Model evince budding for long-term gene silencing

An adeno-associated viral (AAV) vector was used to deliver a modified version of the CRISPR/Cas9 gene-editing tool to liver cells in a mouse model, which resulted in suppression of the serum enzyme Pcsk9 and reduction of cholesterol levels. It is clear that immune response is an important issue,” said Dr Gersbach. To accommodate the limited capacity of the AAV, investigators at Duke University (Durham, NC, USA) replaced the commonly used Cas9 enzyme from Streptococcus pyogenes with a smaller Cas9 enzyme from Staphylococcus aureus. The dCas9 was combined with a KRAB (Krüppel associated box) protein that blocked gene expression, creating a CRISPR/Cas9 repressor that blocked transcription, reduced chromatin accessibility, and silenced gene expression without altering the underlying DNA sequence.
The CRISPR/Cas9 system has been used in research for gene editing (adding, disrupting, or changing the sequence of specific genes) and gene regulation. Each repetition is followed by short segments of “spacer DNA” from previous exposures to a bacterial virus or plasmid. The conventional CRISPR/Cas9 system is composed of two parts: the Cas9 enzyme, which cleaves the DNA molecule and specific RNA guides that shepherd the Cas9 protein to the target gene on a DNA strand. Despite a moderate host immune response to dCas9KRAB expression, Pcsk9 repression was maintained for 24 weeks after a single treatment, demonstrating the potential for long-term gene silencing in living tissues with dCas9KRAB.
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