Transcription activator-like effector nucleases (TALENs) have recently arisen as effective tools for targeted genome engineering. Here, we report streamlined methods for the construction and evaluation of TALENs based on the 'Golden Gate TALEN and TAL Effector Kit' (Addgene). We diminished array vector requirements and increased assembly rates using sixmodule concatemerization. We altered the architecture of the native TALEN protein to increase nuclease activity and replaced the final destination vector with a mammalian expression/ in vitro transcription vector bearing both CMV and T7 promoters. Using our methods, the whole process, from initiating construction to completing evaluation directly in mammalian cells, requires only 1 week. Furthermore, TALENs constructed in this manner may be directly applied to transfection of cultured cells or mRNA synthesis for use in animals and embryos. In this article, we show genomic modification of HEK293T cells, human induced pluripotent stem cells, Drosophila melanogaster, Danio rerio and Xenopus laevis, using custom-made TALENs constructed and evaluated with our protocol. Our methods are more time efficient compared with conventional yeast-based evaluation methods and provide a more accessible and effective protocol for the application of TALENs in various model organisms.

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SummaryRecently, gene editing with transcription activator-like effector nucleases (TALENs) has been used in the life sciences. TALENs can be easily customized to recognize a specific DNA sequence and efficiently introduce double-strand breaks at the targeted genomic locus. Subsequent non-homologous end-joining repair leads to targeted gene disruption by base insertion, deletion, or both. Here, to readily evaluate the efficacy of TALENs in Xenopus laevis embryos, we performed the targeted gene disruption of tyrosinase (tyr) and pax6 genes that are involved in pigmentation and eye formation, respectively. We constructed TALENs targeting tyr and pax6 and injected their mRNAs into fertilized eggs at the one-cell stage. Expectedly, introduction of tyr TALEN mRNA resulted in drastic loss of pigmentation with high efficiency. Similarly, for pax6, TALENs led to deformed eyes in the injected embryos. We confirmed mutations of the target alleles by restriction enzyme digestion and sequence analyses of genomic PCR products. Surprisingly, not only biallelic but also paralogous, gene disruption was observed. Our results demonstrate that targeted gene disruption by TALENs provides a method comparable to antisense morpholinos in analyzing gene function in Xenopus F0 embryos, but also applies beyond embryogenesis to any life stage.

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Although modifications in bowel preparation are needed, CCE-2 might be feasible for assessing the severity of mucosal inflammation in patients with UC.