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PubMed2005

Initial vascularization and tissue differentiation are influenced by fixation stability.

Fracture healing requires a certain degree of mechanical stability and an adequate blood supply. The hypothesis of the present study was that increased interfragmentary shear leads to a reduced initial vascularization and prolonged healing. The aim of the study was to quantitatively analyze the histological appearance of vascularization and tissue differentiation with regard to fracture stability during the course of healing. A mid-shaft osteotomy of the tibia was performed in two groups of sheep and stabilized with either a rigid or semirigid external fixator, differing in bending stiffness. Interfragmentary movements and ground reaction forces were evaluated in vivo during a 9-week period. The sheep were sacrificed at 2, 3, 6, and 9 weeks postoperatively. The tibiae were tested biomechanically and histological sections from the callus were prepared for analysis of tissue differentiation and vascularization. Larger interfragmentary shear movements in the semirigid fixator group were associated with a reduced initial blood supply. At 6 weeks the semirigid fixator group showed a significantly lower percentage of mineralized bone and a higher amount of fibrous tissue leading to a significantly lower stiffness of the callus than the rigid fixator group. This initial delay in healing was compensated for in the later stages with the production of greater volumes of callus tissue so that both groups showed the same callus stiffness at 9 weeks. However, the rigid fixator group showed signs of the beginning of callus remodeling at the latest time points suggesting a faster bone healing. The results indicate the important role of the initial mechanical stability specifically in the vascularization of an osteosynthesis. Further studies should illustrate the precise role of mechanical conditions on the regulation of angiogenesis during early bone healing.

Animals↗
PubMed2002

Vascular tissue differentiation and pattern formation in plants.

Vascular tissues, xylem and phloem, are differentiated from meristematic cells, procambium, and vascular cambium. Auxin and cytokinin have been considered essential for vascular tissue differentiation; this is supported by recent molecular and genetic analyses. Xylogenesis has long been used as a model for study of cell differentiation, and many genes involved in late stages of tracheary element formation have been characterized. A number of mutants affecting vascular differentiation and pattern formation have been isolated in Arabidopsis. Studies of some of these mutants have suggested that vascular tissue organization within the bundles and vascular pattern formation at the organ level are regulated by positional information.

Plant Development↗
PubMed1977

The role of enzyme degradation in enzyme turnover during tissue differentiation.

1. The role of enzyme degradation in enzyme turnover during tissue differentiation has been investigated by the use of equations based on the model of Berlin and Schimke (Mol. Pharmacol. 1 (1965) 149-156). 2. A digital computer has been used to calculate the change in enzyme amounts which would result from different changes in the rates of synthesis and degradation of an enzyme during cell differentiation. The energetics of these alternative processes have been compared. 3. The results demonstrate that changes in the rates of synthesis and degradation of an enzyme after a differentiation stimulus enhance the flexibility and rapidity of changes in enzyme amount during enzyme accumulation. Decreases in the rate of degradation of an enzyme during enzyme accumulation lead to a considerable saving of energy. 4. Hypotheses are proposed to account for the different modes of turnover of protein subgroups during cytodifferentiation in terms of specific changes in the rates of synthesis and degradation of the subgroups.

Cell Differentiation↗
PubMed2003

[Correlation of NDRG1 gene with liver tissue differentiation and hepatocarcinogenesis].

OBJECTIVE: To detect the expression profile of NDRG1 gene in different tissues and cell lines and explore the relationship of NDRG1 with liver tissue differentiation and hepatocarcinogenesis. METHODS: The expression profiles of NDRG1 in hepatocellular carcinoma (HCC) tissues, paired noncancerous liver (PNL) tissues, adult normal liver (NL) tissues, baby mouse liver tissues and fetal liver tissues in different developmental stages and cultured cell lines were performed using RT-PCR and Northern Blot analysis. RESULTS: Expression of NDRG1 was significantly up-regulated in HCC tissues compared to that of NL tissues and PNL tissues, however, the expressions of NDRG1 in NL and PNL tissues showed no evident difference. In ten cell lines, the highest expression was in the 293T human kidney cell line, the next one in liver cell L02, and the lowest one in the undifferentiated HLE cell line. Expression of NDRG1 in liver tissues enhanced with the development of the baby mouse and human fetus. CONCLUSION: NDRG1 is probably related to the liver cell differentiation and is highly expressed in the specific stage of the differentiation. However, it could not be recognized as a marker of differentiation. The high expression of NDRG1 in HCC indicates that HCC is not just distributed to a simple de-differentiation. Much more study is necessary in understanding the comprehensive relationship of the disorder proliferation and differentiation of HCC and the related genes.

