The Note's Must-Reads are a round-up of today's political headlines and stories from ABC News and the top U.S. newspapers. Posted Monday through Friday right here at www.abcnews.com

Compiled by ABC News' Jayce Henderson, Amanda VanAllen, Carrie Halperin and Jordan Mazza

GAY MARRIAGE ABC News' Sunlen Miller: "Majority of Senate Supports Same-Sex Marriage" Republican Sen. Mark Kirk of Illinois has become the second Republican senator to endorse same sex marriage, tipping the balance of opinion in the Senate. LINK

SCIENTIFIC INITIATIVE The Los Angeles Times' Melissa Healy: " Obama outlines private-public project to study the brain" Making good on a promise first hinted at during his State of the Union speech in February, President Obama on Tuesday unveiled the broad outlines of a scientific initiative aimed at mapping the human brain. The project's ambitious goals include understanding how the brain forms memories and controls human behavior; how it becomes damaged by conditions such as Parkinson's disease and autism; and how it can be repaired when afflicted by Alzheimer's disease, post-traumatic stress disorder and other illnesses. LINK

The New York Daily News' Adam Edelman: " Political rival Newt Gingrich praises Obama's plan to study human brain" Politics does, in fact, make strange bedfellows. The adage was given new life blood Tuesday after President Barack Obama elicited praise for his $100 million plan to map the human brain from one of his harshest critics during last year's campaign - former House Speaker and Republican presidential candidate Newt Gingrich. LINK

ECONOMIC INDICATORS Bloomberg's Peter Orzag: " Be Rich, Be Smart, Live Longer" Better-educated Americans increasingly live longer than everyone else, and children from higher-income families in the U.S. are getting more education than other people. These are two of the most disturbing trends in the U.S., and it's entirely plausible that they are related. Economists have recognized many possible connections between health and education, but so far they have done little to link the trends toward greater inequality in each area. LINK

FOREIGN AFFAIRS The Washington Post's Anne Gearan and Chico Harlan: " U.S. struggling to contain nuclear threats from North Korea, Iran" After more than four years of diplomacy, the Obama administration is struggling to contain the nuclear threats posed by North Korea and Iran, a pair of nations already isolated internationally and resistant to the economic incentives offered in return for an end to their programs. The nuclear ambitions of both countries predate the Obama administration, which has focused its efforts on international diplomacy to prevent Iran from developing a nuclear weapon and to stop North Korea from restarting its once-dormant nuclear program. LINK

KOREA The Wall Street Journal's Jay Solomon: "Seoul Seeks Ability to Make Nuclear Fuel" South Korea is pressing the Obama administration for U.S. permission to produce its own nuclear fuel, a move that nonproliferation experts said could trigger a wider nuclear-arms race in North Asia and the Middle East. LINK

DEMOCRATS USA Today's Martha T. Moore: "Democrats see hope against Sanford in Republican S.C." As a special election in South Carolina's first congressional district gets underway, Democrats are hoping that a well-funded candidate with a business background and a celebrity connection will allow them to break a 30-year GOP streak - especially against a Republican with a scandal in his past. LINK

OTHER The Hills' Julian Pecquet: " UN approval of arms trade treaty sets up Obama, Senate showdown" The Obama administration defied a majority of the Senate on Tuesday by voting to approve a United Nations treaty on the trade of small arms and other conventional weapons. The treaty, overwhelmingly approved by the U.N., requires countries to create internal mechanisms to ensure that their arms exports aren't likely to be used to harm civilians or violate human rights laws. LINK

ABC NEWS VIDEO "FBI Busts Alleged Plot to Rig NYC Mayoral Race" LINK

BOOKMARKS The Note: LINK The Must-Reads Online: LINK Top Line Webcast (12noon EST M-F): LINK ABC News Politics: LINK George's Bottom Line (George Stephanopoulos): LINK Follow ABC News on Twitter: LINK ABC News Mobile: LINK ABC News app on your iPhone/iPod Touch/iPad: LINK