CRISPR/Cas9 Epigenome Editing Potential for Rare Imprinting Diseases: A Review

Abstract

Imprinting diseases (IDs) are rare congenital disorders caused by aberrant dosages of imprinted genes. Rare IDs are comprised by a group of several distinct disorders that share a great deal of homology in terms of genetic etiologies and symptoms. Disruption of genetic or epigenetic mechanisms can cause issues with regulating the expression of imprinted genes, thus leading to disease. Genetic mutations affect the imprinted genes, duplications, deletions, and uniparental disomy (UPD) are reoccurring phenomena causing imprinting diseases. Epigenetic alterations on methylation marks in imprinting control centers (ICRs) also alters the expression patterns and the majority of patients with rare IDs carries intact but either silenced or overexpressed imprinted genes. Canonical CRISPR/Cas9 editing relying on double-stranded DNA break repair has little to offer in terms of therapeutics for rare IDs. Instead CRISPR/Cas9 can be used in a more sophisticated way by targeting the epigenome. Catalytically dead Cas9 (dCas9) tethered with effector enzymes such as DNA de- and methyltransferases and histone code editors in addition to systems such as CRISPRa and CRISPRi have been shown to have high epigenome editing efficiency in eukaryotic cells. This new era of CRISPR epigenome editors could arguably be a game-changer for curing and treating rare IDs by refined activation and silencing of disturbed imprinted gene expression. This review describes major CRISPR-based epigenome editors and points out their potential use in research and therapy of rare imprinting diseases.

Novel Approaches to Epigenetic Therapies: From Drug Combinations to Epigenetic Editing

“…The principle of CRISPR/Cas9 used for epigenome editing purposes is based on programmable guide RNA (gRNA), catalytically dead Cas9 (dCas9), and fused (or non-covalently bound) epigenetic effector enzyme/epigenetic modifier [ 104 ]. The gRNA directs dCas9 fused to an epigenetic effector to specific loci.…”

“…The effector is either the activator or repressor of gene transcription. The effectors are derived from epigenetic writers and erasers, such as DNMTs, HATs, HMTs and TETs, HDM, and HDAC, respectively [ 104 ].…”

“…CRISPR epi-editors can be divided into four distinct groups, based on their mode of action: chromatin reorganization, expression regulation, covalent histone, and DNA modification [ 104 ]. However, only the last three groups have been mostly applied so far.…”

Targeting Epigenetic Modifications in Uveal Melanoma

“…Gene expression has been activated by DNA demethylation using Tet1, H3K27 acetylation by p300, or H3K4 trimethylation by PRDM9. The antagonistic effect can be achieved either by promoter methylation employing Dnmt3a, removal of a methyl group from H3K4me1/2 and H3K9me2 by LSD1 or deacetylation of H3K27ac by HDAC3 [ 127 ].…”

Inadvertent nucleotide sequence alterations during mutagenesis: highlighting the vulnerabilities in mouse transgenic technology

“…In general, to study a gene function, the dominant-negative approach, knock-in, complete, partial, tissue-specific, and conditional knockout approaches are utilized based on the needs of the individual investigation. Moreover, recent advances in techniques involving CRISPR/Cas9 have not only expedited transgenesis but also rejuvenated the field of therapeutics as a potential tool in treating diseases like lung cancer as well as the ongoing pandemic, COVID-19 [ 5 , 6 , 36 , 48 ]. Indeed, these techniques have proven to be powerful in understanding the minutiae of gene function, such as how a specifically located amino acid residue in a particular peptide and its corresponding DNA sequence in the gene play a crucial role in determining its function.…”