During these experiments, genomic DNA from control and HS-treated cells was immunoprecipitated with either Tau1 antibody or an antibody directed against the nonstructural NSs protein encoded by the Rift Valley fever computer virus, which was used here as an arbitrary negative control. Tau as a key player in early stress response. studies have shown that purified Tau directly binds to polynucleotides with a preference toward AT-rich DNA compared with GC-rich DNA sequences. However, contradictory results have shown a protective or deleterious role of Tau in DNA integrity (7,C9). In addition, a recent study reported chromosomal aberrations in fibroblasts and lymphocytes from patients carrying a Tau mutation (10). Nevertheless, although Tau has been detected in brain nuclei (11), the function of neuronal nuclear Tau has not yet been elucidated. Furthermore, unlike other proteins present in both cellular compartments, nucleocytoplasmic shuttling of Tau has not yet been reported. The protection of genomic integrity is usually a major challenge for living cells that are constantly exposed to DNA-damaging injuries, especially in the brain. However, whether endogenous Tau has the capacity to protect neuronal DNA has remained an unanswered question. In this study, we aimed to investigate the potential protective effects of Tau against DNA damage in central neurons. EXPERIMENTAL PROCEDURES Primary Embryonic Neuronal Culture Wild-type and knock-out Tau mouse primary cortical cultures were prepared as described previously (12). Adenovirus Growth and Labeling HAdV-5-hTau44Wt (wild-type Tau isoform 2-3-10-) and HAdV-5-hTau44-NLS were constructed using the gateway system (Invitrogen), and they were amplified and purified in our laboratory as described previously (13). HAdV-5-hTau44-NLS was obtained by insertion of a nuclear localization signal (NLS)2 from the Epstein-Barr computer virus mRNA export factor EB2 (14) to the N-terminal a part of human Tau. After standard computer virus purification by ultracentrifugation in CsCl gradient, viral genomes were quantified by measuring UV absorption at 260 nm, and the computer virus titer was expressed as viral YKL-06-061 physical particles per ml. HAdV Contamination Primary cultured cells were YKL-06-061 seeded in six-well culture plates at a density of 1 1.28 106 cells per well. Cells were then infected with 2000 physical particles/cell of HAdV-5-hTau44 or HAdV-5-hTau44NLS vectors for 2 h at 37 C in minimum volume. Culture medium was added following contamination for 24 h at 37 C. Cell Treatment At 10 days (19). The essential actions of the fast halo assay consisted of the following. Slides were immersed in the pH 10.1 lysis solution for 10 min at +4 C in the dark. The slides were then rinsed in PBS for 30 s and neutralized for 15 min in PBS (pH 7.4) containing YKL-06-061 0.1 mg/ml RNase. The DNA was then exposed for 5 min to absolute ethanol to preserve all the halo assay slides. Comet Assay After the top layer of agarose had solidified, the slides were immersed for at least 1 h at +4 C in the dark in a lysis answer consisting of 2.5 m NaCl, 100 mm EDTA, 10 mm Tris, pH 10, to which 1% Triton X-100 and 10% dimethyl sulfoxide were freshly added. The slides were then removed and placed on a horizontal gel electrophoresis unit, and the unit packed was with freshly prepared alkaline buffer (1 mm EDTA and 300 mm NaOH, pH 13) to 0.25 cm above the slides. To reduce the variability YKL-06-061 associated with gel box slide position or multiple electrophoresis runs, slides were randomly distributed. The cells were exposed to the alkaline answer for 20 min Rabbit Polyclonal to PIGY to allow DNA unwinding and expression of single-strand breaks and alkali-labile sites. Next, electrophoresis was conducted for 20 min at 0C4 C by applying an electric current of 0.7 V/cm (25 V/300 mA). All of these actions were conducted in the absence of daylight to prevent additional DNA damage. After electrophoresis, the slides were neutralized with 0.4 m Tris (pH 7.5), and the DNA was exposed for 5 min to absolute ethanol to preserve all the comet assay samples. Subsequently, the slides were air-dried and then stored at room temperature until scored for DNA migration (20). Scoring Just prior to scoring, the DNA was stained using propidium iodide (20 g/ml distilled water; 25 YKL-06-061 l/slide). Slides were coded and examined at 200 magnification using a fluorescent microscope (Leica Microsystems SAS-DM 2000, Heerbrugg, Switzerland), equipped with an excitation filter of 515C560 nm and a barrier filter of 590 nm, connected through a gated monochrome CCD IEEE1394 FireWire video camera (Allied Vision Technologies) to a Comet Assay IV Image Analysis System (version 4.11) with Windows XP Pro Software (Perceptive Devices Ltd, Suffolk, UK). Images of at least.