Spatial and temporal expression of 4f-rnp gene in Drosophila melanogaster.

We have recently discovered that a pre-messenger RNA (mRNA) encoded by the 4f-rnp gene in Drosophila melanogaster undergoes RNA editing by site-specific A-to-G conversions. In this report, we describe the spatial and temporal expression patterns of 4f-rnp mRNA transcripts during fly development. The 4f-rnp locus was mapped by polytene in situ hybridization experiments to the 4F1,2 bands at the distal tip of the X-chromosome, demonstrating that this gene is nuclear. We show that 4f-rnp is a single-copy gene by a combination of genomic Southern blot hybridization and restriction map analysis of clones isolated through chromosome walking techniques. Northern blot analysis indicates that two alternatively spliced messenger RNA transcripts, differing in length by 200-300 nucleotides, are synthesized in adult male and female flies, during embryogenesis and throughout the larval period. Using tissue in situ hybridization techniques that do not distinguish between the transcripts, we find that the distribution of 4f-rnp mRNAs is specific to germline tissue in the ovary, demonstrating that these transcripts are maternally produced. During embryogenesis, 4f-rnp transcripts are localized within cells of most tissues, but they have a very distinct localization pattern within the segmental ganglia of the central nervous system. We discuss the significance that RNA editing is expected to have for the predicted 4F-RNP protein products that may be expressed throughout fly development and in high abundance within the fly's central nervous system.