RNA targeting with CRISPR–Cas13

RNA has important and diverse roles in biology, but molecular tools to manipulate and measure it are limited. For example, RNA interference1-3 can efficiently knockdown RNAs, but it is prone to off-target effects4, and visualizing RNAs typically relies on the introduction of exogenous tags5. Here we demonstrate that the class 2 type VI6,7 RNA-guided RNA-targeting CRISPR-Cas effector Cas13a8(previously known as C2c2) can be engineered for mammalian cell RNA knockdown and binding. After initial screening of 15 orthologues, we identified Cas13a from Leptotrichia wadei (LwaCas13a) as the most effective in an interference assay in Escherichia coli. LwaCas13a can be heterologously expressed in mammalian and plant cells for targeted knockdown of either reporter or endogenous transcripts with comparable levels of knockdown as RNA interference and improved specificity. Catalytically inactive LwaCas13a maintains targeted RNA binding activity, which we leveraged for programmable tracking of transcripts in live cells. Our results establish CRISPR-Cas13a as a flexible platform for studying RNA in mammalian cells and therapeutic development.National Institute of Mental Health (U.S.) (Grant 5DP1-MH100706)National Institute of Mental Health (U.S.) (Grant 1R01-MH110049

Epigenetic polypharmacology: from combination therapy to multitargeted drugs

The modern drug discovery process has largely focused its attention in the so-called magic bullets, single chemical entities that exhibit high selectivity and potency for a particular target. This approach was based on the assumption that the deregulation of a protein was causally linked to a disease state, and the pharmacological intervention through inhibition of the deregulated target was able to restore normal cell function. However, the use of cocktails or multicomponent drugs to address several targets simultaneously is also popular to treat multifactorial diseases such as cancer and neurological disorders. We review the state of the art with such combinations that have an epigenetic target as one of their mechanisms of action. Epigenetic drug discovery is a rapidly advancing field, and drugs targeting epigenetic enzymes are in the clinic for the treatment of hematological cancers. Approved and experimental epigenetic drugs are undergoing clinical trials in combination with other therapeutic agents via fused or linked pharmacophores in order to benefit from synergistic effects of polypharmacology. In addition, ligands are being discovered which, as single chemical entities, are able to modulate multiple epigenetic targets simultaneously (multitarget epigenetic drugs). These multiple ligands should in principle have a lower risk of drug-drug interactions and drug resistance compared to cocktails or multicomponent drugs. This new generation may rival the so-called magic bullets in the treatment of diseases that arise as a consequence of the deregulation of multiple signaling pathways provided the challenge of optimization of the activities shown by the pharmacophores with the different targets is addressed

Prader–Willi syndrome and autism spectrum disorders: an evolving story

Prader–Willi syndrome (PWS) is well-known for its genetic and phenotypic complexities. Caused by a lack of paternally derived imprinted material on chromosome 15q11–q13, individuals with PWS have mild to moderate intellectual disabilities, repetitive and compulsive behaviors, skin picking, tantrums, irritability, hyperphagia, and increased risks of obesity. Many individuals also have co-occurring autism spectrum disorders (ASDs), psychosis, and mood disorders. Although the PWS 15q11–q13 region confers risks for autism, relatively few studies have assessed autism symptoms in PWS or directly compared social, behavioral, and cognitive functioning across groups with autism or PWS. This article identifies areas of phenotypic overlap and difference between PWS and ASD in core autism symptoms and in such comorbidities as psychiatric disorders, and dysregulated sleep and eating. Though future studies are needed, PWS provides a promising alternative lens into specific symptoms and comorbidities of autism

Differentiation Induction In Acute Myeloid Leukemia Using Site-Specific DNA-Targeting

Abstract Hoxa9 and Meis1 are overexpressed in &gt;70% of acute myeloid leukemia (AML) and associated with poor prognosis and survival. Hoxa9 and Meis1 interact with DNA and PBX to achieve transcription of differentiation-blocking genes. We tested transcriptional repression at Hoxa9-PBX-Meis1 genomic binding sites to induce differentiation in a model of human AML We designed a DNA-recognition strategy based on the known structure of the Hoxa9-PBX-DNA complex by fusing the DNA binding helices of Hoxa9 and PBX to create concise homeodomain fusion proteins that target the Hoxa9-PBX DNA recognition sequence. To confer transcription-repressing properties to the proteins, we attached a transcriptional repressor (sin3 interacting) domain and ectopically expressed this protein in Hoxa9-Meis1 immortalized murine progenitors. Introduction of this transcription repressor protein significantly enabled cell differentiation versus control (51.2% Mac-1high Gr-1high cells versus 11.3% for control). Multiple gene transcripts indicative of differentiation, such as GCSFR, myeloperoxidase, neutrophil elastase, and the calcium binding protein, S100A8, were also elevated in repressor-expressing cells. Furthermore, direct transcriptional targets of Hoxa9 (e.g. SOX2, CD34, FOXP1, FLT3R, DNAJC10) were down regulated in repressor-expressing cells. Importantly, a mutant repressor lacking the DNA-interacting amino acids did not affect transcription of Hoxa9 targets, demonstrating on-target specificity. Repressor-expressing cells also exhibited lower surface expression of c-Kit and Flt3 receptors and when transplanted into mice resulted in a significant increase in disease latency with a 94 day median latency versus 62 day latency for the control group (p value = 0.002). Our results demonstrate that site-specific DNA-targeting using homeodomain fusion proteins can enable AML cell differentiation and significantly increase disease latency. Disclosures: Scadden: Fate Therapeutics: Consultancy, Equity Ownership. </jats:sec