Animals↗
PubMed1995

In vitro chick pre-cardiac explant tissue differentiation during spaceflight on SpaceHab-02.

Chick precardiac tissue explants were cultured on the 8-day mission of STS-60, space shuttle Discovery. Development of in vitro cultures of precardiac chick tissue from embryo stages 5 though 8 (H-H) were initiated during orbit and were terminated after approximately fifteen hours of 37 degree C culture. Transmission electron microscopy and tritiated thymidine studies were performed postflight. No significant differences in cell proliferation were observed between flight and ground controls. Electron-microscopic studies revealed stage 8 explants were capable of differentiation during flight in a pattern which matched ground control tissues. As anticipated, stage 7 explant tissues had differentiated to a lesser extent compared to stage 8 tissues. Interestingly, stage 7 precardiac explant flight tissue differentiation was less than ground control tissue. This difference in differentiation between flight and ground cultures was enhanced in stage 6 tissues, as high levels of myofibril organization were only seen in ground controls. Other cellular components such as Golgi apparatus, junctional complexes, and mitochondria were present and appeared normal and healthy.

Animals↗
PubMed2003

An implanted hamster greene melanoma expressing multiple host-tissue differentiation.

After Greene melanoma tissue had been implanted subcutaneously in a Syrian Golden Hamster and allowed to grow there for 10 days, its tissue components were examined by transmission electron microscopy. Amelanotic and melanotic tumor cells, blood vessels and nerve fibers were present. In the amelanotic and melanotic tumor cells the rough endoplasmic reticulum was colonized by spherical endogenous retroviruses, whereas no virus particles could be detected in endothelial or other cells. The cell-type-specific viruses thus mark separate cell lineages and indicate that blood vessels in Greene melanoma are not formed by tumor cells, so that the 'vasculogenic mimicry' currently under controversial discussion for other melanomas is not involved here. The tumor also comprised smooth muscle cells, skeletal muscle fibers and collagen fibers. This remarkable finding implies that tumor growth involves not only the stimulation of angiogenesis and neurogenesis by various growth factors, but also the activation of other cells/tissues in the adjacent host tissues. This influence of the surrounding host tissue produces the observed epiphenomena and can also cause the genotypic character of a tumor to be phenotypically masked (mimicry).

Animals↗
PubMed2006

Human mesenchymal stem cells from adipose tissue: Differentiation into hepatic lineage.

Adipose tissue represents an accessible source of mesenchymal stem cells (ADSCs), with similar characteristics to bone marrow-derived stem cells. The aim of this work was to investigate the transdifferentiation of ADSCs into hepatic lineage cells in vitro. ADSCs were obtained from human adipose tissue from lipectomy. Cells were grown in medium containing 15% AB human serum. Cultures were serum deprived for two days and exposed to a two-step protocol with two different media using growth factors and cytokines. Hepatic differentiation was assessed by RT-PCR of liver-marker genes. ADSCs exhibited a fibroblastic morphology that changed to a cuboidal shape when cells differentiated. Expression of liver genes increased when using one of the two studied media consisting of DMEM supplemented with HGF, bFGF and nicotinamide for 14 days. The results indicate that, under certain specific inducing conditions, ADSCs can be induced to differentiate into hepatic lineage in vitro. Adipose tissue may be an ideal source of high amounts of autologous stem cells.

Adipose Tissue↗
PubMed2006

Comparison of the performance of linear multivariate analysis methods for normal and dyplasia tissues differentiation using autofluorescence spectroscopy.

