Mechanisms of GDF-5 action during skeletal development.
Mutations in GDF-5, a member of the TGF-beta superfamily, result in the autosomal recessive syndromes brachypod (bp) in mice and Hunter-Thompson and Grebe-type chondrodysplasias in humans. These syndromes are all characterised by the shortening of the appendicular skeleton and loss or abnormal development of some joints. To investigate how GDF-5 controls skeletogenesis, we overexpressed GDF-5 during chick limb development using the retrovirus, RCASBP. This resulted in up to a 37.5% increase in length of the skeletal elements, which was predominantly due to an increase in the number of chondrocytes. By injecting virus at different stages of development, we show that GDF-5 can increase both the size of the early cartilage condensation and the later developing skeletal element. Using in vitro micromass cultures as a model system to study the early steps of chondrogenesis, we show that GDF-5 increases chondrogenesis in a dose-dependent manner. We did not detect changes in proliferation. However, cell suspension cultures showed that GDF-5 might act at these stages by increasing cell adhesion, a critical determinant of early chondrogenesis. In contrast, pulse labelling experiments of GDF-5-infected limbs showed that at later stages of skeletal development GDF-5 can increase proliferation of chondrocytes. Thus, here we show two mechanisms of how GDF-5 may control different stages of skeletogenesis. Finally, our data show that levels of GDF-5 expression/activity are important in controlling the size of skeletal elements and provides a possible explanation for the variation in the severity of skeletal defects resulting from mutations in GDF-5. (+info)
Support of the anterior column with allografts in tuberculosis of the spine.
Fresh-frozen allografts from the humerus were used to help to stabilise the spine after anterior decompression for tuberculosis in 47 children with a mean age of 4.2 years (2 to 9). The average angle of the gibbus, before operation, was 53 degrees; at follow-up, two years later, it was 15 degrees. Rejection of the graft or deep sepsis was not seen. Cross trabeculation between the allograft and the vertebral body was observed at six months, with remodelling occurring at approximately 30 months. (+info)
Regulation of chondrocyte differentiation by Cbfa1.
Cbfa1, a developmentally expressed transcription factor of the runt family, was recently shown to be essential for osteoblast differentiation. We have investigated the role of Cbfa1 in endochondral bone formation using Cbfa1-deficient mice. Histology and in situ hybridization with probes for indian hedgehog (Ihh), collagen type X and osteopontin performed at E13.5, E14.5 and E17.5 demonstrated a lack of hypertrophic chondrocytes in the anlagen of the humerus and the phalanges and a delayed onset of hypertrophy in radius/ulna in Cbfa1-/- mice. Detailed analysis of Cbfa1 expression using whole mount in situ hybridization and a lacZ reporter gene reveled strong expression not only in osteoblasts but also in pre-hypertrophic and hypertrophic chondrocytes. Our studies identify Cbfa1 as a major positive regulator of chondrocyte differentiation. (+info)
Retardation of bone growth in triamcinolone-treated mice.
Immature mice were treated for up to 8 weeks with daily doses of triamcinolone diacetate. The epiphyseal cartilage plate and its surrounding bone from the humeral head were studied histologically at regular intervals. Concomitantly, roentgenographic measurements were performed on the humeri in toto. By the tenth injection significant morphological changes were noted in the cartilaginous plate, followed by complete cessation of bone growth. Severe triglyceride accumulation appeared in the experimental livers and humeral bone marrow. Osteoporosis also occurred and became severe from the fifth week of triamcinolone administration. Possible explanations for the above findings are discussed. (+info)
Retinoid signaling is required for chondrocyte maturation and endochondral bone formation during limb skeletogenesis.
