MT1-MMP regulates hMSC invasion and intravasation in vivo. (A) hMSCs were labeled with fluorescent nanobeads (green) and seeded atop the CAM of 11-day-old chick embryos for 2 days. CAM cross-sections were stained with DAPI and visualized by fluorescence microscopy. Dashed lines mark the outline of the upper CAM surface (ie, cells below the dashed line demarcate invading hMSCs). White arrowheads mark the invading cells. Bar, 100 μm. (B) CAM invasion is quantified as the number of hMSCs that cross the CAM surface (mean ± SEM; n = 3) and average depth of the leading front of invading cells (mean ± SEM; n = 3), * and # both represent P < .05, for invasive cells numbers and invasion depth, respectively. (C) hMSCs intravasation/extravasation was detected as Alu-sequences by PCR on DNA extracted from the lower CAM after a 2-day incubation period. Micrographs shown are representative of 3 experiments performed.