The development and expression of pluripotency genes in embryos derived from nuclear transfer and in vitro fertilization

Controlled Cytoplast Arrest and Morula Aggregation Enhance Development, Cryoresilience, and In Vivo Survival of Cloned Sheep Embryos

Zona-free somatic cell transfer (SCT) and embryo aggregation increase throughput and efficiency of cloned embryo and offspring production, respectively, but both approaches have not been widely adopted. Cloning efficiency is further improved by cell cycle coordination between the interphase donor cell and metaphase-arrested recipient cytoplast. This commonly involves inclusion of caffeine and omission of calcium to maintain high mitotic cyclin-dependent kinase activity and low calcium levels, respectively, in the nonactivated cytoplast. The aim of our study was to integrate these various methodological improvements into a single work stream that increases sheep cloning success. We show that omitting calcium during zona-free SCT improved blastocyst development from 6% to 13%, while caffeine treatment reduced spontaneous oocyte activation from 17% to 8%. In a retrospective analysis, morula aggregation produced high morphological quality blastocysts with better in vivo survival to term than nonaggregated controls (15% vs. 9%), particularly after vitrification (14% vs. 0%). By combining cytoplast cell cycle control with zona-free embryo reconstruction and aggregation, this novel SCT protocol maximizes the benefits of vitrification by producing more cryoresilient blastocysts. The presented cloning methodology is relatively easy to operate and further increases throughput and efficiency of cloned embryo and offspring production. Integration of additional reprogramming steps or alternate donor cells is straightforward, providing a flexible workflow that can be adapted to changing experimental requirements.

Identification of lncRNAs by RNA Sequencing Analysis During in Vivo Pre-Implantation Developmental Transformation in the Goat

Pre-implantation development is a dynamic, complex and precisely regulated process that is critical for mammalian development. There is currently no description of the role of the long noncoding RNAs (lncRNAs) during the pre-implantation stages in the goat. The in vivo transcriptomes of oocytes (n = 3) and pre-implantation stages (n=19) at seven developmental stages in the goat were analyzed by RNA sequencing (RNA-Seq). The major zygotic gene activation (ZGA) event was found to occur between the 8- and 16-cell stages in the pre-implantation stages. We identified 5,160 differentially expressed lncRNAs (DELs) in developmental stage comparisons and functional analyses of the major and minor ZGAs. Fourteen lncRNA modules were found corresponding to specific pre-implantation developmental stages by weighted gene co-expression network analysis (WGCNA). A comprehensive analysis of the lncRNAs at each developmental transition of high correlation modules was done. We also identified lncRNA-mRNA networks and hub-lncRNAs for the high correlation modules at each stage. The extensive association of lncRNA target genes with other embryonic genes suggests an important regulatory role for lncRNAs in embryonic development. These data will facilitate further exploration of the role of lncRNAs in the developmental transformation in the pre-implantation stage.

Overexpression of MBD3 Improves Reprogramming of Cloned Pig Embryos

Methyl-CpG-binding domain protein 3 (MBD3) is a core component of the nucleosome remodeling and deacetylase (NuRD) complex, which is crucial for pluripotent stem cell differentiation and embryonic development. MBD3 was shown to play important roles in transcription factor-induced somatic cell reprogramming. Expression level of MBD3 was demonstrated to be higher in somatic cell nuclear transfer-generated cloned pig embryos than in fertilization-derived porcine embryos. However, the functions of MBD3 in nuclear transfer-mediated somatic cell reprogramming are unknown. In this study, MBD3 was overexpressed in cloned pig embryos, and the effects of MBD3 overexpression on gene transcription, DNA methylation, and in vitro developmental competence of cloned pig embryos were analyzed. Results indicated that overexpression of MBD3 in cloned pig embryos not only increased blastocyst rate and number of cells per blastocyst but also upregulated mRNA expression levels and decreased the DNA methylation of NANOG, OCT4, and LINE1 genes to the levels close to those in in vivo fertilization-produced pig embryos. These findings suggest that overexpression of MBD3 improves reprogramming of cloned pig embryos.

Different Donor Cell Culture Methods Can Influence the Developmental Ability of Cloned Sheep Embryos

It was proposed that arresting nuclear donor cells in G0/G1 phase facilitates the development of embryos that are derived from somatic cell nuclear transfer (SCNT). Full confluency or serum starvation is commonly used to arrest in vitro cultured somatic cells in G0/G1 phase. However, it is controversial as to whether these two methods have the same efficiency in arresting somatic cells in G0/G1 phase. Moreover, it is unclear whether the cloned embryos have comparable developmental ability after somatic cells are subjected to one of these methods and then used as nuclear donors in SCNT. In the present study, in vitro cultured sheep skin fibroblasts were divided into four groups: (1) cultured to 70–80% confluency (control group), (2) cultured to full confluency, (3) starved in low serum medium for 4 d, or (4) cultured to full confluency and then further starved for 4 d. Flow cytometry was used to assay the percentage of fibroblasts in G0/G1 phase, and cell counting was used to assay the viability of the fibroblasts. Then, real-time reverse transcription PCR was used to determine the levels of expression of several cell cycle-related genes. Subsequently, the four groups of fibroblasts were separately used as nuclear donors in SCNT, and the developmental ability and the quality of the cloned embryos were compared. The results showed that the percentage of fibroblasts in G0/G1 phase, the viability of fibroblasts, and the expression levels of cell cycle-related genes was different among the four groups of fibroblasts. Moreover, the quality of the cloned embryos was comparable after these four groups of fibroblasts were separately used as nuclear donors in SCNT. However, cloned embryos derived from fibroblasts that were cultured to full confluency combined with serum starvation had the highest developmental ability. The results of the present study indicate that there are synergistic effects of full confluency and serum starvation on arresting fibroblasts in G0/G1 phase, and the short-term treatment of nuclear donor cells with these two methods could improve the efficiency of SCNT.