How can a sense transgene generate double stranded RNA?

Transgenes insert into chromosomal DNA randomly

or

Transgenes often integrate in complexes

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.

Transcriptional Gene silencing in Arabidopsis requiresdsRNA, DNA methyltransferases, histone methylation and histone deacetylation.

RNA directed DNA methylation

DNA methylases associate with histone modification enzymes leading to changes in histone methlyation patterns and histone deacetylation.Condensed chromatin results.

Histone methylation

Maternal Inheritance

Trait is controlled by genes that are not in the nucleus,Cytoplasmic inheritance.

Eg. mitochondrial or chloroplast genome.

female femalemale male

progeny

parents

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

Maternal effects are traits that are expresseddifferently if inherited from mother or father

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?

female male

parents

progeny

female male

Maternal effect mutations in Drosophila affect embryo polarityDevelopmental axes of embryo affected by maternal RNAs

Imprinting causes alleles to be expresseddifferently 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 placentaLimit growth of fetus in utero.

Imprinting is another form of epigenetic gene regulation

ICR – imprintingControl region

Differential methylationleads to differential expression of Maternal and paternal alleles

Establishment of differential methylation

CTCF zinc finger proteinProtects ICR in femalegermline from denovo methylases

Igf2 insulin-related growth factorRepressed in extraembryonic tissuesand in some embryo tissues

Imprinting

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 RNAExpressed from paternal Allele. Initiation or maintenance?

X-innactivation:Paternal X chromosome Not expressed early in embryoAnd in extraembryonic tissuesXist and Tsix expressed on innactive X.

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