Download Cell differentiation

Cell Differentiation and
Cell Fate
Figure 21.x4 Normal and double winged Drosophila
Number and position of body parts
Probably by Photoshop!
Fig. 47-27
Figure 47.26
Lungs
H
Heart
t
Liver
Spleen
Stomach
Large intestine
Normal location
g
of internal organs
Location in
situs inversus
Figure 47.6 Cleavage in an echinoderm (sea urchin) embryo
多細胞生物都由 顆受精卵發育而成的
多細胞生物都由一顆受精卵發育而成的
Figure 47.1 A “homunculus” inside the head of a human sperm
生物的形狀是如何決定的
先成說 ?
還是誘導說?
看青蛙胚胎發育實驗結果如何?
• Roux’s experiment
Concept: Cytoplasmic
determinants and inductive
signals contribute to cell fate
specification
• Determination is the term used to describe the
process by which a cell or group of cells becomes
committed to a particular fate
g
• Differentiation refers to the resulting
specialization in structure and function
© 2011 Pearson Education, Inc.
• Cells in a multicellular organism share the same
genome
• Differences in cell types is the result of the
expression of different sets of genes
© 2011 Pearson Education, Inc.
Fate Mapping
• Fate maps are diagrams showing organs and
other structures that arise from each region of an
embryo
g frogs
g indicated that cell
• Classic studies using
lineage in germ layers is traceable to blastula cells
© 2011 Pearson Education, Inc.
Figure 47.17
Epidermis
Central
nervous
system
Notochord
Epidermis
Mesoderm
Endoderm
g
Neural tube stage
(transverse section)
Blastula
(a) Fate map of a frog embryo
64-cell embryos
Blastomeres
injected with dye
Larvae
(b) Cell lineage analysis in a tunicate
• In mammals
mammals, embryonic cells remain totipotent
until the 8-cell stage, much longer than other
organisms
• Progressive restriction of developmental potential
is a general feature of development in all animals
• In general tissue-specific fates of cells are fixed by
th llate
the
t gastrula
t l stage
t
© 2011 Pearson Education, Inc.
Figure 47.22-1
EXPERIMENT
Control egg
(dorsal view)
Experimental egg
(side view)
1a Control
group
g
p
Gray
crescent
1b Experimental
group
Gray
crescent
Thread
Figure 47.22-2
EXPERIMENT
Control egg
(dorsal view)
Experimental egg
(side view)
1a Control
1b Experimental
group
group
g
p
Gray
crescent
Gray
crescent
Thread
2
RESULTS
Normal
Belly piece
Normal
Restricting Developmental
Potential
• Hans Spemann performed experiments to
determine a cell’s developmental potential (range
of structures to which it can give rise)
• Embryonic fates are affected by distribution of
determinants and the pattern of cleavage
• The first two blastomeres of the frog embryo are
totipotent (can develop into all the possible cell
types)
© 2011 Pearson Education, Inc.
Figure 47.22 The “organizer” of Spemann and Mangold
The “Organizer”
Organizer of Spemann and
Mangold
• Spemann and Mangold transplanted tissues
between earlyy g
gastrulas and found that the
transplanted dorsal lip triggered a second
gastrulation in the host
g
• The dorsal lip functions as an organizer of the
embryo body plan, inducing changes in
surrounding tissues to form notochord, neural tube,
and so on
© 2011 Pearson Education, Inc.
Cell Fate Determination and
Pattern Formation by Inductive
Signals
• As embryonic
y
cells acquire
q
distinct fates,, theyy
influence each other’s fates by induction
© 2011 Pearson Education, Inc.
Formation of the Vertebrate Limb
• Inductive signals play a major role in pattern
formation, development of spatial organization
• The molecular cues that control pattern formation
are called positional information
• This
Thi information
i f
ti tells
t ll a cellll where
h
it iis with
ith respectt
to the body axes
• It determines how the cell and its descendents
respond to future molecular signals
© 2011 Pearson Education, Inc.
• The wings and legs of chicks
chicks, like all vertebrate
limbs, begin as bumps of tissue called limb buds
© 2011 Pearson Education, Inc.
Figure 47.24
Anterior
Limb bud
AER
ZPA
Posterior
Limb buds
50 m
2
Digits
Apical
ectodermal
ridge (AER)
Anterior
3
4
Ventral
Proximal
Distal
Dorsal
Posterior
(a) Organizer regions
(b) Wing of chick embryo
• The embryonic cells in a limb bud respond to
positional information indicating location along
three axes
– Proximal-distal axis
– Anterior-posterior
Anterior posterior axis
– Dorsal-ventral axis
© 2011 Pearson Education, Inc.
