Isolation and characterization of synovial mesenchymal stem cells

Synovial membrane and synovial fluid represent a good source of mesenchymal stem cells. They have been regarded as a promising therapeutic tool for musculoskeletal regeneration. Synovium-derived mesenchymal stem cells have higher expression of CD44 and better chondrogenic potential in vitro than mesenchymal stem cells from other tissues. In this study we compared mesenchymal stem cells from synovium and synovial fluid on the base of morphological, immunophenotype and differentiation features. A heterogeneous population of cells with different morphology was obtained after isolation and 4-day cultivation. The mesenchymal stem cell immunophenotype was confirmed by positive expression of CD105, CD90, and CD44 by flow cytometry and cells were negative for CD45. CD105+ cells were selected by immunomagnetic separation after 2-4 weeks of cultivation. The percentage of CD105+ cells in the mesenchymal stem cell population from synovia was between 40-50 % before immunomagnetic separation and increased to 95 % following the immunomagnetic separation. Von Kossa, Alcian blue and Oil Red O staining was used to assess the differentiation potential of synovial mesenchymal stem cells. Long-term cultivation did not affect the morphology and immunophenotype of synovial mesenchymal stem cells. Our results confirmed that immunomagnetic separation based on CD 105 antigen is a suitable method to enrich the subpopulation of CD105+ synovial mesenchymal stem cells.

The 3D structure of human chromosomes in cell nuclei

The spatial arrangement of some genetic elements relative to chromosome territories and in parallel with the cell nucleus was investigated in human lymphocytes. The structure of the chromosome territories was studied in chromosomes containing regions (clusters) of highly expressed genes (HSA 9, 17) and those without such clusters (HSA 8, 13). In chromosomes containing highly expressed regions, the elements pertaining to these regions were found close to the centre of the nucleus on the inner sides of chromosome territories; those pertaining to regions with low expression were localized close to the nuclear membrane on the opposite sides of the territories. In chromosomes with generally low expression (HSA 8, 13), the elements investigated were found symmetrically distributed over the territories. Based on the investigations of the chromosome structure, the following conclusions are suggested: (1) Chromosome territories have a non-random internal 3D structure with defined average mutual positions between elements. For example, RARalpha, TP53 and Iso-q of HSA 17 are nearer to each other than they are to the HSA 17 centromere. (2) The structure of a chromosome territory reflects the number and chromosome location of clusters of highly expressed genes. (3) Chromosome territories behave to some extent as solid bodies: if the territory is found closer to the nuclear centre, the individual genetic elements of this chromosome are also found, on average, closer the centre of the nucleus. (4) The positions of centromeres are, on average, nearer to the fluorescence weight centre of the territory (FWCT) than to genes. (5) Active genes are not found near the centromeres of their own territory. A simple model of the structure of chromosome territory is proposed.

Influence of cell fixation on chromatin topography

Using in situ hybridization techniques, a fixation step must precede denaturation to prevent disintegration of the chromosomes. The analysis of nuclei fixed by paraformaldehyde, preserving the native structure (three-dimensional or 3D fixation and analysis) has become possible with the development of confocal microscopy; however, the analysis of those fixed by methanol and acetic acid, dehydrating the nuclei (two-dimensional or 2D fixation and analysis), remains a very valuable tool for practical use in diagnostics and also in many cases for research. We compared both types of fixation and analyses using different cell lines and different DNA probes. Fixation of cells by methanol and acetic acid leads to the enlargement of contact of nuclei with the slide surface, resulting in a substantial increase of nuclear diameter, flattening of the nucleus, and consequently to a distortion of gene topology. Our results indicate that chromatin structures located in the outer parts of the nuclear volume (e.g., heterochromatin of some centromeres) are relatively shifted to the membrane of these nuclei, keeping the absolute centromere-membrane distance constant. On the other hand, euchromatin located in the inner parts of the nuclear volume is not shifted outside proportionally to the increase of molecular dimensions; consequently, the relative distances for the center of nucleus to gene are smaller after methanol-acetic acid fixation. The limitations of the analysis of dehydrated preparations for practical use and in research are discussed.

Precise characterisation of monoclonal antibodies to the C-terminal region of p53 protein using the PEPSCAN ELISA technique and a new non-radioactive gel shift assay

The development of human cancers is frequently associated with inactivation of the p53 tumour suppressor protein triggering cell cycle arrest or apoptosis in response to cellular stress. The p53 protein has been identified as a transcription factor with sequence-specific DNA binding properties. The DNA-binding activity is cryptic but can be modulated through the C-terminal region of the p53 protein by several different stimuli, including phosphorylation by casein kinase II (CKII), protein kinase C (PKC) or binding of the C-terminal monoclonal antibody PAb421. Monoclonal antibodies to the C-terminal region of p53 protein are able to activate the latent form of p53 and induce binding to DNA. To characterise such antibodies, we used a combination of the PEPSCAN ELISA procedure and a newly developed non-radioactive gel shift assay. Monoclonal antibodies from the Bp53 series displayed higher affinities for the human, rat and mouse p53 proteins than did the conventional antibody PAb421. In addition, these antibodies were able to activate the sequence-specific DNA binding functions in latent forms of p53 protein and, in contrast to PAb421, they were able to recognise both PKC phosphorylated and PKC non-phosphorylated forms of p53 protein. Our monoclonal antibodies recognising post-translationally modified target epitopes in the C-terminal region of p53 protein might assist the development of more effective molecules for p53-based cancer therapy.