Republican Sen. Scott Brown today launched an attack ad against Elizabeth Warren, his Democratic opponent, about her claims of Cherokee heritage. Warren later hit back with an ad of her own.

Brown’s spot, his first to go negative, spliced together a series of TV news reports about the revelation that Warren, a Harvard University professor and consumer advocate, claimed Native American ancestry intermittently during her academic career.

“Warren admitted to identifying herself as Native American to employers,” a female newswoman says in one clip, “something now genealogists have said they have zero evidence of,” Fox News anchor Megyn Kelly says in the subsequent clip.

The point of the ad, Brown advisers said, is to remind voters of the issue and continue to raise questions about Warren’s character and integrity. It begins airing statewide today.

Brown also mentioned Warren’s heritage in the candidates’ first televised debate last week.

Warren’s campaign was the first to air a negative TV ad in the race.

Warren released another ad today, also airing statewide, defending herself. “Let me be clear,” she says directly to the camera. “I never asked for, never got any benefit because of my heritage. The people who hired me have all said they didn’t even know about it. I’m Elizabeth Warren. I approve this message. Scott Brown can continue attacking my family, but I’m going to keep fighting for yours.”

In an email to supporters today, Warren wrote: “How does Scott Brown plan to win in November? His answer is to talk about anything except how he votes on jobs, education, the environment, oil subsidies or special deals for Wall Street.”

She called the ad “an ugly, nasty attack on my family and our heritage.”

Warren has led Brown in a series of recent polls. Roll Call rates the race as a Tossup.