Enhanced expression of TGF-beta and c-fos mRNAs in the growth plates of developing human long bones

The expression of mRNAs for type I and type II procollagens, transforming growth factor-beta (TGF-beta) and c-fos was studied in developing human long bones by Northern blotting and in situ hybridization. The cells producing bone and cartilage matrix were identified by hybridizations using cDNA probes for types I and II collagen, respectively. Northern blotting revealed that the highest levels of TGF-beta mRNA were associated with the growth plates. By in situ hybridization, this mRNA was localized predominantly in the osteoblasts and osteoclasts of the developing bone, in periosteal fibroblasts and in individual bone marrow cells. These findings are consistent with the view that TGF-beta may have a role in stimulation of type I collagen production and bone formation. Only a low level of TGF-beta mRNA was detected in cartilage where type II collagen mRNA is abundant. In Northern hybridization, the highest levels of c-fos mRNA were detected in epiphyseal cartilage. In situ hybridization revealed two cell types with high levels of c-fos expression: the chondrocytes bordering the joint space and the osteoclasts of developing bone. These differential expression patterns suggest specific roles for TGF-beta and c-fos in osseochondral development.     

Coordinate expression of NGF and α-smooth muscle actin mRNA and protein in cutaneous wound tissue of developing and adult rats

Nerve growth factor (NGF) is synthesized in cutaneous wound tissue, and its higher levels in the neonate may contribute to more efficient wound healing. We used in situ hybridization and immunohistochemistry to define NGF mRNA and protein expression in intact skin and following excision wounding in neonatal and adult rats. To determine whether NGF is associated with wound contractile fibroblasts (myofibroblasts), we also examined expression of !-smooth muscle actin (!-SMA) mRNA and protein, established markers for these cells. In intact skin, NGF mRNA and protein were present in vascular and arrector pili smooth muscle, hair follicle sheath cells, keratinocytes, and hypodermal fibroblasts. Neonatal adipocytes and Schwann cells also expressed NGF mRNA and protein, while adult adipocytes and Schwann cells displayed only NGF-ir. Following wounding, NGF mRNA expression was exuberant in these cell types, and increased similarly at both ages and appeared de novo in skeletal muscle cells. Additionally, both NGF mRNA and protein were present in macrophages and myofibroblasts, and expression in myofibroblasts was significantly greater in neonates. Wound myofibroblasts also expressed !-SMA. Surprisingly, after wounding !-SMA mRNA and protein were present in essentially all cells in which NGF mRNA was detected. We conclude that NGF expression is enhanced in many cell types after wounding, but greater NGF synthesis in neonates appears to be due to a more robust myofibroblast response. In addition, cell types which demonstrated NGF mRNA also expressed !-SMA, and staining for both markers increased following wounding, suggesting synthesis of both proteins is regulated in a coordinated fashion.     

Collagen XVI is expressed by human dermal fibroblasts and keratinocytes and is associated with the microfibrillar apparatus in the upper papillary dermis.

Indirect immunofluorescence staining of normal skin with affinity-purified antibodies revealed a conspicuous presence of collagen XVI at the dermo-epidermal interface where it occurs in close vicinity to collagen VII. In addition, the protein co-localizes with fibrillin 1 at the cutaneous basement membrane zone and the adjacent papillary dermis, but not in deeper layers of the dermis. Both fibronectin and collagen XVI are distributed throughout smooth muscles of hair follicles but do not co-localize. These data suggest, therefore, that collagen XVI contributes to the structural integrity of the dermo-epidermal junction zone by interacting with components of the anchoring complexes and the microfibrillar apparatus. A strong immunofluorescence signal associated with the extracellular matrix of individual cells was observed for keratinocytes or fibroblasts in monolayer cultures. Therefore, both cell types are likely sources of the protein also in situ. The rate of expression of collagen XVI mRNA in keratinocytes is about half of that in normal human skin fibroblasts. In both cell types, TGF-beta2 treatment results in an up-regulation of the collagen XVI-mRNA by approximately 50%. In keratinocytes, synthesis of collagen XVI protein and deposition to the cell layer and the extracellular matrix is stimulated fivefold and twofold, respectively. Since TGF-beta2 also upregulates the biosynthesis of other matrix macromolecules in the subepidermal zone the factor is likely to contribute to the stabilization of matrix zones near basement membranes in healing wounds.     

