The movie, directed by Noah Baumbach, is about "a middle-aged couple whose career and marriage are overturned when a disarming young couple enters their lives," a description of the movie says.
There's no word on what Horovitz's character will be. The film, which is scheduled to be released in 2015, also stars Amanda Seyfried and Adam Driver -- presumably as the young couple -- and Charles Grodin.
James Murphy will score the film, the second time he's collaborated with Baumbach. The first time was on Greenberg.