Serum starvation-induced cell cycle synchronization stimulated mouse rDNA transcription reactivation during somatic cell reprogramming into iPSCs

Early inhibition of BRD4 facilitates iPSC reprogramming via accelerating rDNA dynamic expression

BACKGROUND

iPSC reprogramming technology exhibits significant promise in the realms of clinical therapeutics, disease modeling, pharmaceutical drug discovery, and various other applications. However, the extensive utilization of this technology has encountered impediments in the form of inefficiency, prolonged procedures, and ambiguous biological processes. Consequently, in order to improve this technology, it is of great significance to delve into the underlying mechanisms involved in iPSC reprogramming. The BET protein BRD4 plays a crucial role in the late stage of reprogramming; however, its precise function in the early stage remains unclear.

RESULTS

Our study aims to investigate BRD4's role in the early stages of iPSC reprogramming. Our investigation reveals that early inhibition of BRD4 substantially enhances iPSC reprogramming, whereas its implementation during the middle-late stage impedes the process. During the reprogramming, ribosome DNA expression initially increases before decreasing and then gradually recovers. Early inhibition of BRD4 improved the decline and restoration of rDNA expression in the early and middle-late stages, respectively. Additionally, we uncovered the mechanism of BRD4's regulation of rDNA transcription throughout reprogramming. Specifically, BRD4 interacts with UBF and co-localizes to both the rDNA promoter and enhancer regions. Ultimately, BRD4 facilitates rDNA transcription by promoting the enrichment of histone H3 lysine 27 acetylation in the surrounding chromatin. Moreover, we also discovered that early inhibition of BRD4 facilitates cells' transition out of the somatic cell state and activate pluripotent genes.

CONCLUSIONS

In conclusion, our results demonstrate that early inhibition of BRD4 promotes sequential dynamic expression of rDNA, which improves iPSC reprogramming efficiency.

Serum starvation is as efficient as roscovitine on the cycle synchronization in G0/G1 of red-rumped agouti fibroblasts

Fibroblast cycle synchronization in G0/G1 is an essential step for nuclear reprogramming by cloning or induced cells to pluripotency. Considering the diversity among rodents and the ecological and scientific importance of these animals, we compared the contact inhibition, serum starvation, and 10 µM of roscovitine as methods of synchronization of red-rumped agouti fibroblasts. The effects of each protocol were evaluated on the percentage of cycle phase, morphology, viability, and apoptosis levels. The results showed that culturing the cells to serum starvation for 24 h (75.9%), 48 h (81.6%), 72 h (86.2%), 96 h (84.0%), and 120 h (83.7%) yielded a significantly higher percentage of cells arrested in the G0/G1 (P < 0.05) phase than cells not subjected to any cell cycle synchronization method (31.4%). Also, this effect was not different between the times of 48 and 120 h (P > 0.05). A similar response was observed for cells cultured with roscovitine for 12 h (86.9%), 24 h (74.8%), and 48 h (81.7%), with a higher percentage of synchronized cells in G0/G1 compared to cells not submitted to any synchronization treatment (52.2%). Nevertheless, this effect was best evidenced at 12 h (P < 0.05). Also, the contact inhibition for 24-120 h could not synchronize cells in G0/G1, with values ranging from 70.9 to 77.9% (P > 0.05). Moreover, no difference was observed for morphology, viability, and apoptosis levels in any synchronization method (P > 0.05). Therefore, serum starvation is as efficient as roscovitine on cycle synchronization in G0/G1 of red-rumped agouti fibroblasts.

Epigenetic regulation and factors that influence the effect of iPSCs-derived neural stem/progenitor cells (NS/PCs) in the treatment of spinal cord injury

Spinal cord injury (SCI) is a severe neurological disorder that causes neurological impairment and disability. Neural stem/progenitor cells (NS/PCs) derived from induced pluripotent stem cells (iPSCs) represent a promising cell therapy strategy for spinal cord regeneration and repair. However, iPSC-derived NS/PCs face many challenges and issues in SCI therapy; one of the most significant challenges is epigenetic regulation and that factors that influence this mechanism. Epigenetics refers to the regulation of gene expression and function by DNA methylation, histone modification, and chromatin structure without changing the DNA sequence. Previous research has shown that epigenetics plays a crucial role in the generation, differentiation, and transplantation of iPSCs, and can influence the quality, safety, and outcome of transplanted cells. In this study, we review the effects of epigenetic regulation and various influencing factors on the role of iPSC-derived NS/PCs in SCI therapy at multiple levels, including epigenetic reprogramming, regulation, and the adaptation of iPSCs during generation, differentiation, and transplantation, as well as the impact of other therapeutic tools (e.g., drugs, electrical stimulation, and scaffolds) on the epigenetic status of transplanted cells. We summarize our main findings and insights in this field and identify future challenges and directions that need to be addressed and explored.

