Developmental Biology - PowerPoint PPT Presentation

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Developmental Biology

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Developmental Biology The Spemann Experiment Spemann & Mangold, 1923 Danny Ben-Zvi Overview Developmental Biology Embryological Vocabulary The Spemann experiment ... – PowerPoint PPT presentation

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Title: Developmental Biology


1
Developmental Biology
  • The Spemann Experiment
  • Spemann Mangold, 1923

Danny Ben-Zvi
2
Overview
  • Developmental Biology
  • Embryological Vocabulary
  • The Spemann experiment
  • Prospects

3
Developmental Biology
  • The study of the process by which organisms grow
    and develop wikipedia
  • Grow From a single cell to a multicellular,
    specialized organism. A process repeated
    successfully time after time.
  • Develop developmental processes take place
    throughout life
  • Progenitor cells muscle, bone marrow, neurons,
    skin
  • Tumors

4
Developmental Biology
  • Paradox There are not enough genes to encode the
    organisms complexity
  • Genes are re-used
  • Timing, localization, combinations, dosage
  • The concept of One gene one character is
    generally wrong
  • Self organization
  • Intercellular communication
  • Formation of complex structures

5

Developmental BiologyModel Organisms
  • Why use model organisms?
  • Ethical reasons
  • Grow faster
  • Rapid reproduction, many embryos
  • Extra-organism development
  • Fish, amphibians, insects
  • Development is a highly conserved evolutionary
    process

6
Model Organisms
  • Vertebrates, athropods, mollusks, and even worms
    have many similar proteins and DNA sequences
  • Genes and proteins from one organism can be used
    in other organisms
  • Genomes of many model organisms were sequenced

7
Model Organisms
  • Mouse - Mus musculus
  • Chicken - Gallus gallus
  • Zebrafish - Danio rerio
  • Black Toed Frog Xenopus leavis
  • Salamander Triton cristatus/teaniatus
  • Sea Urchin Strongylocentrotus purpuratus
  • Round Worm - Caernohabitis elegans
  • Fruit Fly Drosophila Melanogaster
  • Various plants

8
Vocabulary - Axes
animal
  • Animal-Vegetal

vegetal
9
First Stages of Embryonic Development
  • Fertilization/Oogenesis
  • Cleavage
  • Gastrulation
  • neurulation

10
Fertilization/Oogenesis
  • Egg activation
  • Formation of the zygotic DNA
  • Initiation of the developmental processes
  • Symmetry breaking event

11
Cleavage
  • Embryo divides in an extraordinary fast rate
    mitosis every 30-40 minutes
  • Virtually no growth in size
  • Controlled by pre-existing maternal
    proteins/mRNA no time for transcription and
    translation new zygote genes
  • Creation of the blastocoel - cleavage cavity and
    blastula - sphere of cells surrounding it
  • movie

12
Animal pole (top) view
13
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14
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15
Gastrulation
  • Formation of three germ layers
  • Ectoderm (outer layer) - skin
  • Mesoderm (middle layer) muscles, bones
  • Endodern (inner layer) digestive track
  • Formation of embryonic axes
  • Activation of zygote genes
  • Considerable movement of cells - without growth

16
Vegetal (bottom) view
movie
17
Vegetal (bottom) view
Blastopore lip
18
side view
animal
vegetal
19
Gastrulation
  • Movie

20
Gastrulation
21
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22
Fate Map
23
Neurulation
  • Elongation of the embryo
  • Formation of the neural tube and notochord (in
    chordates), somites, and early organ
    predecessors kidney, heart

24
Dorsal view
25
Neurulation
  • movie

26
Spemann Experiment
  • Outline Graft a tissue from one embryo into
    another embryo, and see what happens Cut and
    Paste
  • Main observation A graft of a specific tissue
    (the organizer) to a specific location can induce
    Siamese twins connected at the belly.
  • Conclusion The embryos cells are not committed
    to a certain fate.

27
Spemann Experiment
  • movie
  • Experimental details

28
Summary of Results
  • A piece taken from the upper blastopore lip of a
    gastrulating amphibian embryo exerts an
    organizing effect on its environment ... Such a
    piece can therefore be designated as an
    organizer

Vegetal view
29
Summary of Results
  • These secondary embryonic primordia are always
    of mixed origin.
  • an organizer of another species is used for
    induction, then the chimeric composition can be
    established with certainty and great accuracy

30
Controls? Statistics?
  • Control
  • The authors do not present a control experiment
    grafting to other locations, at other times, etc.
  • They do state however, that development is
    impeded after the grafting procedure
  • Statistics
  • From H. Mangolds lab notebooks we can learn that
    only 15 of the embryos survived the graft
  • Spontaneous Siamese twin may occur naturally at
    a lower rate

31
Spemanns innovation
  • Until 1923, an embryo had a predefined fate
    map. Spemann proved that this was not the case
  • Cells up to a certain stage are pluripotent can
    have many developmental fates
  • Spemann established the concept of organizer
  • Stem cells and control over cell fate

32
Prospects
  • Spemann won the Nobel prize in 1935
  • Hilde Mangold died in 1926
  • Spemann Organizer was found in all vertebrates,
    including human
  • Dorsal-Ventral patterning has become the model
    system for embryonic patterning
  • Stem cells are the promise for many future
    therapies
  • summary

33
Molecular Basis of the Organizer
  • A gradient of morphogens determines the fate of
    the cells in the embryo.
  • Morphpgen A polypeptide that governs the
    development of a tissue
  • Morphogens are produced from a defined source
  • Their concentration provides positional
    information regarding the distance from the
    source
  • The organizer secretes both morphogens and their
    inhibitors which diffuse throughout the embryo

34
Molecular Basis of the Organizer
  • There are about 5 main families of morphogens
    used in all the developmental processes
  • These families are shared by almost all
    multi-cellular organisms
  • Drosophila uses the same morphogen as vertebrates
    to pattern its dorsal ventral axis
  • But in the opposite direction

35
Summary
  • Vocabulary
  • Embryo development is highly conserved in
    evolution
  • Cells are not committed to a certain fate
    (pluripotent). They interact and influence each
    other and then specialize
  • Dorsal ventral axis formation is a central model
    system for pattern formation

36
Questions?
37
Cycle Length During Cleavage
Back
38
Choice of Model Organism
  • Extra-cellular development
  • T. teaniatus survives the grafting procedure
  • T.cristatus has less pigmentation than
    T.teaniatus
  • Similar species
  • Though grafting between evolutionary distant
    organisms works as well

39
Experimental Procedures
  • Fertilization
  • Exert sperm (testes) and eggs.
  • Manually fertilize in dish
  • Graft
  • Peel the Chorion off the two embryos
  • Cut the receiving embryo where the graft will be
    inserted
  • Excise the graft from the donating embryo
  • Put the graft on the receiving embryo

Medium Sterility handle with care
40
Grafting Experiments
  • Graft region near the dorsal lip of T.cristatus
    (light) at gastrula and implant it in animal side
    of T.teaniatus/alpestris (dark) at gastrula.
  • Fix the embryo at neurula, make cross sections,
    and characterize the resulting chimera

41
Controlled Experimental Variables
  • Size of graft
  • Exact location of graft from donor embryo
  • Exact developmental stage of each embryo
  • Graft location in the receiving embryo

42
Uncontrolled Experimental Variables
  • Orientation of implant
  • Embryos response to the procedure
  • Contamination
  • Embryo variation

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