Retinoids have long been known to influence skeletogenesis but the specific roles played by these effectors and their nuclear receptors remain unclear. Thus, it is not known whether endogenous retinoids are present in developing skeletal elements, whether expression of the retinoic acid receptor (RAR) genes alpha, beta, and gamma changes during chondrocyte maturation, or how interference with retinoid signaling affects skeletogenesis. We found that immature chondrocytes present in stage 27 (Day 5.5) chick embryo humerus exhibited low and diffuse expression of RARalpha and gamma, while RARbeta expression was strong in perichondrium. Emergence of hypertrophic chondrocytes in Day 8-10 embryo limbs was accompanied by a marked and selective up-regulation of RARgamma gene expression. The RARgamma-rich type X collagen-expressing hypertrophic chondrocytes lay below metaphyseal prehypertrophic chondrocytes expressing Indian hedgehog (Ihh) and were followed by mineralizing chondrocytes undergoing endochondral ossification. Bioassays revealed that cartilaginous elements in Day 5.5, 8.5, and 10 chick embryo limbs all contained endogenous retinoids; strikingly, the perichondrial tissues surrounding the cartilages contained very large amounts of retinoids. Implantation of beads filled with retinoid antagonist Ro 41-5253 or AGN 193109 near the humeral anlagens in stage 21 (Day 3.5) or stage 27 chick embryos severely affected humerus development. In comparison to their normal counterparts, antagonist-treated humeri in Day 8.5-10 chick embryos were significantly shorter and abnormally bent; their diaphyseal chondrocytes had remained prehypertrophic Ihh-expressing cells, did not express RARgamma, and were not undergoing endochondral ossification. Interestingly, formation of an intramembranous bony collar around the diaphysis was not affected by antagonist treatment. Using chondrocyte cultures, we found that the antagonists effectively interfered with the ability of all-trans-retinoic acid to induce terminal cell maturation. The results provide clear evidence that retinoid-dependent and RAR-mediated mechanisms are required for completion of the chondrocyte maturation process and endochondral ossification in the developing limb. These mechanisms may be positively influenced by cooperative interactions between the chondrocytes and their retinoid-rich perichondrial tissues. (+info)
The inferior capsular shift operation for instability of the shoulder. Long-term results in 34 shoulders.
We reviewed 26 patients with 34 shoulders treated by the inferior capsular shift operation for inferior and multidirectional instability. The mean follow-up was 8.3 years. In total, 12 shoulders showed voluntary subluxation. Eight operations used an anterior and posterior approach, 11 were by the posterior route, and 15 shoulders had an anterior approach. In 30 shoulders (85%) the outcome was satisfactory and 20 (59%) scored good or excellent results on the Rowe system. Instability had recurred in nine shoulders (26%) from three months to three years after the operation. Six of the 12 shoulders with voluntary subluxation (50%) had recurrence, as against three of the other 22 (14%), a statistically significant difference. The operation is therefore not indicated for voluntary subluxation. The 19 shoulders which had been assessed in 1987 at a mean of 3.5 years after surgery, were also reviewed in 1995 and found to have no significant changes in instability or Rowe score. This shows that the capsular shift appeared to have maintained its tension over an eight-year period. After the use of a posterior approach, 64% of the shoulders showed a posterolateral defect on radiographs of the humerus. (+info)
Maturational disturbance of chondrocytes in Cbfa1-deficient mice.
Cbfa1, a transcription factor that belongs to the runt-domain gene family, plays an essential role in osteogenesis. Cbfa1-deficient mice completely lacked both intramembranous and endochondral ossification, owing to the maturational arrest of osteoblasts, indicating that Cbfa1 has a fundamental role in osteoblast differentiation. However, Cbfa1 was also expressed in chondrocytes, and its expression was increased according to the maturation of chondrocytes. Terminal hypertrophic chondrocytes expressed Cbfa1 extensively. The significant expression of Cbfa1 in hypertrophic chondrocytes was first detected at embryonic day 13.5 (E13.5), and its expression in hypertrophic chondrocytes was most prominent at E14.5-16.5. In Cbfa1-deficient mice, whose entire skeleton was composed of cartilage, the chondrocyte differentiation was disturbed. Calcification of cartilage occurred in the restricted parts of skeletons, including tibia, fibula, radius, and ulna. Type X collagen, BMP6, and Indian hedgehog were expressed in their hypertrophic chondrocytes. However, osteopontin, bone sialoprotein, and collagenase 3 were not expressed at all, indicating that they are directly regulated by Cbfa1 in the terminal hypertrophic chondrocytes. Chondrocyte differentiation was severely disturbed in the rest of the skeleton. The expression of PTH/PTHrP receptor, Indian hedgehog, type X collagen, and BMP6 was not detected in humerus and femur, indicating that chondrocyte differentiation was blocked before prehypertrophic chondrocytes. These findings demonstrate that Cbfa1 is an important factor for chondrocyte differentiation. (+info)
Adaptation in the vertebral column: a comparative study of patterns of metameric variation in seven species of small mammals.
The pattern of variation of certain vertebral measurements along the vertebral column is known to differ in man and mouse. This paper investigates changes in this pattern in 7 species of small mammals and attempts to correlate them with locomotor adaptations and limb dimensions. (+info)