Effects of embryotoxic chemicals on the in vitro differentiation of genetically engineered embryonic stem cells into cardiac cells

A project has been started using transgenic embryonic stem cells as a toxic ological endpoint in order to register chemical effects on the development of embryonic tissues which are known to be sensitive during their different iation. The green fluorescent protein (GFP) is used as a reporter gene and is linked to a cardiac specific promotor. This construct is integrated into the native DNA of undifferentiated embryonic stem cells. The expression of GFP was switched on after specific activation of the promotor (human-alpha -actin) which allows a quantification of cardiac cells using the fluorescen ce activated cell sorter. Kinetic analysis shows a differentiation of 25% o n cells with activated human-alpha-actin promotor on day 3, increasing to 8 6% on day 7, and decreasing again to 35% on day 11. The known animal terato gens retinoic acid and 5-fluorouracil were chosen and the measurements were compared to the IC50 values given by other in vitro endpoints in order to investigate the potential of this toxicological endpoint. The results show a higher sensitivity of endpoints which analysed specific effects on a sele cted target tissue. The exposure of embryonic stem cells to chemicals lead to the following IC50 values. 1.149 +/- 0.170 ng/ml (cytotoxicity) versus 0 .216 +/- 0.126 ng/ml (GFP expression) after treatment with retinoic acid an d 54.2 +/- 5.2 ng/ml (cytotoxicity) versus 26.7 +/- 2 ng/ml (GFP expression ) after treatment with 5-fluorouracil. The data shows the necessity to deve lop specific in vitro methods which take the complexity of embryotoxicology into account. (C) 1999 Published by Elsevier Science Ltd. All rights reser ved.