(1/822) Spatiotemporal expression of alternatively spliced IGF-I mRNA in the rat costochondral growth plate.
IGF-I acts as a local proliferation and maturation factor for chondrocytes in the growth plate. However, the expression of different alternative IGF-I mRNA classes in the growth plate has not been characterized. Using quantitative reverse transcription PCR, the abundance of each alternative IGF-I mRNA class in resting, proliferative and hypertrophic chondrocytes was measured in rat costochondral growth plates. Class 1Ea mRNA was the most abundant IGF-I transcript overall and was highly expressed in proliferative chondrocytes at 2 and 4 weeks of age; by 6 weeks, the majority of 1Ea mRNA expression had shifted to hypertrophic chondrocytes. Class 1Eb mRNA was the second most abundant transcript and its distribution was uniform across all the cell types at 2 weeks of age. The expression pattern changed with increasing age such that at 6 weeks a gradient existed with hypertrophic chondrocytes expressing higher levels of 1Eb than resting chondrocytes. Class 2Ea mRNA was constitutively expressed at low levels across the growth plate at all ages, while class 2Eb mRNA expression was negligible. The distribution of total IGF-I mRNA also shifted across growth plate cell types as the animals aged from 2 to 6 weeks. These findings suggest that IGF-I class 1 mRNA plays the predominant role in the maturation of the growth plate. (+info)
(2/822) The bcl-2 knockout mouse exhibits marked changes in osteoblast phenotype and collagen deposition in bone as well as a mild growth plate phenotype.
Histological examination of long bones from 1-day-old bcl-2 knockout and age-matched control mice revealed no obvious differences in length of bone, growth plate architecture or stage of endochondral ossification. In 35-day-old bcl-2 knockout mice that are growth retarded or 'dwarfed'. the proliferative zone of the growth plate appeared slightly thinner and the secondary centres of ossification less well developed than their age-matched wild-type controls. The most marked histological effects of bcl-2 ablation were on osteoblasts and bone. 35-day-old knockout mouse bones exhibited far greater numbers of osteoblasts than controls and the osteoblasts had a cuboidal phenotype in comparison with the normal flattened cell appearance. In addition, the collagen deposited by the osteoblasts in the bcl-2 knockout mouse bone was disorganized in comparison with control tissue and had a pseudo-woven appearance. The results suggest an important role for Bcl-2 in controlling osteoblast phenotype and bone deposition in vivo. (+info)
(3/822) A mouse model for achondroplasia produced by targeting fibroblast growth factor receptor 3.
Achondroplasia, the most common form of dwarfism in man, is a dominant genetic disorder caused by a point mutation (G380R) in the transmembrane region of fibroblast growth factor receptor 3 (FGFR3). We used gene targeting to introduce the human achondroplasia mutation into the murine FGFR3 gene. Heterozygotes for this point mutation that carried the neo cassette were normal whereas neo+ homozygotes had a phenotype similar to FGFR3-deficient mice, exhibiting bone overgrowth. This was because of interference with mRNA processing in the presence of the neo cassette. Removal of the neo selection marker by Cre/loxP recombination yielded a dominant dwarf phenotype. These mice are distinguished by their small size, shortened craniofacial area, hypoplasia of the midface with protruding incisors, distorted brain case with anteriorly shifted foramen magnum, kyphosis, and narrowed and distorted growth plates in the long bones, vertebrae, and ribs. These experiments demonstrate that achondroplasia results from a gain-of-FGFR3-function leading to inhibition of chondrocyte proliferation. These achondroplastic dwarf mice represent a reliable and useful model for developing drugs for potential treatment of the human disease. (+info)
(4/822) Aberrant death in dark chondrocytes of the avian growth plate.
