In vitro SCE discrepancy between embryonic and extraembryonic mouse tissues

In vitro sister-chromatid exchange (SCE) background levels and cytokinetics were compared in embryonic (whole embryo cell suspensions) and extraembryonic (yolk sac and amnion, placenta) cells of inbred and outbred strains at various gestational stages (days 12-17). Results indicate a tissue origin (embryonal, extraembryonal) related variation in the formation of baseline SCE frequencies and cytokinetics. The significant higher SCE levels in extraembryonic tissues (maximum increase of 2 X the background values of the embryo cells) were independent of mouse strain and gestational stage. An average of 4-5 SCEs/cell in embryo cells is contrasted by 7-9 SCEs/cell in extraembryo cells. Mitotic index was generally lower and average generation time longer (by 2-3 h) in extraembryonic tissue cells. No significant differences in SCE frequencies and no changes in cytokinetics were detected at the BrdU concentrations used (1.2-4.8 micrograms/ml). The reason for the inter-tissue differences in baseline SCE is still not clear.