Backplane, the startup behind Lady Gaga’s social network (LittleMonsters.com, currently in private beta), this morning announced that it has closed its Series A funding round, with a slew of high-profile investors participating.

According to the Wall Street Journal, Backplane has already raised $6.3 million since its founding in 2011. Investors include Sequoia Capital, Greylock Discovery Fund, Advance/Newhouse Investment Partnership (an affiliate of Conde Nast), Battery Ventures, Formation 8, Google Ventures, (Eric Schmidt-backed) TomorrowVentures, Founders Fund Angel, Menlo Ventures, SV Angel, i/o Ventures, and a group of unnamed individual investors.

Along with closing the new financing round (structured as a convertible note), Backplane says it has completed the acquisition of i/o Ventures startup Cortex, a maker of tools for rapid sharing of online content and multimedia. For the record: Cortex was created by Backplane cofounder Joey Primiani, so I guess it was already part of the family (Backplane’s social syndication is powered by Cortex).

Backplane says LittleMonsters.com will be publicly released in the spring of 2012, and that additional communities will be debuted throughout the year.