The moves, which follow executive changes announced last week, come just a week before the firm releases its fourth quarter financial results.
On the wealth side, Greg Fleming, 47, a former Merrill Lynch president who already led Morgan Stanley's asset management business, will also become president of Global Wealth Management.
He replaces Charles Johnston, president of the Morgan Stanley Smith Barney brokerage joint venture, who leaves the firm at the end of this year.
Johnston, an industry veteran who began his career as a Merrill Lynch financial adviser in 1978 before rising up the ranks at Citigroup Inc
In an internal memo, Morgan Stanley Chief Executive James Gorman said Johnston, 57, was retiring to spend more time on family and charitable pursuits.
Fleming, 47, joined Morgan Stanley in 2009 to revive its struggling asset management division.
The Morgan Stanley culture clearly has the upper hand in the (Smith Barney) joint venture, said Alois Pirker, research director at Aite Group. It seems Gorman is putting his own team in place now.
Morgan Stanley has a 51 percent stake in the joint venture and Gorman also acts as Chairman of the unit.
Gorman also reshuffled management at Morgan Stanley's fixed income sales and trading unit, which has struggled in the past, replacing Jack DiMaio, who joined Morgan Stanley less than a year ago from Credit Suisse Group AG
The firm wants to boost its market share in fixed income, currencies and credit trading, according to a note by Nomura Securities analyst Glenn Schorr in November.
But Morgan Stanley's trading revenues have languished behind rival Goldman Sachs Group Inc
DeRegt, 55, will be replaced as chief risk officer in the interim by Keishi Hotsuki, who is head of the market risk department.
DiMaio, 43, will also leave the firm to return to the buy side, Gorman said in the memo without elaborating.
This is the latest in a series of executive changes announced over the past 10 days. Last Tuesday, the firm announced Jim Rosenthal, the firm's technology chief, would become Chief Operating Officer.
That was followed on Thursday by news that two of its senior executives would also head up international regions for the firm.
(Reporting by Helen Kearney; editing by Gary Hill and Andre Grenon)