Induction of platelet-derived growth factor receptor expression in smooth muscle cells and fibroblasts upon tissue culturing

The expression of platelet-derived growth factor (PDGF) receptors in porcine uterus and human skin in situ, was compared with that of cultured primary cells isolated from the same tissues. PDGF receptor expression was examined by monoclonal antibodies specific for the B type PDGF receptor and by RNA/RNA in situ hybridization with a probe constructed from a cDNA clone encoding the B type PDGF receptor. In porcine uterus tissue both mRNA and the protein product for the PDGF receptor were detected in the endometrium; the myometrium, in contrast, contained much lower amounts. Moreover, freshly isolated myometrial cells were devoid of PDGF receptors. However, after 1 d in culture receptors appeared, and after 2 wk of culturing essentially all of the myometrial cells stained positively with the anti-PDGF receptor antibodies and contained PDGF receptor mRNA. Similarly, B type PDGF receptors were not detected in normal human skin, but fibroblast-like cells from explant cultures of human skin possessed PDGF receptors. When determined by immunoblotting, porcine uterus myometrial membranes contained approximately 20% of the PDGF receptor antigen compared with the amount found in endometrial membranes. In addition, PDGF stimulated the phosphorylation of a 175-kD component, most likely representing autophosphorylation of the B type PDGF receptor in endometrial membranes, whereas only a marginal phosphorylation was seen in myometrial membranes. Taken together, these results demonstrate that PDGF receptor expression varies in normal tissues and that fibroblasts and smooth muscle cells do not uniformly express the receptor in situ. Furthermore, fibroblasts and smooth muscle cells that are released from tissues are induced to express PDGF receptors in response to cell culturing. The data suggest that, in addition to the availability of the ligand, PDGF-mediated cell growth in vivo is dependent on factors regulating expression of the receptor.     

Gamma-interferon inhibits extracellular matrix synthesis and remodeling in collagen lattice cultures of normal and scleroderma skin fibroblasts.

Three-dimensional collagen lattice cultures of fibroblasts mimic the in vivo situation better than monolayer cultures. Here, skin fibroblasts from scleroderma patients and healthy controls were cultivated in collagen lattices, and the effects of recombinant human gamma-interferon (IFN-gamma) on these cultures investigated. IFN-gamma inhibited collagen lattice retraction in a dose-dependent way at concentrations ranging from 10 to 10,000 U/ml. This effect was independent of any alteration to the cell proliferation within the lattices. The inhibition was of the same order of magnitude in normal and pathological fibroblasts. The synthesis of collagen and non-collagen proteins, particularly fibronectin, was increased in scleroderma cultures. It was inhibited in both normal and scleroderma fibroblasts by IFN-gamma, with a maximal effect at the concentration 1000 U/ml, but the inhibition of protein synthesis was far more intense in scleroderma than in normal cells. In situ hybridization, Northern blot and dot blot analyses showed that mRNA coding for pro alpha 1(I) collagen was decreased in IFN-gamma-treated cells, indicating an effect at the pretranslational level. IFN-gamma also inhibited glycosaminoglycan synthesis, but in scleroderma cells only. This study shows that IFN-gamma regulates cell behavior in three-dimensional collagen matrices: (i) it decreases protein and specifically glycosaminoglycan synthesis in scleroderma fibroblasts, (ii) it modulates the interactions between cells and matrix that lead to the retraction of the lattice. Whereas collagen synthesis is largely decreased in lattice cultures like in vivo, it remains increased in the case of scleroderma compared to normal fibroblasts and may be down-regulated by IFN-gamma. Similar conclusions may be drawn for fibronectin and glycosaminoglycans. The inhibitory effect of IFN-gamma on the retraction capacity of fibroblasts and on their ability to synthesize increased amounts of extracellular matrix macromolecules may be of potential interest for therapeutic use of IFN-gamma in scleroderma patients.     

