Developmental Biology

Front 1

Neural Plate and Neural Tube Formation

Back 1

ectoderm above the notochord specified as nueroectoderm

Front 2

nueroectoderm

Back 2

forms the neural tube, which forms the nervous system

Front 3

Spemann Organizer

Back 3

an inductive capacity changes during gastrulation
early grafts induce complete body exes
mid gsatrula grafts induce trunk and tail but no head
late gastrula graft induces just tail

Front 4

Vegetal region of Spemann Organizer

Back 4

(brown)
the ability to induce heads
the 2 regions express different transcription factors and give rise to different regions of mesoderm

Front 5

Dorsal region of the SO

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(red)
can induce trunk and tail structures but not heads

Front 6

Formation of Neural Tissue

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depends on an inductive signal
ventral ectoderm has not yet been determined at this stage
nueral tissue is induced during gastrulation

Front 7

Signals from the Organizer

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2 possibilties for secreted signaling factors
Stimulatory "neutralizing" factor: ectoderm (positive induction)
inhibitory factors that neutralize signals: ectoderm to become epidermal (default mode)

Front 8

key experiment with xenopus

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ectoderm will not form neural tissue unless it is dessaggregated and cells reaggregrated
this process removed a promoter of epidermal fate BMP-4

Front 9

Signals for Neural Induction

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noggin and Chordin from SO inhibit BMP-4
Positive signals are also required
experiments in chick and zebrafish indicate a requirement for FGF

Front 10

Evolutionary Conservation of Induction Mechanisms

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Nueral tissue (proteins)induced from Xenopus animal cap cells using chick Hnesens node

Front 11

Other Tissues also Pattern the Nervous System

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Mesoderm from a neurula embryo induces neural structures from the neural plate of a donor embryo
Anterior mesoderm induces a head (brain)
Posterior mesoderm induces a trunk with a spinal cord

Front 12

Types of Signaling from Mesoderm: Model 1

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an initial signal from the mesoderm induces anterior neural tissue; a graded second signal specifies more posterior structures
Experiments more consistent with model 1.

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Types of Signaling from Mesoderm: Model 2

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Several different signals induce the different types of neural tissue

Front 14

Posteriorizing Factors

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Wnts (in some organisms)

Front 15

Developing Brain is Segmented

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3 regions of the brain: forebrain, midbrain, hindbrain
Visible at 3 days of chick development

Front 16

Hindbrain :segmentation

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eight rhombomeres along the A/P axis

Front 17

Patterning in the spinal cord

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determined by the somites: one dorsal root ganglion (DRG) pair per somite

Front 18

Ephrin Signaling Involved in Rhombomere Formation

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Cell-cell contact required
involves bidirectional signaling
receptors are tyrosine kinases
Ephrins and Eph receptors are separately expressed in alternate rhombomeres
prevents cell mixing

Front 19

rhombomere

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a developmental unit under the control of the same genes

Front 20

Hox Genes Provide Positional Information

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Hox genes provide a possible molecular basis for the identities of rhombomeres, neural crest cells and branchial arches
Similar expression patterns in these regions

Front 21

Hox genes in the Hindbrain

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Signals from the neural tube itself influence Hox gene expression
Transplant rhomobomere from anterior to more posterior location and Hox gene expression changes to that appropriate for the new location

Front 22

Retinoic acid & Hox genes

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absence of Retinoic acid leads to loss of rhombomeres; excess causes homeotic transformations of rhombomeres

Front 23

Hox genes affect cell behavior

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1. misexpression experiment
2. deletion knock-out