Genetic reprogramming of transcription factor ap-2gamma in bovine somatic cell nuclear transfer preimplantation embryos and placentomes

Transcription factor AP-2 gamma affects porcine early embryo development by regulating epigenetic modification

RESEARCH QUESTION

What is the role and mechanism of action of transcription factor AP-2 gamma (TFAP2C) in porcine early embryo development?

DESIGN

TFAP2C siRNA were injected into porcine oocytes, which subsequently underwent IVF. Different stages of embryos were collected for RNA sequencing, quantitative polymerase chain reaction, immunofluorescence staining to explore the affects in gene expression and epigenetic modification. Porcine fetal fibroblasts were transfected with siRNA, and cells were collected for chromatin immunoprecipitation and dual luciferase reporter assays.

RESULTS

The deficiency of TFAP2C led to disorders in early embryonic development; 1208 genes were downregulated and 792 genes were upregulated in TFAP2C knockdown (TFAP2C-KD) embryos. The expression of epigenetic modification enzymes KDM5B, SETD2 were significantly elevated in the TFAP2C-KD group (P < 0.001). Meanwhile, the modification levels of H3K4me3 and H3K4me2 were significantly decreased (P = 0.0021, P = 0.0029), and H3K36me3 and DNA methylation were significantly increased in TFAP2C-KD group (P = 0.0045, P = 0.0025). DNMT1 was mainly expressed in nuclei in the TFAP2C-KD group (P = 0.0103). In addition, TFAP2C could bind to the promoter region of SETD2, and the mutation of the TFAP2C binding site resulted in increased activity of SETD2 promoter (P < 0.001).

CONCLUSIONS

The knockdown of TFAP2C affects early embryonic development by regulating histone modification and DNA methylation.

The landscape of accessible chromatin in bovine oocytes and early embryos

Chromatin reorganization governs the regulation of gene expression during preimplantation development. However, the landscape of chromatin dynamics in this period has not been explored in bovine. In this study, we constructed a genome-wide map of accessible chromatin in bovine oocytes and early embryos using an improved assay for transposase-accessible chromatin with high-throughput sequencing (ATAC-seq) which revealed unique features of the accessible chromatin during bovine early embryo development. We found that chromatin accessibility is low in oocytes and 2-/4-cell embryos, followed by a significant increase in embryos during major embryonic genome activation (EGA), and peaked in elongating day 14 embryos. Genome-wide characteristics of open chromatin showed that ATAC-seq signals in both transcription start sites (TSS) and transcription end sites (TES) were strong. Additionally, the distal ATAC-seq peaks were enriched in repeat elements in a type-specific and stage-specific manner. We further unveiled a series of transcription factor (TF) motifs with distinct variation of enrichment from distal ATAC-seq peaks. By integrated analysis of chromatin accessibility with transcriptomes and DNA methylomes in bovine early embryos, we showed that promoter accessibility was positively correlated with gene expression, especially during major EGA, and was strongly correlated to DNA methylation and CpG density. Finally, we identified the critical chromatin signatures and TFs that differ between in vivo and in vitro derived blastocysts, which provides insights to the potential mechanisms leading to low quality of embryos produced in vitro. Together, this comprehensive analysis revealed critical features of chromatin landscape and epigenetic reprogramming during bovine preimplantation embryo development.

Expression and function of transcription factor AP-2? in early embryonic development of porcine parthenotes

Transcription factor AP-2? (TFAP2C) is a member of the transcription factor activating enhancer binding protein (AP) family. In the present study we determined the temporal and spatial expression patterns of TFAP2C in porcine parthenotes during preimplantation development. Porcine TFAP2C transcripts were expressed at all stages of preimplantation development, with highest expression at the 8-cell stage. In contrast with the mouse, TFAP2C protein was not restricted to the trophectoderm and was also detected in the ICM in blastocyst stage porcine parthenotes. In knockdown (KD) experiments, most TFAP2C-depleted embryos were arrested before the compacted 8-cell stage. This developmental failure is attributed to abnormal expression of genes involved in cell adhesion, tight junction biogenesis and cell proliferation. Interestingly, although the conserved region 4 (CR4) of the porcine OCT4 5? upstream regionlacked the AP2C-binding motif, OCT4 transcript levels were elevated in porcine TFAP2C-KD 8-cell embryos, suggesting TFAP2C may be involved in the regulation of OCT4 in porcine embryos through other mechanisms. In summary, the results suggest that TFAP2C is necessary for the transition from de novo transcript synthesis by activation to compaction and further development, and the different expression patterns of TFAP2C in porcine embryos may reflect species-specific functions during preimplantation embryo development.

Analysis of circulating DNA distribution in pregnant and nonpregnant dairy cows

Circulating nucleic acids (CNAs) are free-floating, cell-free DNA and RNA molecules in the circulation of healthy and diseased humans and animals. The aim of this study was to identify differences in CNA distribution in serum samples from multiparous pregnant (n = 24) and nonpregnant (n = 16) dairy cows at different days of gestation (Days 0, 20, and 40). A modified serial analysis of gene expression procedure was used to generate concatemerized short sequence tags from isolated serum DNA. A total of 6.1 × 10(6) tags were recovered from analyzed samples (n = 40). Significant differences between the pregnant and nonpregnant groups were detected in chromosomal regions, protein-coding sequences, and single genes (P < 0.05). Approximately 23% (1.4 × 10(6) tags) of the total sequence pool were present exclusively in the analyzed serum samples of pregnant cows. Of these tag sequences, seven originated from genomic regions and 13 from repetitive elements. Comparative BLAST analysis identified the repetitive tags as BovB (non-long terminal repeat retrotransposons/long interspersed nuclear elements), Art2A, BovA2, and Bov-tA2 (short interspersed nuclear elements). To our knowledge, this is the first study to comprehensively characterize the circulating, cell-free DNA profile in sera from pregnant and nonpregnant cows across early gestation.

Abnormal levels of transcript abundance of developmentally important genes in various stages of preimplantation bovine somatic cell nuclear transfer embryos

Based on microarray data comparing gene expression of fibroblast donor cells and bovine somatic cell nuclear transfer (SCNT) and in vivo produced (AI) blastocysts, a group of genes including several transcription factors was selected for evaluation of transcript abundance. Using SYBR green-based real-time polymerase chain reaction (Q-PCR) the levels of POU domain class 5 transcription factor (Oct4), snail homolog 2 (Snai2), annexin A1 (Anxa1), thrombospondin (Thbs), tumor-associated calcium signal transducer 1 (Tacstd1), and transcription factor AP2 gamma (Tfap2c) were evaluated in bovine fibroblasts, oocytes, embryos 30 min postfusion (SCNT), 12 h postfertilization/activation, as well as two-cell, four-cell, eight-cell, morula, and blastocyst-stage in vitro fertilized (IVF) and SCNT embryos. For every gene except Oct4, levels of transcript were indistinguishable between IVF and SCNT embryos at the blastocyst stage; however, in many cases levels of these genes during stages prior to blastocyst differed significantly. Altered levels of gene transcripts early in development likely have developmental consequences downstream. These results indicate that experiments evaluating gene expression differences between control and SCNT blastocysts may underestimate the degree of difference between clones and controls, and further offer insights into the dynamics of transcript regulation following SCNT.