Merck & Co. Inc. has tapped Skyhawk Therapeutics Inc. for its expertise in the discovery and development of small molecules that modulate RNA splicing, agreeing to pay it up to $600 million per program target plus royalties on sales of any commercialized products of the collaboration. The deal, focused on potential treatments for certain neurological diseases and cancer, was accompanied by news of an expansion of Skyhawk's collaboration with Biogen Inc., which originally signed on with the Waltham, Mass-based company in January.