[ by Melanie Gretchen ] JPMorgan CEO Jamie Dimon will step into the spotlight - from the witness seat - and testify before the House and Senate respectively later this month, according to people briefed on the matter.  He's scheduled to appear before the Senate Banking Committee on 6/13/12, then testify before a House panel on 6/19/12. Great Expectations. "I expect Mr. Dimon to come prepared to provide the committee a better understanding of this massive trading loss so we can take the implications into account as we continue to conduct our robust oversight over the full implementation of Wall Street reform," Senator Tim Johnson (Dem-SD), who chairs the committee, said in a statement last week. Mr. Dimon's hearing will join a broader examination by Congress into JPMorgan's recent trading debacle in which the bank lost anywhere from $3 to $5 billion on complex positions tied to credit derivatives. Other important dates include 6/6/12, when the Senate committee hosts some of the bank’s main regulators, including the Federal Reserve and Office of the Comptroller of the Currency.  Last week, the committee heard from the leaders of the CFTC and SEC.    [Dealbook, 5/31/12].