Elisabeth Christians

Differential heat shock gene hsp70-1 response to toxicants revealed by in vivo study of lungs in transgenic mice

Abstract Members of heat shock proteins (Hsp70) family have been considered to respond to a large variety of stressful conditions. But it was suggested that, in pulmonary cells, Hsp response depends more closely on the type of stimulus. The lungs are critical organs potentially subjected to air pollution affecting respiratory function and, therefore, these organs are of particular interest with regard to the stress response. To investigate the stress dependence of Hsp70 response in lungs, we created transgenic mice where the firefly luciferase reporter gene is under the control of the murine hsp70-1 promoter and exposed them to different sublethal toxic conditions. For each condition, the level of transgene induction and pulmonary toxicity were assessed. We found that hsp70-1 promoter was stimulated by heat shock and cadmium but not by ozone, paraquat, and parathion, even if these chemicals induced respiratory distress and lung inflammation. Similar observations were made when expression of the endogenous hsp70-1 gene was analyzed, indicating that our transgenic model was accurately detecting hsp70-1 induction. Thereby, it appeared that hsp70-1 response is selective and depends on signaling pathways triggered by the toxicants rather than by their pathologic toxicity per se. Furthermore, because all the chemicals used in our study have been previously described to increase the level of oxidative stress, it indicates that there is no direct and simple correlation between hsp70-1 response and the level of oxidative stress, but more specific oxidative patterns should be involved in Hsp regulation.

Expression of an Xist promoter-luciferase construct during spermatogenesis and in preimplantation embryos : Regulation by DNA methylation

Dosage compensation for X‐linked genes in mammals is accomplished by inactivating one of the two X chromosomes in females, a process involving a regulatory gene, Xist (X‐inactive specific transcript). Xist maps to the X‐inactivation centre and is expressed from the inactive X chromosome in female somatic cells and at the time of X inactivation during spermatogenesis in the male. In female preimplantation embryos, Xist demonstrates imprinting in that the paternal allele inherited from the sperm is preferentially expressed. This preferential paternal Xist expression is correlated with paternal X inactivation in the extraembryonic lineages at the blastocyst stage. We have analysed a 233‐bp Xist promoter fragment (nt −220 to +13) for its ability to direct appropriate expression and its regulation by DNA methylation. This minimal promoter sequence directs expression of the luciferase reporter gene following injection of the construct into one‐cell embryos. In vitro methylation of the construct before injection represses transcription. In six different transgenic lines, expression of the Xist promoter‐luciferase transgene occurs only in the testis of the males (as for the endogenous Xist gene). The testis‐specific expression is correlated with hypomethylation of the transgene, although to different extents in different lines. Following paternal transmission, expression of the Xist promoter‐luciferase construct in preimplantation embryos is correlated with degree of hypomethylation in the testis and the degree of hypomethylation of the transgene in embryos at the morula stage. It is concluded that the patterns of methylation of the transgene in sperm (and in microinjected transgenes) can regulate the activity of the Xist promoter in the preimplantation embryo and thus support the hypothesis that gametic methylation patterns govern imprinted expression of the endogenous Xist gene in development. Mol. Reprod. Dev. 49:356–367, 1998.