BackgroundCRISPR-Cas systems have been broadly embraced as effective tools for genome engineering applications, with most studies to date utilizing the Streptococcus pyogenes Cas9. Here we characterize and manipulate the smaller, 1053 amino acid nuclease Staphylococcus aureus Cas9.ResultsWe find that the S. aureus Cas9 recognizes an NNGRRT protospacer adjacent motif (PAM) and cleaves target DNA at high efficiency with a variety of guide RNA (gRNA) spacer lengths. When directed against genomic targets with mutually permissive NGGRRT PAMs, the S. pyogenes Cas9 and S. aureus Cas9 yield indels at comparable rates. We additionally show D10A and N580A paired nickase activity with S. aureus Cas9, and we further package it with two gRNAs in a single functional adeno-associated virus (AAV) vector. Finally, we assess comparative S. pyogenes and S. aureus Cas9 specificity using GUIDE-seq.ConclusionOur results reveal an S. aureus Cas9 that is effective for a variety of genome engineering purposes, including paired nickase approaches and all-in-one delivery of Cas9 and multiple gRNA expression cassettes with AAV vectors.Electronic supplementary materialThe online version of this article (doi:10.1186/s13059-015-0817-8) contains supplementary material, which is available to authorized users.
The vertebrate intestinal epithelium is renewed continuously from stem cells at the base of the crypt in mammals or base of the fold in fish over the life of the organism. As stem cells divide, newly formed epithelial cells make an initial choice between a secretory or enterocyte fate. This choice has previously been demonstrated to involve Notch signaling as well as Atonal and Her transcription factors in both embryogenesis and adults. Here, we demonstrate that in contrast to the atoh1 in mammals, ascl1a is responsible for formation of secretory cells in zebrafish. ascl1a−/− embryos lack all intestinal epithelial secretory cells and instead differentiate into enterocytes. ascl1a−/− embryos also fail to induce intestinal epithelial expression of deltaD suggesting that ascl1a plays a role in initiation of Notch signaling. Inhibition of Notch signaling increases the number of ascl1a and deltaD expressing intestinal epithelial cells as well as the number of developing secretory cells during two specific time periods: between 30 and 34 hpf and again between 64 and 74 hpf. Loss of enteroendocrine products results in loss of anterograde motility in ascl1a−/− embryos. 5HT produced by enterochromaffin cells is critical in motility and secretion within the intestine. We find that addition of exogenous 5HT to ascl1a−/− embryos at near physiological levels (measured by differential pulse voltammetry) induce anterograde motility at similar levels to wild type velocity, distance, and frequency. Removal or doubling the concentration of 5HT in WT embryos does not significantly affect anterograde motility, suggesting that the loss of additional enteroendocrine products in ascl1a−/− embryos also contributes to intestinal motility. Thus, zebrafish intestinal epithelial cells appear to have a common secretory progenitor from which all subtypes form. Loss of enteroendocrine cells reveals the critical need for enteroendocrine products in maintenance of normal intestinal motility.
The zebrafish (Danio rerio) is frequently being used to investigate the genetics of human diseases as well as resulting pathologies. Ease of both forward and reverse genetic manipulation along with conservation of vertebrate organ systems and disease causing genes has made this system a popular model. Many techniques have been developed to manipulate the genome of zebrafish producing mutants in a vast array of genes. While genetic manipulation of zebrafish has progressed, proteomics have been under-utilized. This review highlights studies that have already been performed using proteomic techniques and as well as our initial proteomic work comparing changes to the proteome between the ascl1a-/- and WT intestine.
The optimal use of many biotherapeutics is restricted by Anti-drug antibodies (ADAs) and hypersensitivity responses which can affect potency and ability to administer a treatment. Here we demonstrate that Re-surfacing can be utilized as a generalizable approach to engineer proteins with extensive surface residue modifications in order to avoid binding by pre-existing ADAs. This technique was applied to E. coli Asparaginase (ASN) to produce functional mutants with up to 58 substitutions resulting in direct modification of 35% of surface residues. Re-surfaced ASNs exhibited significantly reduced binding to murine, rabbit and human polyclonal ADAs, with a negative correlation observed between binding and mutational distance from the native protein. Reductions in ADA binding correlated with diminished hypersensitivity responses in an in vivo mouse model. By using computational design approaches to traverse extended distances in mutational space while maintaining function, protein Re-surfacing may provide a means to generate novel or second line therapies for life-saving drugs with limited therapeutic alternatives.
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