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7/30/2019 03 Cleavage and Implantation Complete
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Cleavage
Cell DivisionCell Cycle Control
MorulaCompaction Blastocyst
Hatching
ImplantationDecidual
Early Cell LineagesInner Cell Mass
Reaction
Trophoblasts (Extra-embryonic)
Anomalies
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Cleavage
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Cleavage
Blastomere
Equal
Asynchronous
40
72
96
hours
hours
hours
4 cells
6-12 cells
16-32 cells
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CleavageMolecular Events
In mammalsno large maternal stores of RNA
and ribosomes
Zygotic transcription begins by 2-4 cell stage Oct-
3Transcription factor expressed in egg KO in
mousearrest at 1 cell stage
Expressed in blastomeres up to morula stageExpressed in germ cells
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Cell Cycle Control
MFP = Maturation-promoting factor, or mitosis-promoting factor
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Cell Cycle Control
MPFMitosis Promoting Factor
Heterodimer (cdc2 and cyclin B) SomeActivities: Nuclear envelope
assembly of mitotic spindle
Cdc2Cell Division Cycle 2
breakdown,
Phosphoprotein (P in S and
Constitutively expressed
Cyclin Bpresent in G2 and MBound to cdc2Phosphoprotein (P in M)
Degraded in G1
G2)
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Morula
32 cell stage
Berry - appearance
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Compaction
Compactionblastomeres: loosely adherent tightly adherent
cytoskeleton reorganization, tight junctions Inner Cell Mass vs.
Outer Cell Mass
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Blastocyst
Embryo pole
Inner cell mass(embryoblast)
Blastocoel
Outer cell mass
(trophoblast)
abembryonic pole
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Hatching
(from zona pellucida)
Hatching: Enzymatic production by Trophoblasts
the Zona Pellucida
- digestion of
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Zona Pellucida - Functions
Species-specific sperm penetration
Permanent block to polyspermy
Acts as a porous selective filter - uterine
signals
Immunological barrier -
tube
no HLA (histocompatibility antigens)Keeps blastomeres together (loosely adherent)
Prevents premature implantation
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Implantation
Decidual reactionProgesterone induced endometrial cell
conversion to secretory decidual cell
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Implantation
Days 612
Adhesion, blastocyst
endometrium
Trophoblast
proliferation
Syncytiotrophoblast
to
Secretion of hydrolyticenzymes
Breakdown of
endometrium
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Day 6
Blastocyst adheres to
endometrium at embryopole
Trophoblast proliferation
production of hCG(maintains corpus luteum)
Embryo
invasion
hydrolytic
enzymesSyncytiotrophoblast
Trophoblasts
Cytotrophoblast
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Day 7-8
Syncytiotrophoblastexpansion
Lacunae formfilled
with fluid (embryotroph)
Embryotroph provides
nutrients to the embryo.
Derived from
maternal blood.
Embryo - Bilaminar germ disc:Epiblast layercavitates to form the amnionic cavity.
Hypoblast layer form the exocoelomic cavity / primary yolk sac
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Day 9-10
Lacunae enlarge
Syncytiotrophoblast
expands around entire
blastocyst
Cytotrophoblasts form
primary villusinitiation
of placenta formation
Implantation Complete
Coagulation Plug forms
Embryo: hypoblast exocoelomic membrane = Hausers membrane
Extraembryonic mesoderm from yolk sac
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D 11 12
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Day 11-12
Syncytiotrophoblast
erode maternal
capillariesformsinusoids
Syncytial lacunae
become continuouswith sinusoids
Maternal blood to enter
lacunae establishing
the uteroplacental
circulation
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Day 11-12Embryo
Yolk sac
extraembryonicmesoderm
Extraembryonic Somatopleuric
mesoderm - layer between amnion
and cytotrophoblst
Extraembryonic Splanchnopleuric
mesoderm - layer between
Primary yolk sac and
cytotrophoblast
Extraembryonic mesoderm becomes confluent and forms
another cavityextraembryonic coelom or chorionic cavity
I l t ti
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Implantation
Uterine Gland
Lacunae
Primary Yolk Sac
Endometrium
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Cytotrophoblast
Amniotic Cavity
Ectoderm
Endoderm
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Summary
Day
Day
Day
Day
0
1
1-3
3-4
Fertilization in Ampulla of uterine tube
Zygotic transcription begins Cleavage
morulacompaction Transport to uterine
cavity
Relaxation of the uterotubal junction
Maturation of blastocyst, hatching
Attachment / penetration of uterine stromaInvasion of uterine stroma
Lacuna formation, erosion of spiral arteries
Day
DayDay
Day
5
6-7
7-9
9-11
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Early Cell
Lineages
Extraembryonic
Somatopleuric
Mesoderm
Extraembryonic
Splanchnopluric
Mesoderm
From BM Carlson, 1999
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Extraembryonic Tissues
7 days
6 days
8 days
From BM Carlson, 1999
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Extraembryonic Tissues
8 days
14 days
9 days
From BM Carlson, 1999
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Amnion
Amnionic Cavity
Cavitation
From BM Carlson, 1999
F
r
oEmxtraembryonic
Somatopleuric
BM Mesoderm
CEaxtraembryonic Splanchnopluric
Mesoderm
r
l
so
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Extraembryonic Tissues
8 days
14 days
9 days
From BM Carlson, 1999
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Implantation Sites
Typical - Mid-Uterus
Distribution of atypicalimplantation sites
From BM Carlson, 1999
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Dizygotic Twins
Dichorial
Monochorial
From TW Sadler, 2000
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Monozygotic
Twins
Dichorial/
Diamniotic
Monochorial/
Diamniotic
Monochorial/
(33%)
(66%)
Monoamniotic (rare)
From TW Sadler, 2000
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Amnionic cavities
4-5 weeks
Amnion
Fetus
8 weeks
Monoamniotic
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Twins, Discordant Growth
Abdominal circumference,
Vanishing twins (triplets)
20% of twin pregnanciesChromosomal or Structural
abnormalities
3rd
Trimester
>25% - associated with
increased morbidity
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PapyraceusDeath of a monochorionic co-twin
Circulatory interactions can cause problems
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bi
015.
