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EMBRYO Exam #1- Lo > 01-16: Cleavage > Flashcards

01-16: Cleavage Flashcards

1
Q

What are the 6 steps of cleavage in the Starfish?

A

Fertilized egg → First cleavage (2 cell stage) → Second cleavage (4 cell stage) → Third cleavage (8 cell stage = morula) → Early blastula → Late blastula

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2
Q

What are the 6 stages of cleavage in the Sea Urchin?

A

Fertilized egg → First cleavage (2 cell stage) → Second cleavage (4 cell stage) → Early morula → Late morula → Blastula

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3
Q

What does the unequal cleavage in the Sea Urchin result in?

A

Micromeres (small cells), Mesomeres (medium cells), Macromeres (large cells)

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4
Q

What happens to the zygote post-fertilization?

A 
1- Becomes metabolically active
2- Begins to undergo cleavage
3- Transported down the uterine tube to the uterus (several days)
4- Loses ZP
5- Implantation
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5
Q

What are the steps of cleavage in humans?

A

Fertilized egg → First cleavage (2 cell stage) → Second cleavage (4 cell stage) → Morula (11 cell stage) → Blastocyst (Inner cell mass & Trophoblast) → Later Blastocyst

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6
Q

How does the blastomere adhere to each other so that compaction can occur?

A

gap junctions, E-cadherins, other Ca+ dependent CAMs

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7
Q

Is the ZP still intact during blastomere compaction?

A

YES because its still in the oviduct

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8
Q

How is the morula formed?

A

(4 days after fertilization) Na+/K-ATPase transporters draw water into ball of cells → forms morula (16 cells) → cavitation → forms blastocoel

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9
Q

What is a blastocyst surrounded by?

A

ZP

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10
Q

How does a blastocoel divide?

A

Eccentrically placed/pushed towards one pole → causes blastocyst to be polarized

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11
Q

When does blastomere polarization occur?

A

at the 8-16 cell stage

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12
Q

What does blastomere polarization do?

A

o Creates recognizable apical and basal surfaces

o Determines whether cells destined to become ICM (embryo) or Trophoblastic (placenta)

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13
Q

What are the 2 theories of Blastomere Polarity Establishment?

A
  • Inside-out Hypothesis

- Cell polarity model

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14
Q

What determines the embryo polarity in the Inside-out hypothesis?

A

position of the blastomere within the embryo

NOT determined by intrinsic properties

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15
Q

What determines the embryo polarity in the cell polarity model?

A

plane of cell division during cleavage

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16
Q

What happens to the daughter cells if they divide PARALLEL to the cleavage plane?

A
  • Outer daughter cell&raquo_space; Trophoblast (POLAR)

- Inner daughter cell&raquo_space; ICM (APOLAR)

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17
Q

What do the outer membrane cells of the outer daughter cells contain?

A
  • microvilli

- ezrin (microfilament stabilizing protein)

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18
Q

What happens to the daughter cells if they divide PERPENDICULAR to the cleavage plane?

A

BOTH daughter cells&raquo_space; Trophoblast (POLAR)

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19
Q

What is the Trophoblast and what does it form?

A
  • Outer layer of Blastocyst

- Forms Extraembryonic structures (Placenta)

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20
Q

What is the Inner Cell Mass and what does it form?

A

-Inner mass of cells of Blastocyst

  • Forms Embryo Proper
  • Forms some Extraembryonic structures (yolk sac)
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21
Q

Where is the ICM located in the blastocyst?

A

at the embryonic pole of the blastocyst

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22
Q

Where is the Abembryonic pole located?

A

opposite to the embryonic pole/ICM

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23
Q

How is cleavage controlled in Invertebrate and Non-Mammalian Vertebrate Embryos?

A

Through gene products transcribed from maternal genome

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24
Q

When do the gene products transcribed from maternal genome appear?

A

after blastulation

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25
Q

How is cleavage controlled in Mammalian Embryos?

A

Through gene transcription mostly by the embryonic genome (4 cell stage)

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26
Q

Why is Mammalian Embryo cleavage controlled by embryonic genome instead of maternal genome?

A

maternal genome products are generally degraded by 2-cell stage

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27
Q

What is methylation?

A

addition of methyl groups to DNA molecules

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28
Q

What does methylation do?

A

Decreases DNA transcription which inactivates genes (such as enhancers and promoters)

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29
Q

When does Demethylation occur?

A

Shortly after fertilization&raquo_space; Early Morula

maternal/paternal genome

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30
Q

When does Remethylation occur?

A
  • Early Morula&raquo_space; Late Blastocyst state (ICM)

- Gemetogenesis

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31
Q

What does Remethylation after gametogenesis lead to?

A

maternal/paternal imprinting

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32
Q

After primordial germ cells enter the genital ridges, what happens to the Methylation levels?

A

Methylation levels fall&raquo_space; Causes the DNA to become more active

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33
Q

What has the max potency/potential?

A

zygote

34
Q

What happens to the potency as the zygote development proceeds?

A

potency becomes more linear (more differentiated)

35
Q

What are the 4 genes involved in differentiation?

A
  • Cdx-2
  • Oct-4
  • Nanog
  • Sox2
36
Q

What is Cdx2 essential for?

A

trophoblast cell differentiation

37
Q

What is Cdz2 antagonistic toward?

A

Oct-4

38
Q

Where is Oct-4 expressed?

A
  • in developing oocytes and zygote

- in all Morula cells

39
Q

What gene is required to permit cleavage to proceed to the 2-cell stage?

