Download Fertilization

General Biology
gy II
Lecture 2-4
Before the class
C p e 477
Chapter
Animal Development
p
• When a life begins?
• How a life of animal starts?
• What are the progress of fertilization?
• How an embryo is developed into an individual?
• How each cell knows its own fate?
݅ ᑣ ٫ Դৣ
[email protected]
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2
Outlines
Overview: A Body-Building Plan
• A human embryo at about 7 weeks after
conception shows development of distinctive
features
• Part1
– Fertilization
– Cleavage
• Part2
Part 2
– Gastrulation
– Organgenesis
• Part3:
– Cellfatedeterminationandpatternformation
Biology
lectured
©General
2011 Pearson
Education,
Inc. by Han-Jia Lin
3
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Stagesofembryonicdevelopment
p
Sperm
AnimalDevelopment
EMBRYONICDEVELOPMENT
• Although animals display different body plans, they
share
h
many basic
b i mechanisms
h i
off d
development
l
and
d
use a common set of regulatory genes
Zygote
• Cleavage
Adult
Egg
f
frog
ϩ຋ය
• Blastula
៶ ය
៶खය
• Gastrulation
Metamorphosis
চဉය
• Organogenesis
Ꮤ‫׎۔‬ԋය
• Metamorphosis Larval
stages
ᡂᄊය
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Blastula
Gastrula
Tailbud
embryo
5
Modelanimals
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Fertilization
• Fertilization is the formation of a diploid
p
zygote
yg
from a haploid egg and sperm
• C.elegans,Drosophila
C l
hil
• Seaurchin,zebrafish,frog,chickandmouse
,
, g,
• Molecules and events at the egg surface play a
crucial role in each step of fertilization
– Sperm penetrate the protective layer around the
egg
– Receptors on the egg surface bind to molecules
on the sperm surface
Nature430,411412
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http://www.imcb.astar.edu.sg/pressarchive/170309p.php
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– Changes at the egg surface prevent polyspermy,
the entry of multiple sperm nuclei into the egg
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Acrosome Reaction
The Acrosomal Reaction )ഗᡏϸᔈ*
Sperm
plasma
membrane
• The acrosomal reaction is triggered when the
sperm meets the egg
Sperm
nucleus
• Th
The acrosome att the
th tip
ti off the
th sperm releases
l
hydrolytic enzymes that digest material
surrounding
di th
the egg
Basal body
(centriole)
p
Sperm
head
• Gamete contact and/or fusion depolarizes
p
the egg
gg
cell membrane and sets up a fast block to
p y p
polyspermy
y
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Fertilization
envelope
l
Acrosomal
process
Actin
filament
Cortical
Fused
granule
plasma
membranes
b
Hydrolytic enzymes
Perivitelline
space
Vitelline layer
Acrosome
Jelly coat
Sperm-binding
receptors
EGG CYTOPLASM
Egg plasma membrane
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Figure 47.4
10
EXPERIMENT
The Cortical Reaction )Ҝ፦ϸᔈ**
• Initiated by the fusion of egg and sperm
• Seconds after the sperm binds to the egg, vesicles
jjust beneath the egg
gg p
plasma membrane release
their contents and form a fertilization envelope
p acts as the slow block
• The fertilization envelope
to polyspermy
• The cortical reaction requires a high concentration
of Ca2 ions in the egg
• Ca2 spread across the egg correlates with the
appearance of the fertilization envelope
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10 sec after
fertilization
25 sec
35 sec
1 min
10 sec after
f tili ti
fertilization
20 sec
30 sec
500 Pm
RESULTS
1 sec before
f tili ti
fertilization
500 Pm
m
CONCLUSION
Point of sperm
nucleus
entry
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Spreading
wave of Ca2
Fertilization
envelope
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Fertilization in Mammals
Egg
gg Activation
• The rise in Ca2+ in the cytosol increases the rates
of cellular respiration and protein synthesis by the
egg cell
• With these rapid changes in metabolism, the egg
i said
is
id tto b
be activated
ti t d
• Secretions in the mammalian female reproductive
t t alter
tract
lt sperm motility
tilit and
d structure
t t
• This is called capacitation,
p
, and must occur before
sperm are able to fertilize an egg
• The p
proteins and mRNAs needed for activation
are already present in the egg
• The sperm nucleus merges with the egg nucleus
and cell division begins
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General Biology lectured by Han-Jia Lin
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Figure 47.5
Capacitation
• Only in mammalian sperm
– Not
N t ready
d tto ffertilize
tili b
before
f
capacitation!
