Lecture 7

Question 1

What is a metastable epiallele?

Give an example

Answer 1

Locus that can be epigenetically modified in a variable and reversible manner. This changes the phenotype of genetically identical cells
E.g. Agouti - Avy - viable yellow

Question 2

What does the agouti gene encode?

Answer 2

A paracrine signalling molecule that promotes hair follicles to change from black to yellow

Question 3

What is the typical agouti pattern?

Answer 3

Hairs that have black base, a yellow band and black tip. Due to agouti being expressed only in the middle part of the hair cycle

Question 4

What causes the viable yellow phenotype in agouti?

Answer 4

An IAP, murine specific retrotransposon with the Avy allele. If the IAP is hypomethylated then it moves the promoter of agouti from its developmental promoter to this ectopic promoter and the yellow phenotype is seen

Question 5

What is the effect of IAP methylation happening at different stages of development?

Answer 5

5 distinct phenotypes - from agouti yellow to pseudo-agoutti brown, with mottled individuals between them

Question 6

Why are the agoutti mice more susceptible to diseases such as diabetes, obesity and cancer?

Answer 6

The ectopic agoutti transcription happens in all cells not just the hair follicles

Question 7

What effect were dietary supplements shown to have on coat colour?

Answer 7

Crossing Avy/a fathers with a/a mothers showed that when the mothers were given supplements during gestation and lactation the offspring shifted towards more of a pseudoagoutti phenotype

Question 8

What caused the effect of having dietary supplements?

Answer 8

Increase in CpG methylaiton at 7 key CpG sites in Avy transposon. Hence more expression by developmental promoter
Shown by bisulphite sequencing

Question 9

Is the effect of dietary supplements inheritable?

Answer 9

F2’s of F0 grandmothers given supplements were more pseudoagoutti

Question 10

Why did taking supplements increase methylation?

Answer 10

More SAM being produced as supplements are providing components of methionine and hence SAM. More SAM available to supply methyl groups so more methylation

Question 11

How can SAM be recycled?

Answer 11

After donating methyl group become SAH. SAH converted to homocsyteine

Question 12

A diet high of what isoflavone mimics the effect of dietary supplements?

Answer 12

Genistein

Question 13

Give an example xenobiotic chemical

What is its effect on agoutti?

Answer 13

BPA
More yellow phenotype - less methylation (especially in sites 4, 5 and 6)
Effect can be lessened by giving supplements

Question 14

What effect does BPA have on rats?

Answer 14

Low-dose exposure to BPA increases susceptibility to cancer by changing DNA methylation pattern of important signalling genes

Question 15

Which IAP has been shown to be affected in mice?

Answer 15

Cabp IAP

Decrease in methylation here too

Question 16

What component of grapes and red wine has been shown to affect yeast?

Answer 16

Resveratol

Question 17

What effect does resveratol have?

Answer 17

Activates Sir2 in yeast and extends life span

Mimics effects of calorie restriction via activation of SIRT1 in mammals

Question 18

How was resveratol investigated using mice?

Answer 18

Mice on low calorie, high calorie or high calorie with resveratol diet.
High calorie individuals life span reduced, slightly increased with resveratol but not to same levels as low calorie diet

Question 19

What effect did diet have on mice’s physical performance?

Answer 19

Low calorie mice become fitter and performed better ad did high calorie and resveratol mice,however, high calorie only mice did not.

Question 20

What other effects did resveratol have on the mice?

Answer 20

Increased insulin sensitivity, improve liver histology, increased mitochondria number and decreased acetylation of genes known to be targets of SIRT1; with the expression pattern shifted closer to that of the mice on low calorie diet

Question 21

What component of green tea effects epigenetics?

How?

Answer 21

Polyphenol

Inactivate DNMT1, resulting in hypomethylation and activation of previously hypermethylated genes

Question 22

What effect did green tea have in human study?

Answer 22

Drinking 6 cups a day hypomethylated genes involved in gastric cancer development.

Question 23

What effect did starvation of mice grandmother have?

Answer 23

Males were insulin intolerant when both mother and father were from starved parents. But if one parent was from non-starved parent then the offspring had normal insulin sensitivity

Question 24

What were the methylation state changes between the mice with grandmothers of different diets?

Answer 24

Non

Probable that it is something to do with histone modifications - but not known

Question 25

What effect does smoking have on epigenetics?

Answer 25

Causes hypomethylation, in particular of AHRR gene, to increase expression

Question 26

What is AHRRs role?

Answer 26

Metabolism of benzopyrene - a very toxic component of cigarettes

Question 27

Outline a link between epigenetics and psychiatric diseases

Answer 27

Bdnf gene is had histone methylated under stress, or taking drugs, which causes depression
Anti-depressants, such as HDAC inhibitors, remove this acetylation to allow expression of the Bdnf

Question 28

How may genes are differentially expressed between workers and queen bees?

Answer 28

over 500

Question 29

What effect did Dnmt3 knockdown have in the larvae?

Answer 29

Results in queen rather than worker due to less mehtlyation of CpG island, e.g. in dynactin 62

Question 30

What natural component of beehives mimics Dnmt3 knockdown?

Answer 30

Royal jelly

Question 31

What happens when a queen dies in some ant colonies?

Answer 31

Worker ant can undergo epigenetic changes to longevity genes, telomerase and Sir proteins to live longer and become egg layers.

Question 32

What type of worker ants exist in C. floridanus?

Answer 32

Major and minor workers, that re genetically identical but due to social context, nutrition and physical factors have epigenetic changes

Question 33

What epigenetic changes occur in C. floridanus?

Answer 33

DNA methylation, changes in H3K27ac by CBP. Affecting neuronal regulation and ageing.

Question 34

How is CBP expression linked to caste?

Answer 34

Higher in workers and leads to increased intelligence