As far as The Master goes with Regenerations, he Regenerated from Derek Jacobi into John Simm, so he got Regenerations from somewhere.
Professor Yana could've been a stolen body ala Tremas or Eric Roberts, but, the John Simm body was definitely a Regeneration.
One Day I hope to be the Man my Cat thinks I am
Where are we going? And why are we in this Handbasket?