Researchers at Rice University have achieved similar success with a new genome editing tool that targets auxiliary roles in the nucleus that are responsible for packaging DNA and helping gene expression. Their work opens the door to new treatments for cancer and other diseases.
Rice bioengineer Isaac Hilton, lead author Jing Li postdoctoral researcher and their colleagues designed an improved CRISPR/Cas9 complex to target specific histones.
Histones help regulate many cellular processes. There are four in each nucleosome (the basic "beads" in DNA), which are activated by exposing genes to help control the structure and function of our genome.
Hilton said: "Nucleosomes can be used as a structural matrix to match our DNA to cells, and can also control our access to key parts of the genome."
Like other proteins, histones can also be triggered by phosphorylation, which is the addition of phosphate groups that can control protein-protein or protein-DNA interactions.
Hilton said: "Histones can display a variety of chemical modifications. These chemical modifications can be used as beacons or regulatory markers, and can tell us which genes should be turned on, when, and to what extent. One of the mysterious Modification is phosphorylation, and our goal is to better clarify the mechanism by which it can quickly turn on and turn off human genes."
He said that no other epigenome editing technology can achieve site-specific control of histone phosphorylation. This programmable tool, called dCas9-dMSK1, combines an inactive "dCas9" protein with an "overactive" human histone kinase, which is an enzyme that catalyzes phosphorylation.
CRISPR/Cas9 usually uses guide RNA and Cas9 "scissors" to target and cut DNA sequences. The new tool program inactivates dCas9 for targeting without cutting the sequence, but uses the recruited dMSK1 enzyme to phosphorylate targeted histones and turn on nearby genes.
Researchers used dCas9-dMSK1 to discover new genes and pathways that play a key role in drug resistance. Li used it to identify three genes previously associated with drug resistance in melanoma. Hilton said: "Then she discovered seven new genes related to anti-melanoma. This is an exciting discovery and we are following up.
"Histones that wrap DNA can have various chemical labels and combinations," he said. "This gave rise to the so-called histone code, and one of our goals is to decipher it."
Li's tool also confirmed how specific histone markers communicate with each other. "The chemical modifications on histones interact. We can prove that it occurs at a specific point in the human genome. This is related to the activation of a gene, so this allows us to control them comprehensively."
Li said that a long-term goal is to target a range of other histone markers. "This is a complicated story. The histones we want to study have many different locations and characteristics."
Hilton added: "Getting these technologies into the patient's body is a long process. But tools like this are the first step and can pave the way for understanding how unfortunately normal cellular processes in human diseases go wrong."
原文检索：Programmable human histone phosphorylation and gene activation using a CRISPR/Cas9-based chromatin kinase
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