To better highlight the great content contributed by our bloggers each and every month, we've decided to start an "Editor's Choice" series. Each month, I'll summarize the most popular post of the month and point out one or more additional posts that deserve a peek in case you missed them.

Update (November 18, 2016): Researchers from a variety of institutions recently reported their inability to recapitulate the results of Gao et al 2016 in a letter to Protein & Cell.

Update (August 3rd, 2017) THE ORIGINAL NgAgo ARTICLE DISCUSSED IN THIS POST HAS BEEN RETRACTED AND FOLLOW UP STUDIES HAVE FAILED TO DEMONSTRATE GENOME EDITING BY THIS TOOL

This post was contributed by guest blogger Pooran Dewari. Any views in this post are those of the guest blogger and do not necessarily represent the views of Addgene. Addgene performs Sanger sequencing on select regions of all distributed plasmids as part of quality control, but does not perform functional tests.

The newest genome engineer sharing the stage with much-lauded CRISPR-Cas9 is DNA-guided endonuclease NgAgo! We'll discuss how NgAgo is faring with users in a minute, but, to start, let's review why NgAgo is in the spotlight and take a moment to remember that NgAgo has only been available for genome editing for a few months. More time is required for its optimization and development before it can truly be pitted against CRISPR head-to-head. 

This post was contributed by guest blogger, Kristian Laursen from Cornell University.

Site directed mutagenesis is a highly versatile technique that can be used to introduce specific nucleotide substitutions (or deletions) in a tailored manner. The approach can be used in conventional cloning (to introduce or remove restriction sites), in mapping of regulatory elements (to mutate promoters/enhancers in reporter constructs), in functional analysis of proteins (to perform alanine scanning mutagenesis or targeted substitution of key residues), and in SNP analysis (to introduce naturally occuring SNPs in a plasmid context). The technique is also highly relevant in this age of CRISPR; site-directed mutagenesis generally applies to plasmids, but may also facilitate genome editing. Tailored mutations are commonly introduced to endogeneous DNA through homology-directed repair (HDR) of a CRISPR/Cas9 induced double-stranded break. This site-directed genome editing requires a template of high homology to the endogenous target, yet to facilitate the repair, the template should be resistant to Cas9 cleavage. If a plasmid contains the template, site-directed mutagenesis can be used to mutate the PAM sequence (an NGG sequence critical for Cas9 cleavage), thereby rendering the resulting construct resistant to Cas9 induced cleavage.

This post was contributed by guest blogger Nathaniel Roquet, a PhD student in the Harvard Biophysics program and researcher in the Lu Lab at MIT.

Note: The following blog post reduces the content of our paper, “Synthetic recombinase-based state machines in living cells” (1), into a more straight-forward, concise explanation of how to adapt our engineered devices, recombinase-based state machines for your own experimental needs. For more context, exposition, and detail, please refer to the paper.

Why Might One Be Interested in State Machine Technology?

Biological research has produced a massive amount of information regarding which regulatory proteins, signaling molecules, mutations, and environmental conditions drive certain cellular behaviors, but little is known about the order or timing of these factors. Recombinase-based state machines (RSMs), which take on a particular DNA-sequence configuration (state) based on the identity and order of a particular set of inputs, may be used to better understand and engineer cellular processes that are influenced by temporally ordered biochemical events.

This post was contributed by guest blogger Didem Goz Ayturk, a Postdoctoral Fellow in Connie Cepko’s Lab at Harvard Medical School with edits from Addgenie Karen Guerin.

Adeno-associated virus (AAV) has emerged as a favorite viral tool for both research and clinical applications. AAV can be used to transiently express a gene of interest in a variety of cell types. It was first described about 50 years ago as a contaminant of adenoviral preparations, hence the name (Atchison et al., 1965) AAV is a single stranded, DNA virus belonging to the family Parvoviridae. It has a "simple" genome packaged in an icosahedral capsid. It does not have a lipid coat, also called an envelope, and thus cannot support the addition of a glycoprotein, such as VSV-G, to its surface. In research applications, the genome is typically gutted so that precious cargo space is opened for gene delivery, and for safety. You can easily complement the virus in a tissue culture setting, in other words “in trans”, by supplying the genes that encode the replicase functions and capsid proteins. This gives researchers the ability to produce more virus in a controlled setting. Even though AAV is isolated from a wide range of organisms, it has not been associated with disease, and it is considered a biosafety level 1 (BSL1) viral agent.