Module 2: Early Brain Development

what is gastrulation?

rearrangement of the embryo into 3 germ layers

what is a germ layer

the cells that provide all of the different cells needed for tissues and organs

what are the three germ layers of the embryo?

ectoderm, mesoderm, and endoderm

what germ layer does all nervous tissue come from?

ectoderm

what is neural induction?

only a portion of the ectoderm becomes nervous tissue

what is the name for the part of the ectoderm that becomes nervous tissue?

neuroectoderm

What is the Spemann Organizer?

dorsal lip at blastopore creates neuroectoderm via chemical signaling

What was the Spemann Organizer experiment?

dorsal lip from newts transported to other news showed that at early gastrulation, the dorsal lip organizes host cells to form a basic nervous system

what proteins does the dorsal lip have?

noggin and chordin

what do the dorsal lip proteins do?

they bind to bone morphogenic proteins (BMPs) and inactivate them, this allows the ectoderm to become neuroectoderm and not skin cells

what is neuralation?

the formation of the neural tube from the neural plate

What is the notochord?

cylinder of mesoderm that sits at the midline of an embryo

what does the notochord do during neuralation?

sends inductive signals to neuroectoderm above it, ends of neural plate fold inward, the neural crest (cells which sit at the edges of the neural plate) move away and form the PNS

how does the notochord cause the neural plate to fold inward (molecular)?

it secretes sonic hedgehog (SHH) which bind to patched receptors on neuroectoderm cells, this causes these cells to transform from a flat plate to a tube

what parts of the nervous system does the neural tube form?

prosencephalon(forebrain), mesencephalon(midbrain), rhombencephalon(hindbrain), spinal cord, and lumen (spaces) that become ventricles

what are the major divisions of the CNS?

prosencephalon, mesencephalon, rhombencephalon, telencephalon, diencephalon,mylencephalon

what does the prosencephalon contain?

telencephalon and diencephalon

what does the mesencephalon contain?

dorsal: tectum which has the inferior and superior colliculi

ventral: tegmentum which has the cerebral peduncles, substantia nigra, and VTA

what does the metencephalon contain?

cerebellum and pons

what does the mylencephalon contain?

medulla oblongata

what do Homeobox (Hox) genes do?

they establish the plan of the nervous system and determine what neural areas should be placed where

where are hox genes found?

on neuromeres which express different Hox genes at different times

what do fibroblast growth factors (FGFs) do?

help to establish the axes of the nervous system, posterior to spinal cord and anterior to other cells

what is the molecular signaling pathway of a FGF?

bind to receptor tyrosine kinases, activate the MAP kinase signaling pathway

what does FGF8 do?

it helps to form the forebrain, midbrain, and hindbrain

what does FGF17 do?

helps to pattern the frontal cortex

what does retinoic acid play a major role in?

pattern the hindbrain

what does retinoic acid do?

activate retinoid receptors inside the nucleus of target cells, can repress or stimulate expression of other genes depending on what protein it binds to

what do irregular amounts of retinoic acid result in?

enlarging or shrinking of brain areas

what do bone morphogenic proteins (BMPs) play a role in?

forming sensory neurons in the dorsal spinal cord

what is the molecular signaling pathway for BMPs?

bind to receptor serine kinases, translates SMAD into the nucleus, regulates gene expression

what is the major role of sonic hedgehog (SHH) genes?

promotes the formation of motor neurons in the ventral neural tube

what is the molecular signaling pathway for SHH genes?

bind to patched receptors on target cell surfaces, smoothened receptor accumulates on the cell surface as a result (acts as an on/off switch), translocation of Gli1 into the nucleus, changes in gene expression

what is neural prolifieration?

neural stem cells rapidly divide

where does neural proliferation occur?

at the ventricular zone (VZ) which is located at the inner surface of the neural tube