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MCP Unit 7 > Imprinting and Epigenetics > Flashcards

Imprinting and Epigenetics Flashcards

1
Q

prader willi and angelman

A
  • best known microdeletion
  • both appear to have same deletion of 15q 11
  • two diseases are completely different
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2
Q

prader willi

A
  • patients are small and hypotonic at birth
  • gain weight rapidly
  • small hands/feet
  • hypogonadism
  • bad temper
  • developmentally delayed, but do well in special ed
  • group homes
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3
Q

angelman

A
  • severely mentally retarded
  • can’t carry on a normal conversation and discourse is often punctuated by bursts of inappropriate laughter
  • hyperactivity, short stature, microcephaly, seizures, ataxia
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4
Q

15q deletion

A
  • could be detected 60% of the time for PW but only 10-20% of the time for AS
  • FISH 65-85% for both
  • still need clinical features because it’s the same deletion
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5
Q

evolving

A
  • PW found in kids with deletion on paternal chromosome, or with maternal disomy
  • AS found in kids with deletion on maternal chromosome, or with paternal disomy
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6
Q

disomy

A

-presence of 2 chromosomes

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7
Q

UPD

A
  • inheritance of a chromosome or chromosomes from 1 parent to the exclusion of the other parent
  • need to use molecular probe to find
  • can be heterodisomy or isodisomy
  • isodisomy leads to loss of heterozygosity
  • come from meiotic non-disjunction
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8
Q

disomy transmission

A

-from a non-disjunction and embryo rescue through duplication of a single chromosome or deletion of a trisomy

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9
Q

CF

A
  • dad is carrier and mom isn’t

- child inherits two deltaF508 from dad

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10
Q

rescue of a trisomy

A
  • 2/3 of the time will still give you bi parental heterodisomy
  • 1/3 gives uniparental heterodisomy
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11
Q

translocation family

A
  • girl with anomalous features and no apparent reason
  • MR, seizures, coarse hair, frontal bossing, kyphoscoliosis, prominent maxilla and mandible
  • father was a balanced carrier of a robertsonian translocation of 13 and 14
  • child had same thing and appeared balanced, but she had the translocation from dad and then the single 14 was also from dad- so both 14s came from dad
  • could be from non-disjunction in both parents- translocation and 14 from dad and just 13 from mom, but unlikely
  • more likely that the dad gave translocation and 14, mom gave normal, and mom’s 14 happened to be kicked out of embryo instead of dad
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12
Q

imprinting

A
  • differential modification of the maternal and paternal genetic contributions to the zygote
  • resulting in the differential expression of parental alleles during development and in the adult
  • for some chromosomal regions, it may be important to have maternal and paternal contribution
  • not all genes or all chromosomes
  • usually associated with methylation, an epigenetic modification
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13
Q

methylation

A
  • addition of methyl groups to cytosine residues in the DNA
  • can occur within a single gene or a group of adjacent genes
  • can occur over a portion of a single chromosome
  • can occur over the full length of one or more chromosomes
  • the pattern of methylation can be different between males and females
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14
Q

imprinting 2

A

-lasts one generation, change occurs at meiosis

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15
Q

meiotic imprinting

A
  • get one copy from mom, one from dad
  • at meiosis, both chromosomes are changed back to original pattern depending on gender
  • paternal gametes changed to paternal pattern and same for maternal
  • if there is an imprinting failure, child can end up with two copies of a gene that are imprinted the same even if it came from the right parent ( dad can pass on a maternal imprinted chromosome)
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16
Q

