Fig. 1: Mkx+ cells populate the calvarial suture mesenchyme and contribute to calvarial bone turnover.
A Diagrams of the MkxCG driver. Mkx-expressing cells are labeled with GFP. Following tamoxifen (TM) administration, Mkx-expressing cells will be permanently labeled with TdTomato (tdT). B Whole-mount fluorescent image (left) and histology of tdT reporter activity (right) in patellar tendon of a 3-month old MkxCG;RtdT mice post TM injection. Arrowhead: patellar tendon. s: tendon sheath. Asterisk: patella. GFP not shown. C Whole-mount fluorescent image (left) and histology of tdT reporter activity (right) in Achilles tendon of a 3-month old MkxCG;R26RtdT (denoted as MkxtdT) mice post TM injection. Arrowhead: Achilles tendon. s: tendon sheath. GFP not shown. D Schematic of TM administration in 15 weeks-old mice, with sample collection at 2 wks and 6 mo. E Top-down whole-mount image of calvarial bones 2 wks after TM injection. C: coronal suture and S: sagittal suture. GFP not shown. F–J Representative images of Mkx reporter activity within F tile scan of parietal bone, G sagittal suture, H squamosal suture, I coronal suture, and J Dura at 2 weeks after TM administration. K, L Colocalization of Mkx reporter activity with K GLI1 and L AXIN2 immunostaining. Reporter activity appears red, immunoreactivity appears green, and colocalization appears yellow (indicated with asterisk). GFP reporter activity not shown. M–P Representative images of Mkx reporter activity within M Tile scan of parietal bone, N sagittal suture, and O suture adjacent osteocytes at 6 months after TM administration. Yellow arrowheads indicate reporter positive osteocyte. P OCN immunostaining and Mkx reporter activity at 6 months after TM administration. GFP reporter activity not shown. n = 4 mice per time point. Scale bars length: B, C (left): 1000 μm. F, M: 100 μm. B, C (right), G–L and N–P: 20 μm.
