Hot Property: 300 Third Ave.

Callahan Construction Managers has begun raising structural steel for a new 4-story, 140,000-square-foot life sciences building in Waltham. 

Hot Property: 91 Hartwell Ave.

Lexington officials have approved construction of a mixed-use campus at 91 Hartwell Ave. containing 125,000 square feet of office space and 95,000 square feet of class A lab facilities.