Lecture 15: Genomic Imprinting

__________________refers to monoallelic expression that occurs in a manner specific to the parent of origin.

genomic imprinting

Usually, both alleles are capable of expression in genomic imprinting._________ of human genes (80 genes) are expressed from one allele. 

<1%

Where is genomic imprinting originated from?

paternal or maternal

Imprinted genes often exist in clusters. ______ of imprinted mammalian genes exist in clusters. (not a rule)

80%

Imprinting is controlled by ____________mechanisms.

epigenetic

Imprinting genes are usually involved in ___________________.

development

Mouse chromosome translocation

• maternal and paternal chromosome can be distinguished

• mammals are diploid and inherit a set of chromosomes from the mom and dad

• mice can be generated

  • inherit two copies of a chromosome from one parent and one copy from another UPD

  • inherit partial chromosome deletion from one parent and a wild type chromosome from other parent

  • inherit chromosomes carrying SNP from one parent and wild type chromosome from a

offspring with UPDs or deletions are likely to display lethal phenotypes, whereas SNPs will allow the production of viable offpsring

UPD

uniparental disomy

What is the imprinting nuclear transplant experiment? 

Placing a sperm and an egg nucleus into an enucleated fertilized cell leads to a normal embryo

In imprinting nuclear transplant experiment, zygote that receive only maternal or paternal nuclei do not_________________. 

survive

In the imprinting nuclear transplant experiment: two parental genomes are NOT equivalent, what does imprinting prevent? 

parthenogenesis

MEDEA (MEA) gene is imprinted.

What do these F MEA/mea x M MEA/MEA alleles mean?

What do these MEA/MEA x MEA/mea alleles mean?

• all seeds viable

• 50% of seeds abort

In the second cross, 50% of the seeds receive the mutant mea allele from their mother.

These seed abort, even though they also have a ________________ MEA allele inherited from their father.

wild-type

What do the paternal allele ( first arrow) represent in this? 

What do the maternal allele (second arrow) represent in this? 

1. The paternal allele is silent. 

2. The phenotype of the progeny is based on the maternal genotype

MEA is ______________ most cells.

silenced

What is MEA methylated by? 

MET1

in vegetative tissues and the male gametophyte

Sexual Reproduction in plants

MEA is demethylated and expressed in the ________________gameotyphyte.

female

In females, the central cell DME removes DNA methylation from maternally expressed genes__________ and __________; and from the paternally expressed gene__________.

MEA and FIS2

PHE1

DNA methylation at these loci are maintained in the ________gametophyte. Another unknown repressor (R) may be required for repression of the paternal allele in of MEA.

male

In endosperm, maternal alleles of MEA and FIS2. The ________complex mediates silencing of maternal allele of PHE.

PRC2

The maternal removal of DNA methylation downstream of the _________gene is required for silencing of it’s maternal allele.

PHE

Comparison of Imprinting in Plants and Mammals

Imprints acquisition and erasure in mammalian development

1st generation imprints

2nd generation maternal imprints: acquired in oocytes

2nd generation: paternal imprints acquired in sperm

Embryonic gonad during imprint acquisition and erasure in mammalian development

imprint erasure precedes sex determination

Embryo, placenta and membrane during imprint acquisition and erasure in mammalian development

imprints remain

Establishment, Maintenance and Erasure of Imprints during Mouse development

Mammalian Imprinted Genes Controlled by _______________ control elements.

imprint

Imprinted genes exist in __________.

clusters

Imprint control elements are required for imprinting:

• deletion of ICE leads to loss of imprinting

• ICEs carry parent of origin specific epigenetic modifications

• these include differentially methylation regions (DMR)

There is at least one _______________(IncRNA) presente, often expressed from chromosome carrying silenced genes. 

long non-coding RNA

Imprinting is controlled by _______.

DMRs

Deletion of __________only causes loss of imprinting when deleted from parental chromosome expressing IncRNA.

ICE