Now that biology professors have begun the exodus from their long-standing Cambridge facility to make way for the incoming stem cell researchers, the Stem Cell and Regenerative Biology Department’s plans to eventually inhabit the Allston Science Complex are growing increasingly uncertain.

To accommodate SCRB, some members of the Department of Molecular and Cellular Biology are currently in the midst of a two-month move-out from the Sherman Fairchild Biochemistry Building.

SCRB had originally been slated to move into the Science Complex, long heralded as the centerpiece of interdisciplinary research in Allston. But with the Dec. 2008 news of the slowdown in Allston construction, the University decided to relocate the SCRB to Fairchild.

To date, the University has not publicly indicated whether the moves planned for the MCB and SCRB departments are permanent measures, creating an uncertain timeline for the construction of the Science Complex.

It remains unclear when the structure will reach completion—and, if it does, which units will eventually occupy the building.

“It is premature to speculate on what departments or programs may or may not be settled into Allston and when,” wrote Faculty of Arts and Sciences spokesman Jeff Neal in an e-mailed statement.

The lack of clarity surrounding SCRB’s long-awaited move into the Science Complex has raised the possibility that the stem cell researchers, once situated, will not leave Fairchild in the near future.

These circumstances have left the soon-to-be former residents of Fairchild in a standstill. Whether the MCB professorswill ever return to Fairchild seems to depend upon the duration of SCRB’s occupation of the building.

“The general understanding is that Allston will someday come alive, but now it’s quite vague,” said MCB Executive Director Susan H. Foster. “We just are living for today.”

MCB Department Chair Catherine Dulac said that the scope of the renovations resulting from the transitions indicate that MCB’s move out of Fairchild is likely a “permanent” change.

Even in the unlikely case that SCRB eventually moves into the Science Complex, MCB professors will be hard-pressed to return to Fairchild, given the difficulties of moving and renovating laboratories, Dulac said.

SCRB expects to move into the gutted and renovated Fairchild building by the fall of 2011 and will remain “for the foreseeable future,” said SCRB Executive Director Kathryn L. Link. “It really all depends on what the University decides about the extended campus.”

Last December, the University formally announced that construction on the Science Complex would be held indefinitely due to financial constraints, but administrators have provided no timetable for its future, nor have they been clear about what form the building will ultimately take.

In a March interview with The Crimson, Bill Purcell, one of the co-chairs of the Harvard Allston Work Team, said that the team’s recommendations for the future of Allston would not be determined by a specific schedule.

“While there are things that will require study over a period of time, this shouldn’t be something where the schedule becomes the driving force: the driving force is knowing the right thing to do,” Purcell said.