


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





Teratology


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





Teratology/medical embryology


Medical Embryology & Teratology

Mathematical Embryology

Mathematical Embryology

Mort Henick

Documents

Developmental Biology – Biology 4361pschoff/documents/TheAnatomicalTradition09.pdf · Germ Layers Germ layer – region of cells that give rise to all tissues and organs germ –