Expression profiling of human fetal growth plate cartilage by EST sequencing

Effects of egg exposure to atrazine and/or glyphosate on bone development in Podocnemis unifilis (Testudines, Podocnemididae)

This study was designed to investigate skeletal changes in Podocnemis unifilis embryos derived from artificially incubated eggs exposed to different concentrations of atrazine, glyphosate or atrazine and glyphosate mixture. Forty-two eggs were randomly allocated to one of seven trays containing vermiculite treated distilled water (control group) or the following solutions: 2 or 200 μg L-1 of atrazine (groups A1 and A2 respectively); 65 or 6500 μg L-1 of glyphosate (groups G1 and G2 respectively); 2 μg L-1 and 65 μg L-1 or 200 μg L-1 and 6500 μg L-1 of atrazine and glyphosate mixture (groups AG1 and AG2 respectively). Three eggs per tray were randomly collected on days 30 and 50 of the incubation period. Embryos were submitted to soft tissue diaphanization and stained with Alizarin red S or Alcian blue for morphological analysis of bone and cartilage tissues; histological analysis was performed to confirm ossification changes. Findings were compared between groups. Morphological changes were limited to sclerotic ring features and number of ribs. Malformations rates differed significantly (p < 0.05) between embryos in the control and treated groups A2, AG1 and AG2. Concurrent exposure to atrazine and glyphosate did not affect the presence or severity of embryonic malformations and was not associated with appendicular skeleton changes in P. unifilis embryos. However, further studies focusing on the axial skeleton with particular emphasis on rib abnormalities are warranted.

A New Look at Causal Factors of Idiopathic Scoliosis: Altered Expression of Genes Controlling Chondroitin Sulfate Sulfation and Corresponding Changes in Protein Synthesis in Vertebral Body Growth Plates

Background: In a previous report, we demonstrated the presence of cells with a neural/glial phenotype on the concave side of the vertebral body growth plate in Idiopathic Scoliosis (IS) and proposed this phenotype alteration as the main etiological factor of IS. In the present study, we utilized the same specimens of vertebral body growth plates removed during surgery for Grade III-IV IS to analyse gene expression. We suggested that phenotype changes observed on the concave side of the vertebral body growth plate can be associated with altered expression of particular genes, which in turn compromise mechanical properties of the concave side. Methods: We used a Real-Time SYBR Green PCR assay to investigate gene expression in vertebral body growth plates removed during surgery for Grade III-IV IS; cartilage tissues from human fetal spine were used as a surrogate control. Special attention was given to genes responsible for growth regulation, chondrocyte differentiation, matrix synthesis, sulfation and transmembrane transport of sulfates. We performed morphological, histochemical, biochemical, and ultrastructural analysis of vertebral body growth plates. Results: Expression of genes that control chondroitin sulfate sulfation and corresponding protein synthesis was significantly lower in scoliotic specimens compared to controls. Biochemical analysis showed 1) a decrease in diffused proteoglycans in the total pool of proteoglycans; 2) a reduced level of their sulfation; 3) a reduction in the amount of chondroitin sulfate coinciding with raising the amount of keratan sulfate; and 4) reduced levels of sulfation on the concave side of the scoliotic deformity. Conclusion: The results suggested that altered expression of genes that control chondroitin sulfate sulfation and corresponding changes in protein synthesis on the concave side of vertebral body growth plates could be causal agents of the scoliotic deformity.

Type XXVII collagen at the transition of cartilage to bone during skeletogenesis

COL27A1 is a member of the collagen fibrillar gene family and is expressed in cartilaginous tissues including the anlage of endochondral bone. To begin to understand its role in skeletogenesis, the temporospatial distributions of its RNA message and protein product, type XXVII collagen, were determined in developing human skeletal tissues. Laser capture microdissection and quantitative reverse-transcription polymerase chain reaction demonstrated that gene expression occurred throughout the growth plate and that it was higher in the resting and proliferative zones than in hypertrophic cartilage. Immunohistochemical analyses showed that type XXVII collagen was most evident in hypertrophic cartilage at the primary ossification center and at the growth plate and that it accumulated in the pericellular matrix. Synthesis of type XXVII collagen overlapped partly with that of type X collagen, a marker of chondrocyte hypertrophy, preceded the transition of cartilage to bone, and was associated with cartilage calcification. Immunogold electron microscopy of extracted ECM components from mouse growth plate showed that type XXVII collagen was a component of long non-banded fibrous structures, filamentous networks, and thin banded fibrils. The timing and location of synthesis suggest that type XXVII collagen plays a role during the calcification of cartilage and the transition of cartilage to bone.

