Efficient enhancement of lentiviral transduction efficiency in murine spermatogonial stem cells

Direct modification of spermatogonial stem cells using lentivirus vectors in vivo leads to efficient generation of transgenic rats

Spermatogonial stem cells (SSCs) transmit genetic information to the next progeny in males. Thus, SSCs are a potential target for germline modifications to generate transgenic animals. In this study, we report a technique for the generation of transgenic rats by in vivo manipulation of SSCs with a high success rate. SSCs in juvenile rats were transduced in vivo with high titers of lentivirus harboring enhanced green fluorescent protein and mated with wild-type females to create founder rats. These founder rats expressed the transgene and passed on the transgene with an overall success rate of 50.0%. Subsequent generations of progeny from the founder rats both expressed and passed on the transgene. Thus, direct modification of SSCs in juvenile rats is an effective means of generating transgenic rats through the male germline. This technology could be adapted to larger animals, in which existing methods for gene modification are inadequate or inapplicable, resulting in the generation of transgenic animals in a variety of species.

A standard procedure for lentiviral-mediated labeling of murine mesenchymal stromal cells in vitro

Tracking of stem cells after transplantation is effectively performed in vivo with imaging systems, assuming the cells are adequately labeled to facilitate their recognition. This study aimed to optimize a protocol for fluorescent labeling of mesenchymal stromal cells (MSCs) in vitro, by using a third-generation lentiviral system. Basically, 293T cells are seeded in high-glucose Dulbecco's modified Eagle medium with 10% FBS one day before transfection. Transfection is done for 24 h using a mix of transfer, packaging, regulatory, and envelope plasmids, in molar ratio of 4:2:1:1, respectively. After transfection, the cells are further cultured for two days. During this period, the viral medium is harvested two times, at 24-h intervals, with the first round being stored at 4°C until the second round is completed. The pooled viral medium is frozen in single-use aliquots. MSCs are transduced with 25 multiplicity of infection (MOI) and one day later the cells are passaged at standard seeding density and further grown for three days, when the fluorescence reach the maximum level. Our protocol provides particular experimental details for permanent MSC labeling that makes the procedure highly effective for therapeutic purposes, without affecting the functional properties of stem cells.

Establishment of an electroporation-mediated gene delivery system in porcine spermatogonial stem cells

Spermatogonial stem cells (SSCs) are a useful tool for the generation of genetically modified transgenic sperm. As a result, the transfer of specific genes into the cytoplasm of SSCs is crucial for the successful generation of transgenic sperm. Here, we report electroporation conditions optimized for SSCs derived from the porcine testis. The highest transfection efficiency and cell viability were observed in porcine SSCs transfected with 1 μg transgenic vector with a single electric pulse from an electroporator at a voltage of 100 V and a capacitor setting of 250 μF. The transfection efficiency and cell viability were constant regardless of the size of the transgenic vector. Furthermore, we did not detect loss of spermatozoa differentiation potential in the transfected porcine SSCs. From these results, we confirm that this electroporation-based gene delivery system can effectively introduce foreign DNA into the genome of porcine SSCs without any loss of the original porcine SSC characteristics, which will be important in the generation of mosaicism-free transgenic pigs produced from transgenic porcine sperm.

A new chemical complex can rapidly concentrate lentivirus and significantly enhance gene transduction

In this study, we developed a new purification method using chondroitin sulfate C (CSC) and protamine sulfate (PS) to concentrate lentivirus. To evaluate the efficiency of this new method, we compared it with several previously described purification protocols, including virus concentrated by ultracentrifugation (Ultra), precipitated by polyethylene glycol (PEG), and sedimented by CSC combined with polybrene (PB). After using the different methods to purify and concentrate equivalent amounts of lentivirus supernatant, the virus pellets precipitated by the different methods were resuspended using the equivalent volumes of DMEM. Subsequently, 10 μl of each lentivirus stock carrying EGFP gene was used to transduce two types of cells, human embryonic kidney 293T (HEK293T) cells and mouse mesenchymal stem cells (mMSC). It was obvious that HEK293T and mMSC appeared much intensiver green fluorescence through virus transduction from PS method than from other methods. To quantitate the transduction efficiency of the viruses, we examined virus titer in the cells after transduction using a real-time PCR-based analysis. Accordingly, we verified that PS precipitation could generate virus with a higher titer (4.39 × 10⁸ IU/ml) than PB (2.43 × 10⁸ IU/ml), Ultra (1.16 × 10⁸ IU/ml), and PEG (0.56 × 10⁸ IU/ml) in HEK293T cells. As for HEK293T cells in mMSC, the PS method also generated virus with a higher titer (4.66 × 10⁸ IU/ml) than the Ultra method (2.36 × 10⁸ IU/ml), and a much higher titer than those of the other chemical-based precipitation methods using PB (4.82 × 10⁶ IU/ml) and PEG (8.98 × 10⁴ IU/ml). Furthermore, the HEK293T cells and mMSC transduced by PS(1X)-virus appeared to have higher cell growth ratios, respectively, than the HEK293T cells and mMSC transduced by lentivirus using the other methods. We conclude that our new method for purifying lentivirus is cost-effective, time-saving, and highly efficient, and that lentivirus purification by this means could possibly be used to transduce a variety of cells, including stem cells.

