Effect of First, Second and Third Chromosome on the Promoter Activity of \u3cem\u3eCyp6a8\u3c/em\u3e Gene of Drosophila Melanogaster

The mechanism of insect CYP gene regulation is largely unknown. In the present investigation, I used Drosophila as a model insect to understand the role of X, 2nd and 3rd chromosomes on the promoter activity of Cyp6a8 gene. Two reporter transgenic strains, 0.8luc110 H-ry and 0.8luc14, carrying 0.8luc-A8 reporter transgene (chimera of 0.8-kb upstream DNA of Cyp6a8 and the firefly luciferase gene) on the 2nd and 3rd chromosomes of ry506, respectively were used. The X, 2nd and 3rd chromosomes of these two transgenic lines were replaced with corresponding chromosomes from DDT-resistant 91-R strain (overproducer of Cyp6a8). The effect was determined by measuring luciferase activity. Results showed that the 3rd chromosome of the 91-R strain had a strong and the 2nd chromosome had a weak stimulatory effect on Cyp6a8 expression. The effect of the 1st chromosome was strongly inhibitory only if the 3rd chromosome from 91-R and the 2nd chromosome from the ry506 strains were present in the genome. Chromosomal effect on the Inducibility of 0.8-kb Cyp6a8 promoter DNA by phenobarbital and barbital was also examined. It was found that these compounds could induce the promoter significantly if the genome had X or second chromosome from the ry506 or 91-R strain. However, no induction was observed when the third chromosome of 91-R was present in the genome but the third chromosome of the ry506 strain supported barbiturate inducibility of the Cyp6a8 promoter. To further investigate if Cyp6a8 is regulated by other genes, I studied the effect of third chromosome-linked DHR96 (mammalian CAR/RXR homolog) mutation on the promoter activity of the 0.8Kb upstream DNA of Cy6a8. I found that the DHR96 mutation gave 7-12 fold higher constitutive expression of Cyp6a8 compared to the wild type strain in all developmental stages. This investigation concludes that Cyp6a8 expression in Drosophila is influenced by all three major chromosomes and the third chromosome-linked DHR96 gene has a negative effect on Cyp6a8 expression