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Twelve cytochrome P450 cDNA fragments were cloned from Drosophila melanogaster by reverse transcriptase/PCR (RT/PCR) using degenerate oligonucleotide primers. The corresponding genes belong to several subfamilies of the CYP4 and CYP9 P450 families. Only two of these genes, Cyp4dl and Cyp4d2, have previously been described. In situ hybridization of each of the cDNA fragments showed two clusters of genes; one near the tip of the X chromosome and the other on the left arm of chromosome 2. Interestingly the latter cluster comprises widely divergent genes belonging both to the CYP9 and CYP4 families and also to the CYP6 family (Cyp6a2). Putative allelic variants of several of the genes were found in different insecticide-resistant and -susceptible strains (Hikone R, Haag 79 and Oregon R). The identification of these genes and alleles will allow us to clarify the involvement of P450s in xenobiotic metabolism and will facilitate a genetic analysis of P450 functions in insects.

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Telomeres are important contributors to genome stability, as they prevent linear chromosome end degradation and contribute to the avoidance of telomeric fusions. An important component of the telomeres is the heterochromatin protein 1a (HP1a). Mutations in Su(var)205, the gene encoding HP1a in Drosophila, result in telomeric fusions, retrotransposon regulation loss and larger telomeres, leading to chromosome instability. Previously, it was found that several proteins physically interact with HP1a, including dXNP and dAdd1 (orthologues to the mammalian ATRX gene). In this study, we found that mutations in the genes encoding the dXNP and dAdd1 proteins affect chromosome stability, causing chromosomal aberrations, including telomeric defects, similar to those observed in Su(var)205 mutants. In somatic cells, we observed that dXNP and dAdd1 participate in the silencing of the telomeric HTT array of retrotransposons, preventing anomalous retrotransposon transcription and integration. Furthermore, the lack of dAdd1 results in the loss of HP1a from the telomeric regions without affecting other chromosomal HP1a binding sites; mutations in dxnp also affected HP1a localization but not at all telomeres, suggesting a specialized role for dAdd1 and dXNP proteins in locating HP1a at the tips of the chromosomes. These results place dAdd1 as an essential regulator of HP1a localization and function in the telomere heterochromatic domain.

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