Recombination between the single FRT sites that are present on each of Dscam1ED69 and Dscam15'HR-10.27.25 has resulted a single copy of Dscam1 in which the genomic region encoding exons 3 to 16 has been replaced with cDNA sequences. This copy of Dscam1 encodes a single ectodomain isoform, containing the variable exons 4.10, 6.27 and 9.25. A single FRT site is present following the cDNA sequences.
C4 da neurons expressing the single Dscam1 isoform containing exons 4.10, 6.27, and 9.25 (Dscam110.27.25) exhibit defective targeting of the synaptic terminals. 47% of Dscam110.27.25 ddaC neurons completely lose their anterior branches and 29.4% lose their contralateral branches, while 100% of wild-type controls exhibit both branches.
Homozygotes, Dscam10.27.25/Dscam3.31.8 and Dscam10.27.25/Dscam6.5.9 animals die in early larval development.
Over 75% of Dscam10.27.25/Dscam23 animals survive to late pupal stages.
Homozygous, Dscam10.27.25/Dscam3.31.8 and Dscam10.27.25/Dscam6.5.9 embryos show defects in the organisation of the central nervous system, showing severely disrupted longitudinal tracts and aberrant midline crossing.
Dscam10.27.25/Dscam23 embryos show defects in the organisation of the central nervous system, showing disrupted longitudinal tracts.
Dscam10.27.25/Dscam- animals have a highly disorganised antennal lobe with no distinct glomerular structure and olfactory receptor neurons form many ectopic termini throughout the antennal lobe.
Almost all Dscam10.27.25/Dscam- mushroom bodies completely lack one lobe (typically the dorsal lobe is missing). Dscam3.31.8/+ animals also show defects in the mushroom body in approximately 90% of cases; either one mushroom body lobe is absent (approximately 60% of cases) or one mushroom body lobe is thinner than the other (approximately 30% of cases).
Sister branches of single Dscam10.27.25 mushroom body neurons in a DscamFRT control background (generated using intragenic MARCM) segregate into the two mushroom body lobes with high fidelity.