Download Neural stem cells

實驗神經概論
楊定一 老師
Course Outline
1.
2.
3.
4.
5.
6.
Plasma membrane
Intracellular organelles
2.1 Nucleus; 2.2 Mitochondria; 2.3 Endoplasmic reticulum
2.4 Golgi; 2.5 Lysosome; 2.6 Peroxisome
Cytoskeleton
Cell signaling
Cell cycle and cell lineage
Cell types in nervous systems
A more realistic view of an eukaryotic cell.
A simplified carton of an eukaryotic cell.
1. Plasma membrane
• Functions
• Structural components:
phospholipids
membrane proteins
integral membrane proteins
peripheral membrane proteins
membrane cytoskeleton
General structure and components of cellular plasma membrane
Functions of plasma membrane
• A boundary to hold the cell constituents together
and to keep other substances from entering, thus
forming a semi-porous barrier to the outside
environment.
• Selective permeability: small molecules (oxygen,
carbon dioxide, and water) pass freely, larger
molecules (amino acids, proteins, sugars and
DNA/RNA) pass under regulation. This is
accomplished by membrane proteins.
Functions of membrane proteins
• Selective transport of certain substances (as
channels or active transport molecules).
• Receptors binding to information-providing ligands
(such as hormones) to transmit signals.
• Enzymatic activity: catalyzing various reactions
related to the plasma membrane.
2. Intracellular Organelles
1. Plasma membrane controls movement of molecules in
and out of the cell and functions in cell-cell signaling
and cell adhesion.
2. Mitochondria generate ATP by oxidation of glucose and
fatty acids.
3. Lysosomes with an acidic lumen degrade material
internalized by the cell and worn-out cellular
membranes and organelles.
4. Nuclear envelop (double layer) encloses the contents of
the nucleus; the outer nuclear membrane is continuous
with the rough ER.
5. Nucleolus is a nuclear sub-compartment where most of
the rRNA is synthesized.
6. Nucleus is filled with chromatin composed of DNA and
proteins.
7. Smooth endoplasmic reticulum (ER) synthesizes lipids and
detoxifies certain hydrophobic compounds.
8. Rough ER functions in the synthesis and sorting of secreted
proteins, lysosomal proteins, and some membrane
proteins.
9. Golgi complex sorts secreted proteins, lysosomal proteins,
and membrane proteins synthesized on the rough ER.
10. Secretory vesicles store and release secreted proteins.
11. Peroxisomes detoxify various molecules and break down
fatty acids to produce acetyl groups for biosynthesis.
12. Cytoskeletal fibers form networks to support cellular
membranes, organize organelles, and participate in cell
movement.
13. Microvilli increase surface area for absorption of
nutrients from surrounding medium.
2.1 Nucleus
• The nucleus, the largest organelle in animal cells
housing the genome of a cell, is surrounded by two
membranes, each one is composed of a
phospholipid bilayer containing many different
types of proteins.
• The inner and outer nuclear membranes are fused
at numerous nuclear pores, through which
materials pass between the nucleus and the cytosol.
The outer nuclear membrane is continuous with
that of the rough ER.
The nucleolus (n) is a
subcompartment of the
nucleus (N) without
membrane and
produce most rRNA.
Heterochromatin is the
condensed and
concentrated DNA.
The ribosomal subunits
as well as tRNAs and
mRNA-containing
particles pass through a
nuclear pore into the
cytosol for protein
synthesis.
2.2 Mitochondria
• A mitochondrion (複數 mitochondria) is a
membrane-enclosed organelle found in most
eukaryotic cells. These organelles range from 0.5 to
10 micrometers (mm) in diameter.
• Mitochondrion comes from the Greek word
meaning mitos (thread) + chondrion (granule).
Therefore, 粒線體 is correct, but粒腺體 is wrong!
A mitochondrion
Some characteristics of mitochondria
• The number of mitochondria in each cell varies.
• Neurons have mitochondria throughout its whole
structures, including soma (cell body), dendrites,
and terminal synapses.
• Mitochondrial DNA and symbiosis.
Structures of mitochondria
• Outer and inner membranes with different
properties.
