Hazardous effects of effluent from the chrome plating industry: 70 kDa heat shock protein expression as a marker of cellular damage in transgenic Drosophila melanogaster - hsp70-lacZ - Research

Environmental Health Perspectives, Dec, 2003 by Indranil Mukhopadhyay, Daya Krishna Saxena, Debapratim Kar Chowdhuri

In the present study, we found hsp70 expressed in salivary glands, brain ganglia, proventriculus, gastric ceca, and midgut of the exposed larvae. Because salivary glands and brain ganglia are nourished by the surrounding hemolymph, they are likely to be exposed when the toxicant reaches the hemolymph. Exposure of the larvae to different concentrations of the effluent occurs through feeding. Therefore, gut tissues of the larvae are likely to be exposed during this process, leading to induction of hsp70. Even hsp70 was unable to protect the gut tissues from damage, as evidenced by trypan blue staining in this region, thus showing the severity of damage caused by the effluent. Malpighian tubules were not found to induce hsp70 against the effluent used in the present study. This may be possibly explained by the time of assaying the [beta]-galactosidase activity in the present study, as we reported previously (Mukhopadhyay et al. 2002b).

Development of the organism was affected in the present study, as evidenced by a delay in the emergence pattern of adult flies and a decrease in the number of flies that emerged at the higher effluent concentrations. Gayathri and Krishnamurthy (1981), using Agallol 3 [Bayer (India) Ltd., Mumbai, India], a mercurial fungicide, and Nazir et al. (2001), using chlorpyrifos, an organophosphate pesticide, observed similar effects in D. melanogaster. Such a change may be due to both genetic and environmental components (Bonnier 1960).

Results presented here from pair-mating of adult flies to examine gender sensitiveness to the test chemicals indicates that the male flies are more sensitive than female flies. Hsp70 synthesis in the male reproductive organs of freshly eclosed adult flies revealed a dose-dependent synthesis of the protein. Interestingly, hsp70 expression was restricted only in the testis lobe. Dix and Hong (1998) showed that a wide range of environmental exposures trigger protective mechanisms in reproductive tissues that are mediated by heat shock proteins. The ability of Hsp70 to protect the testis lobes from damage was evident in our study by normal sperm morphology, motility (Mukherjee I, Kar Chowdhuri D. Unpublished data), and absence of trypan blue staining in this tissue. Interestingly, trypan blue stained positively in the male accessory glands of adult flies grown on food containing 10.0 [micro]L/mL effluent, indicating tissue damage in this gland. This was further confirmed by the ultrastructural observations of the gland. Nonexpression of hsp70 in this gland is intriguing, and at present we are unable to provide any plausible explanation for this.

The male accessory gland in Drosophila serves as the main organ of the male genital apparatus in charge of producing the noncellular portion of the sperm (Bairati 1968). The adult male accessory glands of D. melanogaster synthesize and secrete a few peptide molecules, which are transmitted to the female during mating (Chen et al. 1988; Wolfner 1997). The mated female has an elevated rate of egg laying, stimulation of oviposition, and sexual receptivity (Chapman et al. 1995; Wolfner 1997). The secondary cells, on the other hand, discharge granular filamentous bodies into the lumen of the gland, where they aggregate to form linearly arranged filamentous structures. The role of filamentous bodies has been described previously by Bairati (1968). A significant reduction in fecundity and reproductive performance of adult flies grown on food mixed with 10.0 [micro]L/mL chrome plating effluent (flies did not eclose at the highest concentration of 100.0 [micro]L/mL) in the present study may be attributed to the extensive damage in both the cell types in these groups, thereby affecting the secretion and formation of filamentous structures in the accessory gland lumen. Filamentous structures were very few in number in this group, unlike in controls. Previous studies have shown that increased number and volume of Golgi vesicles signifies acidification of the Golgi compartments (Zhang et al. 1993), which may be linked with aggregation of the subunits of filamentous structures. The reduction in the number of Golgi vesicles signifies a deviation from the original pH and hence may affect the aggregation and packaging process of the filamentous bodies in the treated groups.