IGP Genetics and Development

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IGP Genetics and Development
Lecture 1, October 26, 2005 Introduction
to Vertebrate Development
Bruce Appel Department of Biological
Sciences b.appel_at_vanderbilt.edu
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Animal Development
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Developmental Genetics seeks to answer questions
such as
How do you make top and bottom (rostral and
caudal)? How do you make front and back (ventral
and dorsal)? How do you make left and
right? How do you make organs? How do you
control size? How do you make different cells in
the right number at the right time and
place? How do you control cell migration? How
do you repair injury?
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Invertebrate and vertebrate developmental biology
pose similar questions
and, fortunately, find many similar answers (with
the exception of a few details).
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• Vertebrate developmental biologists use several
  different model organisms
• (frog, chick, zebrafish, mouse) and combine many
  experimental strategies
• embryology
• biochemistry
• molecular genetics
• classical genetics
• Embryological experiments reveal general
  principles of development and
• genetics reveals the molecular mechanisms that
  underlie developmental
• processes.
• For example, tissue transplantation experiments
  reveal sources of
• signaling molecules that pattern surrounding
  cells and genetics is
• used to identify the molecules

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• Overview of my section
• Theme Using vertebrate genetics to investigate
  vertebrate
• problems.
• Lecture 1
• zebrafish and mouse gastrulation
• Embryological investigation of the Organizer
• Lecture 2
• The awesome power of zebrafish genetics
• Zebrafish mutant screens
• Lecture 3
• From phenotype to gene and back again
• Intro to noncanonical Wnt signaling and
  gastrulation
• Lecture 4
• Canonical Wnt signaling and anteroposterior
• patterning of the central nervous system
• Flex Time
• Using zebrafish genetics to investigate microRNA
  function

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All organs and tissues arise from three germ
layers
1) Ectoderm
CNS
neural crest (PNS, pigment, facial
cartilage and bone, connective tissue)
skin
2) Mesoderm
3) Endoderm
muscle spine ribs
kidney gonads
heart blood vessels
gut lungs
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How do we make germ layers? Step 1 Multiple
rounds of cell cleavage
Cleavage of the zebrafish egg and early embryo
0.75 hpf
mid-blastula stage
2.0 hpf
Zebrafish Information Network (ZFIN) http//zfin.o
rg
Cleavage mitotic divisions that reduce cell
volume Blastomere cleavage stage cell
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Multiple rounds of cell division create the
blastula, a ball-like cell mass
2.5 hpf
4.7 hpf
Zebrafish Information Network (ZFIN) http//zfin.o
rg
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Gastrulation is the process of forming the
3-layered body plan from a ball of cells
blastula
yolk cell
5.25 hpf
D
V
D
V
10.0 hpf
Zebrafish Information Network (ZFIN) http//zfin.o
rg
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Epiboly spreading and thinning of the blastula
over the yolk cell Involution internalization
movements at blastula margin, which create germ
layers Convergence cell movements toward dorsal
(D) and away from ventral (V) Extension cell
movements that lengthen the body axis
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Continued growth and morphogenesis shapes the body
10.7 hpf
21.5 hpf
Zebrafish Information Network (ZFIN) http//zfin.o
rg
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Its Showtime.
R. Karlstrom and D. Kane
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Gastrulation entails coordinated cell movements
Epithelial- mesenchymal transition
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There are many similarities between the cell
movements of gastrulation and cancer metastasis
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Early stages of mammalian development
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Mammals gastrulate using essentially the same
cell movements as zebrafish, but the geometry is
different
Involution
this is where embryonic stem cells come from
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Morphogenesis begins to shape the germ layers
convergence
extension
A
V
D
P
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What are the mechanisms that turn a pile of cells
into an embryo?
Hilde Mangold and Hans Spemann found that a piece
of prospective dorsal tissue can organize
formation of an embryo
Spemann was awarded the 1935 Nobel Prize for
Physiology or Medicine. Hilde Mangold died in
1924 as this paper, which was her PhD work, was
being published.
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Spemann and Mangolds demonstration of the
Organizer
Conclusion the dorsal blastopore lip is the
source of signals that pattern the embryo
(both cell movements and cell fate).
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What organizes the organizer?
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Wnt signaling and dorsoventral axis determination
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Differential ?-catenin stability produces
differential gene expression
D
V
ventral
dorsal organizer genes
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What does the organizer do?
The organizer is a source of molecules that
inhibit BMP signaling. This leads, in part, to
induction of neural ectoderm and formation of
different types of mesoderm on the
dorsoventral axis.
Chordin, Noggin Follistatin, Xnr3
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So, what does this have to do with stem cells,
anyway?
Stem cell niches are organizers
Fuchs et al., 2004
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Wnt signaling is important for stem cells
Multipotent hair follicle cells express Wnt
pathway genes
Elevated Wnt signaling promotes hair formation
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To recap Complex cell movements and signaling
interactions shape the vertebrate body form. The
same mechanisms that regulate development regulate
stem cells and are implicated in cancer and
other diseases. How do we figure out the
mechanisms that regulate these processes?
GENETICS