Answer by taking a quote from the following article:

Expose is an American Latin freestyle vocal group. Primarily consisting of lead vocalists Jeanette Jurado, Ann Curless, and Gioia Bruno, the group achieved much of their success between 1984 and 1993, becoming the first group to have four top ten hits on the Billboard Hot 100 chart from its debut album, including the 1988 #1 hit "Seasons Change". In March 2015, Billboard magazine named the group the eighth most-successful girl group of all-time. The group was popular in dance clubs, mainstream Top 40 and adult contemporary charts in the United States.

During the recording of the group's first studio album Exposure, the personnel of the group changed. Reports vary based on the source. According to People magazine, one of the original singers quit while two of the girls were fired midway through the recording of the first album, but according to Billboard, all three were fired. Arista records felt that the three original singers lacked star potential. Martinee states that he made the decision himself to replace the three girls, while Miller maintains it was all their choice, and Jurado confirms that Lorenzo wanted to leave. Shortly thereafter, Casanas pursued a solo career and Lorenzo pursued other ambitions; they were replaced by Jeanette Jurado and Gioia Bruno. Miller began a solo career; she was replaced by Ann Curless.  Lorenzo returned to the dance charts with the Vendetta Records releases "I Wanna Know" in 1988, and "Stop Me if I Fall in Love" in 1990, while Laurie Miller released the 12" single "Parallels" on Atlantic Records and a second single "Love is a Natural Magical Thing" on Meet Me In Miami Records. Laurie evolved into a headline performer frequently showcasing her talents on cruises with a more intimate jazz style, and formed her own entertainment company called Xica productions.  Casanas later resurfaced as a solo artist (Sandee) and released a solo album, Only Time Will Tell, which garnered the club hits "You're The One", "Love Desire", and the Clivilles & Cole-produced bassline-heavy hit "Notice Me". She continued to tour actively in dance clubs and freestyle shows, until her death on December 15, 2008, of a seizure at the age of 46. All three original members: Casanas, Lorenzo and Miller later contributed vocals on songs on the Miami group Will to Power's eponymous 1988 debut album. Gioia Bruno also provided lead vocals on Will to Power's 2004 album, Spirit Warrior.

What were their roles in the band?