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BB20149 > Imprinting > Flashcards

Imprinting Flashcards

1
Q

What are the structures involved with imprinting?

A

DNA methylation, 5-hydroxy-methylcytosine, histone modifications, remodelling complexes, histone variants, architectural proteins (CTCF/Cohesin) and non coding RNA (long non coding RNA).

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2
Q

What are the “players” in imprinting?

A

Epigenetic initiators, maintainers, readers and erasers.

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3
Q

What are the writers/initiators/establishers?

A

De novo methylation, DNmt 3a, 3b, histone methyltransferases, long-non coding RNAs, phosphorylases.

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4
Q

What are the maintainers?

A

Memory during differentiation/cell division - Dnmt1.

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5
Q

What are the readers?

A

DNA methylation binding proteins, transcription factors (bromodomains, chromodomains, PHD fingers, WD40 repeat).

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6
Q

What are the erasers?

A

Deacetylases, demethylases, phosphatases.

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7
Q

What is the function of the epigenome?

A

It maintains DNA integrity during the cell cycle, regulates gene expression, responds to nuclear, cytoplasmic and external environment. It remembers and reprograms.

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8
Q

What are some DNMT inhibitors?

A

Azacitidine, Decitavine, Zebularine.

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9
Q

What are some HDAC inhibitors?

A

Sodium phentylbutyrate, valproic acid, vorinostat, romidepsin, entinostat, panobinostat, belinostat.

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10
Q

Why did John Gurdon win a Nobel prize?

A

He eliminated the nucleus of a frog egg cell and replaced it with the nucleus from a specialised cell from a tadpole - the egg developed into a normal tadpole.

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11
Q

What did McGrath and Solter discover?

A

Completion of mouse embryogenesis requires both the maternal and paternal genomes.

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12
Q

What did Surani, Barton and Norris discover?

A

Development of reconstituted mouse eggs suggests that imprinting of the genome occurs during gametogenesis.

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13
Q

What does parthenogenic mean?

A

When some species eggs can develop into an embryo without need of fertilisation by sperm (female don’t need a male).

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14
Q

What experiments did John Gurdon also do?

A

He replaced a male pronucleus with a female one and the other way around to create embryos with 2 female or 2 male nuclei.

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15
Q

What does the primitive endoderm differentiate into?

A

Parietal endoderm and visceral endoderm.

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16
Q

What does the parietal endoderm form?

A

Part of the parietal yolk sac.

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17
Q

What can the visceral endoderm be divided into at day 6.5?

A

Extraembryonic visceral endoderm (covers the extraembryonic endoderm) and the embryonic visceral endoderm (covers the epiblast).

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18
Q

What do cells from the embryonic visceral endoderm contribute to?

A

The embryonic gut.

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19
Q

What do cells from the extraembryonic visceral endoderm contribute to?

A

The visceral yolk sac.

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20
Q

What is derived from the epiblast?

A

The embryo proper.

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21
Q

What are Prader-Willi/Angelman syndrome caused by?

A

A deletion of a chromosome.

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22
Q

Is it the maternal of paternal chromosome that is deleted in Prader-Willi?

A

Paternal or UPD of chromosome 15q11-q13.

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23
Q

Is it the maternal or paternal chromosome that is deleted in the Angelman syndrome?

A

Maternal copy/mutation of UBE3A gene or UPD of chromosome 15q11-q13.

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24
Q

What are the symptoms of Prader-Willi?

A

Language, motor and developmental delays, excessive weight gain.

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25
Q

What are the symptoms of Angelman?

A

Severe mental redardation, happy demeanor, non-verbal.

26
Q

What are genes called when they DO remember their parental origin?

A

Imprinted genes. This is an example of an epigenetic process.

27
Q

What does genomic imprinting result in?

A

Mono-allelic parent-of-origin-specific gene expression.

28
Q

What is genomic imprinting?

A

It is an epigenetic phenomenon where a subset of genes are epigenetically silenced on one parental allele during germline development. The silenced is maintained throughout development and then reset in the germline of the next generation, making this a trans-generational epigenetic phenomenon.

29
Q

Why does imprinting occur?

A

Genetic conflict (competition of genomes for maternal resources), dosage compensation, placental development and prevention of parthenogenesis.

30
Q

What is the Haig parental conflict hypothesis?