Growth plate chondrocytes of embryonic chick femurs were examined by electron microscopy, cytophotometry and autoradiography. Apart from the well-described 'light' chondrocyte, a different 'dark' type of chondrocyte was present, comprising 10 - 35% of the cell population. They were found at all stages of chondrocyte differentiation and in all ages of the femurs studied. Well developed rough endoplasmatic reticulum and Golgi complex, many secretory vesicles, energetically active mitochondria and a lot of glycogen, indicating high activity of the cytoplasm, were combined with low RNA synthesis, gentle margination and scattered compaction of the chromatin. DNA cytometry revealed that most of dark cells were diploid, but 15 - 30% were tetraploid, with the absence of an S-phase. Substantial loss of DNA was found in about 10% of dark chondrocytes. The TUNEL reaction demonstrated a limited number of DNA strand breaks. Advanced dark cells possessed the nuclear features of both apoptosis and necrosis. Besides chromomeric-chromonemic compaction, a chromatin arrangement similar to that of prometaphase and metaphase, as well as amitotic nuclear segregation, all of them degenerative, were found. Our interpretation is that the dark chondrocytes undergo an aberrant type of cell death which may be combined with aberrant cell cycle. Cell death of dark chondrocytes is preceded by a pre-mortal burst of secretion. (+info)
(5/822) Growth plate cartilage formation and resorption are differentially depressed in growth retarded uremic rats.
To characterize the modifications of growth plate in individuals with growth impairment secondary to chronic renal failure, young rats were made uremic by subtotal nephrectomy (NX) and, after 14 d, their tibial growth plates were studied and compared with those of sham-operated rats fed ad libitum (SAL) or pair-fed with NX (SPF). NX rats were growth retarded and severely uremic. Growth plate height (mean +/- SD) was much greater (P<0.05) in NX (868.4+/-85.4 microm) than SAL (570.1+/-93.5 microm) and SPF (551.9+/-99.7 microm) rats as a result of a higher (P<0.05) hypertrophic zone (661.0+/-89.7 versus 362.8+/-71.6 and 353.0+/-93.9 microm, respectively). The increased size of the growth plate was associated with a greater number of chondrocytes and modifications in their structure, particularly in the hypertrophic zone adjacent to bone. In this zone, chondrocytes of NX animals were significantly (P<0.05) smaller (12080.4+/-1158.3 microm3) and shorter (34.1+/-2.5 microm) than those of SAL (16302.8+/-1483.4 microm3 and 37.8+/-2.0 microm) and SPF (14465.8+/-1521.0 microm3 and 36.3+/-1.8 microm). The interface between the growth plate cartilage and the metaphyseal bone appeared markedly irregular in NX rats. Kinetics of chondrocytes was also modified (P<0.05) in the NX rats, which had lower cell turnover per column per day (5.4+/-0.9), longer duration of hypertrophic phase (89.0+/-15.2 h), and reduced cellular advance velocity (7.4+/-2.2 microm/h) compared with SAL (8.0+/-1.6, 32.1+/-6.7 h, and 11.3+/-2.7 microm/h) and SPF (7.2+/-1.1, 34.8+/-5.1 h, and 10.1+/-2.5 microm/h). Cell proliferation was no different among the three groups. Because the growth plates of SPF and SAL rats were substantially not different, modifications observed in the NX rats cannot be attributed to the nutritional deficit associated with renal failure. These findings indicate that chronic renal failure depresses both the activity of the growth plate cartilage by altering chondrocyte hypertrophy and the replacement of cartilage by bone at the metaphyseal end. The two processes are differentially depressed since cartilage resorption is more severely lowered than cartilage enlargement and this leads to an accumulation of cartilage at the hypertrophic zone. (+info)
(6/822) Measurement of biological activity of somatotropin in hypophysectomized rats.