In situ assessment of mRNA accessibility in heterogeneous tissue samples using elongation factor-1α (EF-1α)

 Elongation factor-1α (EF-1α) is an evolutionarily highly conserved universal cofactor of protein synthesis in all living cells. In this study, its use as a positive control in situ hybridization assays for specific detection of mRNA sequences was evaluated. Northern blot analysis of various non-neoplastic and neoplastic cultured cells of different stages of confluence, cell shape, and cell cycle status revealed that EF-1α had a lower and more homogeneous expression than did β-actin. In situ hybridization assays using digoxigenin-labeled riboprobes for the detection of EF-1α mRNA in routinely formalin-fixed, paraffin-embedded tissue sections showed that EF-1α is a suitable positive control in all types of cells. However, variation of protease pretreatments demonstrated distinct and sometimes mutually exclusive digestion conditions for different cell types within the same tissue sample. Our results indicate that detection of EF-1α mRNA is an appropriate internal standard for in situ hybridization assays and that it is useful to control artifacts such as false negatives caused by inappropriate protease pretreatments. The observed variability of optimal protease pretreatments for different cell types within the same tissue section strengthens the importance of a positive control in in situ hybridization assays. Accepted: 17 December 1996     

Altered fibronectin mRNA splicing in skin fibroblasts from Ehlers-Danlos syndrome patients: in situ hybridization analysis.

The expression of fibronectin (FN) mRNA isoforms generated by alternative splicing of the EDA region was studied by dot-blot and in situ hybridization, using specific FN cDNA probes, in skin fibroblasts from controls and Ehlers-Danlos Syndrome (EDS) patients (types III, IV, VII and non classified). An Image Analysis program was used for the quantitative evaluation and comparison of FN mRNAs levels in the different cell strains. The in situ hybridization analysis showed that FN mRNAs are homogeneously expressed in all cells of each fibroblast strain analyzed. While in control fibroblasts about 70% of FN mRNA isoforms contain the EDA region (EDA+ FN mRNAs), in EDS fibroblasts this fraction is reduced up to about 30%. This indicates that in the EDS fibroblasts analyzed a deregulation of the alternative splicing processes acting at the EDA region takes place.     

Activation of type I collagen genes in cultured scleroderma fibroblasts

Fibroblasts cultured from affected skin areas of five patients with cutaneous scleroderma were found to produce increased amounts of collagen when compared with nonaffected control cells. Total RNA was isolated from the cultures and analyzed for its level of pro alpha 1 (I)collagen mRNA by hybridization of RNA blots with a cloned cDNA probe. The levels of pro alpha 1 (I)collagen mRNAs relative to total RNA were two- to sixfold higher in the samples from affected cells, accounting for the increased synthesis of type I collagen. Cytoplasmic dot hybridizations were performed to measure the cellular content of pro alpha 1 (I)collagen mRNA: up to ninefold increases in the level of this mRNA per cell were found. Upon subculturing, scleroderma fibroblasts were found to reduce gradually the increased synthesis of collagen to the level of nonaffected controls by the tenth passage. The levels of type I collagen mRNAs were also reduced, but more slowly. The results suggest that in scleroderma fibroblasts the genes for type I collagen are activated at procollagen mRNA level or that they are more stable and that the activating factors are lost during prolonged cell culture because cells from affected areas lose their activated state.     

Quantitation of in situ hybridization of ribosomal ribonucleic acids to human diploid cells

The hybridization of 5S and 28S ribosomal RNAs to human fibroblast and leukocyte cells was used as a model system to quantitate the technique of in situ hybridization for human diploid cell types. Quantitation consisted of counting (scoring) the number of grains formed over both interphase nuclei and metaphase chromosomes on slides after various hybridization procedures. The average number of grains/nucleus per slide was then used to determine hybridization percentages. As with nitrocellulose filter hybridizations the kinetics of in situ hybridizations can be fit with a single first-order rate constant. However, the in situ hybridization rate was approximately 10 times slower than the corresponding filter hybridization rate. The efficiency of in situ hybridization was found to range between 5 and 15% for both leukocyte and fibroblast cell types and for both metaphase and interphase nuclei. Determination of the parameters of the in situ hybridization reaction of ribosomal RNAs to diploid chromosomes define the experimental conditions needed for the localization of single copy genes to diploid chromosomes.     

Quantitative analysis of in situ hybridization methods for the detection of actin gene expression.

