A world-beating hedge fund revealed it built a GameStop stake from scratch last quarter, making it a potential winner from the meme stock's explosive leap this week. Renaissance Technologies owned 1 million shares of the video-game retailer at the end of March, a position worth $13 million at the time, its first-quarter portfolio update shows. GameStop stock was up more than 400% at its Tuesday high, briefly valuing RenTech's stake at $65 million if still intact.