Effects of RAD51-stimulatory compound 1 (RS-1) and its vehicle, DMSO, on pig embryo culture

Authors: LUCAS, CAROL - University Of Missouri; Redel, Bethany; CHEN, PAULA - University Of Missouri; SPATE, LEE - University Of Missouri; PRATHER, RANDALL - University Of Missouri; WELLS, KEVIN - University Of Missouri

Submitted to: Reproductive Toxicology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/11/2021
Publication Date: 10/1/2021
Citation: Lucas, C.G., Redel, B.K., Chen, P.R., Spate, L.D., Prather, R.S., Wells, K.D. 2021. Effects of RAD51-stimulatory compound 1 (RS-1) and its vehicle, DMSO, on pig embryo culture. Reproductive Toxicology. 105:44-52. https://doi.org/10.1016/j.reprotox.2021.08.002.
DOI: https://doi.org/10.1016/j.reprotox.2021.08.002

Interpretive Summary: Producing pigs with improved agricultural traits or for validating biomedical models for human health by using a DNA knock-in approach in embryos is currently a very inefficient process. Several strategies have been tested to attempt to improve the efficiency of the incorporation of a site-specific DNA sequence into the genome of rabbit and cow embryos, including the use of a specific compound called RS-1. Here, we assessed the effects of RS-1 on pig embryo development and viability. The addition of RS-1 during embryo culture did not have a negative effect on embryo development or the viability of piglets born after embryos were transferred to a recipient sow. The resulting piglets were healthy, did not show any malformations, and almost half of them had edited DNA. Additional research with RS-1 may document improved efficiency in pig DNA knock-in events in the future.

Technical Abstract: Pigs have become an important model for agricultural and biomedical purposes. The advent of genomic engineering tools, such as the CRISPR/Cas9 system, has facilitated the production of livestock models with desired modifications. However, precise site-specific modifications in pigs through the homology-directed repair (HDR) pathway remains a challenge. In mammalian embryos, the use of small molecules to inhibit non-homologous end joining (NHEJ) or to improve HDR have been tested, but little is known about their toxicity. The compound RS-1 stimulates the activity of the RAD51 protein, which plays a key role in the HDR mechanism, demonstrating enhancement of HDR events in rabbit and bovine zygotes. Thus, in this study, we evaluated the dosage and temporal effects of RS-1 on porcine embryo development and viability. Additionally, we assessed the effects of its vehicle, DMSO, during embryo in vitro culture. Transient exposure to 7.5 µM of RS-1 did not adversely affect early embryo development and was compatible with subsequent development to term. Additionally, low concentrations of its vehicle, DMSO, did not show any toxicity to in vitro produced embryos. The transient use of RS-1 at 7.5 µM during in vitro culture seems to be the best protocol of choice to reduce the potentially toxic effects of RS-1 while attempting to improve HDR in the pig. Direct injection of the CRISPR/Cas9 system, combined with strategies to increase the frequency of targeted modifications via HDR, have become an important tool to simplify and accelerate the production of genetically modified livestock models.