• One limb
limb-bud
bud regulating region is the apical
ectodermal ridge (AER)
• The AER is thickened ectoderm at the bud’s
bud s tip
• The second region is the zone of polarizing
activity
ti it (ZPA)
• The ZPA is mesodermal tissue under the
ectoderm where the posterior side of the bud is
attached to the body
© 2011 Pearson Education, Inc.
• Tissue transplantation experiments support the
hypothesis that the ZPA produces an inductive
signal that conveys positional information
indicating “posterior”
© 2011 Pearson Education, Inc.
Figure 47.25
EXPERIMENT
Anterior
New
ZPA
Donor
limb
bud
Host
limb
bud
ZPA
Posterior
RESULTS
4
3
2
2
4
3
• Sonic hedgehog is an inductive signal for limb
development
• Sonic Hedgehog was named after Sega's video
game character Sonic the Hedgehog.
• SHH is the best studied ligand of the hedgehog
signaling pathway
pathway. It plays a key role in regulating
vertebrate organogenesis, such as in the growth of
digits on limbs and organization of the brain.
• Hox genes also play roles during limb pattern
formation
© 2011 Pearson Education, Inc.
Hox gene
Hox genes (from
H
(f
an abbreviation
bb i ti off homeobox)
h
b )
are a group of related genes that control the
body plan of the embryo along the anterior
anteriorposterior (head-tail) axis. After the embryonic
segments have formed,
formed the Hox proteins
determine the type of segment structures (e.g.
legs,
g , antennae,, and wings
g in fruit flies or the
different vertebrate ribs in humans) that will form
on a given segment. Hox proteins thus confer
segmental identity, but do not form the actual
segments themselves
The products of Hox genes are Hox proteins.
proteins are transcription
p
factors,,
Hox p
which are proteins that are capable of
binding to specific nucleotide sequences
on the DNA called enhancers where they
either activate or repress genes
genes. The
same Hox protein can act as a repressor
at one gene and an activator at another.
• The homeodomain is a 60 amino acid long DNAbinding domain (encoded by its corresponding
180bp DNA sequence, the homeobox). This
amino acid sequence folds into a helix-turn-helix
motif that is stabilized by a third helix. The
consensus polypeptide chain is (typical intron
position noted with dashes)
• RRRKRTA-YTRYQLLE-LEKEFLFNRYLTRRRRIELAHSL-NLTERHIKIWFQNRRMK-WKKEN
Adult
fruit fly
Fruit fly embryo
(10 hours)
Flyy
chromosome
Mouse
chromosomes
h
Mouse embryo
(12 days)
Ad lt mouse
Adult
Figure 21.23
Cilia and Cell Fate
• Ciliary function is essential for proper specification
of cell fate in the human embryo
• Motile cilia play roles in left
left-right
right specification
• Monocilia (nonmotile cilia) play roles in normal
kid
kidney
d
development
l
t
• Kartagener’s syndrome:prone to infections of the
nasal sinuses and bronchi, immotile sperm, situs
inversus (left-right inverse) (one in 10,000
individuals)
© 2011 Pearson Education, Inc.
鍾正明 (Dr. Cheng
Cheng-Ming
Ming Chuong)
鍾正明院士於1983年獲得美國洛克斐勒大學病理學博士
後 隨即進入該校分子生物系擔任助理教授 1987年轉到
後，隨即進入該校分子生物系擔任助理教授，1987年轉到
南加州大學擔任病理系教授至今，從事發育生物學、 ...
早在1998年 鍾院士即推動臺灣的發育生物學發展
早在1998年，鍾院士即推動臺灣的發育生物學發展，
2009年他獲聘臺大特聘講座
Narrower, pointier
i i beaks
b k (right
( i h chick,
hi k versus a controll chick)
hi k) arise
i
when certain proteins are expressed at higher concentrations during
development.
development
Concept: A program of differential
gene expression
g
p
leads to the
different cell types in a
multicellular organism
• During embryonic development
development, a fertilized egg
gives rise to many different cell types
• Cell
C types are organized successively into tissues,
organs, organ systems, and the whole organism
• Gene expression orchestrates the developmental
programs of animals
© 2011 Pearson Education, Inc.
A Genetic Program for
Embryonic Development
• The transformation from zygote to adult results
from cell division
division, cell differentiation
differentiation, and
morphogenesis
© 2011 Pearson Education, Inc.
