Response of Djun and Dfos mRNA abundance to signal transduction pathways in cultured cells of Drosophila melanogaster

Caffeine induction of Cyp6a2 and Cyp6a8 genes of Drosophila melanogaster is modulated by cAMP and D-JUN protein levels

Cytochrome P450 monooxygenases or CYPs, a family of endobiotics and xenobiotics metabolizing enzymes, are found in all organisms. We reported earlier that the promoters of Drosophila Cyp6a2 and Cyp6a8 genes are induced by caffeine. Since caffeine antagonizes adenosine receptor (AdoR) and inhibits cAMP phosphodiesterase (PDE), we used luciferase reporter gene to examine whether in SL-2 cells and adult Drosophila, induction of the two Cyp6 genes is mediated via AdoR and/or PDE pathway. Results showed that AdoR is not involved because AdoR agonists or antagonists do not affect the Cyp6 promoter activities. However, inhibition of PDE by specific inhibitors including caffeine causes induction of both Cyp6 gene promoters. We also found that flies mutant for dunce gene coding for cAMP-PDE, have higher Cyp6a8 promoter activity than the wild-type flies. We demonstrate that caffeine treatment increases intracellular cAMP levels, and cAMP treatment induces the Cyp6 gene promoters. Since both Cyp6 genes have multiple sites for JUN transcription factors, which generally play a positive role in cAMP pathway, effect of Drosophila jun (D-jun) on the Cyp6a8 promoter activity was examined. Results showed that the expression of D-jun sense plasmid causes downregulation rather than activation of the Cyp6a8 promoter. Conversely, expression of antisense plasmid increased the promoter activity. Interestingly, caffeine treatment decreased the D-JUN protein level in SL-2 cells as well as in adult flies. These results suggest that D-jun acts as a negative regulator, and caffeine induction of Cyp6a8 and Cyp6a2 genes is mediated by the upregulation of cAMP pathway and downregulation of the D-JUN protein level.

Phylogenetic and genomewide analyses suggest a functional relationship between kayak, the Drosophila fos homolog, and fig, a predicted protein phosphatase 2c nested within a kayak intron

A gene located within the intron of a larger gene is an uncommon arrangement in any species. Few of these nested gene arrangements have been explored from an evolutionary perspective. Here we report a phylogenetic analysis of kayak (kay) and fos intron gene (fig), a divergently transcribed gene located in a kay intron, utilizing 12 Drosophila species. The evolutionary relationship between these genes is of interest because kay is the homolog of the proto-oncogene c-fos whose function is modulated by serine/threonine phosphorylation and fig is a predicted PP2C phosphatase specific for serine/threonine residues. We found that, despite an extraordinary level of diversification in the intron-exon structure of kay (11 inversions and six independent exon losses), the nested arrangement of kay and fig is conserved in all species. A genomewide analysis of protein-coding nested gene pairs revealed that approximately 20% of nested pairs in D. melanogaster are also nested in D. pseudoobscura and D. virilis. A phylogenetic examination of fig revealed that there are three subfamilies of PP2C phosphatases in all 12 species of Drosophila. Overall, our phylogenetic and genomewide analyses suggest that the nested arrangement of kay and fig may be due to a functional relationship between them.

The gene structure of the Drosophila melanogaster homolog of the human proto-oncogene fos

The Drosophila melanogaster homolog of the human proto-oncogene fos is Dfos. It is the only fos homolog in the Drosophila genome. Fos functions as a subunit of the heterodimeric transcription factor AP-1. There are two models of the Dfos gene. The first comes from a cDNA sequence of Dfos (Perkins et al., Genes Dev. 4 (1990) 822). The second is from the gene sequence published by the Drosophila genome project (Adams et al., Science 287 (2000) 2185), and there are notable contradictions between the two models. The promoter and the 5' end of the transcript sequence were not identified in either model. In this paper, we present the gene structure of Dfos and identify the promoter. This promoter has an initiator and a downstream promoter element sequence, but lacks a TATA box. Through comparison of the mRNA and genomic DNA sequences, three introns varying in length from 66 bp to 17.57 kb were found and verified by RT-PCR. The Dfos gene is 21.2 kb in length, giving a transcript of 3438 bp, coding for a predicted protein of 595 amino acids. The 3' untranslated region is confirmed to be 1092 bp in length.