Apple, Nasdaq and Jim Chanos: WHAT YOU NEED TO KNOW ON WALL STREET

Finance Insider is Business Insider's summary of the top stories of the past 24 hours.

Apple announced late Thursday that it had invested $1 billion in Didi Chuxing, the leading ride-hailing service in China.

The deal came together in less than a month. Here's why the tech giant is backing the Uber of China.

Uber Travis Kalanick CEO had an interesting response to the news. He had a meeting planned with Apple this week

Famous short seller Carson Block walked Business Insider's Bob Bryan through how he picks a takedown target, and Nasdaq CEO Bob Greifeld told Business Insider's Rich Feloni why he stopped taking advice once he hit 35.

Hedge fund billionaire Jim Chanos is on a roll. He revealed on Thursday that he had been shorting Lending Club before its capitulation this week. He also laid out his thinking behind his short position in LNG company Cheniere.

One of the deepest wounds of the US financial crisis has finally healed, Obamacare has been good for the economy, and here's what Goldman Sachs' US workforce looks like.

And lastly, this stunning car should make Audi and Porsche worry.

Here are the top Wall Street headlines at midday:

JANET YELLEN: I won't completely rule out negative interest rates ? Federal Reserve Chair Janet Yellen will not rule out the Fed using negative interest rates.

America's biggest companies say these 4 themes are top of mind right now ? Goldman Sachs has once again published its "beige book" of the biggest themes S&P 500 companies are talking about during earnings season.

We just got another really ominous sign for the retail industry ? The retail sector's having a tough time.

A crazy decision led Thailand to stockpile tons of rice, but everything could be about to change ? In 2011, Thailand was the world's largest exporter of rice, accounting for about 30% of the global market.

4 top investors just presented their stock ideas at the hedge fund conference of the year - here they are ? Four huge names in the hedge fund industry shared their favorite stock idea at the SkyBridge Alternative Conference in Las Vegas on Thursday.

Steve Cohen's giant New York City penthouse is back on the market for a fourth time, but now it costs $72 million ? Billionaire hedge funder Steven A. Cohen is seeking a buyer for his Manhattan duplex penthouse.