A

The idea that most mothers know their offspring is their own, whereas males need to compete with other males to get their genes to the next generation.

31
Q

What is the maternal role in the Haig theory ?

A

Growth suppressing, preservation of maternal resources - tumour suppressors.

32
Q

What is the paternal role in the Haig theory ?

A

Growth promoting, completition of his offspring for maternal resources - onocgenes.

33
Q

How can the conflict hypothesis be tested?

A

Do monogamous species maintain imprinting, and what happens to the progeny when you cross a monogamous with a polyandrous species?

34
Q

Do monogamous species maintain imprinting?

A

Yes.

35
Q

What happens to the progeny if you cross a monogamous with a polyandrous species?

A

There are imprinting defects.

36
Q

What is the coadaptation theory?

A

The idea that imprinted genes act co-adaptively to optimize fetal development as well as maternal provisioning and nurturing. There are a subset of mainly paternally expressed genes that are expressed in both the placenta and the hypothalamus region of the brain.

37
Q

What is the imprint composed of?

A

DNA methylation is one of the primary hallmarks.

38
Q

What are differentially methylated regions? (DMRs)

A

Regions across a genome that have different methylation in different samples.

39
Q

Where are DNA methylation imprints erased and re-established?

A

In primordial germ cells.

40
Q

When does epigenetic reprogramming occur?

A

At two major phases - in the primordial germ cells and then in the imprinted genes resistant after fertilisation.

41
Q

What happens in the first phase of epigenetic repgramming?

A

There is global demethylation and then remethylation and then after fertilisation.

42
Q

What is the lncRNA model?

A

Antisense promoter methylation stops the lncRNA from silencing adjacent genes.

43
Q

What is the boundary model?

A

The idea that there is insulator methylation ??

44
Q

What is an ICR?

A

Imprinting control region - if a DMR acts as a regulatory region for two or more genes within an imprinting cluster it can be called an imprinting control region.

45
Q

How do imprinted genes usually occur?

A

In clusters - 80% of known imprinted genes are in clusters.

46
Q

What are the ways in which an imprinted congenital syndrome (e.g. PWS) can arise?

A

Deletion, UPD or methylation defect.

47
Q

What is hypotonia in PWS?

A

Weak muscle tone and floppiness at birth.

48
Q

What is hypogonadism?

A

Immature development of sexual organisms and other sexual characteristics.

49
Q

What is obesity?

A

Excessive appetite and overeating (hyperphagia) and a decreased calorific requirement owing to low energy expenditure levels.

50
Q

What are the features of central nervous system and endocrine gland dysfunction in those with PWS?

A

Varying learning diability, short stature, hyperphagia, somnolence, poor emotional and social development.

51
Q

What are the characteristic facial and other features of PWS?

A

Almond-shaped eyes, a narrow forehead, a down-turned mouth with a triangular shaped upper lip and small hands and feet.

52
Q

What are some of the features of Angelman syndrome?

A

Developmental delay, speech impairment, mininal use of words, balance disorder.

53
Q

What are the behavioural traits of Angelman syndrome?

A

Frequent laughter/smiling, apparent happy demeanor, easily excitable personality, hand flapping movements.

54
Q

What are some of the more physical symptoms of Angelman?

A

Disproportionate growth in head circumference, seizures, abnormal EEG, characteristic pattern with large amplitude slow-spike waves.

55
Q

What are the features of Beckwith Wiedemann syndrome?

A

Macroglossia, umbilical hernia/exomphalos, overgrowth. High risk for tumours. hemihypertrophy, visceromegaly, hypoglycaemia, characteristic facial appearance.

56
Q

What is hemihypertrophy?

A

One side of the body is larger than the other.

57
Q

What is visceromegaly?

A

Enlargement of the organs inside the abdomen.

58
Q

What are some of the physical features of Silver Russel syndrome?

A

Triangular face, down turned corners of the mouth, incurved fifth digit, short birth length/low birth weight, long, narrow head.

59
Q

What are some of the other features of Silver Russel syndrome?

A

Body asymmetry, growth hormone deficiency, hypoglycemia, late closer of the fontanel, small chin, small crowded teeth, delays in bone age and muscle tone.

60
Q

What functions do imprinted genes have?

A

Fetal growth regulation, regulate metabolism and regulate behaviour.

BB20149 (16 decks)

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