UASp regulatory sequences drive expression of the two exon-8 C-terminal Sxl-F isoforms generated by the use of highly conserved alternative exon-5 splice acceptors. The 5' part of the hybrid fragment is from the female-specific cDNA cF1 and runs from +28 in exon 1 through +10,449 in exon 4. The genomic part that follows runs from +10,450 to +16,546, well beyond the longest exon-8 3' UTR.