Figure 18.16
1 mm
((a)) Fertilized eggs
gg of a frog
g
2 mm
((b)) Newly
y hatched tadpole
p
• Cell differentiation is the process by which cells
become specialized in structure and function
• The physical processes that give an organism its
shape constitute morphogenesis
• Differential gene expression results from genes
being regulated differently in each cell type
• Materials in the egg can set up gene regulation
that is carried out as cells divide
© 2011 Pearson Education, Inc.
Cytoplasmic Determinants and
Inductive Signals
• An egg’s cytoplasm contains RNA, proteins, and
other substances that are distributed unevenly in
the unfertilized egg
• Cytoplasmic
C t l
i determinants
d t
i
t are maternal
t
l
substances in the egg that influence early
d
development
l
t
• As the zygote divides by mitosis, cells contain
different cytoplasmic determinants, which lead to
different gene expression
© 2011 Pearson Education, Inc.
Figure 18.17
((a)) Cytoplasmic
y p
determinants in the egg
gg
((b)) Induction by
y nearby
y cells
Unfertilized egg
Sperm
Fertilization
Early embryo
(32 cells)
N l
Nucleus
Molecules of two
different cytoplasmic
determinants
NUCLEUS
Zygote
(fertilized egg)
Mitotic
cell division
Two-celled
embryo
y
Signal
transduction
pathway
Signal
receptor
Signaling
Si
li
molecule
(inducer)
Figure 18.17a
(a) Cytoplasmic determinants in the egg
Unfertilized egg
Sperm
Fertilization
Zygote
(fertilized egg)
Mitotic
cell division
Two-celled
embryo
b
Nucleus
Molecules
M
l
l off two
t
different cytoplasmic
determinants
• The other important source of developmental
information is the environment around the cell,
especially signals from nearby embryonic cells
• In the process called induction, signal molecules
from embryonic cells cause transcriptional
changes in nearby target cells
• Thus,
Th
iinteractions
t
ti
b
between
t
cells
ll iinduce
d
differentiation of specialized cell types
© 2011 Pearson Education, Inc.
Figure 18.17b (b) Induction by nearby cells
Early embryo
(32 cells)
ll )
NUCLEUS
Signal
transduction
pathway
Signal
receptor
Signaling
molecule
(i d
(inducer)
)
Sequential Regulation of Gene
Expression During Cellular
Differentiation
• Determination commits a cell to its final fate
• Determination precedes differentiation
• Cell
C ll diff
differentiation
ti ti iis marked
k db
by th
the production
d ti off
tissue-specific proteins
© 2011 Pearson Education, Inc.
• Myoblasts produce muscle-specific
muscle specific proteins and
form skeletal muscle cells
• MyoD is one of several “master
master regulatory genes”
genes
that produce proteins that commit the cell to
becoming skeletal muscle
• The MyoD protein is a transcription factor that
bi d tto enhancers
binds
h
off various
i
ttargett genes
© 2011 Pearson Education, Inc.
Figure 18.18-1
Nucleus
Embryonic
precursor cell
Master regulatory
gene myoD
Other muscle-specific genes
DNA
OFF
OFF
Figure 18.18-2
Nucleus
Embryonic
precursor cell
Myoblast
(determined)
Master regulatory
gene myoD
Other muscle-specific genes
DNA
OFF
OFF
mRNA
OFF
MyoD protein
(transcription
factor)
Figure 18.18-3
Nucleus
Embryonic
precursor cell
Master regulatory
gene myoD
Other muscle-specific genes
DNA
Myoblast
(determined)
OFF
OFF
mRNA
OFF
MyoD protein
(transcription
factor)
mRNA
MyoD
Part of a muscle fiber
(fully differentiated cell)
mRNA
Another
transcription
factor
mRNA
mRNA
Myosin, other
muscle proteins,
and cell cycle
cycle–
blocking proteins
Pattern Formation: Setting Up the
Body Plan
• Pattern formation is the development of a spatial
organization of tissues and organs
• In animals, pattern formation begins with the
establishment
t bli h
t off th
the major
j axes
• Positional information, the molecular cues that
control pattern formation, tells a cell its location
relative to the body axes and to neighboring cells
© 2011 Pearson Education, Inc.
• Pattern formation has been extensively studied in
the fruit fly Drosophila melanogaster
• Combining anatomical
anatomical, genetic
genetic, and biochemical
approaches, researchers have discovered
developmental principles common to many other
species, including humans
© 2011 Pearson Education, Inc.