We compared the performance of three widely used linear multivariate methods for autofluorescence spectroscopic tissues differentiation. Principal component analysis (PCA), partial least squares (PLS), and multivariate linear regression (MVLR) were compared for differentiating at normal, tubular adenoma/epithelial dysplasia and cancer in colorectal and oral tissues. The methods' performances were evaluated by cross-validation analysis. The group-averaged predictive diagnostic accuracies were 85% (PCA), 90% (PLS), and 89% (MVLR) for colorectal tissues; 89% (PCA), 90% (PLS), and 90% (MVLR) for oral tissues. This study found that both PLS and MVLR achieved higher diagnostic results than did PCA.

Algorithms↗
PubMed1978

Evolution of isozyme loci and their differential tissue expression. Creatine kinase as a model system.

The phylogeny of the creatine kinase (CK, EC 2.7.3.2) isozyme loci and their differential tissue expressions were determined for representatives of 65 families of vertebrates, with emphasis on the fishes. The transition from the single creatine kinase locus, characteristic of certain echinoderms, to the two creatine kinase loci which are orthologous to those present in all vertebrates, occurred early in the chordate line. The majority of pre-teleostean fishes possesses only these two CK loci (A and C). These loci are relatively generalized in their tissue expressions which are variable among species of primitive fishes. The third and fourth creatine kinase loci (B and D) arose separately in the ancestors of the bony fishes and appear to be the result of regional genome duplications. Concomitant with the increase in the number of isozyme loci has been an increase in the specificity of their tissue expression. In the advanced teleost fishes the four CK loci are differentially expressed in a characteristic manner. The A2 isozyme predominates in skeletal muscle, the B2 isozyme in eye and brain, the C2 isozyme in stomach muscle, and the D2 isozyme is found exclusively in testis. We propose a phylogeny of the creatine kinase genes in the lower chordates based on the time of appearance of new CK loci, the sequence in which the loci achieve a tissue restricted expression, and the immunochemical relatedness of the orthologous and paralogous gene products.

Animals↗
PubMed2002

A mechano-regulation model for tissue differentiation during fracture healing: analysis of gap size and loading.

Bone has a capability to repair itself when it is fractured. Repair involves the generation of intermediate tissues, such as fibrous connective tissue, cartilage and woven bone, before final bone healing can occur. The intermediate tissues serve to stabilise the mechanical environment and provide a scaffold for differentiation of new tissues. The repair process is fundamentally affected by mechanical loading and by the geometric configuration of the fracture fragments. Biomechanical analyses of fracture healing have previously computed the stress distribution within the callus and identified the components of the stress tensor favouring or inhibiting differentiation of particular tissue phenotypes. In this paper, a biphasic poroelastic finite element model of a fracture callus is used to simulate the time-course of tissue differentiation during fracture healing. The simulation begins with granulation tissue (post-inflammation phase) and finishes with bone resorption. The biomechanical regulatory model assumes that tissue differentiation is controlled by a combination of shear strain and fluid flow acting within the tissue. High shear strain and fluid flows are assumed to deform the precursor cells stimulating formation of fibrous connective tissue, lower levels stimulate formation of cartilage, and lower again allows ossification. This mechano-regulatory scheme was tested by simulating healing in fractures with different gap sizes and loading magnitudes. The appearance and disappearance of the various tissues found in a callus was similar to histological observation. The effect of gap size and loading magnitude on the rate of reduction of the interfragmentary strain was sufficiently close to confirm the hypothesis that tissue differentiation phenomena could be governed by the proposed mechano-regulation model.

Bone Remodeling↗
PubMed2003

Mechanobiology of soft skeletal tissue differentiation--a computational approach of a fiber-reinforced poroelastic model based on homogeneous and isotropic simplifications.