A

Oct-4

40
Q

Which gene may play a role in the maintenance of the undifferentiated state?

A

Oct-4

41
Q

What produces Nanog genes?

A

inner cells in the late Morula stage

42
Q

What does Nanog do?

A

maintains integrity of ICM along with Oct-4

43
Q

What happens to the inner cells without Nanog?

A

inner cells differentiate into ECTODERM

44
Q

What happens to the inner cells without Oct-4?

A

inner cells differentiate into TROPHOBLAST

45
Q

When is Sox2 gene first expressed?

A

in 8-cell stage

46
Q

What does Sox2 gene do?

A

Helps control regulation of genes involved in differentiation

47
Q

What gene does Sox2 work with?

A

Oct-4

48
Q

What is genomic imprinting?

A

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

49
Q

What are 2 examples of genomic imprinting?

A
  • Prader-Willi (chromosome 15)
  • Angelman syndromes

**Due to DNA methylation differences in sperm and eggs

50
Q

When does parental imprinting occur?

A

during gametogenesis

51
Q

What happens to the imprinted genes throughout the patient’s life?

A

they are maintained throughout development and perhaps adulthood

**permanent once they are an adult

52
Q

When is imprinting erased and reestablished?

A

with each round of gametogeneis

53
Q

What are the clinical manifestations of Prader-Willi?

A
  • small hands and feet
  • short stature
  • poor sexual development
  • mental retardation
  • voracious appetites
54
Q

Who is the mutation inherited from in Prader-Willi syndrome?

A

father

**Deletion in long arm of chromosome 15

55
Q

What are the clinical manifestations of Angelman syndrome?

A
  • exhibit frequent laughter
  • uncontrolled muscle movement
  • large mouth
  • unusual seizures
56
Q

Who is the mutation inherited from in Angelman syndrome?

A

mother

**Deletion in long arm of chromosome 15

57
Q

When is methylation erased in mammals?

A

in germ cells of each generation

58
Q

Why are there differential expression of male and female alleles in offspring?

A

because sperm and eggs undergo different levels of methylation

59
Q

When does X inactivation take place in humans?

A

during first few weeks of development

60
Q

What happens to the X chromosome after it is inactivated?

A

it remains inactivate in all descendants of the first cell

61
Q

What causes X inactivation?

A

the action of Xist (X Inactivation Specific Transcript)

62
Q

Where is Xist located?

A

on the X chromosome

63
Q

What does Xist produce?

A

an RNA molecule that:

  • Coats the X chromosome
  • Induces X inactivation
64
Q

What does coating the X chromosome with Xist RNA cause?

A
  • Removal of acetyl groups from histone proteins
  • Methylation of histones
  • Alteration of histone composition
65
Q

What region escapes X inactivation?

A

pseudoautosomal region

66
Q

What is the Lyon Hypothesis?

A

the Barr body = inactive X chromosome

67
Q

What is X-inactivation an example of?

A
  • Dosage compensation

- Provides equal expression of X chromosome products in both males and females

68
Q

Why is Lyon Hypothesis not seen in males?

A

because they only have 1 X-chromosome

** unless the male has 2 X-chromosomes

69
Q

How many Barr Bodies can occur in Turner’s syndrome?

A

0 = XO

70
Q

How many Barr Bodies can occur in Klinefleter’s syndrome?

A 
1 = XXY
1 = XXYY
2 = XXXY
3 = XXXXY
71
Q

How many Barr Bodies can occur in Triplo-X syndrome?

A

2 = XXX

72
Q

How many Barr Bodies can occur in Poly-X females?

A 
3 = XXXX
4 = XXXXX
73
Q

How is X-inactivation involved in Tortiseshell cats?

A

Random inactivation of X chromosomes early in embryonic development produces a patchy distribute for the expression of X-linked characteristics

**Single X-linked locus determines orange color

74
Q

What is the difference between imprinting and X-chromosome inactivation?

A

Imprinting = Autosomes

X-Chromosome inactivation = Sex Chromosomes

75
Q

What is the ability of an embryo to compensate for removal of structures or for addition of structures?

A

regulation

76
Q

What are some of the experimental methods of properties of early embros?

A
  • Chimeras/Mosaics
  • Fate mapping
  • Totipotency
  • Production of tetra/hexaparental embryos
  • Production of interspecies chimeras
  • Deletion or ablation experiments
  • Addition experiments
  • Transgenic embryos
  • KO experiments
77
Q

What is the procedure for producing tetraparental embryos?

A

Cleavage stages of 2 different strains of mice&raquo_space; Removal of ZP&raquo_space; Fusion of the 2 embryos&raquo_space; Implantation of embryos into a foster mother&raquo_space; Chimeric offspring obtained from the implanted embryos

78
Q

What are types of twins?

A
  • Fraternal (dizygotic)
  • identical (monozygotic)
  • Conjoined & Parasitic
79
Q

What are the modes of Monozygotic twinning?

A
  • Cleavage of an early embryo, with each half developing as a completely separate embryo
  • Splitting of the ICM of a blastocyst and the formation of 2 embryos enclosed in a common trophoblast
  • If ICM doesn’t completely separate, or if portions of the ICM secondarily rejoin, conjoined twins may result
80
Q

What are the 5 types of conjoined twins?

A
  • Cephalopagus (head to head)
  • Pygopagus (rump to rump)
  • Massive fusion of head and trunk
  • Cephalothoracopagus (head and thorax)
  • Thoracopagus (chest to chest)

EMBRYO Exam #1- Lo (12 decks)

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