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Time course of transcriptional reprogramming in bovine nuclear transfer embryos

ABSTRACT: Somatic cell nuclear transfer (SCNT) into an enucleated oocyte can reprogram a differentiated nucleus to a totipotent state. However, the time course of transcriptional reprogramming has not been determined. To monitor the inactivation of somatic genes after SCNT in the bovine model system, we determined transcript levels of 159 genes highly expressed in fetal fibroblast nuclear donor cells, but not in metaphase II recipient oocytes. For 18 of these genes significantly higher transcript levels were found in four-cell SCNT embryos compared with four-cell embryos derived by in vitro fertilization (IVF), indicating incomplete silencing of somatic genes at this stage. RNA sequencing revealed that nearly 600 genes with no transcripts in oocytes were activated in eight-cell IVF embryos, in agreement with major embryonic genome activation (EGA). De novo transcription in SCNT embryos was delayed (16 genes before the 16-cell stage, 300 and >800 genes at the 16-cell and blastocyst stages). Intron-containing primary transcripts as another option to detect embryonic gene transcription revealed activation of >2,200 genes in IVF embryos at the eight-cell stage, while only 828 genes were activated in SCNT embryos. At the 16-cell stage, a higher number of activated genes was found in SCNT (1,917) than in IVF embryos (738). Self-organizing tree algorithm clustering confirmed that in SCNT embryos transcription of genes that are normally activated during major EGA is delayed. Our study provides detailed insight into the timing of genome activation in cloned embryos that is substantially different from IVF embryos in spite of similar developmental kinetics.

ORGANISM(S): Bos taurus

PROVIDER: GSE125724 | GEO | 2021/05/31

REPOSITORIES: GEO

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Project description:Although somatic cell nuclear transfer (SCNT) cloning is more efficient in bovine than in all other species tested so far, there is a high rate of pregnancy failure that has been linked to structural and functional abnormalities of the placenta. We tested the hypothesis that these changes may originate from disturbed embryo-maternal interactions in the pre-implantation period. Therefore, we evaluated the transcriptome response of the endometrium to SCNT embryos (produced from five different donor cell cultures) as compared to embryos derived from in vitro fertilization (IVF). SCNT embryos and IVF embryos were cultured under identical conditions to the blastocyst stage (Day 8) and transferred to recipients. The recipients were slaughtered at day 18 of pregnancy and the uterus was recovered. Pregnancy was verified by the presence of at least one normally developed embryo. Transcriptome profiling of endometrium samples using a custom cDNA microarray covering transcripts expressed in the endometrium and/or oviduct epithelium revealed 58 transcripts that were differently abundant between endometrium samples from SCNT vs. IVF pregnancies. Prominent examples are NR2F2 (encoding the orphan nuclear receptor COUP-TFII) and GJA1 (encoding connexin 43). Both transcripts are known to play important roles in placentation and were significantly less abundant in endometrium from SCNT vs. IVF pregnancies. These findings suggest that placental failure in bovine clone pregnancies may originate from abnormal embryo-maternal communication already in the pre- or peri-implantation period. Endometrium transcriptome profiles may serve as a novel readout to evaluate SCNT embryos for their ability to induce pregnancy with a functional placenta. Keywords: response to different embryos Nineteen German Fleckvieh (Simmental) heifers were slaughtered at day 18 of pregnancy. Cycle-synchronized recipient heifers received either IVP or SCNT embryos at day 7 of the estrous cycle. Animals were slaughtered at day 18. Endometrial (intercaruncular) tissue samples were obtained from 10 pregnant animals after transfer of IVP embryos and from 9 pregnant animals after transfer of SCNT embryos.

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Time course of transcriptional reprogramming in bovine nuclear transfer embryos

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