Silence gene with siRNA.

. RNAi's applications in basic and medical research are based on the silencing
gene
siRNA. There are two main types of siRNA currently used in vivo or in vitro RNAi: RNA and
DNA
vectors.1, RNA(1) siRNA: Chemical synthesis or in-body transcription method to obtain two small RNA of 21nt, after admission to form up to 19 bases complementary, on both sides 3?Each end has 2 base-protruding siRNAs. Such siRNA is currently the most widely used. In particular, modified siRNA can still perform specific gene silencing, providing possible prospects for its application in the body.(2) esiRNA: Because the effectiveness of the siRNA gene inhibition described above lies in the selection of the target gene sequence fragments, it is not known which part of the mRNA is more sensitive to siRNA, so the long dsRNA designed according to the target gene mRNA is cut by Dicer into a series of siRNA - collectively known as esiRNA, which may be more effective and easier to inhibit gene expression.(3) hairpin RNA: hairpin RNA designed according to miRNA, or siRNA-based hairpin RNA, exhibits effective gene inhibition in the body.2, DNA vectorBecause RNAi amplification mechanisms do not exist in mammals and fruit flies, the RNAi effects produced by importing the above RNA are inevitably transient. To overcome this weakness, some research groups have developed techniques for expressing siRNA in the body based on DNA vectors. This vector can be a proton, a virus, or even a fragment of DNA.(1) Expression system based on RNA polymerase II promoter: in
tissues
or cells with weak or no interferon response, long hairpin RNA can be built and further cut into siRNAs by Dicer. The advantage of this expression system is that it allows tissue or cell-specific dsRNA expression, but most mammalian cells have a non-specific effect on interferon responses to long hairpin RNA, limiting the widespread use of such expression systems.
(2) expression system based on RNA polymerase III promoters: currently mainly used U6 promoters and H1 promoters, on the one hand, they have a high transcription efficiency in the body, on the other hand, with several consecutive T as the termination signal, limiting the size of the RNA so as not to cause interferon non-specific effects. Such expression systems can also be divided into three categories: a prosurface vector designed to express hairpin RNA based on the gene silencing effect of hairpin RNA; In particular, the latter
easily obtained
PCR method, greatly expanding its application..