Reverse transcription was carried using 2 μg of each RNA sample and the Mix reagents acquired from BioRad (California, USA – 170-8897), following the manufacture’s instructions. For cDNA amplification, gene-specific primers targeted to M-Cadherin  and GAPDH (glyceraldehyde 3-phosphate dehydrogenase) were used. PCR was carried out in a final volume of 10 μL, with 1 μL target cDNA, 5 pmol of each primer, 200 μM each desoxyribonucleotide triphosphate (dNTP) (Promega, Wisconsin, USA), 0.8 units TaqDNA polymerase (Cenbiot, Rio Grande do Sul, Brazil) in a buffer containing 10 mM Tris-HCl, pH 8.5, 50 mM KCl, 1.5 mM MgCl2 as previously described . PCR analysis considered
for 30 cycles (denaturation at 94°C for 60 sec, annealing at 56°C or 54°C for M-Cadherin and GAPDH, respectively, and extension at 72°C for 60 sec). PCR products were visualized on 8% silver stained polyacrylamide gels. Gel images were acquired (Epson Perfection 4180 Photo, California, USA). Statistical analysis Densitometric analysis was performed using the Image J software (NIH) or Quantity One (BioRad, for western blot quantification). Student’s t -test was used to determine the significance of differences between means in Western blot, RT-PCR and quantitative assays. A p value ≤ 0.05 was considered significant. Results T. gondii infectivity of SkMC Only the number of infected myoblasts and myotubes was evaluated, independently of the number of parasites internalized. The total number of infected
cells (harboring at least one internalized parasite), after 24 h of SkMC – parasite interaction, represented 61% of myoblasts and 38% of myotubes. These data indicate that myotubes either were 1.6-fold less infected than myoblasts (Figure 1A). Figure 1B shows young and mature uninfected myotubes surrounded by several heavily infected myoblasts after 48 h of interaction. Figure 1 Percentage of T. gondii infected SkMC after 24 h of interaction. (A) Percentage of myoblasts (61%) and myotubes (38%) infected with T. gondii after 24 h of interaction. Student’s T-test (*) p ≤ 0.05. (B) Details of SkMC cultures profile observed by fluorescence microscopy with phaloidin-TRITC labeling showing actin filaments in red; nuclei of the cells and the parasites labeled with DAPI, in blue. Infected cultures present myoblasts containing several parasites (thick arrow) and young myotubes with 2 nuclei BB-94 without parasites (thin arrows). Bars, 20 μm Effect of T. gondii infection on SkMC myogenesis We also analysed the influence of T. gondii infection on SkMC myogenesis. Even at low parasite-host cell ratios (1:1), after 24 h of interaction, the infection percentage was 43% ± 0.06. In uninfected 3-day-old cultures the myotube percentage was 19.5% of the number of total cells.