– Take place in female reproduction tract
• Biochemical event
• Reported in 1951 by both Min Chueh
Chang and Collin Russel Austin,
independently.
p
y
No fast
block in
mammlian!
Zona pellucida
Follicle cell
Key and
Lock!
Dr. Min Chueh Chang
஭ܴ᝺ റγ
2:19.2::2
Sperm
Sperm
nucleus
basal body
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Cortical
granules
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Cleavage
DurationofCleavageStage
• Fertilizationisfollowedbycleavage,aperiodofrapid
celldivisionwithoutgrowth
• Cleavage
Cleavagepartitionsthecytoplasmofonelargecell
partitions the cytoplasm of one large cell
intomanysmallercellscalledblastomeres (खယಒझ)
• Theblastula(៶ख)isaballofcellswithafluidfilled
cavitycalledablastocoel (៶ख๚)
• In mammals the first cell division occurs 1236
h
hours
after
ft sperm bi
binding
di
• The diploid nucleus forms after this first division of
the zygote
• Zebrafish (cleavage2hr,blastula5hr)
• Chicken(~24hr)
• Mouseandhuman
Blastocoel
(5~6days)
50 Pm
50Pm
(a)Fertilizedegg
(b)Fourcellstage
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(c)Earlyblastula
Blastula(atleast128cells)
(d)Laterblastula
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Cleavagepattern
First2cleavage
• PolarityofZygote
• Cytokinesis (SÆMÆSÆMphase)
– Yolkisthekeyfactorforcleavage
• Cleavagefurrowռ຋ྎ
• Th
Thevegetalpolehasmoreyolk;theanimalpole
t l l h
lk th
i l l
haslessyolk
• Thefirst2cleavageproduce4blastomeres
h f
l
d
bl
ofequal
f
l
size
• Meroblastic:theyolk
istoobigthatcleavage
furrow cannot pass
furrowcannotpass
throughit(bird,frog,
fish…)
• Holoblastic:human
Animal p
pole ୏‫ނ‬
ཱུ
V
Vegetal
t l pole
l ෌‫ނ‬
ཱུ
Graycrescent
Zygote
yg
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0 25
0.25mm
19
2cellstage
forming
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4cellstage
forming
• Graycrescent:ԪД୔
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The3rd cleavage
Inmostinsects
• Equatorial
• Spermandeggnucleifusewithinyolk!
• Maybeasymmetric:becauseofthehugeyolkin
meroblastic embryo!
embryo!
• Multipleroundsofmitosisoccurwithout
cytokinesis!
– Nocellmembranesformaroundtheearlynuclei
(blastomeresinanimalpolearesmaller)
0.25mm
Animalpole
– Nucleimigratetotheouteredgeoftheembryo
aandtheplasmamembraneformÆ
d t e p as a e b a e o
6000cells
6000
ce s
surrondingamassofyolk(similartoblastula)
Animal
pole
Graycrescent
Vegetalpole
4cellstage
2cellstage
forming
forming
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Zygote
8cellstage
8cellstage(viewed
fromtheanimalpole)
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Regulationofcleavage
End of Part 1
• Howanembryoknowstheendofcleavagestage?
Ask yourself….
– theratioofmaterialinthenucleusrelativetothe
cytoplasm is sufficiently large
cytoplasmissufficientlylarge
22
• How eggs could prevent polyspermy?
• Wh
What’s
t’ diff
differentt between
b t
mammalian
li
fertilization and other animals?
– Exp:halfofthecytoplasmremoveÆ onefewer
cleavageoccur…
l
• When is the start point of cleavage?
• Theendofcleavagemeans…
g
• What is animal pole and vegetal pole?
– EnoughcellsÆ enoughcopiesofchromosomeÆ
enough RNA to program the cell’ssmetabolism
enoughRNAtoprogramthecell
metabolism
• What is the sequence of cleavage?
• How to control cleavage?
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General Biology lectured by Han-Jia Lin
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Morphogenesis
Gastrulation
• Thecellularandtissuebasedprocessesbywhich
theanimalbodytakesshapes.