The Life Cycle of Drosophila
• In Drosophila,
Drosophila cytoplasmic determinants in the
unfertilized egg determine the axes before
fertilization
• After fertilization, the embryo develops into a
segmented larva with three larval stages
© 2011 Pearson Education, Inc.
Figure
18.19
Thorax Abdomen
Head
1 Egg
developing within
ovarian follicle
Follicle cell
Nucleus
Egg
gg
0.5 mm
Nurse cell
Dorsal
BODY
AXES
Anterior
Left
Right
Posterior
2 Unfertilized egg
Depleted
nurse cells
Ventral
(a) Adult
Egg
shell
Fertilization
Laying of egg
3 Fertilized egg
Embryonic
development
4 Segmented
embryo
0.1 mm
Body
segments
5 Larval stage
g
(b) Development from egg to larva
Hatching
Figure 18.19a
Head Thorax
Abdomen
0 5 mm
0.5
Dorsal
BODY
AXES
Anterior
Left
Ventral
(a) Adult
Right
Posterior
Figure 18.19b
Follicle cell
1 Egg
Nucleus
developing within
ovarian follicle
Egg
Nurse cell
2 Unfertilized egg
Depleted
nurse cells
Egg
shell
Fertilization
Laying of egg
3 Fertilized egg
Embryonic
development
4 Segmented
embryo
Body segments
0.1 mm
Hatching
5 Larval stage
(b) Development from egg to larva
Genetic Analysis of Early
Development: Scientific Inquiry
• Edward B. Lewis, Christiane Nüsslein-Volhard,
and Eric Wieschaus won a Nobel 1995 Prize for
decoding pattern formation in Drosophila
• Lewis
L i di
discovered
d th
the homeotic
h
ti genes, which
hi h
control pattern formation in late embryo, larva,
and
d adult
d lt stages
t
© 2011 Pearson Education, Inc.
Figure 18.20
Eye
y
Leg
Antenna
Wild type
Mutant
• Nüsslein-Volhard
Nüsslein Volhard and Wieschaus studied segment
formation
• They created mutants
mutants, conducted breeding
experiments, and looked for corresponding genes
• Many of the identified mutations were embryonic
lethals, causing death during embryogenesis
• They found 120 genes essential for normal
segmentation
© 2011 Pearson Education, Inc.
Axis Establishment
• Maternal effect genes encode for cytoplasmic
determinants that initially establish the axes of the
body of Drosophila
• These maternal effect genes are also called eggpolarity genes because they control orientation of
the egg and consequently the fly
© 2011 Pearson Education, Inc.
Bicoid: A Morphogen Determining Head
Structures
• O
One maternal effect
ff
gene, the bicoid gene, affects
ff
the front half of the body
• An embryo whose mother has no functional bicoid
gene lacks the front half of its body and has
duplicate posterior structures at both ends
© 2011 Pearson Education, Inc.
Figure 18.21
Head
Tail
A8
T1 T2 T3
A1
A2 A3 A4 A5
A6
Wild-type larva
A7
250 m
Tail
Tail
A8
A8
A7
A6
A7
Mutant larva (bicoid)
• This phenotype suggests that the product of the
mother’s bicoid gene is concentrated at the future
anterior end
• This hypothesis is an example of the morphogen
gradient hypothesis
hypothesis, in which gradients of
substances called morphogens establish an
embryo’s
embryo
s axes and other features
© 2011 Pearson Education, Inc.
Figure 18.22
100 m
RESULTS
Anterior end
Fertilization,
t
translation
l ti off
bicoid mRNA
Bicoid mRNA in mature
unfertilized egg
Bicoid
Bi
id mRNA
RNA iin mature
t
unfertilized egg
Bicoid protein in
early embryo
Bicoid
Bi
id protein
i in
i
early embryo
• The bicoid research is important for three reasons
– It identified a specific protein required for some
early steps in pattern formation
– It increased understanding of the mother’s role in
embryo development
– It demonstrated a key developmental principle that
a gradient of molecules can determine polarity
and position in the embryo
© 2011 Pearson Education, Inc.
• Later studies of C. elegans used the ablation
(destruction) of single cells to determine the
structures that normally arise from each cell
• The researchers were able to determine the
lineage of each of the 959 somatic cells in the
worm
© 2011 Pearson Education, Inc.
