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 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.

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.

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 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?

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

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.

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

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

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.

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