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MD2002 > Epigenetics and Abnormal Gene Expression > Flashcards

Epigenetics and Abnormal Gene Expression Flashcards

1
Q

what is x-chromosome inactivation?

A

X-inactivation (also called lyonization) is a process by which one of the copies of the X chromosome present in females is inactivated.

The inactive X chromosome is silenced by its being packaged in such a way that it has a transcriptionally inactive structure called heterochromatin

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2
Q

what initiates the mechanism of silencing?

A

Xist - x-inactive-specific-transcript

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3
Q

what mechanism follows silencing?

A

DNA methylation

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4
Q

what is Rett Syndrome?

A
  • dominant x-linked syndrome
  • variable phenotypes
  • neurodegenerative disorder
  • affects females only
  • caused by mutation in gene encoding MeCP2 which leads to loss of gene silencing at many loci
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5
Q

what is genomic imprinting?

A

the epigenetic phenomenon by which certain genes are expressed in a parent-of-origin-specific manner. If the allele inherited from the father is imprinted, it is thereby silenced, and only the allele from the mother is expressed.

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6
Q

what are features of genomic imprinting?

A
  • ~80 imprinted genes on autosomes
  • imprinted genes only expressed from one allele
  • dependent on parental origin
  • imprinting resets on passage through germline
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7
Q

what are features of the mechanism of imprinting?

A
  • must be somatically stable
  • must be reversible during gametogenesis
  • DNA methylation is the best candidate (=epigenetic modification)
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8
Q

what is uniparental disomy?

A

can result in a disruption of the expression of imprinted genes:

  • both copies of a chromosome are inherited from the same parent
  • individual is missing the chromosome from one parent
  • expression altered of imprinted genes on affected chromosome
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9
Q

what are the results of UPD on chromosome 15?

A

Prader-Willi Syndrome (PWS) and Angelman Syndrome (AS)

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10
Q

what are the results of UPD on chromosome 11?

A

Wilms’ tumour

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11
Q

which UPD related condition is a result of maternal deficiency?

A

Angelman Syndrome

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12
Q

which UPD related condition is a result of paternal deficiency?

A

Prader- Willi Syndrome

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13
Q

what causes uniparental disomy?

A

non-disjunction in meiosis II

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14
Q

what causes uniparental heterodisomy?

A

non-disjunction in meiosis I

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15
Q

what does non-disjunction in meiosis II cause?

A

uniparental disomy

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16
Q

what does non-disjunction in meiosis I cause?

A

uniparental heterodisomy

17
Q

what are some diseases associated with genomic imprinting?

A
  • beckwith-wiedman syndrome (BWS)
  • fragile x syndrome
  • myotonic dystrophy (congenital)
  • prader-willi syndrome
  • angelman syndrome
  • wilms’ tumour
18
Q

what drug is approved for the treatment of patients with myelodysplastic syndrome?

A

VIDAZA

19
Q

what is VIDAZA used to treat?

A

myelodysplastic syndrome

20
Q

what is Brg1?

A
  • chromatin regulator that “opens” chromatin and suppresses tumours
  • low BRg1-expressing tumours have worse outcome
21
Q

what mechanisms are involved in epigenetic gene silencing?

A
  • DNA methylation
  • histone modifications
  • nucleosome remodelling
22
Q

what does DNA methylation do?

A

inhibits gene transcription

23
Q

how does DNA methylation inhibit gene transcription?

A
  • prevents binding of transcription factors to the promoter and inhibits transcription by converting chromatin from an open to closed formation
  • methyl CpG binding proteins contain a methyl binding domainthat specifically recognizes methylated CpGs
  • recruits other proteins such as histone deacetylases whichremove acetyl groups, favouring compact chromatin
24
Q

what are the differences between heterochromatin and euchromatin?

A

H: highly condensed in interphase
E: organised in 30nm fibre during interphase

H: transcriptionally inactive (contains few genes)
E: transcriptionally active

H: replicates late in S phase
E: replicated early in S phase

25
Q

what is the result of the spreading of heterochromatin into euchromatic regions?

A

cell to cell variability in gene expression

26
Q

what is position effect?

A

the spreading of heterochromatin into euchromatic regions causing cell to cell variability in gene expression

27
Q

what are desirable features for an imprinting mechanism?

A
  • must be somatically stable
  • must be reversible during gametogenesis
    (DNA methylation is the best candidate = epigenetic modification)
28
Q

what are features of androgenetic cells/embryos?

A
  • poor growth of embryo
  • large placenta
  • non-viable
29
Q

what are features of gynogenetic cells/embryos?

A
  • embryo OK
  • small placenta
  • non-viable
30
Q

which chromosome are both PWS and AS both linked to the same imprinted region of?

A

chromosome 15

31
Q

what occurs with DNA methylation in cancer?

A

tumour suppressor genes are silenced

MD2002 (85 decks)

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