Transcript Neurotrophins

Brain—Target interactions
Genes
Hormones-Thyroid
Proliferation
MZ
Migration
IZ
Differentiation
VZ
IZ
Maturation
Interactions
Limb
LMC
Neuron Death
Trophic Factors
• Victor Hamburger
The Nature of Science
• The Dogma:
• Observation; Hypothesis; Experimental
tests; Conclusions.
The Most important factors.
Curiosity
• Preparation
• Free your mind
• And the rest will Follow
• Serendipity
Indirect Factors
Timing!
• Appropriate Questions.
• Money
• Technical skills and the availability of
appropriate scientific equipment
• The Old Boy/Old Girl Network
• Mentoring and Sponsorship
Neurotrophins
• Trophic factors (survival signals). First discovered
in 1950’s
• Gene family. In mammals includes NGF, BDNF,
NT3 and NT4/5.
• Individual neurotrophins activate different
different receptor tyrosine kinases
• Have a primary role in promoting the survival of
motor neurons and peripheral sensory neurons. It
is known that survival of neurons that innervate
the periphery depend on the size of target tissue
(Neurotrophic Factor Hypothesis ).
• Also have a role in regulating proliferation and
differentiation of neuronal and glial precursors.
Rita-Levi
Montalcini
(1909-?)
Turin Italy
Nobel Prize-1986
102 yrs old
2011
Life is Good,
But Parental Rebellion
Rita Levi-Montalcini describes being raised in a cultured,
intellectually stimulating environment, even though her
father believed that “a professional career would interfere
with the duties of a wife and mother. At twenty (1929),
I realized that I could not possibly adjust to a
feminine role as conceived by my father, and
asked him permission to engage in a
professional career. In eight months I filled my
gaps in Latin, Greek and mathematics,
graduated from high school, and entered
medical school in Turin.
Invasions; Decisions
Trying years
Nerve Growth & Neoplasms
(crazy experiments)
In a 1948 article, a former student of Viktor Hamburger,
Elmer Bueker, reported the results of a bold and
imaginative experiment consisting in grafting fragments
of mouse sarcoma 180 into the body wall of three-day
chick embryos. The histological study of the embryos
fixed 3-5 days later, showed that sensory nerve fibers
emerging form adjacent dorsal root ganglia had gained
access into the neoplastic tissue while no motor nerve
fibers entered into the tumor.
Figure 3. Drawings illustrating the in vitro "halo" effect on 8-day
chick embryo sensory ganglia cultured in the presence of
fragments of mouse sarcoma 180 for 24 hours (b) or 48 hours (c).
In (a), the ganglion, which faces a fragment of chick embryonic
tissue, shows fibroblasts but few nerve fibers. In (b) and (c), the
ganglia, facing fragments of sarcoma 180, show the typical "halo"
effect elicited by the growth factor released from the sarcoma.
Note in (c) the first evidence of a neurotropic effect of the growth
factor.
Stanley Cohen
Fractionated tumor homogenate
Got an active nucleoprotein
Nerve growth factor
Serendipity:snake venom
Snake venom was known to contain phosphodiesterases that should break down the nucleic
acid part of the nucleo protein
NGF-snake venom 2
• Either the snake venom destroyed an
inhibitor factor in the tumoral fraction—that
is the tumoral fraction might contain a
“brake” on its ability to stimulate nerve
outgrowth; or the snake venom itself could
stimulate outgrowth.
• In 1957 Cohen purified the NGF from snake
venom.
•Mouse salivary glands—even better
Cohen made an NGF antiserum
Caused immunosympathectomy
• Neurotrophin Receptors TRK receptors
• A digression: Viruses and transforming
viruses
• A second digression, Oncogenes and
Protooncogenes.
• A third digression, skeletal muscle
physiology—tropomyosin
Contraction
and myosin
heads
– A human oncogene formed by the fusion of
truncated tropomyosin and protein tyrosine kinase
sequences was called trk for tropomyosin receptor
kinase. The name trk was then taken for the
neurotrophin receptors.
– Martin-Zanca D, Hughes SH, Barbacid M.
– A biologically active complementary DNA clone of a
transforming gene present in a human colon carcinoma
contains gene sequences of both tropomyosin and a
previously unknown protein tyrosine kinase. The
predicted protein (641 amino acids) encoded by this
oncogene seems to have been formed by a somatic
rearrangement that replaced the extracellular domain of
a putative transmembrane receptor by the first 221
amino acids of a non-muscle tropomyosin molecule.
Parada: Trk tyrosine kinase is a
receptor for NGF; antibody to
phosphotyrosine on precipitated
trk protein with and without NGF
NGF-induced phosphorylation of
trk protein in DRG cells
Neurotrophins bind to a family of receptor
tyrosine kinases called Trks
NOTE: Like
BDNF,
NT4/5
binds to
TrkB
Different neurotrophins are required for the survival of
distinct populations of neurons in the nervous system
Nerve growth factor (NGF) mediated signaling
P75NTR
binds all
NT’s with
low affinity.
Its intracellular
domain
has no
catalytic
activity but
it interacts
with
adapters
Thoenen and Sendtner, 2002. Nature Neuroscience 5:1046-1050
22.13 The influence of
neurotrophins. (Part 1)
22.13 The influence of
neurotrophins. (Part 2)
Cerebral Cortex neurons: Left-transfected
with green fluorescent protein(GFP) right—
transfected with GFP + BDNF
22.14 Evidence that NGF can
influence neurite growth by local
action.
22.15 Neurotrophin receptors and their
specificity for the neurotrophins.
22.16 Signaling through the
neurotrophins and their receptors.