Mesenchymal stem cells (MSC) have a therapeutic potential in patients with fractures to reduce the time of healing and treat non-unions. The use of MSC to treat fractures is attractive as it would be implementing a reparative process that should be in place but occurs to be defective or protracted and MSC effects would be needed only for the repairing time that is relatively brief. However, an integrated approach to define the multiple regenerative contributions of MSC to the fracture repair process is necessary before clinical trials are initiated. In this study, using a stabilized tibia fracture mouse model, we determined the dynamic migration of transplanted MSC to the fracture site, their contributions to the repair process initiation and their role in modulating the injury-related inflammatory responses. Using MSC expressing luciferase, we determined by bioluminescence imaging that the MSC migration at the fracture site is time- and dose-dependent and, it is exclusively CXCR4-dependent. MSC improved the fracture healing affecting the callus biomechanical properties and such improvement correlated with an increase in cartilage and bone content, and changes in callus morphology as determined by micro-computed-tomography and histological studies. Transplanting CMV-Cre-R26R-LacZ-MSC, we found that MSC engrafted within the callus endosteal niche. Using MSC from BMP-2-Lac-Z mice genetically modified using a bacterial artificial chromosome system to be β-gal reporters for BMP-2 expression, we found that MSC contributed to the callus initiation by expressing BMP-2. The knowledge of the multiple MSC regenerative abilities in fracture healing will allow to design novel MSC-based therapies to treat fractures.

There are several human syndromes which involve defects of the limbs and the Müllerian ducts or its derivatives. The hand-foot-genital (HFG) syndrome is an autosomal dominant, fully penetrant disorder that was originally described by Stern et al. Additional reports describing other affected families have also been published. Limb anomalies include short first metacarpals of normal thickness, small distal phalanges of the thumbs, short middle phalanges of the fifth fingers, and fusion or delayed ossification of wrist bones. In the feet, the great toe is shorter due to a short first metatarsal and a small, pointed distal phalanx. Uterine anomalies are common in females with HFG, and typically involve a partially divided (bicornuate) or completely divided (didelphic) uterus, representing defects of Müllerian duct fusion. Urinary tract malformations in affected HFG females include a displaced urethral opening and malposition of ureteral orifices in the bladder wall; affected males may have hypospadias (ventrally misplaced urethral opening) of variable severity. We report the identification of a HOXA13 nonsense mutation in a family with hand-foot-genital syndrome. The mutation converts a highly conserved tryptophan residue in the homeodomain to a stop codon, which truncates 20 amino acids from the protein and likely eliminates or greatly reduces the ability of the protein to bind to DNA.

Classic tissue recombination and in vitro lineage tracing studies suggest that condensed metanephric mesenchyme (MM) gives rise to nephronic epithelium of the adult kidney. However, these studies do not distinguish between cap mesenchyme and pre-tubular aggregates comprising the condensed MM, nor do they establish whether these cells have self-renewing capacity. To address these questions, we generated Cited1-CreER(T2) BAC transgenic mice, which express tamoxifen-regulated Cre recombinase exclusively in the cap mesenchyme. Fate mapping was performed by crossing these mice with the Rosa26R(LacZ) reporter line and evaluating the location and cellular characteristics of LacZ positive cells at different time points following tamoxifen injection. These studies confirmed expected results from previous in vitro analysis of MM cell fate, and provide in vivo evidence that the cap mesenchyme does not contribute to collecting duct epithelium in the adult. Furthermore, by exploiting the temporally regulated Cre recombinase, these studies show that nephronic epithelium arising at different stages of nephrogenesis has distinct spatial distribution in the adult kidney, and demonstrate for the first time that the cap mesenchyme includes a population of self-renewing epithelial progenitor cells.

Despite its clinical significance, joint morphogenesis is still an obscure process. In this study, we determine the role of transforming growth factor β (TGF-β) signaling in mice lacking the TGF-β type II receptor gene (Tgfbr2) in their limbs (Tgfbr2PRX-1KO). In Tgfbr2PRX-1KO mice, the loss of TGF-β responsiveness resulted in the absence of interphalangeal joints. The Tgfbr2Prx1KO joint phenotype is similar to that in patients with symphalangism (SYM1-OMIM185800). By generating a Tgfbr2–green fluorescent protein–β–GEO–bacterial artificial chromosome β-galactosidase reporter transgenic mouse and by in situ hybridization and immunofluorescence, we determined that Tgfbr2 is highly and specifically expressed in developing joints. We demonstrated that in Tgfbr2PRX-1KO mice, the failure of joint interzone development resulted from an aberrant persistence of differentiated chondrocytes and failure of Jagged-1 expression. We found that TGF-β receptor II signaling regulates Noggin, Wnt9a, and growth and differentiation factor-5 joint morphogenic gene expressions. In Tgfbr2PRX-1KO growth plates adjacent to interphalangeal joints, Indian hedgehog expression is increased, whereas Collagen 10 expression decreased. We propose a model for joint development in which TGF-β signaling represents a means of entry to initiate the process.

Hand-foot-genital syndrome (HFGS) is a rare, dominantly inherited condition affecting the distal limbs and genitourinary tract. A nonsense mutation in the homeobox of HOXA13 has been identified in one affected family, making HFGS the second human syndrome shown to be caused by a HOX gene mutation. We have therefore examined HOXA13 in two new and four previously reported families with features of HFGS. In families 1, 2, and 3, nonsense mutations truncating the encoded protein N-terminal to or within the homeodomain produce typical limb and genitourinary abnormalities; in family 4, an expansion of an N-terminal polyalanine tract produces a similar phenotype; in family 5, a missense mutation, which alters an invariant domain, produces an exceptionally severe limb phenotype; and in family 6, in which limb abnormalities were atypical, no HOXA13 mutation could be detected. Mutations in HOXA13 can therefore cause more-severe limb abnormalities than previously suspected and may act by more than one mechanism.