DNA supercoiling factor positively regulates expression of the homeotic gene Abdominal-B in Drosophila melanogaster.

DNA supercoiling factor (SCF) generates unconstrained negative supercoils of DNA in conjunction with eukaryotic topoisomerase II. In Drosophila melanogaster, SCF localizes to puffs on polytene chromosomes and is required for dosage compensation via hypertranscripton of genes on the male X chromosome. The present study investigated the role of SCF on autosomes. Although RNAi knockdown of scf results in male lethality, some escapers showed anterior homeotic transformation of the male sixth abdominal segment, similar to that arising from reduced expression of Abdominal-B (Abd-B). Heterozygotes for an scf mutant allele (scf(1)) displayed suppression of Pc mutation-dependent posterior transformation and enhancement of anterior transformation caused by trxG mutations. The level of Abd-B mRNA decreased in scf(1) embryos compared with wild-type. Tiling array experiments showed the presence of significant SCF signals in an Abd-B promoter region. Expression from the basal Abd-B promoter on a transgene was reduced in scf(1) embryos compared with wild-type. Collectively, these results demonstrate that SCF occupies the promoter region of Abd-B and activates expression for the proper formation of abdominal segments. Furthermore, preferential occupancy of SCF around transcription start sites of many active genes suggests a role for the factor in positive regulation of promoters.