پیشرفت فعلی ویرایش ژنوم در دام
Abstract
1- Introduction
2- Conventional approach to generate genetically engineered livestock
3- Development of genome editing technology
4- Application of genome editing technology in livestock
5- Genetically engineered livestock produced using genome editing technology
6- Future prospective and current limitations
7- Conclusion
References
Abstract
Historically, genetic engineering in livestock proved to be challenging. Without stable embryonic stem cell lines to utilize, somatic cell nuclear transfer (SCNT) had to be employed to produce many of the genetically engineered (GE) livestock models. Through the genetic engineering of somatic cells followed by SCNT, GE livestock models could be generated carrying site-specific modifications. Although successful, only a few GE livestock models were generated because of low efficiency and associated birth defects. Recently, there have been major strides in the development of genome editing tools: Zinc-Finger Nucleases (ZFNs), Transcription activator-like effector nucleases (TALENS), and Clustered regularly interspaced short palindromic repeats (CRISPR) and CRISPR-associated 9 (Cas9) system. These tools rely on the generation of a double strand DNA break, followed by one of two repair pathways: non-homologous end joining (NHEJ) or homology directed repair (HDR). Compared to the traditional approaches, these tools dramatically reduce time and effort needed to establish a GE animal. Another benefit of utilizing genome editing tools is the application of direct injection into developing embryos to induce targeted mutations, therefore, eliminating side effects associated with SCNT. Emerging technological advancements of genome editing systems have dramatically improved efficiency to generate GE livestock models for both biomedical and agricultural purposes. Although the efficiency of genome editing tools has revolutionized GE livestock production, improvements for safe and consistent application are desired. This review will provide an overview of genome editing techniques, as well as examples of GE livestock models for agricultural and biomedical purposes.
Introduction
54 The ability to engineer the genome has been limited in livestock species, in part due to 55 the lack of stable embryonic stem (ES) cells that can contribute to the germline. In the mouse, 56 targeted disruption of genes can be performed in ES cells, then the ES cells carrying desired 57 genotypes can be introduced into recipient blastocysts to generate chimeric mice that can 58 transmit the desired genotype to the germline [1-3]. This strategy has been effective, thus 59 establishing the mouse as the main model in biomedicine to elucidate the function of target 60 genes. Since true ES cells that can contribute to the germline have not been fully identified in 61 livestock species, the development of somatic cell nuclear transfer (SCNT) technology [4] 62 allowed researchers to generate genetically engineered (GE) livestock. Genetic modification of 63 somatic cells followed by SCNT allowed for the generation of GE livestock with targeted 64 modifications [5]. Although possible, efficiency to produce GE animals through the route is poor; 65 therefore, only selective GE models have been produced [6, 7].