Three Democrats have already lined up to run for the 7th Suffolk District House seat, which veteran Rep. Gloria Fox will relinquish this fall after more than 30 years representing Roxbury on Beacon Hill.

Even before Fox publicly announced her intentions last week, two candidates had filed paperwork to run for the seat that represents Dudley Square, Washington Park, the Northeastern University campus and the rapidly-growing Longwood medical area.

Soon after Fox announced her retirement plans, her own top aide jumped in the race to succeed the longtime lawmaker.

Chynah Tyler, a former aide to Sen. Sonia Chang Diaz, filed to run for the seat on March 23 and on Monday announced that she has filed more than 500 signatures with the secretary of state's office to get on the ballot.

A 27-year-old Roxbury native, Tyler attended Boston Public Schools and charter schools before participating in the Crimson Summer Academy at Harvard University and then obtaining a bachelor's degree in criminal justice from Northeastern University.

"I will work diligently to develop and improve policies in efforts to further enrich our community," Tyler said in a statement. "I look forward to advancing the legacy of our community as your state representative."

Marydith Tuitt, Fox's chief of staff at the State House, filed with the Office of Campaign and Political Finance less than 48 hours after sending out the press release that announced Fox's impending retirement.

Tuitt, a 1985 Boston Technical High School graduate and 14-year veteran of the U.S. Navy, was unsuccessful in two previous runs for office, having sought the 12th Suffolk district seat in a special Democratic primary in 2013 and the District 3 Boston City Council seat in 2011.

Tuitt said Fox has been a mentor who has enhanced her own passion for public service and for the Roxbury community.

"I've watched and learned over the years and I know I can continue to be a strong voice for the 7th Suffolk," she said. "I want the people to see me, a young African-American veteran who has been serving my country and my community. I want to continue to do that to be a role model for young sisters and brothers who might think they can't do it."

Before joining Fox's staff, Tuitt served as constituent services coordinator for former Boston City Councilor Charles Yancey. She also serves on the Massachusetts Commission on the Status of Women, which last year honored another 7th Suffolk seat contender, Monica Cannon.

Cannon, who organizes the annual Back to School Block Party for Peace in her Roxbury neighborhood, currently works as a community liaison for Roca Inc., an organization that aims to break the cycle of recidivism and poverty. She previously served as executive director of the Tito Jackson Community Fund, according to her LinkedIn profile.

In June Cannon was honored as an "unsung heroine" by the Massachusetts Commission on the Status of Women for the block parties at which she distributes hundreds of donated backpacks and school supplies to children in her neighborhood.

"I got started because there was such high crime in my neighborhood," Cannon told the News Service in June. "I got angry, but I also got active. I knew that the more involved I got, the more I could get the kids in my neighborhood involved."