• Five distinct compartments in a mitochondrion:
–
–
–
–
–
outer mitochondrial membrane
intermembrane space
inner mitochondrial membrane
crista space (formed by infoldings of the inner membrane)
matrix (space within the inner membrane)
Functions of mitochondria
• Production of ATP by oxidizing the major products
of glucose, pyruvate, and NADH (reducing power) in
the presence of oxygen
• Heat production
• Calcium storage in the mitochondrial matrix
• Apoptosis by releasing cytochrome C and other proapoptotic proteins into cytosol
Oxidative phosphorylation
to produce ATP
2.3 Endoplasmic reticulum (ER)
• Synthesis of lipids (in smooth ER) as well as
membrane proteins and secreted proteins (rough
ER), but NOT soluble cytosolic proteins (in cytosol).
See next slide.
• Enzymes in the smooth ER also detoxify
hydrophobic chemicals such as pesticides and
carcinogens to be excreted from the body.
Rough ER: flattened sheets
Smooth ER: tubular structures
• Rough ER is characterized by the ribosomes attached to
the cytosolic (outer surface) of membrane. Smooth ER is
smooth because of the absence of ribosomes attached
to the membrane.
2.4 Golgi complex
• Golgi complex contains three regions (cis  medial
 trans) to process secreted and membrane
proteins.
2.5 Lysosome
• Lysosomes contain acid hydrolases. The name
lysosome derives from the Greek words lysis, which
means dissolution or destruction, and soma, which
means body.
• Lysosome is the garbage disposal system in a cell.
• Lysosomes digest excess or worn-out organelles,
food particles, and engulfed viruses or bacteria. The
membrane around a lysosome allows the digestive
enzymes to work at low pH (4.5).
2.6. Peroxisomes
• Peroxisomes participate in the metabolism of fatty
acids and other metabolites. Peroxisomes catablize
toxic peroxides (過氧化物質) in the cells.
3. Cytoskeleton
1. Microtubules and motor proteins
2. Intermediate filaments (neurofilaments in
neurons)
3. Microfilaments
3.1 Microtubules
• Tubulins belong to GTPase protein family that
polymerize to form microtubules, hollow cylindrical
structures 25 nm in diameter.
• Microtubules exhibit structural polarity. Subunits
are added and lost preferentially at one end, the “+”
end.
• Assembly and disassembly of microtubules depends
on the critical concentrations (CC) of ab-tubulin
subunits. Above CC, microtubules assembly and
below CC, disassembly.
Axonal transport along microtubules
in both directions
• All the axonal microtubules are all oriented with
their “+” ends toward the terminal (synapse). In
dendrites, however, microtubules are oriented in
both ends.
• Anterograde axonal transport proceeds from the
cell body to the synaptic terminals and is associated
with axonal growth and the delivery of synaptic
vesicles.
• Retrograde axonal transport is in the opposite
direction from nerve terminus to cell body.
MTOC: microtubule organizing center
Motor proteins for microtubulekinesin
• Kinesin is responsible for anterograde axonal
transport. Most kinesins are processive “+” enddirected movements.
• The head domains of kinesin bind microtubules.
The tail domains of kinesin bind to the membrane
of vesicles to determine their cargos.
Motor proteins for microtubuledynein
• Dynein is responsible for retrograde axonal transport
and other “–” end-directed movements.
• Dynactin is a large protein complex that links vesicles to
the dynein light chains.
3.2 Neurofilaments
• cytokeratin family including
glial fibrillary acidic protein
(GFAP; an astrocyte marker)
• 10 nm in diameter
• stable polymers
• 1 neurofilament  32
monomer
– 8 protofilaments in each
neurofilament
– 4 monomers in each
protofilament
3.3 Microfilaments
•
•
•
•
•
subunits: b- and g-actin monomer
3-5 nm in diameter
polar, dynamic structure
ATP
With actin-binding proteins, actin
filaments form a dense network lying
underneath the plasmalemma. This
matrix plays a key role in the
formation of pre- and postsynaptic
morphologic specializations.
• In axon, all the microtubules are arranged with the plus
end pointing away from the cell body, minus end facing
the cell body.
• In dendrites, microtubules with opposite polarities are
mixed.
microtubule
neurofilament
microfilament
a-tubulin
b-tubulin (G)
cytokeratins
GFAP etc (F)
b-actin
g-actin (G)
GTP
none
ATP
25-28 nm
10 nm
3-5 nm
dynamic but
more stable in
mature axons
and dendrites
stable and
polymerized
dynamic, ～ ½
of the actin in
neurons can be
unpolymerized
4. Cell signaling
• The level of secondary messengers, such as Ca2+, cAMP,
cGMP, and IP3, increases or decreases in response to
binding of ligand (primary messenger) to cell-surface
receptors.
