The firm that manages Harvard’s endowment is shaking up a quarter of its staff after the fund plunged 22 percent in the four months up to last October. The Harvard Management Company’s executive, Jane Mendillo ’80 SOM ’84, will fire as many as 50 of the firm’s 200 workers, including some investment professionals. Harvard’s endowment is expected to fall 30 percent by the end of the fiscal year in June. Unlike Yale, which outsources the direct management of its endowment, the Harvard Management Company manages about a third of Harvard’s fund in-house.