PW/AS

A
  • can now also occur through imprinting error
  • so PW is paternal deletion, maternal disomy, or imprinting error resulting in only maternal alleles
  • AS is maternal deletion, paternal disomy, or imprinting error resulting in only paternal alleles
17
Q

detection now

A
  • FISH 70-80% for PW, 70% for AS
  • UPD 15-20% of PW, only 2-3% AS
  • imprinting failure 2-4% for PW, 2-3% for AS
  • other mutations- 25% UBE3A in AS
  • chromosome rearrangement 1% for both
18
Q

differences in paternal imprints

A
  • maternal copy has UBE3A expression (SNRPN and necdin methylated)
  • paternal copy has SNRPN and necdin expressed (UBE3A methylated)
  • if correctly inherited, get all 3 expressed at right amount
  • if missing paternal- have all copies of UBE3A but no SNRPN or necdin
  • if missing maternal, will only have SRPN and necdin, no UBE3A
19
Q

imprinting 3

A
  • important mutational mechanism
  • high frequency of developmental genes
  • probably very important in very early development of the zygote
  • important to actually have one chromosome from mom and one from dad
  • errors can be an important mutational mechanism
20
Q

epigenetics

A
  • study of heritable changes in gene function that are not caused by change in the DNA sequence
  • modification of transcription that alters gene expression and thus phenotype
  • normal process required for normal cell function
  • change in epigenetic effects can result in up or down regulation of genes and can result in disease
21
Q

categories of epigenetic modifications

A
  • methylation
  • histone modification
  • chromatin remodeling
22
Q

methylation

A
  • results in modification of function or complete inactivation
  • can affect a single gene, a group of adjacent genes, or a whole chromosome
  • x inactivation
  • imprinting-specific patterns associated with the parent of origin
23
Q

transcription modification

A
  • TFs, repressors

- increase or decrease expression

24
Q

histone and nucleosome modification

A
  • 5’ and 3’ regions of a transcriptionally active gene promoter are nucleosome free, which allows for assembly and disassembly of transcription machinery
  • methylated DNA is condensed so nucleosomes will be in their normal patterns
  • methylation and histone positioning can block transcription, whereas unmethylated DNA without histones is open to transcription
25
Q

development

A
  • stem cells retain the ability to differentiate into any cell type
  • as the organism develops, differentiation occurs, resulting in different cell types with different functions
  • a specific patterns of genes must be active whereas others are inactivated to create specific tissue and organ phenotypes
  • mechanisms include DNA methylation, histone modification, remodeling of chromatin structure
26
Q

TFs

A
  • bind to DNA and alter gene transcription
  • can act as an activator or repressor
  • bind specifically to enhancer or promoter regions of the DNA adjacent to a specific gene
27
Q

microRNA

A
  • small, non-coding RNAs
  • miRNA binds to mRNA to regulate gene expression
  • this can prevent translation or interfere with the translation process
  • down regulation of miRNA caused by hypermethylation at the miRNA promotors is reported in a number of tumors
  • miR15a and miR-16-1 downregulated in leukemia
  • down regulation of miR107 is linked to pathogenesis in AD
  • miR21 is upregulated in breast cancer
  • present targets for therapy and drug development
28
Q

epigenetics and human disease

A
  • cancer-breast, ovarian, pancreatic, melanoma, leukemia, lymphoma
  • AI- arthritis, diabetes, MS
  • neurodevelopmental disease-Rett,Coffin-Lowry
  • neurological and neurodegenerative-fragile X, AD, PW/AS, Parkinson, Huntingtons
  • aging
29
Q

Rett syndrome

A
  • neurodevelopmental disorder
  • affects primarily females
  • normal early development followed by arrested development the regression
  • disruption of motor functions, problems with control of hands and feet
  • intellectual disability
  • loss of speech
  • seizures
  • variable phenotype-partially dependent on the frequency of mutant alleles that are inactivated
  • Xq28
  • MECP2- TF that can activate or repress transcription
  • normal function required for maturation of neurons and normal development
30
Q

conclusions

A
  • understanding epigenetics is critical for understanding many common diseases
  • moves genetics beyond realm of purely inherited entities
  • epigenetics expands targets for drug and therapy development

MCP Unit 7 (14 decks)

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