Embryogenesis Flashcards Preview

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Flashcards in Embryogenesis Deck (94):
1

What do oviduct epithelial cells do?

Bind sperm

Make them briefly immobile

Stabilise sperm after capacitation

2

When do sperm reacquire mobility?

Ovulation

3

How is oocyte moved to the ampulla?

Swept along by cilia and muscle contractions

4

Where does fertilisation take place?

The ampulla

5

What three events does fertilisation require?

1. Activation of sperm
2. Establishment of diploidy
3. Activation of ovum

6

What induces sperm activation?

1. Progesterone from cumulus cells
2. Binding to zona proteins on oocyte

7

What does sperm activation cause?

1. Hyperactive tail movement - whiplash
2. Acrosome reaction

8

What promotes hyperactive sperm tail movement?

Opening of calcium channels to activate PKC

9

What is the acrosome reaction?

1. Fusion of outer acrosome and sperm plasma membranes
2. Phospholipase C and SNARE proteins involved
3. Release of hyaluronidase and exposure of acrosin on inner acrosome membrane

10

What are the zona pellucida proteins?

Glycoproteins

ZP1-4

11

What do ZP1, ZP3 and ZP4 do?

1. Bind capacitated sperm
2. Induce acrosome reaction

12

What pathway does ZP3 activate?

Gi protein-coupled receptors on sperm

13

What does ZP2 do?

Weakly binds capacitated sperm to allow progression through zona

14

What allows sperm to burrow through zona pellucida?

1. Acrosin - protease
2. Physical movement

15

What space does sperm enter once it penetrates zona?

Perivitelline space

16

Where does membrane fusion occur in the mouse?

Equatorial region away from female pronucleus

Enveloped by microvilli

17

What does the microvillus-free area of the oocyte signify?

Position of female pronucleus

18

What are the three proteins essential for binding?

1. Izumo1 (sperm)
2. Juno
3. CD9

19

What is Izumo1?

Ligand on sperm essential for binding

20

What is Juno?

Izumo1 receptor on oocyte

21

What is CD9?

Tetraspanin on oocyte

Binding partner for Juno

22

What is syngamy?

Combining of chromosomes

23

How is the oocyte activated?

1. Wave of calcium release across oocyte from site of sperm fusion
2. Initiated by PLCζ enzyme from sperm
3. Helps to prevent polyspermy

24

What is the cortical reaction?

Release of cortical granules stimulated by calcium waves

Fill perivitelline space

Ovastatin cleaves binding sites on ZP3/4 and ZP2 so that sperm can no longer bind

Zona proteins become cross-linked

Juno receptor exocytosed

25

When does the secondary oocyte re-enter meiosis?

After the cortical reaction

26

How is the sperm pronucleus formed?

1. Nuclear envelope breaks down
2. Sperm protamines replaced with histones to decondense chromatin

27

How is the single diploid nucleus formed?

1. Pronuclear membranes break down
2. Chromosomes become orientated on common mitotic spindle

28

What does the oocyte contribute to the zygote?

1. Mitochondria
2. Golgi apparatus
3. Ribosomes
4. Membrane
5. Endoplasmic reticulum
6. Maternal cytoplasm
7. Centrosomes and mitotic spindles
8. DNA

29

What does the sperm contribute to the zygote?

1. DNA
2. Centriole
3. Small non-coding RNAs
4. Proteins targeted for destruction once they enter the oocyte

30

Why are sperm mitochondria degraded?

More susceptible to mutation through oxidative stress

mtDNA not protected by histones and no DNA repair mechanisms in sperm

31

Where are sperm naturally exposed to ROS?

1. Leukocytes in epididymis
2. Transit to female tract
3. Energetics of sperm movement

32

What is parthenogenesis?

Oocyte activation in absence of sperm fusion

Lacks male chromosomes and centriole

Gynogenetic diploid if polar body not expelled

33

At what point in human gestation do parthenogenetic embryos die?

During first cleavage as no centriole

34

What kind of development does a gynogenetic conceptus favour?

Embryo

35

What kind of development does an androgenetic conceptus favour?

Extraembryonic

36

What are imprinted genes?

Genes only expressed by one parental allele

Silenced by methylation on the other parental allele

37

What is a hydatidiform mole?

All chromosomes of paternal origin due to loss of female pronucleus and duplication of male pronucleus

Absence of fetal tissue and overgrowth of placental tissues

Placental villi are oedematous

38

Give three examples of epigenetic modifications

1. DNA methylation
2. Histone methylation
3. ncRNAs

39

What is the effect of DNA methylation?

Changes conformation of DNA to prevent access of transcription factors

40

Which pronucleus is more methylated at fertilisation?

Male

41

When does DNA demethylation take place?

After fertilisation

42

When does DNA remethylation take place?

Blastocyst stage

43

Which loci are resistant to demethylation?

Imprinted loci

44

What are imprinted genes important for?

1. Placenta development
2. Reproductive behaviour

45

What is the conflict theory?

Paternal genes drive growth of placenta whilst maternal genes constrain fetal growth to prevent nutrient depletion and facilitate delivery

46

What is the morula?

