Induction of hsp70 in transgenic Drosophila: biomarker of exposure against phthalimide group of chemicals.

The expression of stress genes is suggested to be a potentially sensitive indicator of any chemical or physical assault. This led us to explore the possibility of using expression of one of the major stress genes, hsp70, in Drosophila as a biomarker against phthalimide group of chemicals, which may accordingly provide an early indication of exposure to these hazardous chemicals. We exposed third instar larvae of transgenic Drosophila melanogaster (hsp70-lacZ) Bg(9) to different concentrations of the test chemicals (Captan, Captafol and Folpet) for various time intervals (2-48 h) to evaluate expression of hsp70 by X-gal staining, ONPG assay and whole organ in situ immunohistochemistry. The study was further extended to examine the effect of the said chemicals on development of the organism and tissue damage occurring in them, thus raising the possibility of evaluating comparative deleterious effect inducing potential of the test chemicals. Our results showed a strong hsp70 expression in the Captafol-exposed larvae followed by weaker expression in Captan- and Folpet-treated larvae. The effect was further reflected on development as revealed by a delay in emergence of the flies by 3 days in 200 ppm Captafol-exposed group. Hsp70 was found not to be induced at 0.0002 ppm Captafol and at 0.002 ppm Captan and Folpet. The present study suggests that (a). hsp70 induction is sensitive enough to be used as a biomarker against phthalimide group of chemicals, (b). amongst the three test chemicals, Captafol is the most deleterious compound followed by Captan and Folpet, (c). 0.0002 ppm for Captafol and 0.002 ppm for Captan and Folpet, respectively, can be regarded as no observed adverse effect level (NOAEL).