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Embryology Exam I > Cleavage > Flashcards

Cleavage Flashcards

1
Q

How is cleavage in the sea urchin different from the starfish?

A
  • no blastula

- unequal cleavage that results in three sizes of cells

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2
Q

What happens to the zygote after fertilization?

A
  • zygote becomes metabolically active
  • zygote begins to undergo cleavage
  • zygote is transported down uterine tubes to uterus (several day journey)
  • zygote loses ZP prior to implantation
  • implantation
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3
Q

During cleavage is the ZP. Intact?

A

Yes

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4
Q

What are the cleavage events outlined in lecture?

A
  • zygote undergo mitosis to form an 8-cell embryo
  • cell division continues and compaction occurs
  • water is transported into the ball of cells (morula - 16 cells) -> after this the embryo is known as the blastocyst
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5
Q

What happens in compaction?

A
  • outer blastomeres adhere via gap junctions and appear to lose their individual identity
  • involves E-cadherins and other calcium dependent CAMs
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6
Q

When does water transportation into the morula occur? What happens with this event? What does this process require?

A
  • occurs 4 days after fertilization
  • results in the formation of a blastocoel as a result of cavitation
  • requires Na and K-ATPase transporters
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7
Q

What are some features of the blastocyst?

A
  • surrounded by ZP
  • large, eccentrically placed blastocoel
  • two types of cells (outer: trophoblast, inner: ICM)
  • blastocyst is polarized
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8
Q

Why is the blastocyst polarized?

A
  • eccentric placement of blastocoel and ICM
  • embryonic pole marks the pole of the blastocyst where the ICM is located
  • a embryonic pole marks the opposite pole
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9
Q

What are the cleavage stages of a human?

A
  • fertilized egg
  • 2-cell stage
  • 4-cell stage
  • 11-cell stage morula
  • blastocyst (trophoblast and ICM)
  • later blastocyst
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10
Q

Outline the genetic control of cleavage in invertebrates and non-mammalian vertebrates.

A

-early control of cleavage is through gene products transcribed from the maternal genome and embryonic gene products often do not appear until after blastululation

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11
Q

Outline genetic control of cleavage in mammalian embryos.

A
  • maternal gene products are produced but generally are degraded by the 2-cell stage of development
  • by the 4-cell stage, most transcription is via the embryonic genome
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12
Q

What does methylation do?

A

Inactivates genes

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13
Q

DNA of mature eggs ANS sperm are highly methylated, where does demethylation occur?

A

-demethylation of maternal and paternal genomes occurs shortly after fertilization until the early morula

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14
Q

When does remethylation occur?

A
  • remethylation of ICM occurs until late blastocyst stage
  • methylation levels fall after primordial germ cells enter genital ridges
  • remethylation occurs later during Gametogenesis and may lead to maternal/paternal imprinting
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15
Q

What is polarization?

A

-determination of whether cells are destined to become part of the ICM or the trophoblast

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16
Q

When does polarization occur?

A

-occurs at 8-16 cells stages creating recognizable apical and basal surfaces

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17
Q

What are the two theories of polarity?

A
  • inside out hypothesis

- cell polarity model

18
Q

What is the inside out hypothesis?

A

-fate of the blastomeres is determined by its position within the embryo, not from intrinsic properties

19
Q

What is the cell polarity model?

A

-depends on plane of cell division during cleavage
+cleavage plane parallel to the outer surface of the embryo
+outer daughter cell -> trophoblast cells (polar)
1) cells pick up a patch of outer cell membrane containing microvilli and ezrin
+inner daughter cell -> ICM cell (a polar)

+cleavage plane perpendicular to outer surface of embryo
1) both daughter cells become trophoblast cells

20
Q

What are the genes involved in differentiation?

A
  • Cdx-2
  • Oct-4
  • Nanog
  • Sox2
21
Q

What does Cdx-2 do?

A
  • essential for trophoblast cell differentiation

- antagonistic toward Oct-4

22
Q

What does Oct-4 do?

A
  • expressed in developing oocytes and zygote
  • required to permit cleavage to proceed to 2-cell stage
  • expressed in all morula cells
  • may play a role in the maintenance of the undifferentiated state
  • without Oct-4 inner cells differentiate into trophoblast
23
Q

What does Nanog do?

A
  • produced by inner cells in later morula stage
  • maintains integrity of ICM along with Oct-4
  • without Nanog inner cells differentiate into endoderm
24
Q

What does Sox2 do?

A
  • first expressed in 8-cell stage

- along with Oct-4 it helps to control regulation of genes involved in differentiation

25
Q

Outline the the cleavage events in starfish.

A
  • fertilized egg
  • first cleavage -> 2-cell stage
  • second cleavage -> 4-cell stage
  • third cleavage -> 8-cell morula
  • early blastula
  • late blastula
26
Q

What is genomic imprinting?

A

-differential gene expression depending on whether a chromosome is inherited from the male or the female parent

Ex. Prader-Willi and Angelman syndrome

27
Q

When does imprinting occur?

A
  • during gametogenesis
  • involves methylation of DNA
  • maintained throughout development and adulthood
28
Q

Imprinting is ___________ and _______________ with each round of gametogenesis.

A
  • erased

- reestablished

29
Q

Differentiate between Prader-Willi and Angelman syndrome.

A

Prader-Willi:

  • small hands and feet
  • short stature
  • poor sexual development
  • mental retardation
  • voracious appetites (typically obese)
  • mutation always inherited from father (deletion in long arm of chromosome 15)

Angelman syndrome:

  • exhibit frequent laughter
  • uncontrolled muscle movement
  • large mouth
  • unusual seizures
  • mutation is always inherited from the mother (deletion of long arm of chromosome 15)
30
Q

What is an example of imprinting in mice? What do each of the alleles do?

A

IgF2 gene

  • paternal -> active and stimulates fetal growth (placenta)
  • maternal -> silent and does not further stimulate fetal growth (
31
Q

Where is IgF2 found in mice vs humans?

A
  • humans: short arm of chromosome 11

- mice: chromosome 7

32
Q

What is X activation and when does this occur?

A
  • takes place in first few weeks of development

- once X is inactivated it remains inactive in all descendants of the first cell

33
Q

What inactivated the X chromosome?

A
  • Xist (X inactivation specific transcript)

- located on X chromosome -> produces RNA molecule that coats the X and induces inactivation

34
Q

What does coating the X chromosome with Xist cause?

A
  • removal of acetyl groups from his tone proteins
  • methylation of histones
  • alteration of histone composition
  • pseudo autosomal region escapes inactivation
35
Q

What is the structure thought to inactivate the X chromosome?

A
  • Barr body

- Lyon hypothesis

36
Q

What is dosage compensation?

A

-provides equal expression of X chromosome products in both males and females (one X in females must be inactivated)

37
Q

What is a pronounced example of X inactivation?

A
  • tortoiseshell cats!

- single X-linked locus determines orange color

38
Q

What is an example of X inactivation in humans?

A

-sweat gland inactivation

39
Q

What is regulation?

A

-refers to the ability of embryo to compensate for removal or addition of structures

40
Q

What are the experimental methods for developing properties of early embryos? Or regulation?

A
  • chimeras or mosaics
  • fate mapping
  • totipotency
  • production of tetra or hexaparental embryos
  • production of interspecies chimera
  • deletion or ablation experiments
  • addition experiments
  • transgenic embryos
  • knock-out experiments
41
Q

What. is Bateson’s rule?

A

-when duplicated structures are joined during critical development stages, one structure is the mirror image of the other

Embryology Exam I (10 decks)

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