• Gastrulation rearrangesthecellsofablastula
g
intoathreelayeredembryo,calledagastrula
(চဉख)
• Thethreelayersproducedbygastrulation
Th h
l
d db
l i are
calledembryonicgermlayers (खቫ)
– Gastrulation
• Asetofcellsfromsurfaceofblastulamovesto
i
interiorlocation
i l
i
– The
Theectodermformstheouterlayer
ectoderm forms the outer layer
– Theendodermlinesthedigestivetract
– Themesodermpartlyfillsthespacebetweenthe
The mesoderm partly fills the space between the
endodermandectoderm
• Celllayersestablished(2or3layers)
y
(
y )
• Aprimitivedigestivetubeisformed
• Animalswithbilateralsymmetryaretriplobasts,
h i
havingmesoderm
d
• Eachgermlayercontributestospecificstructures
in the adult animal
intheadultanimal
– Organogenesis
• Theformationoforgans
The formation of organs
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ECTODERM(outerlayerofembryo)
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GastrulationinSeaUrchins
•Epidermisofskinanditsderivatives(includingsweatglands,
hairfollicles)
•Nervousandsensorysystems
• Pituitary gland adrenal medulla
•Pituitarygland,adrenalmedulla
•Jawsandteeth
•Germcells
• Gastrulation beginsatthevegetalpoleofthe
begins at the vegetal pole of the
blastula
• Mesenchyme cellsmigrateintotheblastocoel
cells migrate into the blastocoel
MESODERM(middlelayerofembryo)
• Thevegetalplateformsfromtheremainingcells
ofthevegetalpoleandbucklesinwardthrough
invagination
•Skeletalandmuscularsystems
•Circulatoryandlymphaticsystems
•Excretoryandreproductivesystems(exceptgermcells)
•Dermisofskin
• Adrenal cortex
•Adrenalcortex
• Thenewlyformedcavityiscalledthe
archenteron (চဉ)
archenteron(চဉ)
ENDODERM(innerlayerofembryo)
•Epithelialliningofdigestivetractandassociatedorgans
(liver,pancreas)
•Epithelialliningofrespiratory,excretory,andreproductivetracts
andducts
dd
•Thymus,thyroid,andparathyroidglands
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• Thisopensthroughtheblastopore (खα orচα),
which will become the anus
whichwillbecometheanus
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Gastrulationbegins
withthemigrationof
mesenchymecells
h
ll
(໔ယಒझ)
Animal
pole
Blastocoel
Mesenchyme
cells
Vegetalplate
Threeaxisofbilaterallyanimals
Vegetal
pole
Protostomes(চα୏‫)ނ‬
Protostomes
(চα୏‫)ނ‬
BlastoporeÆ mouth
Blastocoel
Deuterostomes(ࡕα୏‫)ނ‬
Deuterostomes
(ࡕα୏‫)ނ‬
BlastoporeÆ anus
Aftergastrulation,the
After
gastrulation the
larvaesofSeaurchinare
zooplankton
Filopodia
Mesenchyme
cells
Archenteron
Bl t
Blastopore
Aftermetamorphogenesis,
theadultseaurchinsinkto
theseafloor.
50Pm
Blastocoel
Ectoderm
Key
A h t
Archenteron
Blastopore
Mouth
Futureectoderm
Future
ectoderm
Futuremesoderm
Futureendoderm
Mesenchyme
(mesodermforms
futureskeleton)
Digestivetube(endoderm)
b ( d d
)
Anus(fromblastopore)
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GastrulationinFrogs
• Cellscontinuetomovefromtheembryosurface
ll
i
f
h
b
f
intotheembryobyinvolution(खजϣᙯ)
• This
Thisformsacreasealongtheregionwherethegray
forms a crease along the region where the gray
crescent(ԪД୔) formed
– Thesecellsbecometheendodermandmesoderm
– Cellsontheembryosurfacewillformtheectoderm
C ll
th
b
f
ill f
th
t d
• Th
Thepartabovethecreaseiscalledthedorsallip
t b
th
i
ll d th d
l li
(ङয)oftheblastopore
1
Key
Future
ectoderm
Future
mesoderm
Early
Vegetalpole
Future
gastrula
endoderm
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EmbryoInvolution
• Frog
Froggastrulationbeginswhenagroupofcellsonthe
gastrulation begins when a group of cells on the
dorsalsideoftheblastulabeginstoinvaginate
SURFACEVIEW
SURFACE
VIEW
Animalpole
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CROSS SECTION
CROSSSECTION
Key
Blastocoel
Dorsal
