Ignyta Inc. said it started an underwritten public offering of $125 million of its common shares.

The company expects to grant the underwriters an option to buy up to an additional $18.8 million of shares.

Ignyta expects to use the net proceeds from the offering to fund research and development activities for its development programs and for working capital and other general corporate purposes.

J.P. Morgan Securities LLC and Jefferies LLC are acting as joint book-running managers for the offering.