Xconomy Boston — Gene editing biotech Beam Therapeutics raised $180 million in its initial public offering Wednesday after offering 48 percent more shares than it initially anticipated. Beam, which was slated to begin trading Thursday on the Nasdaq exchange under the stock symbol “BEAM,” sold 9.25 million shares, up from the 6.25 million it said it planned to offer in a Jan. 30 securities filing. The company priced its IPO at $17 per share late Wednesday, the top of the $15 t