Dorsal
lipof
blasto
pore
Blastopore
Blastocoel
shrinking
Archenteron
Future
ectoderm
d
Future
mesoderm
Future
Future
endoderm
Dorsal
lipof
blastopore
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LateGastrulationinFrog
Gastrulationinchicks
• Priortogastrulation,theembryoiscomposedof
anupperandlowerlayer,theepiblast(΢खቫ)
andhypoblast(Πखቫ),respectively
• Theblastocoeliscompletelyreplacedbythe
endodermlined
endoderm
linedarchenteron
archenteron
3
Future
ectoderm
Future
mesoderm
Future
Future
endoderm
Ectoderm
Mesoderm
Endoderm
Blastocoel
remnant
Key
Late
gastrula
Blastopore
• During
Duringgastrulation,epiblastcellsmovetoward
gastrulation epiblast cells move toward
themidlineoftheblastodermandthenintothe
embryotowardtheyolk
b
t
d th
lk
• Themidlinethickensandiscalledtheprimitive
p
streak(চచ)
Blastopore
Yolk plug
Yolkplug
A h t
Archenteron
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• Allthecellsthatwillformthe
embryocomefromtheepiblast
• Thehypoblastcellsdonot
h h bl
ll d
contributetotheembryo
• itcontributestothesac
it contributes to the sac that
that
surroundstheyolkandaconnection
betweentheyolkandtheembryo
y
y
Fertilizedegg
Primitive
streak
Embryo
Yolk
Gastrulationinhuman
• human blastocyst (notblastulabecauseoflittle
yolk)Æ
Æ day6,>100cells
Thetrophoblast
trophoblast (෷Ꭶቫ)istheouterepithelial
(෷Ꭶቫ) is the outer epithelial
– The
layeroftheblastocyst anddoesnotcontribute
to the embryo but instead initiates implantation
totheembryo,butinsteadinitiatesimplantation
Epiblast
Future
Future
ectoderm
Endometrialepithelium
(uterinelining)
Uterus
Blastocoel
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– Theinnercellmass isaclusterofcellsatone
endoftheblastocyst
Primitivestreak
Migrating
cells
(mesoderm)
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Innercellmass
Trophoblast
Endoderm
Hypoblast
Blastocoel
YOLK
35
1 Blastocystreachesuterus.
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Implantation
BeginningofGastrulation
• Thetrophoblast cellssecretenzymesto
b kd
breakdownandinvadetheendometrium
d i d th
d
ti
of
f
uterus(η৐ϣጢ).
• Afterimplantation,trophoblast
f i l
i
h bl continuesto
i
expandandasetofextraembryonic membranes
is formed
isformed.
• Innercellmassformaflatdiskwithepiblast and
hypoblast
Expandingregionof
trophoblast
Amnioticcavity
Epiblast
Hypoblast
Yolksac(fromhypoblast)
Expandingregionof
trophoblast
Maternal
blood
vessel
Epiblast
Hypoblast
Extraembryonicmesoderm
cells(fromepiblast)
cells (from epiblast)
Chorion(fromtrophoblast)
Trophoblast
2
Blastocystimplants
Blastocyst
implants
(7daysafterfertilization).
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LateGastrulationinhuman
• Thefourextraembryonic membranes that form
aroundtheembryoofamniotes(Բጢ୏‫)ނ‬,
Բ ୏‫ނ‬
includingreptiles,birdsandmammals
– Likechickembryo,cellsmoveinwardfromthe
epiblastthroughaprimitivestreakandform
mesodermandendoderm
Allantois
4 Gastrulationhasproduceda
threelayeredembryowith
fourextraembryonic
membranes.
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DevelopmentalAdaptationsofAmniotes
• Embryo:
y
Amnion
Chorion
Ectoderm
Mesoderm
Endoderm
Yolksac
3 Extraembryonicmembranes
(
y ),
starttoform(10–11days),
andgastrulationbegins
(13days).
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– Thechorion (้Лጢ)functionsingasexchange
– Theamnion (Բጢ* enclosestheamnioticfluid
– Theyolksac(ռ໳៶ጢ) enclosestheyolkintheeggof
reptilesandisthesiteofearlyformationofbloodin
mamals
– Theallantois (ֿ៶ጢ)disposesofwasteproductsin
reptileeggandincorporatedintotheumbilicalcord(ᙏ
஥)inmammals
• Placenta:
– Invading
trophoblast
– Cellsfromepiblast
– Adjacent
endometrum
• butnotinfishandamphibians,why?
