Search

Twenty-eight independent extraembryonic endoderm (XEN) stem cell lines have been obtained from morula and blastocyst cells of common voles. Most cell lines form very few cell-cell contacts when growing and morphologically correspond to the XEN that were earlier described in mice. In addition, XEN cell lines with atypical morphology forming colonies have been obtained for the first time. Both types of XEN lines rapidly proliferate, retain their morphology and karyotype during more than 25 passages in cell culture, and express genes characteristic of XEN. One of two X chromosomes in XEN lines with karyotype XX has been shown to be inactive and associated with the Xist gene transcript. It has been demonstrated that the paternal X chromosome is inactive.

It is well known that artificial increase in expression of growth factors and their receptors can lead to tumorigenic transformation of cells. Additionally, multiple data on the increased expression of growth factors in many human and animal tumorigenic cells have been published. Nevertheless description of the functional role of endogenous growth factors in maintenance of tumorigenic phenotype remains obscure. Previously, we described a new model for studying neoplastic transformation and dormant metastasis. This model consists of cognate tumorigenic and nontumorigenic cell clones, the latter being obtained as a result of spontaneous reversion of tumorigenic ones. All revertant clones demonstrate the three well known features of normal cells: monolayer growth on a plastic, incapability to grow in soft agar with regular culture media with 10% FCS, and incapability to form tumors in syngeneic animals. Using RT-PCR, we measured expression ratios of main growth factors, commonly believed to be associated with malignization, in tumorigenic and revertant clones of our model. For some of these clones, we also measured an activity of growth factors in conditioned media. The data obtained argue that the levels of growth factor expression, measured by both the methods, are distributed between tumorigenic and revertant clones in a sporadic manner and do not correlate with cell tumorigenicity. Thus, our experimental observations enable us to consider the variability of growth factor expression as insignificant events in the reversion of tumorigenic cells to a nontumorigenic phenotype.

Using gel-retardation assay we have investigated binding of nuclear proteins to the mouse c-fos promoter region 30 b.p. long (nucleotides (-464) - (-435) from TATA-box), localized upstream of PDGF-dependent induction element. It was found that some factors from nuclear extracts of various human and murine cells bind to this promoter region. After gel-retardation of DNA- protein complexes from nuclear extracts of quiescent and stimulated with 20% fetal calf serum cells we observed only one retarded band, while after gel-retardation of DNA-protein complexes from proliferating pseudonormal and tumorigenic cells we observed the appearance of additional retarded band with higher mobility in PAAG. We also have determined the molecular weights of factors interacting with investigated c-fos promoter region by affinity modification method. The molecular weights of both factors are 59 kDa. The equality of molecular weights of investigated factors suggests that these factors might be different forms of one nuclear protein.