Earlier this week we reported that Ian McKellen and Patrick Stewart were signed on to play Magneto and Professor X respectively. However, the comic book storyline the film is named after centers around Wolverine and Kitty Pryde - and Singer now has half of that duo in Jackman.
What remains to be seen is how the cast of X-Men: First Class will be used. Presumably they will be the X-Men in the past contacted by Pryde in an effort to change the dystopian future she and Wolverine try to survive in. In the comic, she contacts a younger version of herself - but the movie version of Pryde is way too young to be around the First Class team that started in the 60s. Perhaps she contacts Jennifer Lawrence's Mystique, instead?
X-Men: Days of Future Past is currently scheduled for a July 2014 release.