39
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Figure 47.13a
Neural folds
Organogenesis
• Cellmovement
Frog
neurulation
– Gastrulation Æ massmovement
– OrganogenesisÆ localmovement
– MorphogenesisÆ
Æ moveandchangeofshape(animalonly)
• Duringorganogenesis,variousregionsofthegermlayers
developintorudimentaryorgans
– Ex:theneurulationÆ brainandspinalcord(ૉᡎ)
– Notochord(ૉ઩)Æ startfromdorsalmesoderm(arod)
– Neuralplate(ઓ࿶݈)Æ ectodermabovethenotochord,
i d d b i li
inducedbysignalingmoleculesfrommesodermalcellsand
l l f
d
l ll
d
others
• Neuraltube(ઓ࿶ᆅ)Æ
Neural tube (ઓ࿶ᆅ) Æ rolledfromneuralplateÆ
rolled from neural plate Æ central
central
nervoussystem(brainandspinalcord)
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1 mm
Neural
plate
Notochord
Ectoderm
Mesoderm
Endoderm
A h t
Archenteron
(a) Neural plate formation
41
Neural
fold
Neural
fold
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Neural tube related cells in vertebrate
development
Neural plate
• Neuralcrestcells (ઓ࿶ૉಒझ)
(
)
– Developalongtheneuraltube(ectoderm)
– Migrationtoformvariouspartsoftheembryo(peripheral
g
p
y (p p
nerves,partsofteeth,skullbones,andsoon)
Question:
Our CNS comes from which
germ layer?
• Somites (ᡏ࿯)
Neural
crest cells
Neural
crest cells
(b) Neural tube formation
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Neural
tube
– Lateraltothenotochordformsblocks(mesoderm)
– MigrationofmesenchymecellsÆ vertebraeformationand
musclesassociatedwith
– Themesodermsplitstoformthecoelom(bodycavity)
– Somitebecomeslessobviouslaterindevelopment
– Notochorddisappearedbeforebirth(someleavein
vertebraldisk෎໔ዬ)
b l di k ෎໔ዬ)
Outer layer
y
of ectoderm
Figure 47.13b-3
43
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Figure 47.13c
Eye
Somites
Tail bud
Chick neurulation
• Early
Earlyorganogenesisinothervertebratesissimilarto
organogenesis in other vertebrates is similar to
thatinthefrog
SEM
Neural tube
Notochord
Coelom
• Chickneurulation
Chi k
l ti Æ threelayertube
th
l
t b
1 mm
Neurall
N
crest
cells
Neural tube
Notochord
)ઓ࿶ૉಒझ*
Eye
Forebrain
Somite
Coelom
E d d
Endoderm
Mesoderm
Ectoderm
Archenteron
Lateral
fold
Heart
Blood
vessels
Somites
Somite
(c) Somites
Yolk stalk
)ᡏ࿯*
These layers
y
form extraembryonic
membranes.
Archenteron
(di
(digestive
ti
cavity)
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Yolk sac
Neural
tube
YOLK
(a) Early organogenesis
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(b) Late organogenesis (3 day old)
Spina bifida (ૉࢊ຋)
Organogenesis in invertebrates
• A portion of the neural tube fails to develop or
close properly
• Themechanismsaresimilar
46
– Alsoinvolvemanycellmigrationandsignaling
• Surgical repair
– Themolecularsignalingpathwaysareverysimilar
The molecular signaling pathways are very similar
• Nerve damage Æ
• Butthebodyplanisverydifferent
– Ininsects,theneuraltubedevelopsalongtheventralside
oftheembryo(vertebratesÆ dorsal)
permanent Æ
paralysis
1~2
2 per 1
1,000
000 in
• 1
US
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General Biology lectured by Han-Jia Lin
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Ectoderm
MechanismsofMorphogenesis
Neural
plate
• MovementofcellsÆ changeoftheshapeÆ
cytoskeleton(ಒझମࢎ)
k l
( झମࢎ)
Microtubules
• Cytoskeleton:microtubules(༾λᆅ)and
y
(
)
microfilaments(༾ํ)
• Reorganization
Reorganizationofthecytoskeletonisamajorforcein
of the cytoskeleton is a major force in
changingcellshapeduringdevelopment
Actin
filaments
• Ex:inneurulation
Wedge-shaped cells
ུ‫׎‬
Not only in vertebrate
Not only in neuralation
– microtubules
microtubulesorientedfromdorsaltoventralinasheetof
oriented from dorsal to ventral in a sheet of
ectodermalcellshelplengthenthecellsalongthataxis
Neural tube
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General Biology lectured by Han-Jia Lin
Figure 47.15-5
50
Convergence extension in sea urchin development
Convergent extension
• Thecytoskeletonpromoteselongationofthe
archenteron in the sea urchin embryo
archenteronintheseaurchinembryo
• rearrangementofcellsofatissuethatcauseitto
becomenarrower(converge)andlonger(extend)
Convergentextensionoccursinotherdevelopmental
extension occurs in other developmental
• Convergent
processesÆ frogdevelopment
Similar!
