MMP-9 is predominantly expressed by osteoclasts in mouse calvaria. Serial coronal sections of vehicle or RANKL-treated mouse calvaria were stained for TRAP (red), MMP-9 (brown), or IgG as indicated. represents an osteoclast present in 3 serial sections, positive for both TRAP and MMP-9. Insets shown at original magnification ×60 are indicated by boxes. Images were acquired with a Nikon Eclipse E800 microscope fitted with a Plan Fluor 20×/0.5 NA objective or Plan Apo 60×/1.4 NA objective (oil), and an Olympus America SN CG603057-H camera with Magnifire software. Auto contrast adjustments were performed with Adobe Photoshop software (original magnifications: ×20 or ×60 as indicated). Results are from 1 representative experiment of 2 performed.