Michigan's ban on gay marriage goes on trial Tuesday in a federal court challenge brought by a same-sex couple from suburban Detroit who were barred from marrying or from adopting each other's children.

April DeBoer and Jayne Rowse had sued the state initially over Michigan's adoption law and later expanded their challenge to include the state's ban on gay marriage, which was approved as a constitutional amendment by voters in 2004.

The trial in U.S. District Court in Detroit is the latest in a series of challenges brought by gay rights supporters that are winding their way through federal and state courts following two key decisions from the U.S. Supreme Court last year.

The U.S. Supreme Court in June threw out a key part of the Defense of Marriage Act, which denied same-sex couples federal benefits that are available to heterosexual couples. A separate decision allowed same-sex marriage in California.

"They are cautiously optimistic," attorney Dana Nessel, who represents DeBoer and Rowse, said of the couple.

Michigan's attorney general has said in court papers the marriage amendment voters adopted in 2004 is rationally related to legitimate state interests and marriage between one man and one woman is "uniquely suited to the rearing of children."

"There is no dispute that there is a fundamental right to marry," the attorney general said in court papers. "But there is no fundamental right to marry a person of the same sex."

A decade ago, only one state was preparing to allow same-sex marriages. Overall, 17 states and the District of Columbia now allow same-sex nuptials.

In the Michigan case, Judge Bernard Friedman in October ordered a trial on the state's marriage ban and adoption law. Several courts around the country have struck down same-sex marriage bans since he ordered the trial.

Federal judges ruled gay marriage bans unconstitutional in Utah, Oklahoma and Virginia in decisions that have been stayed pending appeal. The New Mexico Supreme Court also has ruled gay marriage legal in that state.

Nessel said Michigan's ban on same-sex marriage and adoption leaves DeBoer, who has an adopted daughter, and Rowse, who has two adopted sons, vulnerable.

Last week, Rowse underwent a common surgery and had she been incapacitated or worse, DeBoer would not have had control of her sons, Nessel said.

"Every single day that our clients don't have legal rights to their own children is another day that those children are left unprotected," Nessel said.

(Reporting by James B. Kelleher in Detroit and David Bailey in Minneapolis; Editing by Ken Wills)