• Th
Thecytoskeletonalsodirectscellmigration(amoeboid
t k l t
l di t
ll i ti (
b id
movement)
– Transmembrane glycoprotein:celladhesionmolecules
– Extracellularmatrix(ECM)
(
)
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51
47.16
General BiologyFigure
lectured
by Han-Jia Lin
52
ProgrammedCellDeath
End of Part 2
• Programmedcelldeathisalsocalledapoptosis
Ask yourself….
• Atvarioustimesduringdevelopment,individualcells,
setsofcells,orwholetissuesstopdevelopingandare
engulfedbyneighboringcells
• How many germ layers we have?
• Wh
Whatt different
diff
t in
i the
th gastrulation
t l ti between
b t
sea
urchin, chick and human?
• For
Forexample,manymoreneuronsareproducedin
example many more neurons are produced in
developingembryosthanwillbeneeded
• What’s different in the neuron development
between invertebrates and vertebrates?
• Extraneuronsareremovedbyapoptosis,why?
E t
db
t i
h ?
General Biology lectured by Han-Jia Lin
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Cell fates:
determination and differentiation
General Biology lectured by Han-Jia Lin
54
FateMapping
• Fatemapsarediagramsshowingorgansandother
structuresthatarisefromeachregionofanembryo
h
f
h
f
b
• Determination isthetermusedtodescribethe
processbywhichacellorgroupofcellsbecomes
committedtoaparticularfate(beginning)
• Classicstudiesusingfrogsindicatedthatcelllineagein
g g
g
germlayersistraceabletoblastulacells
• Differentiation referstotheresultingspecialization
in structure and function (result)
instructureandfunction(result)
• How?Æ Cellsinamulticellularorganismsharethe
samegenome
– Differencesincelltypesistheresultoftheexpressionof
differentsetsofgenes
– Cytoplasmicdeterminantsandinductivesignals
y p
g
contributetocellfatespecification
General Biology lectured by Han-Jia Lin
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General Biology lectured by Han-Jia Lin
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Technologies for embryologists
Study of C. elegans (ጕᙝ)
• Dye injection Æ Æ Æ Specific marker gene
• Development
Developmentfinishedin3.5daywith959cellsina
finished in 3 5 day with 959 cells in a
worm
• Cell ablation
• Ablation(destruction)ofsinglecellstodetermine
thestructuresthatnormallyarisefromeachcell
64-cell embryos
– thelineageofeachofthe959somaticcellsisknown
Blastomeres
injected with dye
• Question:why959cells?
Larvae
(b) Cell lineage analysis in a tunicate
General Biology lectured by Han-Jia Lin
Time affter fertilization (h
hours)
Figure 47.18
57
General Biology lectured by Han-Jia Lin
1 mm
58
Zygote
0
Tracing the formation of germ cells
First cell division
Nervous
system,
outer skin,,
musculature
Musculature, gonads
Outer skin,
nervous system
Germ line
(future
gametes))
g
• Germcellsarethespecializedcellsthatgiveriseto
spermoreggs
Musculature
• ComplexesofRNAandproteinareinvolvedinthe
p
p
specificationofgermcellfate
10
Hatching
g
• In
InC.elegans,suchcomplexesarecalledPgranules,
C elegans such complexes are called P granules
persistthroughoutdevelopment,andcanbe
detected in germ cells of the adult worm
detectedingermcellsoftheadultworm
Intestine
Intestine
Anus
Mouth
Eggs
P granule
protein in the
gonad of adult
worm
Vulva
POSTERIOR
ANTERIOR
1.2 mm
General Biology lectured by Han-Jia Lin
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General Biology lectured by Han-Jia Lin
60
20 Pm
Cytoplasmic determinants move before
cell cleavage
Determination by P granules
1 Newly fertilized egg
• Pgranulesactascytoplasmicdeterminants,fixing
g
y p
g
germcellfateattheearlieststageofdevelopment
• P
Pgranulesaredistributedthroughoutthenewly
granules are distributed throughout the newly
fertilizedeggandmovetotheposteriorendbefore
the first cleavage division
thefirstcleavagedivision
2 Zygote
yg
prior
p
to first division
• Witheachsubsequentcleavage,thePgranulesare
partitionedintotheposteriormostcells
3 Two-cell embryo
Using the same idea, the
fates of all cells during C.
elegans development are
known…
There are 131 cells die
during development….
Q: How many rounds of
mitosis must be done
during C. elegans
development?
4 Four-cell embryo
General Biology lectured by Han-Jia Lin
61
Little worm, great discovery!
By
y using
g C. elegans
g
as a model
system, the Laureates have
identified key genes regulating
these processes
processes. They have
also shown that corresponding
genes exist in higher species,
including man
man.