First cleavage divisions

~8-16 cells

Cells are totipotent

Cells can be removed for genetic diagnosis

47

What is maternal cytoplasmic inheritance?

First cell division under influence of maternal mRNA and proteins generated in oocyte during folliculogenesis

48

When is transcription of embryonic genome initiated?

4-8 cell stage

49

Until what point does maternal RNA persist?

Blastocyst stage

50

What is compaction?

1. Creating cell polarity
2. Initiating cell specialisation

51

Where is concanavalin A expressed?

Junctions between cells of morula

52

How is the blastocoel formed?

Establishment of ion gradients causes influx of water

53

What does the blastocyst consist of?

Trophectoderm and inner cell mass

54

What is the trophectoderm?

Trophoblast contributes to formation of placenta

55

What is the inner cell mass?

Forms embryo and contributes mesoderm to placenta

56

At what stage of development does the embryo implant?

Blastocyst stage

57

What are Cdx2 and Oct4

Transcription factors that determine cell fate

58

What is the role of Oct4?

Regulates pluripotency

59

What is the role of Cdx2?

Trophoblast lineage determinant

60

Where is Oct4 expressed?

8-cell stage: nuclei of all blastomeres
Blastocyst stage: inner cell mass

61

Where is Cdx2 expressed?

8-cell stage: nuclei of all blastomeres
Blastocyst stage: trophoblast

62

What regulates Cdx2 expression?

Degree of cell-cell contact

Activated by Yap and Tead4

63

What is hippo?

A kinase

Active in non-polarised cells

Phosphorylates Yap, preventing it from entering the nucleus - inhibits Cdx2 expression

64

After how many days does conceptus enter uterus?

3.5 days after fertilisation

65

What may be the effect of chlamydia infection?

Scarring and narrowing of Fallopian tube

66

What is the pO2 in the Fallopian tube?

Low

10-30mmHg

67

Where does the zygote get its nutrition from?

1. Secretions from cells of oviduct
2. Then endometrial glands

68

What is the source of energy for the fertilised ovum?

Pyruvate

69

What is the source of energy at the 2-cell stage?

Pyruvate and lactate

70

What is the source of energy at the 8-cell stage?

Glucose and essential amino acids

71

What is the source of energy at the blastocyst stage?

Simple sugars

72

How does the blastocyst hatch from the zona pellucida?

Proteases

73

Where does implantation occur?

Near fundus of uterus

74

What is placenta praevia?

Placenta covers cervical opening

Associated with increased risk of antepartum haemorrhage

75

How does the conceptus implant into the uterus?

Invasive interstitial implantation

Completely embedded in uterine wall

76

What does receptivity of the endometrium involve?

1. Downregulation of inhibitory mechanisms
2. Upregulation of factors promoting attachment

77

What is the window of implantation?

Period of progesterone dominance

Progesterone and oestrogen ready the uterus for implantation

Oestrogen prepares the conceptus for implantation

Burst of oestrogen synthesis required for implantation

78

Give five features of the endometrium in the pre-receptive window

1. Embryotoxic
2. High progesterone receptor expression
3. Thick mucin glycoprotein coat
4. Negative charge on surface membrane
5. Long microvilli

79

Give seven features of the endometrium in the receptive window

1. Safe for embryos to implant
2. Progesterone receptors decrease
3. Thinner mucin glycoprotein coat
4. Loss of negative charge on surface membrane
5. Pinopodes to absorb uterine fluid
6. LIF-dependent
7. Shorter/absent microvilli

80

What is the effect of reduced glycosylation of MUC1?

Allows protein-protein interactions between blastocyst and uterine lining, leading to implantation

81

Give three actions of LIF

1. Acts on trophoblast and uterine lining
2. Leads to upregulation of HB-EGF on uterine epithelium
3. Induces uterine α2 expression, and trophoblast integrins α6 and β5 expression

82

What does invasion of endometrium involve?

Matrix metalloproteases

83

At what point after fertilisation does implantation take place?

7 days

Fully embedded after 11 days

84

What are decidual cells formed from?

Spindly stromal cells

85

Give two features of decidual cells

1. Large and round
2. Secrete cytokines

86

What cytokines do decidual cells secrete?

1. IGF-binding proteins
2. Prolactin

87

What are the three regions of the decidua?

1. Basalis - beneath conceptus
2. Capsularis - over conceptus
3. Parietalis - around the rest of the conceptus

88

What is amplification?

Extensive decidualisation after implantation

89

What is menstruation?

Shedding of decidual cells because they cannot de-differentiate if fertilisation does not occur

90

What secretes human chorionic gonadotropin?

Trophoblast

91

What is the role of hCG?

1. Maintains corpus luteum so that it continues secreting progesterone to prevent menstruation

92

How long is the corpus luteum maintained?

10 weeks until placenta produces sufficient progesterone

93

What is the percentage of conceptuses that become live births?

~30%

94

What is vanishing twin phenomenon?

One twin miscarries and the other twin resorbs it