In: Biology
comment on the significance of RNAi for understanding epigenetic control of the human genome. In particular, respond to this statement: "RNAi provides an attractive model to explain how epigenetic histone modifications are targeted to specific genomic loci".
Answere : Epigenetic change include such processes that alter gene activity without changing the DNA sequence, and leads to modication that can be transmiited to daughter cells. These include histone modification, DNA methylation etc.
NcRNAs or noncoding RNAs (such as miRNA, siRNAs etc.) function to regulate gene expression at the trancription and post-transcription level. These NcRNAs play a role in heterochromatin formation, histone modification, DNA methylation targetting, and gene silencing.
In case of siRNAs or small interfering RNAs bind to specific target mRNA with a complementary sequence to induce cleavage, or degradation or block translation. It mediate post-transcription gene silencing (PTGS) as a result of mRNA degradation. In addition to this function, siRNAs have also been shown to induce heterochromatin formation via RNA-induced transcription silencing(RIGS) complex which when bound to siRNA promote H3K9 methylation and chromatin condensation.