Fig. 1
From: BMP9 stimulates joint regeneration at digit amputation wounds in mice
Bone morphogenetic protein 9 (BMP9) stimulates regeneration of joint structures. a Bmp9 transcripts are localized to digit joints undergoing cavitation (arrowhead) in E18.5 embryos. b P2 level amputation of neonatal digits is used to test for induced regeneration. Following amputation (red line) at postnatal day 3 (PN3), epidermal closure is completed 4 days later (PN7), and an agarose microcarrier bead (blue dot) is implanted between the wound epidermis and the stump. c Microcomputed tomography (µCT) rendering of a BMP9-treated digit showing regeneration of a skeletal element articulating with the stump after 4 weeks (PN35). d Mallory trichrome staining of BMP9-treated digit 9 weeks after BMP9 treatment (PN70). Regenerated skeletal element (arrow) forms a joint-like structure with the digit stump. Articular cartilage of the P1/P2 joint is shown at higher magnification in the inset. e Higher magnification of the inset in (d) shows a cavity (c) separating a layer of articular cartilage (arrowhead) lining the regenerated skeletal element (n) and the stump bone (s). Small patches of articular cartilage (star) form on the stump bone. f–j In situ hybridization of cavity (arrow)-forming BMP9-treated digits showing localization of transcripts to the regenerated chondrogenic nodule but not the digit stump (s) 72 h after bead (*) implantation. f Col2a1. g Sox9. h Acan. i Fmod. j Ucma. k, l Immunofluorescence staining of Doublecortin (Dcx) expression. k Immunostaining shows Dcx+ cells (arrowhead) lining the synovial cavity of an uninjured joint at PN10. l Isolated superficial cells of the BMP9-induced nodule express Dcx (arrowhead) 72 h after treatment (PN10). The cavity is outlined with dashed white lines. Dcx+ cells are also observed internal to the superficial layer. m–q In situ hybridization of bovine serum albumin (BSA)-treated control digits 72 h after bead implantation showing no expression associated with the amputation wound distal to the stump. m Col2a1. n Sox9. o Acan. p Fmod. q Ucma. r–v In situ hybridization of non-cavity-forming BMP9-treated digits showing localization of transcripts to the distal stump 72 h after bead implantation. r Col2a1. s Sox9. t Acan. u Fmod. v Ucma. Right is distal, top is dorsal. Scale bars: a, f–j, m–v = 100 µm; d = 250 µm; e, k = 50 µm; l = 25 µm
