03 cleavage and implantation complete

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



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8 days

14 days

9 days



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Amnion

Amnionic Cavity

Cavitation


F

r

oEmxtraembryonic

Somatopleuric

BM Mesoderm

CEaxtraembryonic Splanchnopluric

Mesoderm

r

l

so


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8 days

14 days

9 days



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Implantation Sites

Typical - Mid-Uterus

Distribution of atypicalimplantation sites



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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



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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



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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)


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

03 cleavage and implantation complete

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