Mutation analysis of Drosophila dikar/CG32394, homologue of the chromatin-remodelling gene CECR2.

The mammalian CECR2 protein contains a highly conserved bromodomain and forms a chromatin-remodelling complex with the ISWI homologue SNF2L. Mutation of the mouse CECR2 homologue results in a neural tube defect. Here we describe the characterization of the Drosophila melanogaster homologue of CECR2. Originally annotated as 2 genes, dikar and CG32394 now appear to encode both a long dikar/CG32394 transcript homologous to CECR2 and a truncated transcript missing the bromodomain. This truncated transcript may be specific to Diptera, as it is predicted from the genomic sequences of several other dipteran species but it is not predicted in the honey bee, Apis mellifera, and it is not found in mammals. Five different P element-mediated 5' deletions of the Drosophila dikar gene were generated. All mutants were homozygous-viable and the 3 mutants examined further displayed continued, albeit aberrant, transcription of dikar/CG32394. In a previous study, a dikar insertion mutation was associated with long-term memory deficits. However, the 2 deletion mutants tested here showed normal long-term memory, suggesting that the memory deficit associated with the dikar P element insertion is not due to disruption of dikar. No genetic interaction was seen between Iswi and dikar mutations. This study therefore suggests that the lack of a visible phenotype in dikar mutants is due to compensation by a second gene, possibly acf1.