Time affter fertilization (h
hours)
Figure 47.18
0
Zygote
First cell division
Nervous
system,
outer skin,,
musculature
10
Musculature, gonads
Outer skin,
nervous system
Germ line
(future
gametes))
g
Musculature
Hatching
g
Intestine
Intestine
Anus
Mouth
Eggs
Vulva
POSTERIOR
ANTERIOR
1.2 mm
• Germ cells are the specialized cells that give rise
to sperm or eggs
• Complexes of RNA and protein are involved in the
specification of germ cell fate
• In
I C.
C elegans,
l
such
h complexes
l
are called
ll d P
granules, persist throughout development, and
can be
b d
detected
t t d iin germ cells
ll off th
the adult
d lt worm
© 2011 Pearson Education, Inc.
Figure 47.19
100 m
• P granules are distributed throughout the newly
fertilized egg and move to the posterior end before
the first cleavage division
• With each subsequent cleavage, the P granules
are partitioned into the posterior-most cells
• P granules act as cytoplasmic determinants, fixing
germ cellll ffate
t att the
th earliest
li t stage
t
off development
d
l
t
© 2011 Pearson Education, Inc.
Figure 47.20
20 m
1 Newly fertilized egg
2 Zygote prior to first division
3 Two-cell embryo
4 Four-cell embryo
Figure 47.21
Dorsal
Right
Anterior
Posterior
Left
Ventral
(a) The three axes of the fully developed embryo
Animal pole
Animal
hemisphere
Vegetal
hemisphere
Vegetal pole
(b) Establishing the axes
Point of
sperm
nucleus
entry
Gray
crescent
Pigmented
cortex
Future
dorsal
side
First
cleavage
Concept : Noncoding RNAs play
multiple roles in controlling gene
expression
p
• Only a small fraction of DNA codes for proteins,
and a very
y small fraction of the non-protein-coding
p
g
DNA consists of genes for RNA such as rRNA and
tRNA
• A significant amount of the genome may be
transcribed into noncoding RNAs (ncRNAs)
• Noncoding RNAs regulate gene expression at two
points: mRNA translation and chromatin
configuration
fi
ti
© 2011 Pearson Education, Inc.
Effects on mRNAs by MicroRNAs
and Small Interfering RNAs
• MicroRNAs (miRNAs) are small single-stranded
RNA molecules that can bind to mRNA
• These can degrade mRNA or block its translation
© 2011 Pearson Education, Inc.
Figure 18.15
Hairpin
Hydrogen
y
g
bond
miRNA
Dicer
5 3
(a) Primary miRNA transcript
miRNA
miRNAprotein
complex
l
mRNA
RNA d
degraded
d d Translation
T
l ti blocked
bl k d
(b) Generation and function of miRNAs
• The phenomenon of inhibition of gene expression
by RNA molecules is called RNA interference
(RNAi)
• RNAi is caused by small interfering RNAs
(siRNAs)
• siRNAs and miRNAs are similar but form from
diff
different
t RNA precursors
© 2011 Pearson Education, Inc.
Chromatin Remodeling
g and
Effects on Transcription by
ncRNAs
• IIn some yeasts
t siRNAs
iRNA play
l a role
l iin
heterochromatin formation and can block large
regions
i
off th
the chromosome
h
• Small ncRNAs called piwi-associated RNAs
(piRNAs) induce heterochromatin, blocking the
expression of parasitic DNA elements in the
genome, known as transposons
y also block
• RNA-based mechanisms may
transcription of single genes
© 2011 Pearson Education, Inc.
The Evolutionary Significance of
Small ncRNAs
• Small ncRNAs can regulate gene expression at
multiple steps
• An increase in the number of miRNAs in a species
may have
h
allowed
ll
d morphological
h l i l complexity
l it tto
increase over evolutionary time
• siRNAs may have evolved first, followed by
miRNAs and later piRNAs
© 2011 Pearson Education, Inc.
Concept: Cloning organisms may
lead to production of stem cells
for research and other
applications
• Organismal cloning produces one or more
organisms genetically identical to the “parent” that
donated the single cell
© 2011 Pearson Education, Inc.
Cloning Plants: Single-Cell
C lt
Cultures
• One experimental approach for testing genomic
equivalence is to see whether a differentiated cell
can generate a whole organism
• A totipotent cell is one that can generate a
complete new organism
• Plant
Pl t cloning
l i is
i used
d extensively
t
i l iin agriculture
i lt
© 2011 Pearson Education, Inc.
Figure 20.17
Cross
section of
carrot root
2-mg
fragments
Fragments were
cultured in nutrient medium;
stirring caused
single cells to
shear off into
the liquid.
