Supporters of Airbnb hold a rally on the steps of New York City Hall showing support for the company, Oct. 30, 2015.

Check out the companies making headlines in premarket trading.

Zynex, Coherus BioSciences, Universal Insurance Holdings — Coherus, Zynex and Universal Insurance stock fell on news from S&P 500 Dow Jones indices that the stocks would be moving within small-cap indexes. Coherus is leaving the MidCap 400 for the MidCap 600, while Universal Insurance is leaving the MidCap 600 altogether. Zynex tumbled nearly 6% on news that the firm is leaving the SmallCap 600 index.