Boulder-based Zayo Group--ahead of what looks like an IPO effort for the company--has shuffled its board, saying it has added Linda Rottenberg, CEO of Endeavor, as a new member ofits board. Zayo also said that Tony Downer of Oak Investment Group, and Lawrence Fey of GTCR have resigned from the company's board as part of the effort. It's not unusual for companies looking for an IPO to adjust the makeup of their board members ahead of any offering. Zayo is now has more than $1 billion in annual revenues. The company offers up fiber bandwidth, colocation, and other related services and infrastructure.