The material properties of multipotent mesenchymal tissue change dramatically during the differentiation process associated with skeletal regeneration. Using a mechanobiological tissue differentiation concept, and homogeneous and isotropic simplifications of a fiber-reinforced poroelastic model of soft skeletal tissues, we have developed a mathematical approach for describing time-dependent material property changes during the formation of cartilage, fibrocartilage, and fibrous tissue under various loading histories. In this approach, intermittently imposed fluid pressure and tensile strain regulate proteoglycan synthesis and collagen fibrillogenesis, assembly, cross-linking, and alignment to cause changes in tissue permeability (k), compressive aggregate modulus (H(A)), and tensile elastic modulus (E). In our isotropic model, k represents the permeability in the least permeable direction (perpendicular to the fibers) and E represents the tensile elastic modulus in the stiffest direction (parallel to the fibers). Cyclic fluid pressure causes an increase in proteoglycan synthesis, resulting in a decrease in k and increase in H(A) caused by the hydrophilic nature and large size of the aggregating proteoglycans. It further causes a slight increase in E owing to the stiffness added by newly synthesized type II collagen. Tensile strain increases the density, size, alignment, and cross-linking of collagen fibers thereby increasing E while also decreasing k as a result of an increased flow path length. The Poisson's ratio of the solid matrix, nu(s), is assumed to remain constant (near zero) for all soft tissues. Implementing a computer algorithm based on these concepts, we simulate progressive changes in material properties for differentiating tissues. Beginning with initial values of E=0.05 MPa, H(A)=0 MPa, and k=1 x 10(-13) m(4)/Ns for multipotent mesenchymal tissue, we predict final values of E=11 MPa, H(A)=1 MPa, and k=4.8 x 10(-15) m(4)/Ns for articular cartilage, E=339 MPa, H(A)=1 MPa, and k=9.5 x 10(-16) m(4)/Ns for fibrocartilage, and E=1,000 MPa, H(A)=0 MPa, and k=7.5 x 10(-16) m(4)/Ns for fibrous tissue. These final values are consistent with the values reported by other investigators and the time-dependent acquisition of these values is consistent with current knowledge of the differentiation process.

Algorithms↗
PubMed2002

The effect of mechanical stability on local vascularization and tissue differentiation in callus healing.

To investigate the influence of the stability of an osteotomy fixation on the local vascularization and tissue differentiation in callus healing, a transverse osteotomy of the right metatarsal with a gap size of 2 mm was performed in 10 sheep and stabilized with an external fixator. This fixator permitted a defined axial movement. Two groups of 5 sheep were each operated upon to allow 0.2 mm (group A) or 1 mm (group B) of axial movement. Nine weeks after surgery, the callus was dissected and histological sections prepared. The type of tissue and the vessel distribution were determined. Larger interfragmentary movements led to significantly more fibrocartilage (small axial movement A: 6.2%, large axial movement B: 21.6%) and significantly less bone formation (A: 38.2%, B: 26.3%). On average, and particularly close to the periosteum the number of vessels in the callus healing area was greater in the group with smaller movements than in the group with larger movements. There was a significant difference between the distribution of small (< 20 microm) and large (> 40 microm) vessels across the whole healing area for both groups. Whereas the large vessels showed maximum density in the medullary cavity, the small vessels showed the highest frequency in the peripheral part of the periosteal callus.

Animals↗
PubMed1981

Cyclic AMP-binding capacities and histone kinase activation in subcellular components of neocortical tissue. Differential responses to three neurohumoural agents.

1. Noradrenaline and histamine, when added to superfused guinea-pig cerebral-cortical tissues, increased both cyclic AMP-dependent and -independent histone kinase activities of some, but not of all, subsequently isolated subcellular fractions, and decreased their cyclic [(3)H]AMP-binding capacity, which was concluded to be due to an increase in endogenously bound cyclic AMP. 2. Adenosine and 2-chloroadenosine also diminished the cyclic [(3)H]AMP-binding capacities, but did not affect the histone kinase activities. 3. DEAE-cellulose chromatography and stability to KCl additions showed that the greater part of the histone kinase of the present preparations corresponded to the type II enzyme [of Corbin, Keely & Park (1975) J. Biol. Chem.250, 218-225], with a lesser amount of type I activity. Different sites of cyclic AMP accumulation in relation to these or other kinases are considered in interpreting the differential tissue responses to the neurohumoural agents examined.

Adenosine↗
PubMed1995

Gene transfer by jet injection into differentiated tissues of living animals and in organ culture.