AIM: To develop a method for measurement of biological activity of recombinant DNA-derived somatotropin (rhGH). METHODS: The effects of varying the route, frequency and period of administration of GH, the sex of test animals on the biological responses, body weight gain (BWG), and tibial epiphyseal width (TEW), of hypophysectomized (Hypox) rats were compared, respectively. 4-d BWG, 6-d BWG, and 6-d TEW tests were carried out simultaneously in the same group of Hypox rats to determine the biopotency of GH preparations according to a parallel line bioassay (6-point assay). The final result was chosen from the test which had smaller values for the index of precision (lambda) and the average rate of fiducial limits (ARFL) than other tests. RESULTS: No significant differences in the responses between male and female rats, between sc and im, once daily and twice daily injections of bGH were found. But the BWG and TEW of Hypox rats injected with 0.045 and 0.135 IU.d-1 of bGH for 6 d were significantly greater than that for 4 d. Both 4-d BWG test and 6-d BWG test in the range from 0.020 to 0.500 IU.d-1 had values for lambda = 0.0660 and 0.1747, and for r = 0.9000 and 0.9237, respectively. Three estimates of rhGH preparation compared with the International Standard for somatotropin (IShGH), 4.6132, 3.9829, and 4.8023 IU/ampoule, were obtained separately from 4-d BWG test, 6-d BWG test and 6-d TEW test. And the result from 6-d BWG test was reported finally because it had smaller values for lambda and ARFL (0.0608 and 37.907%) than other two tests. CONCLUSION: Both BWG test and TEW test can be carried out simultaneously in the same group of Hypox rats. 6-d BWG test seemed to be more suitable for potency determination of GH preparations than 4-d BWG test and 6-d TEW test. (+info)
(7/822) Immunohistochemical observations on the initial disorders of the epiphyseal growth plate in rats induced by high dose of vitamin A.
The initial disorders of the epiphyseal growth plate cartilage were immunohistochemically examined in the proximal tibia of rats administered a high dose of vitamin A. Male Wistar rats were given 100,000 IU/100 g body weight/day of vitamin A for administration periods of 1 to 5 days (Day 1 to 5) from 4 weeks after birth or were given deionized water and used as control. They were sacrificed after 5-bromo-2'-deoxyuridine (BrdU) injection on Day 1 to Day 5 to remove the tibiae. The tibiae were processed for immunohistochemical examinations using antibodies against type I, II, X collagens and BrdU. BrdU-incorporated chondrocytes and type X collagen-negative area were reduced since Day 2 and type X collagen-positive area was reduced since Day 4. The cartilage matrix partially lost type II collagen and deposited type I collagen in the epiphyseal growth plate near the periosteum on Day 5. These findings suggest that a high dose of vitamin A initially disturbed the differentiation from resting to proliferating chondrocytes, subsequently inhibited the differentiation from proliferating to hypertrophic chondrocytes, caused the chondrocytes to deviate from the process of normal differentiation, and finally resulted in the deformation of the epiphyseal growth plate. (+info)
(8/822) Cathepsin expression during skeletal development.
Cysteine proteinases, cathepsins B, H, K, L and S, have been implicated in several proteolytic processes during development, growth, remodeling and aging, as well as in a variety of pathological processes. For systematic analysis of cathepsin gene expression we have produced cDNA clones for mouse and human cysteine cathepsins. Northern analysis of a panel of total RNAs isolated from 16-19 different human and mouse tissues revealed the presence of mRNAs for cathepsin B, H, K, L and S in most tissues, but each with a distinct profile. Of the different cathepsin mRNAs, those for cathepsin K were clearly the highest in bone and cartilage. However, relatively high mRNA levels for the other cathepsins were also present in these tissues. To better understand the roles of different cathepsins during endochondral ossification in mouse long bones, cathepsin mRNAs were localized by in situ hybridization. Cathepsin K mRNAs were predominantly seen in multinucleated chondroclastic and osteoclastic cells at the osteochondral junction and on the surface of bone spicules. The other cathepsin mRNAs were also seen in osteoclasts, and in hypertrophic and proliferating chondrocytes. These observations were confirmed by immunohistochemistry and suggest that all cysteine cathepsins are involved in matrix degradation during endochondral ossification. (+info)