Single cells
free in
suspension
began to
divide.
Embryonic
plant developed
from a cultured
single cell.
Plantlet was
cultured on
agar medium.
Later it was
planted in soil.
Adult
plant
Cloning Animals: Nuclear
Transplantation
• In nuclear transplantation, the nucleus of an
unfertilized egg cell or zygote is replaced with the
nucleus of a differentiated cell
• Experiments with frog embryos have shown that a
transplanted nucleus can often support normal
development of the egg
• However,
However the older the donor nucleus
nucleus, the lower
the percentage of normally developing tadpoles
© 2011 Pearson Education, Inc.
Figure 20.18
EXPERIMENT Frog embryo
Frog egg cell
Frog tadpole
UV
Less differentiated cell
Fully differentiated
(intestinal) cell
Donor
D
nucleus
transplanted
Donor
D
nucleus
transplanted
l t d
Enucleated
egg cell
Egg with donor nucleus
activated to begin
development
RESULTS
Most develop
into tadpoles.
Most stop developing
before tadpole stage.
Reproductive
R
d ti Cl
Cloning
i off
Mammals
• In 1997,
1997 Scottish researchers announced the birth
of Dolly, a lamb cloned from an adult sheep by
nuclear transplantation from a differentiated
mammary cell
• Dolly
Dolly’s
s premature death in 2003
2003, as well as her
arthritis, led to speculation that her cells were not
as healthy as those of a normal sheep
sheep, possibly
reflecting incomplete reprogramming of the
original transplanted nucleus
© 2011 Pearson Education, Inc.
Figure TECHNIQUE
20.19
Mammary
cell donor
Egg cell
donor
1
Cultured
y
mammary
cells
2
Egg
cell from
ovary
3 Cells fused
4 Grown in culture
Nucleus
removed
Nucleus from
mammary cell
ll
Early embryo
5 Implanted in uterus
of a third sheep
Surrogate
mother
6 Embryonic
development
RESULTS
Lamb (“Dolly”) genetically
identical to mammary cell donor
Figure 20.19a
TECHNIQUE
Mammary
cell donor
1
Cultured
mammary
cells
Egg cell
donor
gg
Egg
cell from
ovary
2
Nucleus
removed
d
3 Cells fused
Nucleus from
mammary cell
Figure 20.19b
Nucleus from
mammary cell
4 Grown in culture
Early embryo
5 Implanted in uterus
of a third sheep
Surrogate
mother
6 Embryonic
d
development
l
t
RESULTS
Lamb (“Dolly”)
( Dolly ) genetically
identical to mammary cell donor
• Since 1997,
1997 cloning has been demonstrated in
many mammals, including mice, cats, cows,
horses,, mules,, pigs,
p g , and dogs
g
• CC (for Carbon Copy) was the first cat cloned;
however,, CC differed somewhat from her female
“parent”
y look or behave
• Cloned animals do not always
exactly the same
© 2011 Pearson Education, Inc.
Figure 20.20
Problems Associated with Animal
Cloning
• In most nuclear transplantation studies
studies, only a
small percentage of cloned embryos have
developed normally to birth
birth, and many cloned
animals exhibit defects
• Many
M
epigenetic
i
ti changes,
h
such
h as acetylation
t l ti off
histones or methylation of DNA, must be reversed
i th
in
the nucleus
l
ffrom a d
donor animal
i l iin order
d ffor
genes to be expressed or repressed appropriately
f early
for
l stages
t
off development
d
l
t
© 2011 Pearson Education, Inc.
Stem Cells of Animals
• A stem cell is a relatively unspecialized cell that
can reproduce itself indefinitely and differentiate
into specialized cells of one or more types
• Stem cells isolated from early embryos at the
blastocyst stage are called embryonic stem (ES)
cells; these are able to differentiate into all cell
types
• The adult body also has stem cells, which replace
nonreproducing
d i specialized
i li d cells
ll
© 2011 Pearson Education, Inc.
