Week 6 - Epigenetic Action

Positional Effect Variegation

Movement of gene to heterochromatic region silences gene expression

Positional Effect Variegation - Example

Drosophilia white gene

Drosophilia White Gene - Normal vs Silenced vs Some

Red

White

Mix

DNA Methylation - Region

Regulatory

Genome-Wide De-Methylation During - 3

DNA replication

Gametogenesis

Embryogenesis

Gametogenesis - Demethylation

Early development primordial germ cells

Gametogenesis - Remethylation

Before meiosis

Re-methylation Occurs Earlier In

Males

Embryogenesis - Demethylation

After fertilisation

Embryogenesis - Retmethylation

Implantation

Monoallelic Expression

Only 1 copy of allele transcribed

Imprinting

Gene expression depends on chromosome parent of origin

Somatic Cells

Maintain imprints

Germ Cells

Erase old imprints

New paternal or maternal imprint

Prader Willi Syndrome

Normal - paternal expressed

PWS - missing paternal PWS allele

Angelmans Syndrome

Normal - maternal expressed

AS - missing maternal AS allele

Facultative Heterochromatin

Not always condensed