Clue: Brutal ace found out, put in cell? (9)
Answer: TRABECULA
Explanation: Definition: cell
An anagram ('found out') of 'brutal ace'. A trabecula ('originally singular, with plural trabeculae, although sometimes treated as a neuter plural trabecula with singular trabeculum) is an element of tissue in the form of a rod with supportive and connective functions in various organs. I think the definition, whether 'cell' or 'in cell' 'put in cell', definitely requires the question mark.