Transcript Early Vertebrate Developement

Steps in setting up the Nervous system
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Induction and Patterning of a neuron-forming region
Birth and migration of neurons and glia
Specification of cell fates
Guidance of axonal growth cones to specific targets
Formation of synaptic connections
Binding of trophic factors for survival and differentiation
Competitive rearrangement of functional synapses
Continued synaptic plasticity during lifetime
Neuronal development
• Ectoderm differentiation: Epidermis, nerve tissue, or neural
crest cells?
• Nerve tissue: Neuron or glial cell?
Neuronal development
• Ectoderm differentiation: Epidermis, nerve tissue, or neural
crest cells?
• Nerve tissue: Neuron or glial cell?
Neuronal development
Nerve Outgrowth
• Filapodia-based movements
• Rely on Cytoskeleton and factors that rearrange the
cytoskeleton (GTPases).
Types of Tissue organization in the Neural
Tube
Spinal Cord
Cerebellum
• Important for motor control
• Purkinje fibers
• BMP and Granular layer
Movement of Neurons
• Glial cells serve as track.
• Nerve Birthdays: Determine how deep in the cortex a neuron
will enter.
Cerebrum
• Similar to Cerebellum
• Neocortex: subdivided into
6 layers (old cells closest to
ventricular zone).
• Cortex divided horizontally
(approx. 40 sections).
• Fate decided early on
(before S phase)
Cortical Neurons
Spinal Cord
Motor Neuron Specification
• Sonic hedgehog (Shh) secreted by floor plate.
Target specification of Motor neuron
• As Nerves pass through the cortex, different transcriptional
regulators are expressed.
• Limb innervation determined by repulsion
– If Lim1 is present, Eph A4 (receptor) is expressed; Eph A5 repels neuron
– If no Lim1, neuropilin-2 expressed.
(Axial muscles)
Following diffusible signals
• Netrin-1 and Netrin-2
• SLIT and ROBO
Nerve Outgrowth
• Filapodia-based movements
• Rely on Cytoskeleton and factors that rearrange the
cytoskeleton (GTPases).
Finding a place to hang out
Neural Crest Cells
• Neurons/glial cells of
sensory, sympathetic, and
parasympathetic nerves
• Epinephrine-producing cells
of adrenal gland
• Pigment containing cells
• Skeletal/connective tissue
of head
• 4th germ layer?
Ventral Migration of Neural Crest
Neural Crest Cell specification
Neural Crest Regionalization
• Cranial
– Cartilage, bone, cranial nerves,
glia, connective tissues
• Cardiac
– Melanocytes, neurons,
cartilage, musculo-connective
tissue wall of large arteries
• Trunk
– Dorsal root ganglia,
sympathetic ganglia, adrenal
medulla, nerve clusters around
aorta
• Vagal and Sacral
– Parasympathetic ganglia of gut
Trunk Neural Crest Cells: Migration
• Dorso-lateral inhibited
• At first, between somites,
but Semaphorin-3F causes
movement through somites.
Further migration
• Cells that stop in sclerotomedorsal root ganglia
• Cells past sclerotome-lack wnt
and neurotropin receptorsparasympathetic and
sympathetic nerves.
• BMPs from aorta convert cells
to sympathetic and adrenal
lineage
• Glucocorticoidsadrenomedullary cells.
• Neural crest cells committed
to path early, but differentiate
to determine final location.
Cranial Neural Crest
• Head is most anatomically sophisticated portion of vertebrate
body.
• Mainly composed of neural crest cells
Cranial Neural Crest: Bone Formation
Neural Crest and neurocranium
• Viscerocranium (jaws, pharyngeal arches) well established as
being of Neural crest origin…neurocranium controversial
origin
The Face reflects the brain!
Cardiac Neural Crest
Cranial placodes