Zhenglin Hou

Bio: Zhenglin Hou is an academic researcher from DuPont Pioneer. The author has contributed to research in topics: Genome editing & CRISPR. The author has an hindex of 4, co-authored 8 publications receiving 100 citations.

PAM recognition by miniature CRISPR-Cas12f nucleases triggers programmable double-stranded DNA target cleavage.

Abstract: In recent years, CRISPR-associated (Cas) nucleases have revolutionized the genome editing field. Being guided by an RNA to cleave double-stranded (ds) DNA targets near a short sequence termed a protospacer adjacent motif (PAM), Cas9 and Cas12 offer unprecedented flexibility, however, more compact versions would simplify delivery and extend application. Here, we present a collection of 10 exceptionally compact (422-603 amino acids) CRISPR-Cas12f nucleases that recognize and cleave dsDNA in a PAM dependent manner. Categorized as class 2 type V-F, they originate from the previously identified Cas14 family and distantly related type V-U3 Cas proteins found in bacteria. Using biochemical methods, we demonstrate that a 5' T- or C-rich PAM sequence triggers dsDNA target cleavage. Based on this discovery, we evaluated whether they can protect against invading dsDNA in Escherichia coli and find that some but not all can. Altogether, our findings show that miniature Cas12f nucleases can protect against invading dsDNA like much larger class 2 CRISPR effectors and have the potential to be harnessed as programmable nucleases for genome editing.

A catalogue of biochemically diverse CRISPR-Cas9 orthologs.

Abstract: Bacterial Cas9 nucleases from type II CRISPR-Cas antiviral defence systems have been repurposed as genome editing tools. Although these proteins are found in many microbes, only a handful of variants are used for these applications. Here, we use bioinformatic and biochemical analyses to explore this largely uncharacterized diversity. We apply cell-free biochemical screens to assess the protospacer adjacent motif (PAM) and guide RNA (gRNA) requirements of 79 Cas9 proteins, thus identifying at least 7 distinct gRNA classes and 50 different PAM sequence requirements. PAM recognition spans the entire spectrum of T-, A-, C-, and G-rich nucleotides, from single nucleotide recognition to sequence strings longer than 4 nucleotides. Characterization of a subset of Cas9 orthologs using purified components reveals additional biochemical diversity, including both narrow and broad ranges of temperature dependence, staggered-end DNA target cleavage, and a requirement for long stretches of homology between gRNA and DNA target. Our results expand the available toolset of RNA-programmable CRISPR-associated nucleases. A few bacterial Cas9 nucleases have been repurposed as genome editing tools. Here, the authors use bioinformatic and biochemical analyses to characterize 79 Cas9 proteins, revealing substantial functional diversity and thus expanding the available toolbox of RNA-programmable CRISPR-associated nucleases.

PAM recognition by miniature CRISPR nucleases triggers programmable double-stranded DNA target cleavage

Abstract: In recent years, CRISPR-associated (Cas) nucleases have revolutionized the genome editing field. Being guided by an RNA to cleave double-stranded (ds) DNA targets near a short sequence termed a protospacer adjacent motif (PAM), Cas9 and Cas12 offer unprecedented flexibility, however, more compact versions would simplify delivery and extend application. Here, we present a collection of 10 exceptionally compact (422-603 amino acids) CRISPR-Cas nucleases that recognize and cleave dsDNA in PAM dependent manner. Categorized as class 2 type V-F they come from the Cas14 family and distantly related type V-U3 Cas proteins found in bacteria. Using biochemical methods, we demonstrate that a 5’ T- or C-rich PAM sequence triggers double stranded (ds) DNA target cleavage. Based on this discovery, we evaluated whether they can protect against invading dsDNA in E. coli and find that some but not all can. Altogether, our findings show that miniature Cas nucleases are functional CRISPR-Cas defense systems and have the potential to be harnessed as programmable nucleases for genome editing.