Effects of Incubation Time and Method of Cell Cycle Synchronization on Collared Peccary Skin-Derived Fibroblast Cell Lines

The success of cloning by somatic cell nuclear transfer depends on the efficiency of nuclear reprogramming, with the cycle stage of the donor cell playing a crucial role. Therefore, the aim was to evaluate three different approaches for cell cycle synchronization: (i) serum starvation (SS) for 1 to 4 days, (ii) contact inhibition (CI) for 1 to 3 days, and (iii) using cell cycle regulatory inhibitors (dimethyl sulfoxide, cycloheximide, cytochalasin B, or 6-dimethylaminopurine) for 1 and 2 days, in terms of their effects on synchronization in G0/G1 phases and viability of collared peccary skin fibroblasts. Flow cytometry analysis revealed that SS for 4 days (79.0% ± 1.6) and CI for 3 days (78.0% ± 1.4) increased the percentage of fibroblasts in G0/G1 compared to growing cells GC (68.1% ± 8.6). However, SS for 3 and 4 days reduced the viability evaluated by differential staining (81.4% ± 0.03 and 81.6% ± 0.06) compared to growing cells (GC, 95.9% ± 0.06). CI did not affect the viability at any of the analyzed time intervals. No cell cycle inhibitors promoted synchronization in G0/G1. These results indicate that CI for 3 days was the most efficient method for cell cycle synchronization in peccary fibroblasts.

Effect of cell cycle synchronization on cadmium-induced apoptosis and necrosis in NRK-52E cells

Heavy metal pollution is a problem that cannot be ignored. Due to the prevalence of cadmium in the environment and its harmful effects on humans, cadmium pollution has become a research hotspot recently. The mechanism of cadmium-induced toxicity has also drawn much attention and most studies have been conducted using whole cells, but the toxicological mechanism of cadmium remains unclear. In this study, we aimed to obtain NRK-52E cells at different growth stages by various methods and analyze the differences in cadmium toxicity. The results show that the cadmium sensitivity of cells in each phase was different and the late apoptotic rate was increased significantly after 5 µM Cd treatment. In addition, cadmium easily induces apoptosis of G0- and S-phase cells, as well as necrosis of S- and M-phase cells, but has no significant effect on G1-phase cells. Overall, we first explored the differences in the effects of cadmium on NRK-52E cells at various growth phases. Besides, the findings of this study might provide a theoretical basis for further exploration of the toxicological mechanism of cadmium.Abbreviations Cd: cadmium; CDK: cyclin-dependent kinases; DAPI 2-(4-amidinophenyl)-1H-indole-6-carboxamidine; TBST: Tris-buffered saline with Tween-20; PI: propidium iodide; DMEM: Dulbecco's Modified Eagle Medium; BCA: bicinchoninic acid.

Transient inhibition of rDNA transcription in donor cells improves ribosome biogenesis and preimplantation development of embryos derived from somatic cell nuclear transfer

Ribosomal DNA (rDNA) transcription is a limiting step in ribosome biogenesis, crucial for protein synthesis and cell growth-especially at the early stages of embryonic development-and is regulated in a mammalian target of rapamycin (mTOR)-dependent manner. Our previous report demonstrated that treatment with mTOR inhibitors during artificial embryonic activation improved the development of embryos derived from somatic cell nuclear transfer (SCNT). We hypothesize that inhibition of ribosome biogenesis in somatic cells facilitates reactivation of embryonic nucleolar establishment and ribosome biogenesis in SCNT embryos. Herein, we show that mTOR inhibitors suppressed ribosome biogenesis in somatic cells, and more importantly, improved development potential of SCNT embryos (blastocyst rate, 34% vs 24%). SCNT embryos derived from drug-treated somatic cells exhibited higher levels of 47S, 18S, and 5S rRNAs, upstream binding factor (UBF) mRNA, ribosomal protein S6; they also improved the rebuilding of the nucleolar ultrastructure. In addition, treatment of donor cells with the RNA polymerase I (Pol I) inhibitor cx5461 caused similar effects on SCNT embryos. These results indicated that transient inhibition of rDNA transcription in donor cells facilitated the establishment of functional nucleoli and improved preimplantation development of SCNT embryos.

