Lagging Strand Initiation Processes in DNA Replication of Eukaryotes-Strings of Highly Coordinated Reactions Governed by Multiprotein Complexes

In their influential reviews, Hanahan and Weinberg coined the term 'Hallmarks of Cancer' and described genome instability as a property of cells enabling cancer development. Accurate DNA replication of genomes is central to diminishing genome instability. Here, the understanding of the initiation of DNA synthesis in origins of DNA replication to start leading strand synthesis and the initiation of Okazaki fragment on the lagging strand are crucial to control genome instability. Recent findings have provided new insights into the mechanism of the remodelling of the prime initiation enzyme, DNA polymerase α-primase (Pol-prim), during primer synthesis, how the enzyme complex achieves lagging strand synthesis, and how it is linked to replication forks to achieve optimal initiation of Okazaki fragments. Moreover, the central roles of RNA primer synthesis by Pol-prim in multiple genome stability pathways such as replication fork restart and protection of DNA against degradation by exonucleases during double-strand break repair are discussed.

A comprehensive study of p53 protein

The protein p53 has been extensively investigated since it was found 43 years ago and has become a "guardian of the genome" that regulates the division of cells by preventing the growth of cells and dividing them, that is, inhibits the development of tumors. Initial proof of protein existence by researchers in the mid-1970s was found by altering and regulating the SV40 big T antigen termed the A protein. Researchers demonstrated how viruses play a role in cancer by employing viruses' ability to create T-antigens complex with viral tumors, which was discovered in 1979 following a viral analysis and cancer analog research. Researchers later in the year 1989 explained that in Murine Friend, a virus-caused erythroleukemia, commonly found that p53 was inactivated to suggest that p53 could be a "tumor suppressor gene." The TP53 gene, encoding p53, is one of human cancer's most frequently altered genes. The protein-regulated biological functions of all p53s include cell cycles, apoptosis, senescence, metabolism of the DNA, angiogenesis, cell differentiation, and immunological response. We tried to unfold the history of the p53 protein, which was discovered long back in 1979, that is, 43 years of research on p53, and how p53's function has been developed through time in this article.

Immortalization of primary sheep embryo kidney cells

Sheep primary epithelial cells are short-lived in cell culture systems. For long-term in vitro studies, primary cells need to be immortalized. This study aims to establish and characterize T immortalized sheep embryo kidney cells (TISEKC). In this study, we used fetal lamb kidneys to derive primary cultures of epithelial cells. We subsequently immortalized these cells using the large T SV40 antigen to generate crude TISEKC and isolate TISEKC clones. Among numerous clones of immortalized cells, the selected TISEKC-5 maintained active division and cell growth over 20 passages but lacked expression of the oncogenic large T SV40 antigen. Morphologically, TISEKC-5 maintained their epithelial aspect similar to the parental primary epithelial cells. However, their growth properties showed quite different patterns. Crude TISEKC, as well as the clones of TISEKC proliferated highly in culture compared to the parental primary cells. In the early passages, immortalized cells showed heterogeneous polyploidy but in the late passages the karyotype of immortalized cells became progressively stable, identical to that of the primary cells, because the TISEKC-5 cell line has lost the large SV40 T antigen expression, this cell line is a valuable tool for veterinary sciences and biotechnological productions.

Design and Testing of Vector-Producing HEK293T Cells Bearing a Genomic Deletion of the SV40 T Antigen Coding Region

The use of the human embryonic kidney (HEK) 293T cell line to manufacture vectors for in vivo applications raises safety concerns due to the presence of SV40 T antigen-encoding sequences. We used CRISPR-Cas9 genome editing to remove the SV40 T antigen-encoding sequences from HEK293T cells by transfecting them with a recombinant plasmid expressing Cas9 and two distinct single guide RNAs (sgRNAs) corresponding to the beginning and end of the T antigen coding region. Cell clones lacking T antigen-encoding sequences were identified using PCR. Whole-genome (WG) and targeted locus amplification (TLA) sequencing of the parental HEK293T cell line revealed multiple SV40 T antigen-encoding sequences replacing cellular sequences on chromosome 3. The putative T antigen null clones demonstrated a loss of sequence reads mapping to T antigen-encoding sequences. Western blot analysis of cell extracts prepared from the T antigen null clones confirmed that the SV40 large and small T antigen proteins were absent. Lentiviral vectors produced using the T antigen null clones exhibited titers up to 1.5 × 107 transducing units (TU)/mL, while the titers obtained from the parent HEK293T cell line were up to 4 × 107 TU/mL. The capacity of the T antigen-negative cells to produce high titer adeno-associated virus (AAV) vectors was also evaluated. The results obtained revealed that the lack of T antigen sequences did not impact AAV vector titers.

Establishment and functional characterization of the reversibly immortalized mouse glomerular podocytes (imPODs)

Glomerular podocytes are highly specialized epithelial cells and play an essential role in establishing the selective permeability of the glomerular filtration barrier of kidney. Maintaining the viability and structural integrity of podocytes is critical to the clinical management of glomerular diseases, which requires a thorough understanding of podocyte cell biology. As mature podocytes lose proliferative capacity, a conditionally SV40 mutant tsA58-immortalized mouse podocyte line (designated as tsPC) was established from the Immortomouse over 20 years ago. However, the utility of the tsPC cells is hampered by the practical inconvenience of culturing these cells. In this study, we establish a user-friendly and reversibly-immortalized mouse podocyte line (designated as imPOD), on the basis of the tsPC cells by stably expressing the wildtype SV40 T-antigen, which is flanked with FRT sites. We show the imPOD cells exhibit long-term high proliferative activity, which can be effectively reversed by FLP recombinase. The imPOD cells express most podocyte-related markers, including WT-1, Nephrin, Tubulin and Vinculin, but not differentiation marker Synaptopodin. The imPOD cells do not form tumor-like masses in vivo. We further demonstrate that TGFβ1 induces a podocyte injury-like response in the FLP-reverted imPOD cells by suppressing the expression of slit diaphragm-associated proteins P-Cadherin and ZO-1 and upregulating the expression of mesenchymal markers, α-SMA, Vimentin and Nestin, as well as fibrogenic factors CTGF and Col1a1. Collectively, our results strongly demonstrate that the newly engineered imPOD cells should be a valuable tool to study podocyte biology both under normal and under pathological conditions.