中國時報 96年11月22日
iPS iPSC and four genes
iPS,
Reprogramming of somatic cells to
pluripotent
p
stem cells
induced p
(iPSCs) can be high efficiency
upon inducible
i d ibl expression
i off Oct4,
O t4
Klf4 c-Myc
Klf4,
c Myc, and Sox2
John Gurdon (1958)—nuclear transplant
I Wilmut
Ian
Wil t (1997)
(1997)--Dolly
D ll
Shinya Yamanaka (2006)—reprogramming genes for iPSC
• Induction of Pluripotent Stem Cells from
Mouse Embryonic and Adult Fibroblast
Cultures by Defined Factors
• Kazutoshi Takahashi1 and Shinya
Y
Yamanaka1,2,*
k 12*
• 1Department of Stem Cell Biology, Institute
for Frontier Medical Sciences, Kyoto
y Kyoto
y
606-8507, Japan
p
University,
• 2CREST, Japan Science and Technology
Agency Kawaguchi 332-0012
Agency,
332 0012, Japan
• *Contact: [email protected]
• DOI 10
10.1016/j.cell.2006.07.024
1016/j ll 2006 07 024
中國時報
中國時報 96年11月22日
The Nobel Prize in Physiology
or Medicine 2012
•
•
Sir John B. Gurdon
Figure 20.21
Embryonic
stem cells
Adult
stem cells
Cells generating
some cell types
Cells generating
all embryonic
cell types
Cultured
stem cells
Different
culture
conditions
Different
types of
differentiated
cells
Liver
cells
ll
Nerve
cells
ll
Blood
ll
cells
• Researchers can transform skin cells into ES cells
by using viruses to introduce stem cell master
regulatory genes
• These transformed cells are called iPS cells
(induced pluripotent cells)
• These cells can be used to treat some diseases
and
d to
t replace
l
nonfunctional
f
ti
l ti
tissues
© 2011 Pearson Education, Inc.
Figure 20.22
1 R
Remove skin
ki cells
ll
from patient.
2 Reprogram skin cells
so the cells become
i d
induced
d pluripotent
l i t t
stem (iPS) cells.
Patient with
damaged heart
tissue or other
disease
3 Treat iPS cells so
that they differentiate
into a specific
cell type
type.
4 Return cells to
patient, where
p
they can repair
damaged tissue.
Diagnosis and Treatment of
Diseases
• Scientists can diagnose
g
many
y human g
genetic
disorders using PCR and sequence-specific
primers,, then sequencing
p
q
g the amplified
p
p
product to
look for the disease-causing mutation
disease-causing
causing
• SNPs may be associated with a disease
mutation
• SNPs may also be correlated with increased risks
for conditions such as heart disease or certain
types of cancer
© 2011 Pearson Education, Inc.
Human Gene Therapy
• Gene therapy is the alteration of an afflicted
individual’s genes
• Gene therapy holds great potential for treating
disorders traceable to a single defective gene
• Vectors are used for delivery of genes into
specific types of cells, for example bone marrow
• Gene therapy provokes both technical and ethical
questions
© 2011 Pearson Education, Inc.
FigureCloned
20.23 gene
1 IInsertt RNA version
i
off normall allele
ll l
into retrovirus.
Viral RNA
Retrovirus
capsid
2 Let retrovirus infect bone marrow cells
that have been removed from the
patient and cultured.
3 Viral DNA carrying the normal
allele inserts into chromosome.
Bone
marrow
cell from
patient
4 Inject engineered
cells into patient.
Bone
B
marrow
Terminology related to
developmental biology
•
•
•
•
•
•
•
Determination
Totipotent
Pluripotent
Differentiation
Dedifferentiation
Transdifferentiation
Stem cells ((embryonic
y
and somatic))
Re-programming
p g
g
What happen when parasites, bacteria, and
viruses
i
enter
t h
hostt cells
ll
Do they
y affect the g
gene expression
p
of host
cells?
Most of the viruses shut off host’s protein
expression by CAP-independent
translational mechanism, especially those
positive-stranded RNA virus
p
Bacteria (Listeria and Shigella) use host’s
actin as an intracellular movement
apparatus
Grevy’s zebra in LA zoo (origin from Kenya)
Plains zebra in Tanzania
Cell differentiation
A process by which cells become different from
each other,
other acquiring distinct identities and specialized
functions.
Differentiated cells serve specialized functions and have
achieved a terminal and stable state.
state
Differentiated Cell Types
The central feature of cell differentiation is a change in gene
expression. This eventually leads to the production of
cell-specific proteins.
Cell differentiation is a gradual process, occurs over
successive cell generations.
g
Cell fate and differentiation modified by
changes in gene expression
Fibroblast
Oct-3/4, Sox2
c-myc, klf4
Pluripotent
p
stem cells
Master g
genes in cell fate
determination
can induce tissue-specific differentiation
in cells that do not normally undergo it
• Muscle system: bHLH myogenic proteins
such as MyoD, MRF4, myogenin.
