Molecular Genetics Lecture 13 - Epigenetics

Why does gene expression need to be regulated?

all cells in an organism contain the same gene (DNA) and whenever cells need the protein the genes are turned on and vice versa and there are signals that induce gene expression

What are the two ways genes are tightly regulated?

temporal regulation, spatial regulation

What is temporal regulation?

specific proteins are required at specific times only and cells do not always need all the proteins

What is spatial regulation (cell or tissue specific expression)?

specific proteins are needed in only specific cell or tissue types, not all the proteins need to be expressed in all tissues or organs

What are the steps of gene expression

1. epigenetics/transcriptional regulation

2. mRNA processing

3. regulation of mature mRNA

4. regulation of translation

5. post-translational regulation

What is epigenetics?

heritable changes in phenotypes caused by mechanisms independent of DNA sequence (not by mutations or changes in nucleotide of DNA)

What is DNA methylation?

when DNA methyl transferase (DNMT) enzyme catalyzes the transfer of methyl groups to the 5’ carbon of cytosine nucleotide

What recognizes CG dinucleotide clusters (CpG islands) recognized?

DNMTase (p-phosphodieaster bond)

How are genes repressed (OFF)?

high DNA methylation in CpG sequences

How are genes active (ON)?

no DNA methylation in CpG sequences

Transposons and repeat sequences are silenced by ________

DNA methylation

What are two mechanisms of repression by DNA methylation?

inhibiting the binding of activator proteins to regulatory DNA sequences and inducing heterochromatin

What is imprinting?

marks that are recognized and inherited

Genomic imprinting is an epigenetic phenomenon controlled by

DNA methylation

What is genomic imprinting?

expression of identical copies of a gene depends on whether it’s maternal or paternal

What is maternal imprinting?

mother’s copy of the gene is inactive/silenced

What is paternal imprinting?

father’s copy of the gene is inactive/silenced

The silencing of imprinted genes are caused by _______ NOT by _______

caused by DNA methylation, not by nucleotide changes/mutations

IGF2 is _______ imprinting because ….

maternal because the gene from the mother never expresses the phenotype since it is silenced by DNA methylation

The IGF2 gene is only expressed if it is inherited from the _____

father

H19 gene is _____ imprinting because…

paternal because the gene is only expressed if it is inherited from the mother and the gene is inactive from the father

What does the H19 gene control?

body weight and also affects cancer

The aguoti mouse are an example of what type of epigenetic inheritance?

transgenerational epigenetic inheritance

What is the universal donor of methyl group?

S-adenosyl methione (SAM)

What hyperactivates the agouti gene constitutively in all cells which leads to the yellow mouse phenotype?

IAP promoter

What silences the UAP promoter which results in the brown mouse phenotype controlled by its own hair-cycle specific promter?

DNA methylation

DNA methylation silences transposon ______ of agouti gene.

upstream

What is the phenotype of mice with a high methyl group diet?

brown, normal

What is the phenotype of mice with a low methyl group diet?

mottled

What is the phenotype of mice with a no methyl group diet?

yellow, obese, tumors

How do queen bees and worker bees differ?

only in diet, larvae feed with royal jelly develop into queen bees while larvae fed with honey develop into workers

Queen bees and worker bees are genetically identical, but have different phenotypes (anatomy, physiology, behavior). True or false.

True