Retrovirus-mediated conditional immortalization and analysis of established cell lines of osteoclast precursor cells

Conditional Immortalization Using SV40 Large T Antigen and Its Effects on Induced Pluripotent Stem Cell Differentiation Toward Retinal Progenitor Cells

Current treatments for retinal degenerative diseases are limited and cell replacement therapies, in tandem with a supportive biomaterial scaffold, serve as a promising emerging option. However, the development and in vitro testing of these therapies require large quantities of human retinal progenitor cells (RPCs) to thoroughly assess the impact of material properties, culture conditions, and surgical parameters on cell survival and fate to refine and optimize this approach. Although induced pluripotent stem cells (iPSCs) are an ideal cell source for human RPC derivation, large-scale production is resource-intensive and requires specialized expertise. In this study, our objective was to address this barrier by creating conditional, Tet-On SV40-T immortalized RPCs derived from human iPSCs. In our approach, we employ the Tet-On system to conditionally immortalize RPCs by inducing a SV40 large T (SV40-T) antigen, a gene known to influence cell cycle regulation and differentiation. We transduced human iPSCs with the Tet-On SV40-T system and analyzed their proliferation and RPC differentiation capabilities in the presence and absence of doxycycline (a tetracycline class of antibiotics). Our results revealed that while SV40-T immortalization increased cell proliferation, it adversely impacted the expression of crucial RPC markers (PAX6, SOX2, CHX10), leading to a significant loss of RPC identity and multipotency. This de-differentiation was irreversible, even after removing doxycycline, indicating permanent alterations in differentiation potential. Overall, this study highlights the challenges associated with generating and maintaining an immortal human RPC cell line, particularly with respect to balancing proliferation and differentiation. Our findings prompt further research into optimizing conditional immortalization techniques, culture conditions, and proliferation timing to maintain the integrity and functional characteristics of RPCs. Such advancements are crucial for reducing labor and costs associated with in vitro testing of therapeutics as we work toward the development of improved stem cell-based interventions for retinal disease.

Rac1 and Rac2 in osteoclastogenesis: a cell immortalization model

Cell lines generated from primary cells with a particular gene deletion are useful for examining the function of the specific deleted genes and provide the opportunity to genetically rescue the lost genes using standard gene transfection techniques. In the present study, bone marrow monocytes from wild-type (WT), Rac1 null, and Rac2 null mice were primed with macrophage colony-stimulating factor and soluble receptor activator of NF-kappaB ligand to generate preosteoclasts. This was followed by transduction of a retrovirus containing simian virus 40 large T-antigen and a neomycin-resistant cassette. Seven to 19 immortalized cell lines from each genotype were established. Among them, WT2, Rac1 null-D9, and Rac2 null-A2 were characterized to verify that osteoclastogenesis and osteoclast functions were identical to the parental primary cells. Results showed that immortalized WT2 cells were able to differentiate into mature, multinucleated, functional, tartrate-resistant acid phosphatase-positive osteoclasts. Immortal Rac1 null cells, as with their primary cell counterparts, displayed a severe defect in osteoclastogenesis and function. Transfection of the Rac1 gene into Rac1 null cells was sufficient to rescue osteoclastogenesis. We believe this method of generating immortalized preosteoclasts will provide a key tool for studying the signaling mechanisms involved in osteoclastogenesis.

A novel immortalization vector for the establishment of penaeid shrimp cell lines

Cell immortalization technology based on gene transfer has been successfully used to generate cell lines from a wide variety of cell types. The inability to stably introduce and express foreign genes has hampered application of this strategy in shrimp cells. We report here the use of replication-defective pantropic retrovirus to achieve a novel immortalization vector in which simian virus 40 large T antigen (SV40T) gene is expressed from Moloney murine leukemia virus (MoMLV) promoter. Data confirmed the presence of transferred SV40T gene and its stable mRNA expression in transduced lymphoid cells of Penaeus chinensis. The transduced cells showed a higher growth rate and a longer replication life-span compared with their untransduced counterparts. These results indicate the pantropic retrovirus-based immortalization-inducing gene delivery system is a potential tool for establishing cell lines from shrimp.