Lecture 19 Epigenetics

Question 1

Epigenetics
(What is epigenetics)
(2 categories of epigenetics, 3 for the first categories, 1 for the second categories)
E.g. DNA methylation, agouti gene in mice
(How does DNA methylation control mice coat color)

Answer 1

Heritable changes in gene expression not due to changes in base sequence of DNA.

Modifying chromatin structure, altering DNA accessibility
DNA methylation at CpG
Covalent modification of histone
E.g. acetylation, methylation, ubiquitination.
Non-covalent modification of histone
E.g. chromatin remodeling, histone variants

Transcriptional silencing
Non-coding RNAs (iRNA)

IAP, a retrotransposon inserted upstream of Agouti gene, contains a cryptic promoter that will disrupt the expression of agouti if activated.
Methylated IAP: brown/grey
Unmethylated IAP: yellow

Question 2

Parental imprinting: a epigenetic inheritance pattern
Somatic cell
Maternally imprinted gene
Phenotype depends on…

Paternally imprinted gene
Phenotype depends on…

gamete formation
In female gamete,
In male gamete,

E.g. igf2 and H19 in mice
Igf2 is ____
H19 is ____
(How?)

Answer 2

Maternally imprinted gene on maternal chromosome is silenced, on paternal chromosome is expressed.
Phenotype depends on paternal chromosome, mutations on maternal chromosome don’t matter.

Paternally imprinted gene on paternal chromosome is silenced, on maternal chromosome is expressed.
Phenotype depends on maternal chromosome

In female gamete, paternal imprints are erased, maternal imprints erased and form on both chromosomes.
In male gamete, maternal imprints are erased, paternal imprints erased and form on both chromosomes.

Igf2 is maternally imprinted
H19 is paternally imprinted
Enhancer downstream of H19 controls the expression of both genes
Maternal chromosome: CTCF binds to insulator blocking igf2 activation
Paternal chromosome: methylation blocking H19 activation