Polybrene: Observations on cochlear hair cell necrosis and minimal lentiviral transduction of cochlear hair cells

Polybrene is widely used to enhance viral transduction; however, little is known about the utility thereof, in enhancing lentiviral transduction of cochlear cells. In the present study, we examined the cytotoxic effects of polybrene, and the further effects thereof, on lentiviral transduction of cochlear cells, especially sensory hair cells. Cochlear basilar membranes of newborn rats were cultured and treated with 0.1-10 μg/mL polybrene for 24h to explore the potential development of ototoxicity. PI staining and TUNEL detection were used to evaluate necrosis or apoptosis of hair cell. Various doses of lentivirus-GFP were added to cochlear organotypic cultures with safe concentrations of polybrene, incubated for 24h, and cultured (in the absence of the virus and polybrene) for a further 48 h. Transduction efficiencies were evaluated. The results showed that polybrene at 0.1 μg/mL was safe to cochlear cells, and 0.5-10 μg/mL concentration induced hair cell necrosis in a dose-dependent manner. However, supporting cells were not damaged. Lentiviral vectors transduced into cochlear cells and 0.1 μg/mL polybrene enhanced transduction efficiency. However, hair cells were hardly transduced with lentiviral vectors either alone or in the presence of 0.1 μg/mL polybrene. The use of polybrene to aid lentiviral transduction of cochlear hair cells requires further attention.

The histone methyltransferase ESET is required for the survival of spermatogonial stem/progenitor cells in mice

Self-renewal and differentiation of spermatogonial stem cells (SSCs) are the foundation of spermatogenesis throughout a male's life. SSC transplantation will be a valuable solution for young male patients to preserve their fertility. As SSCs in the collected testis tissue from the patients are very limited, it is necessary to expansion the SSCs in vitro. Previous studies suggested that histone methyltransferase ERG-associated protein with SET domain (ESET) represses gene expression and is essential for the maintenance of the pool of embryonic stem cells and neurons. The objective of this study was to determine the role of ESET in SSCs using in vitrocell culture and germ cell transplantation. Cell transplantation assay showed that knockdown of ESET reduced the number of seminiferous tubules with spermatogenesis when compared with that of the control. Knockdown of ESET also upregulated the expression of apoptosis-associated genes (such as P53, Caspase9, Apaf1), whereas inhibited the expression of apoptosis-suppressing genes (such as Bcl2l1, X-linked inhibitor of apoptosis protein). In addition, suppression of ESET led to increase in expression of Caspase9 and activation of Caspase3 (P17) as well as cleavage of poly (ADP-ribose) polymerase. Among the five ESET-targeting genes (Cox4i2, spermatogenesis and oogenesis Specific Basic Helix-Loop-Helix 2, Nobox, Foxn1 and Dazl) examined by ChIP assay, Cox4i2 was found to regulate SSC apoptosis by the rescue experiment. BSP analyses further showed that DNA methylation in the promoter loci of Cox4i2was influenced by ESET, indicating that ESET also regulated gene expression through DNA methylation in addition to histone methylation. In conclusion, we found that ESET regulated SSC apoptosis by suppressing of Cox4i2 expression through histone H3 lysine 9 tri-methylation and DNA methylation. The results obtained will provide unique insights that would broaden the research on SSC biology and contribute to the treatment of male infertility.