PAM recognition by miniature CRISPR-Cas14 triggers programmable double-stranded DNA cleavage

Abstract: Small and robust CRISPR-Cas nucleases are highly desirable for genome editing applications. Being guided by a RNA to cleave targets near a short sequence termed a protospacer adjacent motif (PAM), Cas9 and Cas12 offer unprecedented flexibility, however, smaller more compact versions would simplify delivery and extend application. Recently, a new class 2 system encoding a miniature (529 amino acids) effector, Cas14a1, has been shown to exclusively function as a PAM-independent single stranded DNA nuclease. Using biochemical methods, we show that a T-rich PAM sequence triggers Cas14 proteins to also cut double-stranded DNA generating staggered ends. Finally, we demonstrate the ability of Cas14a1 to target and cleave cellular human chromosomal DNA paving the way for genome editing applications with Cas14s.

Novel cas9 orthologs

Abstract: Compositions and methods are provided for novel Cas9 orthologs, including, but not limiting to, novel guide polynucleotide/Cas9 endonucleases complexes, single or dual guide RNAs, guide RNA elements, and Cas9 endonucleases. The present disclosure also describes methods for creating a double strand break in a target polynucleotide, methods for genome modification of a target sequence under various in vivo and in vitro conditions, in the genome of a cell, for gene editing, and for inserting a polynucleotide of interest into the genome of a cell. Also provided are nucleic acid constructs and cells having a modified target site or altered polynucleotide of interest produced by the methods described herein.

Evolutionary classification of CRISPR-Cas systems: a burst of class 2 and derived variants.

Abstract: The number and diversity of known CRISPR-Cas systems have substantially increased in recent years. Here, we provide an updated evolutionary classification of CRISPR-Cas systems and cas genes, with an emphasis on the major developments that have occurred since the publication of the latest classification, in 2015. The new classification includes 2 classes, 6 types and 33 subtypes, compared with 5 types and 16 subtypes in 2015. A key development is the ongoing discovery of multiple, novel class 2 CRISPR-Cas systems, which now include 3 types and 17 subtypes. A second major novelty is the discovery of numerous derived CRISPR-Cas variants, often associated with mobile genetic elements that lack the nucleases required for interference. Some of these variants are involved in RNA-guided transposition, whereas others are predicted to perform functions distinct from adaptive immunity that remain to be characterized experimentally. The third highlight is the discovery of numerous families of ancillary CRISPR-linked genes, often implicated in signal transduction. Together, these findings substantially clarify the functional diversity and evolutionary history of CRISPR-Cas.

Genome editing with CRISPR–Cas nucleases, base editors, transposases and prime editors

Abstract: The development of new CRISPR-Cas genome editing tools continues to drive major advances in the life sciences. Four classes of CRISPR-Cas-derived genome editing agents-nucleases, base editors, transposases/recombinases and prime editors-are currently available for modifying genomes in experimental systems. Some of these agents have also moved rapidly into the clinic. Each tool comes with its own capabilities and limitations, and major efforts have broadened their editing capabilities, expanded their targeting scope and improved editing specificity. We analyze key considerations when choosing genome editing agents and identify opportunities for future improvements and applications in basic research and therapeutics.

CRISPR technologies and the search for the PAM-free nuclease

Abstract: The ever-expanding set of CRISPR technologies and their programmable RNA-guided nucleases exhibit remarkable flexibility in DNA targeting. However, this flexibility comes with an ever-present constraint: the requirement for a protospacer adjacent motif (PAM) flanking each target. While PAMs play an essential role in self/nonself discrimination by CRISPR-Cas immune systems, this constraint has launched a far-reaching expedition for nucleases with relaxed PAM requirements. Here, we review ongoing efforts toward realizing PAM-free nucleases through natural ortholog mining and protein engineering. We also address potential consequences of fully eliminating PAM recognition and instead propose an alternative nuclease repertoire covering all possible PAM sequences.