Ucma--A novel secreted factor represents a highly specific marker for distal chondrocytes

Growth and development of most parts of the vertebrate skeleton takes place by endochondral ossification, a process during which chondrocytes undergo distinct stages of differentiation resulting in a successive replacement of the cartilage anlagen by bone. In the context of an EST project we isolated a novel transcript from a human fetal growth plate cartilage cDNA library. The transcript which we called Ucma (unique cartilage matrix-associated protein) encodes a short protein of 138 amino acids. The protein sequence is evolutionary conserved throughout vertebrates and comprises a signal peptide, a coiled-coil domain, and a putative dibasic cleavage site for proprotein convertases. Using RNA in situ hybridization and immunohistochemistry with a polyclonal anti-Ucma antibody we found high expression of Ucma uniquely in distal (resting) chondrocytes in developing long bones of wildtype mice. This restricted expression could also be observed in Ihh(-/-), Ihh(-/-); Gli3(-/-), Gli3(-/-) mice, and in mice that overexpress Ihh under the control of the Col2a1 promoter indicating that expression of Ucma is regulated independent of hedgehog signaling. During insulin-induced differentiation of ATDC5 cells we found gradual increase of Ucma expression at day 21 with a maximum at day 24 and a decrease correlating with a simultaneous increase in the expression of cartilage link protein (Crtl1), a protein with maximum expression in column-forming proliferating chondrocytes. The present data strongly suggest an important function of Ucma in the early phase of chondrocyte differentiation.

Cartilage-selective genes identified in genome-scale analysis of non-cartilage and cartilage gene expression

Background

Cartilage plays a fundamental role in the development of the human skeleton. Early in embryogenesis, mesenchymal cells condense and differentiate into chondrocytes to shape the early skeleton. Subsequently, the cartilage anlagen differentiate to form the growth plates, which are responsible for linear bone growth, and the articular chondrocytes, which facilitate joint function. However, despite the multiplicity of roles of cartilage during human fetal life, surprisingly little is known about its transcriptome. To address this, a whole genome microarray expression profile was generated using RNA isolated from 18–22 week human distal femur fetal cartilage and compared with a database of control normal human tissues aggregated at UCLA, termed Celsius.

Results

161 cartilage-selective genes were identified, defined as genes significantly expressed in cartilage with low expression and little variation across a panel of 34 non-cartilage tissues. Among these 161 genes were cartilage-specific genes such as cartilage collagen genes and 25 genes which have been associated with skeletal phenotypes in humans and/or mice. Many of the other cartilage-selective genes do not have established roles in cartilage or are novel, unannotated genes. Quantitative RT-PCR confirmed the unique pattern of gene expression observed by microarray analysis.

Conclusion

Defining the gene expression pattern for cartilage has identified new genes that may contribute to human skeletogenesis as well as provided further candidate genes for skeletal dysplasias. The data suggest that fetal cartilage is a complex and transcriptionally active tissue and demonstrate that the set of genes selectively expressed in the tissue has been greatly underestimated.

Changes in mRNA gene expression during growth in the femoral head of the young rat

The rate of physeal growth slows as an animal matures with changes in mRNA gene expression due to the altered cellular activity. To measure the change in gene expression during the juvenile growth period, the femoral head, enclosing the proximal femoral physis, primary spongiosa, and articular cartilage, was collected from both femora of 16 female Sprague-Dawley rats between 4 and 10 weeks of age. One femur of each rat had had a mid-diaphyseal femoral fracture at 4 weeks of age. RNA was extracted and hybridized to 16 Affymetrix Rat Genomic 230 2.0 GeneChip microarrays with probe sets for 31,000 genes of which 18,200 were expressed. Of these, 8002 genes had a significant change in gene expression during growth, about half increasing and half decreasing. These changes included up-regulation with time of genes related to cartilage, blood vessels, osteoprotegerin, osteomodulin, and most ribosomal proteins. There was down-regulation with maturity of genes related to bone, growth-promoting cytokines, G proteins, GTPase-mediated signal transduction factors, cytokine receptors, mitosis, integrin-linked kinase, and the cytoskeleton. In summary, the slowing of growth with maturity was associated with changes in mRNA gene expression in the femoral head for a large number of genes. These changes in gene expression between young and mature rats suggest factors which are important for the support of the rapid linear growth during early life.

Neonatal growth cartilage: Equine tissue specific gene expression

Endochondral bone formation is an important process in development and growth of the skeleton; still many of the mechanisms of growth cartilage remain unknown. The aim of this study was to identify genes specifically expressed in growth cartilage by constructing a subtraction cDNA library of the articular-epiphyseal cartilage complex from neonatal foal. Two hundred and eighty-four differently expressed clones, representing five novel and 37 known genes, were detected by subtraction hybridization. The tissue specificity of these genes was verified by reverse Northern analysis, and tissue distribution was determined by Northern blot analysis. Genes were classified according to predicted function. The largest functional group was the extracellular matrix, followed by transcription, signalling, cytokines and growth factors. Gremlin, Angiopoietin-like 7, and Small acidic protein have previously not been detected in growth cartilage. Based on earlier descriptions of these genes, they may represent interesting candidates in future studies of developmental orthopedic disorders.

Chondrocyte genomics: implications for disease modification in osteoarthritis

Advances in genomic technologies have made genome-wide-association and gene-expression studies a reality. Despite technical and analytical challenges, the application of genomic technologies to osteoarthritis research will lead to a better understanding of the disease at the molecular level. Functional genomics will identify genes involved in the chondrocyte response to cartilage injury and cartilage repair, and will help clarify the role of chondrocytes in arthritis onset, progression and outcome. Systems biology will enable researchers to develop a full portrait of osteoarthritis, a complex and multifactorial disease that involves not only articular cartilage but also synovium, synovial fluid, subchondral bone and peripheral blood. Ultimately such an approach will result in novel diagnostic and therapeutic targets and better disease management.