Ratio of the zygote cytoplasm to the paternal genome affects the reprogramming and developmental efficiency of androgenetic embryos

Uniparental embryos have uniparental genomes and are very useful models for studying the specific gene expression of parents or for exploring the biological significance of genomic imprinting in mammals. However, the early developmental efficiency of androgenetic embryos is significantly lower than that of parthenogenetic embryos. In addition, oocytes are able to reprogram sperm nuclei after fertilization to guarantee embryonic development by maternally derived reprogramming factors, which accumulate during oogenesis. However, the importance of maternal material in the efficiency of reprogramming the pronucleus of androgenetic embryos is not known. In this study, androgenetic embryos were constructed artificially by pronucleus transfer (PT) or double sperm injection (DS). Compared with DS embryos, PT embryos that were derived from two zygotes contained more maternal material, like 10-11 translocation methylcytosine deoxygenase 3 (Tet3) and histone variant 3.3 (H3.3). Our experiments confirmed the better developmental potential of PT embryos, which had higher blastocyst rates, a stronger expression of pluripotent genes, a lower expression of apoptotic genes, and superior blastocyst quality. Our findings indicate that the aggregation of more maternal materials in the paternal pronucleus facilitate the reprogramming of the paternal genome, improving embryonic development in PT androgenesis.

Conditional depletion of the RNA polymerase I subunit PAF53 reveals that it is essential for mitosis and enables identification of functional domains

Our knowledge of the mechanism of rDNA transcription has benefited from the combined application of genetic and biochemical techniques in yeast. Nomura's laboratory (Nogi, Y., Vu, L., and Nomura, M. (1991) Proc. Natl. Acad. Sci. U.S.A. 88, 7026-7030 and Nogi, Y., Yano, R., and Nomura, M. (1991) Proc. Natl. Acad. Sci. U.S.A. 88, 3962-3966) developed a system in yeast to identify genes essential for ribosome biogenesis. Such systems have allowed investigators to determine whether a gene was essential and to determine its function in rDNA transcription. However, there are significant differences in both the structures and components of the transcription apparatus and the patterns of regulation between mammals and yeast. Thus, there are significant deficits in our understanding of mammalian rDNA transcription. We have developed a system combining CRISPR/Cas9 and an auxin-inducible degron that enables combining a "genetics-like"approach with biochemistry to study mammalian rDNA transcription. We now show that the mammalian orthologue of yeast RPA49, PAF53, is required for rDNA transcription and mitotic growth. We have studied the domains of the protein required for activity. We have found that the C-terminal, DNA-binding domain (tandem-winged helix), the heterodimerization, and the linker domain were essential. Analysis of the linker identified a putative helix-turn-helix (HTH) DNA-binding domain. This HTH constitutes a second DNA-binding domain within PAF53. The HTH of the yeast and mammalian orthologues is essential for function. In summary, we show that an auxin-dependent degron system can be used to rapidly deplete nucleolar proteins in mammalian cells, that PAF53 is necessary for rDNA transcription and cell growth, and that all three PAF53 domains are necessary for its function.

Kdm6a overexpression improves the development of cloned mouse embryos

Somatic cell nuclear transfer (SCNT) is an important technique for life science research. However, most SCNT embryos fail to develop to term due to undefined reprogramming defects. Here, we show that abnormal Xi occurs in somatic cell NT blastocysts, whereas in female blastocysts derived from cumulus cell nuclear transfer, both X chromosomes were inactive. H3K27me3 removal by Kdm6a mRNA overexpression could significantly improve preimplantation development of NT embryos, and even reached a 70.2% blastocyst rate of cleaved embryos compared with the 38.5% rate of the control. H3K27me3 levels were significantly reduced in blastomeres from cloned blastocysts after overexpression of Kdm6a. qPCR indicated that rDNA transcription increased in both NT embryos and 293T cells after overexpression of Kdm6a. Our findings demonstrate that overexpression of Kdm6a improved the development of cloned mouse embryos by reducing H3K27me3 and increasing rDNA transcription.