General Biology lectured by Han-Jia Lin
63
http://www.nobelprize.org/nobel prizes/medici
General Biology lectured by Han-Jia Lin
Figure 47.20
62
AxisFormation(ᡏື‫׎‬ԋ)
• Inbilateralsymmetry(‫ୁٿ‬ჹᆀ)animals
• Thisbodyplanexhibits
– Almostsymmetry:rightleftaxis
Almost symmetry: right left axis
– Asymmetry:dorsalventralandanteriorposterioraxes
General Biology lectured by Han-Jia Lin
64
Rotation of egg surface after fertilization
in frog
Establish the axis
• Uponfusionoftheeggandsperm,theeggsurface
rotates withrespecttotheinnercytoplasm
with respect to the inner cytoplasm
• Veryearlyindevelopment
• Thiscorticalrotationbringsmoleculesfromonearea
oftheinnercytoplasmoftheanimalhemisphereto
interactwithmoleculesinthevegetalcortex
– Theanteriorposterioraxisofthefrogembryois
p
g
y
determinedduringoogenesis
• Thefollowingstatementsarealltrue
The following statements are all true
• Thisleadstoexpressionofdorsal (wheresperm
entered the egg) and ventralspecific
enteredtheegg)andventral
specificgeneexpression
gene expression
– The animalvegetalasymmetryindicateswhere
theanteriorposterioraxisforms
h
i
i
i f
– Thedorsalventralaxisisnotdetermineduntil
fertilization
Confusing?
General –
Biology
lectured by Han-Jia Lin
65
General Biology lectured by Han-Jia Lin
66
RestrictingDevelopmentalPotential
Axis establishment in other animals
• Ininsects
– Morphogen gradientsdeterminebothAPandDV(dorsal
ventral)axes
• Progressiverestrictionofdevelopmentalpotentialis
a general feature of development in all animals
ageneralfeatureofdevelopmentinallanimals
• Inchicks
• Ingeneraltissuespecificfatesofcellsarefixedby
thelategastrulastage
– gravityisinvolvedinestablishingtheAPaxis
gravity is involved in establishing the A P axis
– Later,pHdifferencesbetweenthetwosidesofthe
bl t d
blastoderm
establishtheDVaxis
t bli h th D V i
p
p
(
) determinea
• HansSpemann’sexperiments(1938)Æ
cell䇻sdevelopmentalpotential(rangeofstructures
g
)
towhichitcangiverise)
• Inmammals,experimentssuggestthatorientationof
theeggandspermnucleibeforefusionmayhelp
establishembryonicaxes
• Embryonicfatesareaffectedbydistributionof
determinants and the pattern of cleavage
determinantsandthepatternofcleavage
• OnceAPandDVaxesfixed,LRaxisisfixed!
General Biology lectured by Han-Jia Lin
67
General Biology lectured by Han-Jia Lin
68
Figure 47.22-2
EXPERIMENT
Control egg
(dorsal view)
Loss of totipotent
Experimental egg
(side view)
1a Control
1b Experimental
group
group
g
p
Gray
crescent
Gray
crescent
• Th
Thefirsttwoblastomeres
fi t t bl t
ofthefrogembryoare
f th f
b
totipotent (candevelopintoallthepossiblecell
t
types)
)
Thread
• Inmammals,embryoniccellsremaintotipotentuntil
the8cellstage,muchlongerthanotherorganisms
2
– 16cell
16 cellstageÆ
stage Æ trophoblast orinnercellmass
or inner cell mass
determined
RESULTS
Normal
General Biology lectured by Han-Jia Lin
• Cellfatecommitmentisirreversiblefromwhen?
Belly piece
Normal
69
General Biology lectured by Han-Jia Lin
70
Not only did a transplanted dorsal lip of the
bl t
blastopore
continue
ti
to
t be
b a blastopore
bl t
lip,
li it also
l
triggered gastrulation of the surrounding tissue!
