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PATH3305 > 5 - Epigenetic Variation > Flashcards

5 - Epigenetic Variation Flashcards

1
Q

Epigenetics

A

Study of reversible heritable changes in gene function that occur without a change in the sequence of DNA

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2
Q

Epigenetic processes

A
  • Histone modification & chromatin remodeling
  • DNA methylation
  • Non-coding RNA mediated regulation
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3
Q

Chromosomes

A

DNA + protein (Chromatin)

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4
Q

Examples of epigenetic processes

A
  • Cat spotting
  • Honey bees (workers vs queens)
  • Host immunity (e.g. against retrovirus)
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5
Q

Histones

A

Nucleosomes arranged as an octamer of histone proteins with protruding N-terminal ends

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6
Q

What are the four core histones

A

Two each of H2A, H2B, H3 and H4

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7
Q

Histone H1

A
  • The linker protein
  • Bound to DNA between nucleosomes.
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8
Q

Histone tags that control histones

A
  • Acetyl
  • Phosphate
  • Methyl
  • Ubiquitin
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9
Q

Modifications of histone tails

A

Act as epigenetic marks that control expression of chromosomal regions (controlled by transcription factors)

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10
Q

HIstone code hypothesis

A

States that no one histone modification occurs in isolation but instead effect each other

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11
Q

What charge is DNA

A

negative

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12
Q

What charge are histones

A

positive

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13
Q

Histone acetylation

A
  • Acetylation of histones occur in the lysine residues of histone tails
  • Neutralises the positive charge & decreases their affinity for DNA
  • DNA is less tightly wound & permits transcription
  • Histones near active genes are hyperacetylated
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14
Q

Acetylated lysine residues

A

Transcriptional activation (gene expression)

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15
Q

Deacetylated lysine residues

A

Transcription repression (gene silencing)

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16
Q

HAT & HDAC

A

Histone acetylase (HAT) & histone deacetylase (HDAC) enzymes add/remove acetyl groups

17
Q

DNA Methylation

A
  • Involved in gene regulation
  • Involves the addition of methyl groups to histone proteins
18
Q

Methylation normal processes

A
  • Embryonic development
  • X chromosome inactivation
  • Imprinting
  • Gene silencing
19
Q

X chromosome inactivation

A
  • Silencing of one X chromosome in females (done at random, all descendants of that cell keep same pattern)
  • Human females are functionally mosaic
  • early female embryo has both X’s active.
  • Most of the genes on one X chromosome are inactivated (by methylation) in every cell
20
Q

Mechanism of X inactivation

A
  • At ~1000 cell stage, cell chooses one X to remain ON.
  • Other X is inactivated via XIST
  • XIST coats the X chr leading to heterochromatin spreading (silencing) & methylation
21
Q

XIST

A
  • X Inactivation Specific Transcript
  • An X chromosome-encoded
    lncRNA
22
Q

Skewed X inactivation

A
  • X activation sometimes is non-random (skewed)
  • The severity of disease can be related to how many cells are expressing the mutated allele
23
Q

Agouti mouse model

A
  • When the Agouti gene is methylated (off), mice
    are brown & healthy
  • When the gene is unmethylated (on), mice are
    yellow & unhealthy
24
Q

Genomic imprinting

A
  • Parent-specific expression or repression of genes
    or chromosomes in offspring
  • Two copies of a given gene are inherited (one from each parent) only the maternal or paternal allele is expressed.
  • The non expressed allele is said to be imprinted
25
Q

Imprinting and disease

A
  • Diseases are characterised by non-mendelian inheritance patterns that exhibit parental-origin effects.
  • Role of imprinted genes in growth regulation during embryonic and post-natal development, brain function and behavior.
26
Q

Diseases associated with genomic imprinting

A
  • Beckwith–Wiedemann syndrome
  • Prader–Willi syndrome
  • Angelman syndrome
  • Fragile X
27
Q

Angelman syndrome

A
  • Severe mental retardation
  • Microcephaly
  • Lack of speech
  • Frequent laughter.
  • Deletion of maternal 15q11-q13
28
Q

Prader-Willi syndrome

A
  • Mild mental retardation
  • Obesity
  • Short stature.
  • Deletion of paternal 15q11-q13
29
Q

Features of Beckwith–Wiedemann syndrome

A

Embryonic and placental overgrowth, predisposition to childhood tumors

30
Q

Cause of Beckwith Wiedemann syndrome

A
  • Genetic and epigenetic changes in a region of about 1 megabase on chromosome 11p
  • Increased expression of IGF2, and suppression of CDKN1C are major cause
31
Q

IGF2

A
  • Insulin-like growth factor
  • Normally this gene is only expressed by the paternal chromosome
32
Q

CDKN1C

A

700kb away from IGF2 and is maternally expressed

PATH3305 (25 decks)

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