• These non-protein intracellular signaling molecules then
regulate the activities of enzymes and non-enzymatic
proteins.
• Rapid termination of signaling once a particular ligand is
withdrawn help cells respond appropriately under different
circumstances.
Examples of some second messengers.
Seven major classes of cell surface
receptors
Amplification of an external signal downstream from
a cell-surface receptor
5. Cell cycle and cell lineage
• Cell cycle is divided into four major phases: G1, S,
G2, M.
• In cycling somatic cells, cells synthesize RNAs and
proteins during the G1 phase, preparing for DNA
synthesis and chromosome replication during the S
(synthesis) phase.
• After progressing through the G2 phase, cells begin
the complicated process of mitosis (mitotic) phase.
Overview of the birth, lineage, and
death of cells
• Two daughter cells resulting from asymmetric division differ
from birth with different fates.
• Asymmetric division commonly is preceded by the
localization of regulatory molecules (green) in one part of
the parent cell.
• A series of symmetric and/or asymmetric cell divisions,
called a cell lineage, gives birth to each of the specialized cell
types found in a multicellular organism.
• Programmed cell death (PCD) occurs during normal
development and in response to infection or poison. A series
of specific programmed events, called apoptosis, is activated
during PCD.
Stem cells give rise to stem cells and
to differentiating cells
(a) Division of a stem cell produces two cells, one is similar
to the mother cell to maintain the population of stem cells.
(b) The other daughter cell-a stem cell of more restricted
potential-starts on a pathway toward producing more
differentiated cells. When it divides, one of the daughters
will be the same sort of restricted potential stem cell as the
mother and the other will be a progenitor cell for a certain
type of differentiated cell.
(c) Progenitor cells can divide to reproduce themselves and
can differentiate into a terminally differentiated, nondividing cell.
Adult neural stem cells
• Neural stem cells (NSCs) are the self-renewing,
multipotent cells that generate the main
phenotypes of the nervous system.
• Neural progenitor and stem cells were isolated in
1992 from the striatal tissue, including the
subventricular zone, thus demonstrating the
existence of adult NSCs.
• Epidermal growth factor (EGF) and fibroblast
growth factor (FGF) are mitogens that promote
neural progenitor and stem cell growth in vitro.
Adult neurogenesis
• In the subventricular zone (SVZ) of the lateral
ventricle wall, differentiated cells migrate through
the rostral migratory stream into the olfactory bulb
to become interneurons.
• The dentate gyrus subgranular zone (SGZ) of the
hippocampus also contains neural stem cells that
differentiate into interneurons.
LV: lateral ventricle
SGZ: subgranular zone
Cell types in nervous systems
• Neuron
• Glia
– CNS: astrocyte, oligodendrocyte, microglia
– PNS: Schwann cell
Functional roles of astrocytes
• Providing some degree of mechanical integrity to
tissue
• Maintaining the composition of the extracellular
milieu
• Participating in synaptic function and plasticity
• Providing neurotransmitters and energy substrates
to neurons and cleaning up the extracellular
neurotransmitters
• Regulating blood flow
• Formation of blood-brain-barrier (BBB)
Astrocytes
The above image depicts two
adjacent astrocytes from the
rat brain hippocampus
injected with two different
color dyes to elucidate their
individual morphology.
Another astrocyte image
Red: MAP-2-positive rat
cortical neurons
Green: GFAP-positive rat
astrocytes
Oligodendrocytes and Schwann cells
• Myelination is achieved by oligodendrocytes in CNS:
one oligodendrocyte can myelinate several
neuronal axons.
• Myelination is achieved by Schwann cells in PNS:
each Schwann cell myelinates one segment of
axons.
Oligodendrocytes and microglia
Oligodendrocytes generated
from mouse neural stem cells
Microglia are the main resident
immunological cells the CNS. This is a
high-power view of two microglia stained
with a silver method.
Microglia
• Microglia: the resident macrophages of the brain and spinal
cord, act as the first and main form of active immune defense
in CNS.
• Microglia are constantly excavating the CNS for damaged
neurons, plaques, and infectious agents. The brain and spinal
cord are considered "immune privileged" organs because BBB
prevents most infections from reaching the vulnerable
nervous tissue.