InductiveSignals
• Asembryoniccellsacquiredistinctfates,they
influencefatesofeachotherbyinduction
fl
f
f
h h b d
p
g
Æ organizerexperminent
g
p
• Ex1:SpemannandMangold
EXPERIMENT
Dorsall lip
D
li off
blastopore
– Thedorsallipfunctionsasanorganizeroftheembryobody
plan inducing changes in surrounding tissues to form
plan,inducingchangesinsurroundingtissuestoform
notochord,neuraltube,andsoon
Pigmented
gastrula
(donor embryo)
• Ex2:limbformationinvertebrate
Ex2: limb formation in vertebrate
RESULTS
Primary embryo
Secondary
(induced) embryo
Nonpigmented
gastrula
(recipient embryo)
Now, we know dorsal
lip region inhibit a
“
“determinant”,
BMP-4
Primary structures:
Neural tube
Notochord
Secondary structures:
Notochord (pigmented cells)
Neural tube
(
(mostly
tl nonpigmented
i
t d cells)
ll )
Figure 47.23
General Biology lectured by Han-Jia Lin
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General Biology lectured by Han-Jia Lin
72
FormationoftheVertebrateLimb
Pattern formation of chick wings
• Inductivesignalsplayamajorroleinpattern
f
formation,developmentofspatialorganization
i
d l
f
l
• Thewingsandlegsofchicks,likeallvertebratelimbs,
beginasbumpsoftissuecalledlimbbuds
• Theembryoniccellsinalimbbudrespondto
positionalinformationindicatinglocationalongthree
axes
• Themolecularcuesthatcontrolpatternformationare
p
calledpositionalinformation
• This
Thisinformationtellsacellwhereitiswithrespectto
information tells a cell where it is with respect to
thebodyaxes
– PDaxis
((shoulder– fingertip)
g p)
– APaxis
(Thumblittle
(Thumb
littlefinger)
finger)
– DVaxis
(Knucklepalm)
(Knuckle
palm)
• Itdetermineshowthecellanditsdescendents
respondtofuturemolecularsignals
• Thewingsandlegsofchicks,likeallvertebratelimbs,
begin as bumps of tissue called limb buds
beginasbumpsoftissuecalledlimbbuds
General Biology lectured by Han-Jia Lin
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2
Digits
A t i
Anterior
Ventral
Distal
Proximal
Dorsal
Figure 47.24b
Posterior
General Biology lectured by Han-Jia Lin
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Two organizers in chick’s limb buds
ZPAproducesaninductivesignal
• AER(apicalectodermal
ridge)
• TissuetransplantationexperimentsÆ ZPAproduces
positionalinformationindicating䇾posterior䇿
l f
d
䇾
䇿
Anterior
Limb bud
– thickened
thickenedectodermat
ectoderm at
thebud’stip
• ZPA
ZPA(zoneofpolarizing
(
f l ii
activity)
– mesodermal tissue
under the ectoderm
undertheectoderm
wheretheposterior
side of the bud is
sideofthebudis
attachedtothebody
General Biology lectured by Han-Jia Lin
AER
ZPA
Posterior
Limb buds
• ZPAsecretÆ Sonichedgehog(aninductivesignalfor
g
g(
g
limbdevelopment)
– Similar
SimilartoDrosophilaHedgehoggene(Hox):Thisgene
to Drosophila Hedgehog gene (Hox): This gene
familyalsoplayrolesofpatternformationinmanyanimals
50 Pm
RESULTS
EXPERIMENT
Apical
ectodermal
ridge (AER)
Anterior
ZPA
Figure 47.24a
3
4
75
Donor
limb
bud
Posterior
General Biology lectured by Han-Jia
Lin
New
ZPA
Host
limb
bud
4
3
22
4 3
76
Cilia (ᠼЛ) and Cell Fate
Kartagener’s syndrome
• Two types of cilia: motile or nonmotile
• Ciliary
Cili
f
function
ti iis essential
ti l ffor h
human embryo
b
• Described by Dr. Kartagener in 1923
• Motile cilia
• ~25%
25% was PCD ((primary
i
ciliary
ili
d ki
dyskinesia)
i )
– Propel fluid over cell surface or in sperm
• Nasal sinuses and
– Play
Pl roles
l iin lleft-right
ft i ht specification
ifi ti
bronchi infection
– Kartagener’s syndrome
H
Heart
t
• Male infertility
• Monocilia (nonmotile cilia)
Liver
p
Spleen
• Situs
Sit inversus
i
– A
Act as antenna to receive
i signal
i
l (f
(from sonic
i
hedgehog….)
Stomach
1/10,000 chance
• ~1/10,000
– play roles in normal kidney development
General Biology lectured by Han-Jia Lin
Lungs
77
General Biology lectured by Han-Jia Lin
Large intestine
Normal location
of internal organs
Location in
situs inversus
End of Part 3
End of the class
Ask yourself…
• The key concepts which you have learned in
• How embryologists establish fate map?
• Part 1
• What is cytoplasmic determinants? How they
work?
• Part 2
78
• What is organizers?
• How cilia determines cell fates?
General Biology lectured by Han-Jia Lin
• Part 3
79
General Biology lectured by Han-Jia Lin
80