Lester Holt, the anchor and managing editor of "NBC Nightly News" for a decade, announced Monday that he is stepping down from the long-running broadcast at the beginning of the summer. Holt will continue to be a fixture at the network with a full-time role at "Dateline," where he has been the principal anchor for almost 15 years, according to a memo shared with network staff Monday. NBC News did not immediately name Holt's successor. Holt was named anchor of "Nightly News" in June 2015 after steering weekend editions of the news broadcast for eight years and co-anchoring "Weekend TODAY" for 12 years. He has served as principal anchor of "Dateline" since September 2011.