title: Joint TGF-β type II receptor-expressing cells: ontogeny and characterization as joint progenitors.
abstract: TGF-β type II receptor (Tgfbr2) signaling plays an essential role in joint-element development. The Tgfbr2(PRX-1KO) mouse, in which the Tgfbr2 is conditionally inactivated in developing limbs, lacks interphalangeal joints and tendons. In this study, we used the Tgfbr2-β-Gal-GFP-BAC mouse as a LacZ/green fluorescent protein (GFP)-based read-out to determine: the spatial and temporally regulated expression pattern of Tgfbr2-expressing cells within joint elements; their expression profile; and their slow-cycling labeling with bromodeoxyuridine (BrdU). Tgfbr2-β-Gal activity was first detected at embryonic day (E) 13.5 within the interphalangeal joint interzone. By E16.5, and throughout adulthood, Tgfbr2-expressing cells clustered in a contiguous niche that comprises the groove of Ranvier and the synovio-entheseal complex including part of the perichondrium, the synovium, the articular cartilage superficial layer, and the tendon's entheses. Tgfbr2-expressing cells were found in the synovio-entheseal complex niche with similar temporal pattern in the knee, where they were also detected in meniscal surface, ligaments, and the synovial lining of the infrapatellar fat pad. Tgfbr2-β-Gal-positive cells were positive for phospho-Smad2, signifying that the Tgfbr2 reporter was accurate. Developmental-stage studies showed that Tgfbr2 expression was in synchrony with expression of joint-morphogenic genes such as Noggin, GDF5, Notch1, and Jagged1. Prenatal and postnatal BrdU-incorporation studies showed that within this synovio-entheseal-articular-cartilage niche most of the Tgfbr2-expressing cells labeled as slow-proliferating cells, namely, stem/progenitor cells. Tgfbr2-positive cells, isolated from embryonic limb mesenchyme, expressed joint progenitor markers in a time- and TGF-β-dependent manner. Our studies provide evidence that joint Tgfbr2-expressing cells have anatomical, ontogenic, slow-cycling trait and in-vivo and ex-vivo expression profiles of progenitor joint cells.
authors.affiliation: Department of Pediatrics, University of North Carolina at Chapel Hill , Chapel Hill, NC 27599-7039, USA.
authors.forename: Tieshi
authors.initials: T
authors.lastname: Li
authors.forename: Lara
authors.initials: L
authors.lastname: Longobardi
authors.forename: Timothy J
authors.initials: TJ
authors.lastname: Myers
authors.forename: Joseph D
authors.initials: JD
authors.lastname: Temple
authors.forename: Ronald L
authors.initials: RL
authors.lastname: Chandler
authors.forename: Huseyin
authors.initials: H
authors.lastname: Ozkan
authors.forename: Clara
authors.initials: C
authors.lastname: Contaldo
authors.forename: Anna
authors.initials: A
authors.lastname: Spagnoli
mesh_terms: D000818:Animals; D000943:Antigens, Differentiation / Q000378:metabolism; D002358:Cartilage, Articular / Q000378:metabolism; D049109:Cell Proliferation; D002478:Cells, Cultured; D005260:Female; D033023:Foot Joints / Q000166:cytology / Q000378:metabolism*; D005552:Forelimb / Q000166:cytology / Q000378:metabolism; D015870:Gene Expression; D018507:Gene Expression Regulation, Developmental; D008297:Male; D051379:Mice; D008822:Mice, Transgenic; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism*; D000077294:Receptor, Transforming Growth Factor-beta Type II; D018125:Receptors, Transforming Growth Factor beta / Q000235:genetics / Q000378:metabolism*; D055153:Stem Cell Niche; D013234:Stem Cells / Q000378:metabolism; D013583:Synovial Membrane / Q000378:metabolism
chemical_list: D000943:Antigens, Differentiation; D018125:Receptors, Transforming Growth Factor beta; D017346:Protein Serine-Threonine Kinases; D000077294:Receptor, Transforming Growth Factor-beta Type II