Developmental regulation and complex organization of the promoter of the non-coding hsr(omega) gene of Drosophila melanogaster.

The nucleus-limited large non-coding hsr(omega)-n RNA product of the 93D or the hsr(omega) gene of Drosophila melanogaster binds to a variety of RNA-binding proteins involved in nuclear RNA processing. We examined the developmental and heat shock induced expression of this gene by in situ hybridization of nonradioactively labelled riboprobe to cellular transcripts in intact embryos, larval and adult somatic tissues of wild type and an enhancer-trap line carrying the hsr(omega) 05241 allele due to insertion of a P-LacZ-rosy+ transposon at -130 bp position of the hsr(omega) promoter. We also examined LacZ expression in the enhancer-trap line and in two transgenic lines carrying different lengths of the hsr(omega) promoter upstream of the LacZ reporter. The hsr(omega) gene is expressed widely at all developmental stages; in later embryonic stages, its expression in the developing central nervous system was prominent. In spite of insertion of a big transposon in the promoter, expression of the hsr(omega) 05241 allele in the enhancer-trap line, as revealed by in situ hybridization to hsr(omega) transcripts in cells, was similar to that of the wild type allele in all the embryonic, larval and adult somatic tissues examined. Expression of the LacZ gene in this enhancer-trap line was similar to that of the hsr(omega) RNA in all diploid cell types in embryos and larvae but in the polytene cells, the LacZ gene did not express at all, neither during normal development nor after heat shock. Comparison of the expression patterns of hsr(omega) gene and those of the LacZ reporter gene under its various promoter regions in the enhancer-trap and transgenic lines revealed a complex pattern of regulation, which seems to be essential for its dynamically varying expression in diverse cell types.