1. How can a sense transgene generate
double stranded RNA?

2. Transgenes insert into chromosomal DNA randomlyor

3. Transgenes often integrate in complexes

5. Transcriptional gene silencing is initiated by
RNA directed methylation of promoter regions
dsRNA homologous to promoters leads to
methylation and inactivation by recruitment of
chromatin remodeling enzymes.

6. Transcriptional Gene silencing in Arabidopsis requires
dsRNA, DNA methyltransferases, histone methylation and
histone deacetylation.
RNA directed
DNA methylation
Histone
methylation
DNA methylases associate with histone modification
enzymes leading to changes in histone methlyation
patterns and histone deacetylation.
Condensed chromatin results.

7. Maternal Inheritance
male
female
female
male
parents
progeny
Trait is controlled by genes that are not in the nucleus,
Cytoplasmic inheritance.
Eg. mitochondrial or chloroplast genome.

8. Maternally inherited human diseases:
Leber’s hereditary optic atrophy
Kearns-Sayre Syndrome - eye muscle atrophy
Progressive external opthalmoplegia
MELAS mitochondrial encephalomyopathy
lactic acidosis and strokes
Myoclonus epilepsy – muscle disorder

9. Maternal effects are traits that are expressed
differently if inherited from mother or father
female
female
male
male
parents
progeny
Tissue in next generation is really derived from mother.
Seed coat controlled by mother’s genome.
Trait is not related to embryo’s genome.
What would happen in next generation?

10. Maternal effect mutations in Drosophila
affect embryo polarity
Developmental axes of embryo
affected by maternal RNAs

11. Imprinting causes alleles to be expressed
differently if they come from the female
or the male parent.
Imprinting tends to be important for placental development:
Turn off cellular markers from father’s genome in placenta
Limit growth of fetus in utero.

12. Imprinting is another form of epigenetic gene regulation
ICR – imprinting
Control region
Differential
methylation
leads to
differential
expression of
Maternal and
paternal alleles

13. Establishment of differential methylation
Igf2 insulin-related growth factor
Repressed in
extraembryonic
tissues
and in some
embryo tissues
Imprinting
CTCF zinc finger
protein
Protects ICR in female
germline from
denovo methylases

14. RNA can mediate differential expression of genes on same chromosome
Igf2r and distant,
linked genes:
Maternal ICR is
methylated,
Paternal alleles are
not expressed.
Small non-translated RNA
Expressed from paternal
Allele. Initiation or maintenance?
X-innactivation:
Paternal X chromosome
Not expressed early in embryo
And in extraembryonic tissues
Xist and Tsix expressed on innactive X.

18. RNA world We are currently discovering that RNA
has many roles in regulation of gene expression.
It is not just an intermediate in protein synthesis anymore