A 4.5kb Dscam promoter fragment from -261 to +4309 bp (this fragment includes the 5' untranslated sequences of exon 1 and up to the exon 2 ATG codon) is fused to a Dscam cDNA that encodes exons 2-18 followed by a genomic fragment encoding Dscam exons 18-24. The cDNA fragment contains the alternative exons 4.3, 6.36, 9.25 and 17.1.
Dscam4.3-6.36-9.25-17.1 shows only minimal rescue of the axon branching defects seen in single cell clones of mushroom body α/β neurons that are homozygous for Dscam18; 28% of clones show lack of segregation of sister branches and 34% show generation of additional branches at the bifurcation points (compared to 35% and 42% respectively in the absence of Dscam4.3-6.36-9.25-17.1).
Co-expression of both Dscam4.3-6.36-9.25-17.1 and Dscam4.3-6.36-9.25-17.2 partially rescues the early larval lethality of Dscam18/DscamB17-1 animals, such that some some animals survive to the adult stage. These adults are vegetative after eclosion and need special care for survival (some of these flies can survive for 3 days within wet chambers on grape juice agar plates). The rescued adults show multiple signs of poor brain development; all major brain compartments (including the supraesophageal ganglion, the subesophageal ganglion and the optic lobes) appear rudimentary and the paired brain lobes are incompletely fused. Loss of dorsal or medial mushroom body lobes is seen and the brains lack ellipsoid body-like structures.