Jet injection can be used to introduce genes into the cells of differentiated tissues of living animals and organ cultures. When a solution of plasmid DNA is jet injected into a selected tissue or organ, cells lying in or near the path of the jet injection are transfected with the DNA and the introduced gene(s) are expressed. Since there is minimal morbidity from each jet injection, multiple injections can be performed at the same or nearby sites. Both mRNA and protein expression from transfected genes can be quantitated using standard methods. In addition, the technique is an efficient means of DNA immunization. Methodology for using jet injection to transfer plasmid DNA into the cells of skin, fat, mammary gland, and muscle are described.

Adipose Tissue↗
PubMed1989

Extracellular matrix and cell surface as determinants of connective tissue differentiation.

This paper reviews in vitro studies, largely from the author's laboratory, concerning the conditions that are permissive for the differentiation of limb bud mesenchymal cells into chondrocytes. In high-density cell culture, even in a defined medium, the same normal sequence of events that is found in vivo in developing cartilage is also observed. This system can be used to study heritable disorders in model systems such as in mutant mouse embryos. In addition, single mesenchymal cells can differentiate into hypertrophic chondrocytes in hydrated collagen gel or agarose cultures. A rounded cell shape promotes chondrogenesis, while a flattened cell shape promotes fibroblast differentiation. The actin cytoskeleton is shown to play a central role in regulating connective tissue cell differentiation. By use of such cell culture manipulations, it is now possible to grow large numbers of fibroblastic cells from human biopsy material for storage and to carry out experimental studies after re-expression of chondrogenesis in gel cultures. It is suggested that cytoskeletal-extracellular matrix interactions play a fundamental role in connective tissue differentiation. Matrix receptors might be developmentally regulated and modify epithelial effects on mesenchymal cells. In this way mesenchymal cells differentiate in a highly organized manner in spatial and temporal terms.

Animals↗
PubMed1979

Tissue differentiation as a prerequisite for transplacental carcinogenesis in the hamster respiratory system, with specific respect to the trachea.

The significance of tissue differentiation for the transplacental carcinogenicity of DEN was examined. In one experiment, pregnant Syrian golden hamsters received a single sc injection of DEN on one of the different days of pregnancy. Approximately 95% of the offspring of those mothers treated on one of the last 4 days (days 12--15) of gestation developed respiratory tract tumors. Transplacental DEN treatment before the 12th prenatal day failed to induce any neoplastic response in the young. In the second experiment, the differentiation of the prenatal Syrian golden hamster tracheal epithelium was examined histologically and by electron microscopy. We found that on the 12th prenatal day the ER occurred for the first time in its functionally competent form. On earlier prenatal days, the epithelial cells lacked this organelle. We conclude that this development of ER is a prerequisite for transplacental DEN carcinogenesis, since this organelle contains the nonspecific enzyme systems necessary for the transformation of DEN to its ultimate carcinogen.

Animals↗
PubMed2000

The influence of mechanical stimulus on the pattern of tissue differentiation in a long bone fracture--an FEM study.

2D, coronal plane, finite elements models (FEMs) were developed from orthogonal radiographs of a diaphyseal tibial fracture and its reparative tissue at four different time points during healing. Each callus was separated into regions of common tissue histology by computerised radiographic analysis. Starting point values of tissue material properties from the literature were refined by the model to simulate exactly the mechanical behaviour of the subject's callus and bone during loading. This was achieved by matching measured inter-fragmentary displacements with calculated inter-fragmentary forces. Stress and strain distributions in the callus and bone were calculated from peak inter-fragmentary displacements measured during natural walking activity, and were correlated with the subsequently observed pattern of tissue differentiation and maturation of the callus. The growth and stiffening of the external callus progressively reduced the inter-fragmentary gap strain. Partial maturation of the gap tissue was apparent only one week before fixator removal. Principal stresses in the callus were compared with 'yield stresses' in corresponding tissue from the literature. This indicated the presence of stress concentrations medial and lateral to the fracture gap, which probably caused tissue damage during normal activity levels. Tissue damage may also have precipitated partial structural failure of the callus, both of which were believed to have delayed healing during the middle third of the fixation period. Had the fixation device provided greater inter-fragmentary support during early healing, this may have prevented callus failure and the consequent delay in healing. A further benefit of this would have been the reduction of the initially high intra-gap tissue strains to a magnitude more conducive to earlier maturation of the bridging tissue that united the bone.

Adult↗