• Neural system: bHLH proneural proteins such
as Mash, Math, neuroD.
• Eye determination gene: Pax6 and eyeless
Differentiation of striated muscle in culture
Myogenic precursor cell
(bipolar)
Actin, myosin II,
Actin
II
Tropomyosin,
Creatine phosphate kinase
MyoD: master gene for muscle development
Muscle
l differentiation
diff
i i can be
b induced
i d d in
i fibroblast
fib bl in
i culture
l
(as
( well
ll
as in other cell types) by transfecting the cells with the myoD gene.
myoD, myogenin, myf-5, mrf4: bHLH protein, induce
muscle differentiation in fibroblast
This family of genes are only expressed in muscle precursor and
muscle,
l can lead
l d to the
h activation
i i off muscle-specific
l
ifi
genes and cause muscle differentiation.
bHLH protein forms heterodimer
myoD E12
CANNTG
E box
Key features of the differentiation of skeletal muscle
mrf4
myoD and myf
5 are expressed in proliferating
proliferating, undifferentiated myogenic cells,
myf-5
cells
myogenine is expressed during muscle differentiation.
Developmental process of
nervous system
Neural patterning
Proneural protein
Neurogenesis
g
Differentiation
(cell migration and axon guidance)
Targeting and synapse formation
Cell differentiation controlled by
environment
Cell differentiation
E
External
l signals
i l
(permissive and selective)
I
Internal
l state
Induction
Organizer: organization of a complete embryonic body
Spemann
p
organizer
g
External signals can activate genes
Signal transduction:
Wnt/Wingless,
TGF transforming growth factor),
TGF-transforming
factor)
Hedgehog,
Notch
p tyrosine
y
kinase),
)
RTK ((receptor
Nuclear receptor,
Jak/STAT
Signals:
environment (hormone stimulation,
y stimulation,, etc))
olfactory
other cells (cell-cell
(cell cell interaction)
Cell Cell interactions
Cell-Cell
Contact
C
t t between
b t
the
th inducing
i d i
And responding cells
Diffusion of inducing signals
from one cell to another
Signaling to more cells with gradient of ligands
Morphogen
Signaling cell
responding
cells
Si li to
Signaling
t surrounding
di cells
ll
Lateral inhibition
Contact-dependent signaling
Signal transduction: relay of signals
Changes in membrane receptor activity
Changes in intracellular protein activity
Nuclear migration
Changes in nuclear protein activity
Signal transduction: changes in responding cells
cytoskeleton
Gene expression
Cell cycle
Figure 47.2
EMBRYONIC DEVELOPMENT
Sperm
Zygote
Adult
frog
Egg
Metamorphosis
Blastula
Larval
stages
Gastrula
Tail-bud
embryo
Mechanisms of Morphogenesis
• Morphogenesis in animals but not plants involves
movement of cells
© 2011 Pearson Education, Inc.
The Cytoskeleton in
Morphogenesis
• Reorganization of the cytoskeleton is a major force
in changing cell shape during development
• For example,
example in neurulation,
neurulation microtubules oriented
from dorsal to ventral in a sheet of ectodermal
cells help lengthen the cells along that axis
© 2011 Pearson Education, Inc.
Figure 47.15-1
Ectoderm
Figure 47.15-2
Ectoderm
Neural
plate
Microtubules
Figure 47.15-3
Ectoderm
Neural
plate
Microtubules
Actin
filaments
Figure 47.15-4
Ectoderm
Neural
plate
Microtubules
Actin
filaments
Figure 47.15-5
Ectoderm
Neural
plate
Microtubules
Actin
filaments
Neural tube
• The cytoskeleton promotes elongation of the
archenteron in the sea urchin embryo
• Thi
This iis convergentt extension,
t
i
th
the
rearrangement of cells of a tissue that cause it to
become narrower (converge) and longer (extend)
• Convergent extension occurs in other
d
developmental
l
t l processes
• The cytoskeleton also directs cell migration
© 2011 Pearson Education, Inc.
Figure 47.16
• In chicks,
chicks gravity is involved in establishing the
anterior-posterior axis
• Later,
Later pH differences between the two sides of the
blastoderm establish the dorsal-ventral axis
• In
I mammals,
l experiments
i
t suggestt that
th t orientation
i t ti
of the egg and sperm nuclei before fusion may
h l establish
help
t bli h embryonic
b
i axes
© 2011 Pearson Education, Inc.
中國時報 96年11月22日
中國時報 96年11月22日