Cleavage Flashcards
A 4-Cell stage has ____ cells while a Morula Stage has ______ cells.
- Totipotent
2. Pluripotent
Dev Embryo Regulation
Ability of Embryo to Compensate for Removal of structures for Addition of Structures
Features of a Blastocyst
- Surrounded by ZP
- Large Blastocoel
- Trophoblast w/ Inner cell mass
- Polarized
Without Oct-4, ICM would differentiate to what?
TROPHOBLAST
For an embryo to be Normal, it must posses both of what?
- Pronucleus from SPERM
- Pronucleus from EGG
The Genes involved in differentiation
- Cdx-2
- Oct-4
- Nanog
- Sox2
Establishment of Poalrity
- Polarization creates a recognizable APICAL & BASAL Surfaces
- Polarization of Blastomeres determines whether cells are destined to become part of the ICM or Trophoblast
What stage is the Zygote considered an Embryo
Blastocyst at the 58-cell stage
What happens when the ICM does not properly separate?
- Conjoined twins
Mutation of Prader-Willi is ALWAYS inherited from Whom? How?
From Father
- Deletion of LONG arm on Chrom 15
Sox2
- Helps to control Regulation of genes involved in differentiation
- Works along with Oct-4
Cleavage of a Fertilized egg (Zygote)
- Zygote
- 2-cell
- 4-cell
- Morula
- Blastula
- Gastrula
T/F: Potency is Greater than Fate.
True
OCT-4
- Expressed in dev Oocytes and Zygotes
- Req for 2-cell cleavage
T/F: The Zygote loses the ZP prior to Implantation.
True
When is Sox2 first expressed?
8-cell stage
X-inactivation takes place when?
During first few weeks of Dev
X-inactivation is brought about by what transcript?
Xist
When does the maternal gene products stop production in the developing zygote?
Immediately After the 2-Cell stage of development
What stage does Polarization take place?
8-16 cell stage
Cell Polarity Model
Depends on PLANE of Cell division during cleavage
PARALLEL
Or
PERPENDICULAR
Cdx-2
- Essential for Troph cell DIFFERENTIATION
Oct-4 is expressed in what type of cells?
All MORULA cells
Without Nanog, ICM would differentiate to what?
ENDODERM
Prader-Willi Characteristics
- Small Hands and Feet
- Short Stature
- Poor sexual dev
- Mental retardation
What happens when the ICM splits in ONE Blastocyst?
- Identical Twins
- Formed in one Trophoblast
- One sac
What is the Stage where the cells do NOT Divide evenly?
Morula Stage
Methylation Cycle
- Egg and Sperm Highly methylated
- Demethylation of parental genomes occur shortly after Fertilization
- Then Remethylation in Late Blastocyst
- Methylation fall after genital ridges
- Remethylation occurs during late gametogenesis
Coating the X-Chrom with Xist causes what?
- Methylation of Histones
- Alteration of Histone composition
- removal of acetyl groups from histones
Hatching
Blastocyst protruding out of the ZP
Purpose of X-inactivation
To Provide EQUAL expression of X-Chrom in Both Males and Female
Post fertilization Events
The Zygote
- Becomes metabolically active
- Undergoes cleavage
- Transported down Uterine tube to uterus (Several Days)
- Implantation
Parental Imprinting Characteristics
- Involves the methylation of DNA
- Maintained throughout development
- ERASED and REESTABLISHED w/ each round of Gametogenesis
In terms of Polarity, in Parallel cleavage the Troph will be ____ and the ICM will be ____.
- Polar
2. Apolar
Inner Cell Mass
- Inner collection of Cells
- Forms Embryo and its structures
Parental Imprinting occurs when?
During Gametogenesis
Cleavage plane PERPENDICULAR to outer embryo surface
BOTH Daughter cells become Trophoblast cells
Trophoblast
- Outer Layer of cells
- Forms EXTRA-embryonic structures (Placenta)
Inside-Out Hypothesis
- Fate of Blastomere is determined by its POSITION w/in the Embryo
- NOT by Intrinsic properties
Two theories of Polarity
- Inside-Out Hypothesis
2. Cell Polarity Model
Genetics control of cleavage in Invertebrates/Non-mammals Vs. Mammals
Inv:
- Controlled through gene products from the MOTHER
Mam:
- Controlled via the EMBRYONIC genome
What happens when an embryo has early cleavage?
- Identical twins
- 2 placentas
Purpose of Methylation
When added to specific regions of DNA molecules it Inactivates
- Genes
- Enhancers
- Promoters
Angelman Syndrome Characteristics
- Exhibit freq LAUGHTER
- Uncontrolled Muscle Movement
- Seizures
Nanog
- Produces by ICM
- Maintains integrity
Cleavage plane PARALLEL to outer embryo surface
- Outer cells -> Troph
- Inner cells -> ICM
X-inactivation Characteristics
Once inactivated, remains inactivated
- In ALL descendants of the first cell
Mutation of Angelman Syndrome is ALWAYS inherited from Whom? How?
From the Mother
- Deletion in Long arm of Chrom 15
