Signiture Assignment Biol 1610

Ema Condori-Teves Professor Carpenter BIOL1610 2 April 2019 Article Summary-Signature Assignment Use of gene-editing technology to introduce targeted modifications in pigs by Junghyun Ryu1, Randall S. Prather2,3 and Kiho Lee Article Summary Manipulation and altering of the genome in organisms have been around for millennia through selective breeding and other means to alter more desirable phenotypes. Genetically Modified animals have been a resource that has helped make major developments in the biomedicine field. Mouse models have been useful due to their ability to reproduce/develop quickly, and their short generation time which has allowed for many studies to have been conducted. The disadvantage to using genetically engineered mice has been partially due to the anatomical and physiological difference between animals and humans which has not allowed for mice to accurately represent certain human diseases. Pigs on the other hand, have similar: physiology, anatomy, immunology, and metabolic features that allow them to more closely replicate the human phenotype of human diseases. An advantage of genetically engineered mice that genetically engineered pigs lack is the ability for embryonic stem (ES) cells to be used for genetic engineering which allows for site specific or targeted modifications. Embryonic stem cells are traditionally produced by introducing targeted modifications through somatic cell nuclear transfer (SCNT) which can be an expensive and time-consuming process to de performed-on pigs. However, developments of engineered endonucleases have helped overcome this obstacle. So far, there are three types of engineered endonucleases: Zinc-Finger Nucleases (ZFNs), Transcription Activator-like Effector Nucleases (TALENs), and Clustered Regularly Interspaced

Short Palindromic Repeat (CRISPR/Cas 9 system). These engineered endonucleases systems work by using DNA double-strand break (DSB) to introduce targeted modifications into the genome. This double strand breaks works as molecular scissors by targeting a specific location on the genome which will then cause for endogenous DNA processes During this repair, if a DNA donor is available then site specific recombination through homology-directed repair (HDR) occurs, if no DNA donor is available then non-homologous end joining (NHEJ) occurs. In NHEJ, which more commonly occurs, DNA insertion or deletions (indels) create targeted gene knockouts. Zinc Finger Nucleotides was the first among the three engineered endonucleases. Although this method of gene knockout was used successfully in smaller organisms, it was not common for larger organisms. ZFNs used to generate genetically engineered pigs dramatically reduced the time necessary to produce a GE pig although side effects included difficulty assembling effective ZFN pairs. Transcription Activator-like effector nucleuses was developed from pathogenic plant bacteria. TALENs have been more successfully applied to GE pig production because they provide more flexibility in target sequences than ZFNs. Site specific modifications using TALENs have proposed pigs to be resistant to African Swine Fever Virus. The application of CRISPR in pigs was by introducing the system into developing zygotes. The CRISPR system has so far proven to be successful through its direct injection of endonucleases into zygotes although a portion of animals born using this method have had developmental defects. CRISPR gene knock-in systems have also bee used with some rates of succession as well. Success in gene-editing have shown that pigs can be used as good biomedical models because of their anatomical, physiological, and genetic similarities to humans. Genetically

editing pigs are also generated quickly which reduces the cost required to perform these studies successfully where it would otherwise take decades to do through conventional genetic engineering technology. Although there are still many concerns, there have been many suggestions and strategies presented to try and overcome these shortcomings and advancements in biomedicine seems promising with the introduction of gene-editing technology.