Histone posttranslational modifications that accompany DNA replication, nucleosome assembly, and H2A/H2B exchange were examined in human tissue culture cells. Through microsequencing analysis and chromatin immunoprecipitation, it was found that a subset of newly synthesized H3.2/H3.3 is modified by acetylation and methylation at sites that correlate with transcriptional competence. Immunoprecipitation experiments suggest that cytosolic predeposition complexes purified from cells expressing FLAG-H4 contain H3/H4 dimers, not tetramers. Studies of the deposition of newly synthesized H2A/ H2B onto replicating and nonreplicating chromatin demonstrated that H2A/H2B exchange takes place in chromatin regions that contain acetylated H4; however, there is no single pattern of H4 acetylation that accompanies exchange. H2A/H2B exchange is also largely independent of the deposition of replacement histone variant, H3.3. Finally, immunoprecipitation of nucleosomes replicated in the absence of de novo nucleosome assembly showed that histone modifications do not prevent the transfer of parental histones to newly replicated DNA and thus have the potential to serve as means of epigenetic inheritance. Our experiments provide an in-depth analysis of the "histone code" associated with chromatin replication and dynamic histone exchange in human cells.

Pluripotent stem cells can differentiate into various lineages but undergo genetic and epigenetic changes during long-term cultivation and, therefore, require regular monitoring. The expression patterns of cancer-testis antigens (CTAs) MAGE-A2, -A3, -A4, -A6, -A8, -B2, and GAGE were examined in undifferentiated human embryonic stem (hES) cells, their differentiated derivatives, teratocarcinoma (hEC) cells, and cancer cell lines of neuroectodermal and mesodermal origin. Undifferentiated hES cells and embryoid body cells expressed MAGE-A3, -A6, -A4, -A8, and GAGEs while later differentiated derivatives expressed only MAGE-A8 or MAGE-A4. Likewise, mouse pluripotent stem cells also express CTAs of Magea but not Mageb family. Despite similarity of the hES and hEC cell expression patterns, MAGE-A2 and MAGE-B2 were detected only in hEC cells but not in hES cells. Moreover, our analysis has shown that CTAs are aberrantly expressed in cancer cell lines and display low tissue specificity. The identification of CTA expression patterns in pluripotent stem cells and their derivatives may be useful for isolation of abnormally CTA-expressing cells to improve the safety of stem-cell based therapy.

New human nonimmortalized fibroblast like cell lines were derived from various sources: from embryonic stem cells (ESCs) (the SC5 MSC and SC3a MSC lines), from bone marrow of a 5 to 6 week old fetus (the FetMSC line), and from foreskin of a 3 year old child (the FRSN line). All the lines are suc cessfully used as feeders during cultivation of human ESCs. The mean doubling time of the cell populations fluctuates depending on the line from 25.5 h in the SC5 MSC line to 38.8 h in the SC3a MSC line. The growth curves indicate active cell proliferation of all lines. Numerical and structural karyotypical analysis has shown these lines to have a normal karyotype: 46, XX (SC5 MSC and SC3a MSC) and 46, XY (FetMSC and FRSN). To determine the status of these lines, comparative analysis of surface markers was performed with the aid of flow cytofluorimetry, and expression of the c antigens characteristic of human mesenchymal stem cells (MSCs) was revealed: CD44, CD73, CD90, CD105, and HLA ABC and the absence of expression of CD34 and HLA DR. Interlinear differences in the expression level of the marker CD117 (c kit) were revealed. Immunofluorescent and cytofluorimetric analysis of expression of surface markers and transcrip tion factor Oct 4 that are characteristic of human ESCs has shown that, in all four lines, expression of TRA 1 60 and Oct 4 is absent, whereas in expression of SSEA 4 there are observed the interlinear differ ences not depending on the origin of cells. At present it is not yet clear whether the revealed interlinear dif ferences affect essentially the functional status of mesenchymal stem cells. Immunofluorescent analysis in cells of all lines showed expression of markers of early differentiation into derivatives of three germ layers characterizing ESCs, which might possibly provide wide MSC possibilities during reparation of different tis sue damages, depending on the corresponding microenvironment. The capability of cells of all lines for directed differentiation into the adipogenic and osteogenic directions was revealed.

Background Chinese hamster ovary cell lines, also known as CHO cells, represent a large family of related, yet quite different, cell lines which are metabolic mutants derived from the original cell line, CHO-ori. Dihydrofolate reductase-deficient DXB-11 cell line, one of the first CHO derivatives, serves as the host cell line for the production of therapeutic proteins. It is generally assumed that DXB-11 is identical to DUKX or CHO-DUK cell lines, but, to our knowledge, DXB-11 karyotype has not been described yet. Results Using differential staining approaches (G-, C-banding and Ag-staining), we presented DXB-11 karyotype and revealed that karyotypes of DXB-11 and CHO-DUK cells have a number of differences. Although the number of chromosomes is equal—20 in each cell line—DXB-11 has normal chromosomes of the 1st and 5th pairs as well as an intact chromosome 8. Besides, in DXB-11 line, chromosome der(Z9) includes the material of chromosomes X and 6, whereas in CHO-DUK it results from the translocation of chromosomes 1 and 6. Ag-positive nucleolar organizer regions were revealed in the long arms of chromosome del(4)(q11q12) and both chromosome 5 homologues, as well as in the short arms of chromosomes 8 and add(8)(q11). Only 19 from 112 (16.96%) DXB-11 cells display identical chromosome complement accepted as the main structural variant of karyotype. The karyotype heterogeneity of all the rest of cells (93, 83.04%) occurs due to clonal and nonclonal additional structural rearrangements of chromosomes. Estimation of the frequency of chromosome involvement in these rearrangements allowed us to reveal that chromosomes 9, der(X)t(X;3;4), del(2)(p21p23), del(2)(q11q22) /Z2, der(4) /Z7, add(6)(p11) /Z8 are the most stable, whereas mar2, probably der(10), is the most unstable chromosome. A comparative analysis of our own and literary data on CHO karyotypes allowed to designate conservative chromosomes, both normal and rearranged, that remain unchanged in different CHO cell lines, as well as variable chromosomes that determine the individuality of karyotypes of CHO derivatives. Conclusion DXB-11and CHO-DUK cell lines differ in karyotypes. The revealed differential instability of DXB-11 chromosomes is likely not incidental and results in karyotype heterogeneity of cell population.

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