• If infectious agents are directly introduced to the brain or
cross the BBB, microglial cells must react quickly to increase
inflammation and destroy the infectious agents.
Activated microglia: M1 and M2
• M1-type: classical and proinflammatory activationneurotoxic
– M1 markers: interleukin (IL)-1β, IL-6, IL-12, IL-23, tumor
necrosis factor (TNF)-α, inducible nitric oxide synthase
(iNOS), etc
• M2-type: alternative and anti-inflammatory
activation-neuroprotective
– M2 markers: insulin-like growth factor (IGF)-1, triggering
receptor expressed on myeloid cells 2 (TREM2), chitinase
3-like 3 (Ym-1), etc
Biochem Pharmacol. 2016 Mar 1;103:1-16
A single Purkinje neuron of the cerebellum made visible by introducing a
fluorescent protein. The cell body is the bulb at the bottom.
Four Basic Structural Components of
Neurons
• Cell body (soma) contains the nucleus and is the site of
synthesis of virtually all neuronal proteins and membranes.
Some proteins are synthesized in dendrites but none are
made in axon or axon terminals.
• Axon is specialized for conduction of action potentials.
• Axon terminals are small branches of the axon that form the
synapses with other cells.
• Dendrites extend outward from the cell body and are
specialized to receive chemical signals (neurotransmitters)
from the axon termini of other neurons. Dendrites convert
signals into small electric impulses and conduct them
toward the cell body.
Typical morphology of two types of mammalian neurons
Selective distribution of membranous
organelles in neurons
• A sharp functional boundary at the axon hillock, certain
organelles are absent in axon
– protein biosynthetic machinery (ribosomes, rough ER,
Golgi complex).
– lysosomes
• Axons are rich in
– synaptic vesicles
– endocytic intermediates involved in synaptic vesicle
traffic
– synaptic vesicle precursor membranes
• Mitochondria and smooth ER (Ca2+ regulation) are present in
all neuronal compartment including axon.
Voltage-gated ion channels and
propagation of action potentials
• Neurons are specialized to generate and conduct a particular
type of electric impulse, the action potential.
• Action potential is a series of sudden changes in the voltage
(or equivalently electric potential) across the plasma
membrane caused by the opening and closing of certain
voltage-gated ion channels.
• Electric signals (action potential) carry information within a
nerve cell, while chemical signals (neurotransmitters)
transmit information from one neuron to another or from a
neuron to other target cell.
Arrival of action potential triggers opening of voltage-sensitive
calcium channels, causing calcium influx and thus fusion of
small vesicles containing neurotransmitters with plasma
membrane, thereby releasing neurotransmitters into synaptic
cleft.
Myelination
• Myelin sheath is a
stack of specialized
plasma membrane
sheets produced by a
glial cell that wraps
itself around the axon.
• Myelination is achieved
by Schwann cells in
peripheral nervous
system and
oligodendrocytes in
central nervous system.
Myelination increases the velocity of
impulse conduction
• In non-myelinated neurons, the conduction velocity
of an action potential is roughly proportional to the
diameter of the axon. A thicker axon will have
greater numbers of ions that can diffuse.
• In myelinated neurons, the presence of myelin
sheath around an axon increases the velocity of
impulse conduction up to 100 fold.
• Node of Ranvier
Node of Ranvier
• The myelin sheath surrounding an axon is formed
from many glial cells.
• Each region of myelin formed by an individual glial
cell is separated from the next region by an
unmyelinated area of axonal membrane about 1
mm in length called Node of Ranvier.
• All the voltage-gated Na+ channels and all the
Na+/K+ pumps are located in the nodes for
regeneration of action potential.
Action potential spread passively through the axonal cytosol to the next node
with very little loss or attenuation, because ions cannot cross myelinated
axonal membrane. In effect, the action potential “jump” from node to node.
Composition of myelin
• Basic phospholipid bilayer structure with far fewer
types of proteins than found in other membranes.
• Peripheral myelin proteins: P0 (causes adjacent plasma
membranes to stack tightly together) and PMP22.
• In the central nervous system, a different membrane
protein and a proteolipid together function similarly to
P0.
• The major cytosolic protein in all myelin sheaths is
myelin basic protein (MBP).
MS: myelin sheath