Cleavage Flashcards

1
Q

early stages in human development

A
fertilized egg = zygote
2 cell stage
4 cell stage
11 cell stage morula
blastocyst
late blastocyst
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2
Q

post-fertilization events of the zygote

A
  1. becomes metabolically active
  2. cleavage = mitosis
  3. travels down oviduct – takes days
  4. loses zona pellucida before implantation
  5. implantation
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3
Q

zygote does mitosis to become 8 cell embryo, ______ continues and ______ occurs

A

cell division
compaction

note zona pellucida is still intact here

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4
Q

4 days post fertilization, _____ is transported into ? and results in the formation of a ?

A

water
ball of cells = morula 16 cells

blastocoel - the result of cavitation

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5
Q

blastocoel formation requires?

A

Na/K ATPase transporters

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6
Q

when is the embryo referred to as a blastocyst?

A

58 cell stage

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7
Q

features of the blastocyst

A
  1. zona pellucida
  2. large central blastocoel
  3. consists of 2 cell types
  4. polarized
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8
Q

what are the cell types in the blastocyst?

A

outer cells = trophoblasts

inner cells = inner cell mass

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9
Q

trophoblasts

A

form extraembryonic structures such as the placenta

outer cell layer of blastocyst

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10
Q

ICM

A

forms embryo proper plus some extraembryonic structures

inner cell mass of blastocyst

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11
Q

what causes polarity of the blastocyst?

A

because of the eccentric placement of blastocoel and inner cell mass

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12
Q

embryonic pole vs. abembryonic pole

A

pole of the blastocyst where ICM is located

pole marks opposite pole

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13
Q

control of cleavage

A

maternal genes til 2 cell stage

embryonic genome control by 4 cell stage

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14
Q

what is methylation?

A

addition of methyl groups to specific DNA regions

inactivates genes
including some enhancers/promoters

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15
Q

methylation cycle

A
  1. mature eggs/sperm highly methylated
  2. demethylation of ma/pa genomes shortly after fertilization
  3. remethylation of ICM
  4. levels fall after primordial germ cells enter genital ridges
  5. remethylation late in gemetogenesis
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16
Q

remethylation occurs later is gametogenesis and may lead to ?

A

maternal/paternal imprinting

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17
Q

what does polarization of blastomeres cause?

A

at 8-16 cell stages creates recognizable apical and basal surfaces

determines whether cells are destined for ICM or outer layer

18
Q

what are the 2 theories of polarization?

A

inside-out hypothesis

cell polarity model

19
Q

inside-out hypothesis

A

fate of blastomere is determined by its position w/in the embryo

not from intrinsic properties

20
Q

cell polarity model

A

–depends on plane of cell division during cleavage

–cleavage plane parallel to outer surface of embryo = can become either

–cleavage plane perpendicular to outer surface of embryo = only trophoblast destiny

21
Q

developmental potential =

A

potency

potency is greater than fate

22
Q

genes involved in differentiation?

A

cdx-2
oct-4
nanog
sox2

23
Q

Cdx-2

A

essential for trophoblast cell differentiation

antagonistic to oct-4

24
Q

Oct-4

A
  1. expressed by oocytes and zygotes
  2. required for cleavage
  3. expressed in all morula cells
  4. role in maintenance of undifferentiated cells

w/o this inner cells become trophoblasts

25
Nanog
1. produced by ICM 2. maintain integrity of ICM 3. w/o this inner cells become endoderm
26
Sox2
first expressed in 8 cell stage along w/ oct4, helps control regulation of genes involved in differentiation
27
define genomic imprinting
is differential gene expression depending on whether a chromosome is inherited from ma or pa certain genes derived from egg differs from expression of same genes derived from sperm
28
what causes genomic imprinting ? examples
due to DNA methylation differences in sperm and eggs ex. prader-willi and angelman syndromes
29
parental imprinting
1. occurs during gametogenesis 2. involves methylation 3. imprinted genes can be maintained for life
30
relate imprinting and rounds of gametogenesis
imprinting is erased and reestablished w/ each round of gametogenesis
31
Prader-Willi Syndrome
``` small hands and feet short poor sexual development retardation usually obese ``` mutation always inherited from father -- deletion long arm chr15
32
Angelman Syndrome
exhibit frequent laughter uncontrolled muscle mvt large mouth unusual seizures mutation always from mom deletion long arm chr15
33
X inactivation
occurs in humans in first few weeks of development once inactivated it remains that way in all daughter cells then on brought about by xist gene
34
XIST gene
X inactivation specific gene located on x chr produces RNA molecule that coats X chr and induces inactivation
35
RNA coat X chr
causes: 1. removal of acetyl groups from histones 2. methylation of histones 3. alteration of histone composition
36
_____ region escapes X inactivation
pseudoautosomal
37
Barr body
- -found by murray barr | - -mary lyon proposed barr body = inactive x chromosome
38
define regulation
refers to ability of embryo to compensate for removal of structures or for addition of structures
39
list experimental methods
1. chimeras or mosaics 2. fate mapping 3. totipotency 4. production of tetra - hexparental embryos 5. production of interspecies chimeras 6. deletion/ablation exp. 7. addition exp. 8. transgenic embryos 9. knock-out experiments
40
need book for further definition reviews
clinical correlation 3.2