Cleavage

Question 1

early stages in human development

Answer 1

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

Question 2

post-fertilization events of the zygote

Answer 2

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

Question 3

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

Answer 3

cell division
compaction

note zona pellucida is still intact here

Question 4

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

Answer 4

water
ball of cells = morula 16 cells

blastocoel - the result of cavitation

Question 5

blastocoel formation requires?

Answer 5

Na/K ATPase transporters

Question 6

when is the embryo referred to as a blastocyst?

Answer 6

58 cell stage

Question 7

features of the blastocyst

Answer 7

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

Question 8

what are the cell types in the blastocyst?

Answer 8

outer cells = trophoblasts

inner cells = inner cell mass

Question 9

trophoblasts

Answer 9

form extraembryonic structures such as the placenta

outer cell layer of blastocyst

Question 10

ICM

Answer 10

forms embryo proper plus some extraembryonic structures

inner cell mass of blastocyst

Question 11

what causes polarity of the blastocyst?

Answer 11

because of the eccentric placement of blastocoel and inner cell mass

Question 12

embryonic pole vs. abembryonic pole

Answer 12

pole of the blastocyst where ICM is located

pole marks opposite pole

Question 13

control of cleavage

Answer 13

maternal genes til 2 cell stage

embryonic genome control by 4 cell stage

Question 14

what is methylation?

Answer 14

addition of methyl groups to specific DNA regions

inactivates genes
including some enhancers/promoters

Question 15

methylation cycle

Answer 15

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

Question 16

remethylation occurs later is gametogenesis and may lead to ?

Answer 16

maternal/paternal imprinting

Question 17

what does polarization of blastomeres cause?

Answer 17

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

determines whether cells are destined for ICM or outer layer

Question 18

what are the 2 theories of polarization?

Answer 18

inside-out hypothesis

cell polarity model

Question 19

inside-out hypothesis

Answer 19

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

not from intrinsic properties

Question 20

cell polarity model

Answer 20

–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

Question 21

developmental potential =

Answer 21

potency

potency is greater than fate

Question 22

genes involved in differentiation?

Answer 22

cdx-2
oct-4
nanog
sox2

Question 23

Cdx-2

Answer 23

essential for trophoblast cell differentiation

antagonistic to oct-4

Question 24

Oct-4

Answer 24

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

Question 25

Nanog

Answer 25

1. produced by ICM
2. maintain integrity of ICM
3. w/o this inner cells become endoderm

Question 26

Sox2

Answer 26

first expressed in 8 cell stage

along w/ oct4, helps control regulation of genes involved in differentiation

Question 27

define genomic imprinting

Answer 27

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

Question 28

what causes genomic imprinting ? examples

Answer 28

due to DNA methylation differences in sperm and eggs

ex. prader-willi and angelman syndromes

Question 29

parental imprinting

Answer 29

1. occurs during gametogenesis
2. involves methylation
3. imprinted genes can be maintained for life

Question 30

relate imprinting and rounds of gametogenesis

Answer 30

imprinting is erased and reestablished w/ each round of gametogenesis

Question 31

Prader-Willi Syndrome

Answer 31

small hands and feet
short
poor sexual development
retardation
usually obese

mutation always inherited from father – deletion long arm chr15

Question 32

Angelman Syndrome

Answer 32

exhibit frequent laughter
uncontrolled muscle mvt
large mouth
unusual seizures

mutation always from mom
deletion long arm chr15

Question 33

X inactivation

Answer 33

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

Question 34

XIST gene

Answer 34

X inactivation specific gene

located on x chr

produces RNA molecule that coats X chr and induces inactivation

Question 35

RNA coat X chr

Answer 35

causes:

1. removal of acetyl groups from histones
2. methylation of histones
3. alteration of histone composition

Question 36

_____ region escapes X inactivation

Answer 36

pseudoautosomal

Question 37

Barr body

Answer 37

• -found by murray barr

- -mary lyon proposed barr body = inactive x chromosome

Question 38

define regulation

Answer 38

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

Question 39

list experimental methods

Answer 39

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

Question 40

need book for further definition reviews

Answer 40

clinical correlation 3.2