8
C j i d
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ConjoinedTwins
Cephalopagus
Pygopagus
Cephalothoracopagus
Thoracopagus
From BM Carlson, 1999
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Stomach
Spine
SpineShared Liver
Stomach
Ultrasound of conjoined twins
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Pygopagus
Posterior union of the rump
19% of all conjoined twins.
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Parapagus
Lateral union of the lower half
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Cephalopagus
Anterior union of the upper half of the body with two
faces on opposite sides of a conjoined head.
The heart is sometimes involved.
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Cephalothoracopagus
Union of head and chest
There is only one brain
Hearts and gastrointestinal tracts
are fused.
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Craniopagus
Cranial fusion only
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Parasitic Conjoined Twins
One twin without brain or heart
From BM Carlson, 1999
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Thoracopagus
Anterior union of the upper half of the trunk.
The most common form of conjoined twins (about
Always sharing the heart.
75%)
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Hydatidiform Mole
Pregnancy without an embryo (complete or partial mole)
Complete Mole = Only a placenta / No fetusDiploid
with 2 sets of paternal chromosomes, no maternal
contribution
Partial Mole = Triploid (Maternal, 1N; Paternal, 2N)
Diagnosishigh hCG levels; ploidy analysis (flow
cytometry)
1:1200 pregnancies in US; 1:200 pregnancies in Latin
America/Asia
but
H d tidif M l
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Hydatidiform MoleSnow Storm appearance Cystic
Areas (white arrows)
No fetus
Placenta (open black arrows)
Partial Molecystic areas
present
Fetus is present commonly
triploid
twin with mole in one sac
(rare)
From BM Carlson, 1999
i i
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Imprinting
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Parental Imprinting
Identical genes derived from maternal andpaternal DNA display differential expression
Selected genes are turned off duringgametogenesis by methylation of certain bases
Imprinted patterns are not passed on to progeny,imprints erased during gametogenesis
Beckwith-Wiedemann syndrome -Igf2
Long arm Chr 15 deletion
Angelmans syndrome - Maternal deletion
Prader-Willi syndrome - Paternal deletion
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Beckwith-Wiedemann Syndrome
Chromosome 11
- Igf2 (Insulin-like Growth Factor)growth promoter
- H19a growth suppressor
Mental deficiencymild to moderate
Macrosomiaexcessive growth, muscle, subcutaneous
tissues Macroglossiaprotruding tongue, overgrowth of
other
craniofacial structures
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Angelmans Syndrome
Happy Puppet Syndrome
Maternal long arm of Chromosome 15deletion
Severe mental deficiencymarked delays in motormilestones, absent
frequent seizures
Puppet like gait
Widely spaced teeth
Macroglossia
speech, frequent laughter,
Decreased occular pigment pale blue eyes
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Prader-Willi Syndrome
Paternal long arm of Chromosome 15
deletion
Mental deficiencymild-moderateNormal birth sizedecreased growth
Short stature / Obesity
Very small hands, feet, genitalia
Fair skin, blue eyes, sun-sensitivity
rate
Craniofacialalmond-shaped, narrow bifrontal
diameter
X-Chromosome
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X-ChromosomeInactivation
Inequality of Genetic Expression
Female-specific, 1 X-chromosome is inactive
Barr bodyextreme condensationBoth Xs are active thru cleavage
Blastocyst - Trophoblastpaternal X inactivated
Inner Cell Massboth are active
Egg cylinder stagedifferential X inactivation incell lineages
Oogenesisboth Xs become active
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X-Inactivation
l i l
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Regulative Development
Ability of an embryo or organ to developnormally after removal or addition of parts
Fate of cells is not irreversibly
by environment
Contrast Mosaic Development
Fate Mapping studies
fixedinfluenced
Developmental PotencyTotipotency
Stem Cells
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Tetra-Parental Mice
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Position-Specific
Differentiation
Inside-Outside
Hypothesis
Potency > Fate Map
8-16 Cell Stage -
Totipotent
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One blastomere
killed with
needle
Transfer into
a different-colored mother
Transfer to
foster mother
Normal
offspring
Mosaic
offspring
Transgenic Mice
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Transgenic Mice
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J . Obtain stem
cells from
embryo
4. Transfer
blastocyst
into host mouse2. Gene transferinto embryonic
cells in vitro
stem3. Inject embryonic
stem cell into
blastocyst
7. If progeny aregenetically altered,
the changes have been
incorporated into germ line
5. Chim
mouse
6. Chimeric
mouse breeds
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CloningDolly