Winx Club uses a serial format (modelled on American teen dramas) that has an ongoing storyline, with individual story arcs comprising each season. Initially, Straffi planned for the plot to last three seasons, but he decided to continue the story following the show's success. In 2010, Nickelodeon became a co-producer of Winx Club and its parent company Viacom gained 30% ownership of Rainbow in 2011. Production on the fifth and sixth seasons was divided between Rainbow and Nickelodeon Animation Studio. To attract an American audience, Viacom assembled a voice cast of Nickelodeon actors (including Elizabeth Gillies and Ariana Grande), invested US$100 million in advertising for the series, and inducted Winx Club into Nickelodeon's franchise of Nicktoons.