We have implemented an efficient, quantitative approach for the optimization of in situ hybridization using double-stranded recombinant DNA probes. The model system studied was actin mRNA expression in chicken embryonic muscle cultures. Actin and control (pBR322) probes were nick-translated with p32 labeled nucleotides, hybridized to cells grown on coverslips, and quantitated in a scintillation counter. Cellular RNA retention was monitored via the incorporation of H3-Uridine into RNA prior to cell fixation. Over a thousand samples were analyzed, and among the technical variables examined were the fixation protocol, proteolytic cell pretreatment, the time course of hybridization, saturation kinetics, hybridization efficiency, and effect of probe size on hybridization and network formation. Results have allowed us to develop a reproducible in situ hybridization methodology which is simpler and less destructive to cellular RNA and morphology than other protocols. Moreover, this technique is highly sensitive and efficient in detection of cellular RNAs. Lastly, the rapid quantitative approach used for this analysis is valuable in itself as a potential alternative to filter or solution hybridizations.     

Matrilin-2, a large, oligomeric matrix protein, is expressed by a great variety of cells and forms fibrillar networks

Matrilin-2 is a member of the protein superfamily with von Willebrand factor type A-like modules. Mouse matrilin-2 cDNA fragments were expressed in 293-EBNA cells, and the protein was purified, characterized, and used to immunize rabbits. The affinity-purified antiserum detects matrilin-2 in dense and loose connective tissue structures, subepithelial connective tissue of the skin and digestive tract, specialized cartilages, and blood vessel walls. In situ hybridization of 35S-labeled riboprobes localizes the matrilin-2 mRNA to fibroblasts of dermis, tendon, ligaments, perichondrium, and periosteum; connective tissue elements in the heart; smooth muscle cells; and epithelia and loose connective tissue cells of the alimentary canal and respiratory tract. RNA blot hybridization and immunoblotting revealed both matrilin-2 mRNA and protein in cultures of a variety of cell types, confirming the tissue distribution. Alternative splicing affects a module unique for matrilin-2 in all of the above RNA sources. SDS-polyacrylamide gel electrophoresis and electron microscopy reveals matrilin-2 from tissue extracts and cell line cultures as a mixture of mono-, di-, tri-, and tetramers. Matrilin-2 is substituted with N-linked oligosaccharides but not with glycosaminoglycans. Because of other, yet unidentified, cell-type dependent posttranslational modifications, the monomer is heterogeneous in size. Immunofluorescence showed that matrilin-2 functions by forming an extracellular, filamentous network.     

Study of fibronectin expression in tumour cells by dot-blot and in situ hybridization: quantitative evaluation by image analysis

An Image Analysis program was used for the quantitative evaluation and comparison of the fibronectin (FN) mRNA detected by dot-blot and in situ hybridization in different cell lines. These techniques were applied for the evaluation of FN mRNA synthesized by human normal fibroblasts (Flow 7000) and by four tumour-derived cell lines (HeLa, epithelioid carcinoma; 8387, fibrosarcoma; RD, rhabdomyosarcoma; SK Hep-1, hepatocarcinoma). Dot-blot analysis showed that the cell types analysed synthesize different levels of FN mRNA. Flow 7000 are the highest producers while HeLa the lowest. In situ hybridization confirmed these results and furthermore showed that while Flow 7000, 8387 and HeLa cells synthesized homogeneous levels of FN mRNA, RD and SK Hep-1 could be subdivided into two populations expressing high or low levels of FN mRNA. The combined analysis of dot-blot, in situ hybridization and Image Analysis allowed the quantitation of the number of FN mRNA molecules expressed by single cells. This approach is therefore an invaluable tool when evaluating mRNA expression in heterogeneous cell populations like tumour-derived cell lines, during cell cycle or in histological tissue sections.     

Identification of genes preferentially expressed in periodontal ligament: specific expression of a novel secreted protein, FDC-SP

Gene expression in human periodontal ligament (PDL) was examined by suppression subtractive hybridization to identify genes that are preferentially expressed in tissue compared to cultured PDL fibroblasts. The most enriched genes in a subtracted cDNA library are primarily genes for extracellular matrix components, types I and III collagen, lumican, periostin, and asporin, among others, whose expression conveys unique mechanical properties to the PDL. Also within this group is the gene for follicular dendritic cell secreted protein (FDC-SP), a small protein like statherin in saliva, not previously found in PDL. FDC-SP's presence in PDL was confirmed by in situ hybridization in mouse which also showed that it was definitely present in the parotid gland, but, surprisingly, not in the other salivary glands: submandibular and sublingual. Since only normal tissue was examined, these findings suggest that FDC-SP plays an important but previously unsuspected role within oral connective tissue.