Delay in cleavage of porcine embryos after intracytoplasmic sperm injection (ICSI) shows poorer embryonic development

Comparison of ICSI, IVF, and in vivo derived embryos to produce CRISPR-Cas9 gene-edited pigs for xenotransplantation

Genome editing in pigs for xenotransplantation has seen significant advances in recent years. This study compared three methodologies to generate gene-edited embryos, including co-injection of sperm together with the CRISPR-Cas9 system into oocytes, named ICSI-MGE (mediated gene editing); microinjection of CRISPR-Cas9 components into oocytes followed by in vitro fertilization (IVF), and microinjection of in vivo fertilized zygotes with the CRISPR-Cas9 system. Our goal was to knock-out (KO) porcine genes involved in the biosynthesis of xenoantigens responsible for the hyperacute rejection of interspecific xenografts, namely GGTA1, CMAH, and β4GalNT2. Additionally, we attempted to KO the growth hormone receptor (GHR) gene with the aim of limiting the growth of porcine organs to a size that is physiologically suitable for human transplantation. Embryo development, pregnancy, and gene editing rates were evaluated. We found an efficient mutation of the GGTA1 gene following ICSI-MGE, comparable to the results obtained through the microinjection of oocytes followed by IVF. ICSI-MGE also showed higher rates of biallelic mutations compared to the other techniques. Five healthy piglets were born from in vivo-derived embryos, all of them exhibiting biallelic mutations in the GGTA1 gene, with three displaying mutations in the GHR gene. No mutations were observed in the CMAH and β4GalNT2 genes. In conclusion, in vitro methodologies showed high rates of gene-edited embryos. Specifically, ICSI-MGE proved to be an efficient technique for obtaining homozygous biallelic mutated embryos. Lastly, only live births were obtained from in vivo-derived embryos showing efficient multiple gene editing for GGTA1 and GHR.

Challenges and Considerations during In Vitro Production of Porcine Embryos

Genetically modified pigs have become valuable tools for generating advances in animal agriculture and human medicine. Importantly, in vitro production and manipulation of embryos is an essential step in the process of creating porcine models. As the in vitro environment is still suboptimal, it is imperative to examine the porcine embryo culture system from several angles to identify methods for improvement. Understanding metabolic characteristics of porcine embryos and considering comparisons with other mammalian species is useful for optimizing culture media formulations. Furthermore, stressors arising from the environment and maternal or paternal factors must be taken into consideration to produce healthy embryos in vitro. In this review, we progress stepwise through in vitro oocyte maturation, fertilization, and embryo culture in pigs to assess the status of current culture systems and address points where improvements can be made.

Transcriptome Analyses Reveal Differential Transcriptional Profiles in Early- and Late-Dividing Porcine Somatic Cell Nuclear Transfer Embryos

Somatic cell nuclear transfer (SCNT) is not only a valuable tool for understanding nuclear reprogramming, but it also facilitates the generation of genetically modified animals. However, the development of SCNT embryos has remained an uncontrollable process. It was reported that the SCNT embryos that complete the first cell division sooner are more likely to develop to the blastocyst stage, suggesting their better developmental competence. Therefore, to better understand the underlying molecular mechanisms, RNA-seq of pig SCNT embryos that were early-dividing (24 h postactivation) and late-dividing (36 h postactivation) was performed. Our analysis revealed that early- and late-dividing embryos have distinct RNA profiles, and, in all, 3077 genes were differentially expressed. Gene ontology (GO)and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses revealed that early-dividing embryos exhibited higher expression in genes that participated in the meiotic cell cycle, while enrichment of RNA processing- and translation-related genes was found in late-dividing embryos. There are also fewer somatic memory genes such as FLRT2, ADAMTS1, and FOXR1, which are abnormally activated or suppressed in early-dividing cloned embryos. These results show that early-dividing SCNT embryos have different transcriptional profiles than late-dividing embryos. Early division of SCNT embryos may be associated with their better reprogramming capacity, and somatic memory genes may act as a reprogramming barrier in pig SCNT reprogramming.

An efficiency comparison of different in vitro fertilization methods: IVF, ICSI, and PICSI for embryo development to the blastocyst stage from vitrified porcine immature oocytes

Background

Most studies carried out to evaluate recovery and development after porcine oocyte vitrification, reported better rates when cryopreserved in embryonic development stages or zygotes, but not in immature oocytes. For this reason, many studies are performed to improve immature oocyte vitrification protocols testing the use of different cryoprotectant concentrations, cooling devices, incubation times; but only a few of them have evaluated which fertilization procedure enhances blastocyst rates in vitrified oocytes. Therefore, this study was aimed to evaluate: 1) if the sperm selection with hyaluronic acid (HA) or polyvinylpyrrolidone (PVP) before injection could play a key role in increasing fertilization and blastocyst formation and 2) the embryo developmental ability and blastocyst production of porcine immature oocytes retrieved after vitrification-warming and co-cultured with granulosa cells during IVM, using different fertilization techniques: in vitro fertilization (IVF), intracytoplasmic sperm injection (ICSI) and conventional ICSI with hyaluronic acid (HA) sperm selection, known as physiological intracytoplasmic sperm injection (PICSI) and.

Results

Sperm selected with HA-PICSI displayed a higher percentage of live/acrosome reacted status compared to those in control and exposed to PVP. Higher dead/acrosome reacted rates were obtained after PVP exposure compared to control and HA. In oocytes, viability significantly decreased after IVM in vitrified oocytes. Besides, IVM rates were not different between control denuded oocytes cultured with granulosa cells (DO-GC) and vitrified oocytes. Regarding fertilization parameters, IVF showed higher percentages of total fertilization rate than those obtained by ICSI and PICSI. However, results demonstrate that PICSI fertilization increased the blastocysts formation rate in control DO-GC and vitrified oocytes compared to IVF and ICSI.

Conclusions

To achieve high blastocyst formation rates from vitrified GV oocytes, it is recommended that sperm should be selected with HA instead of PVP before injection since high viability and acrosome reaction rates were obtained. Also, PICSI fertilization was the best method to produce higher blastocyst rates compared to the IVF and ICSI procedures.