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 17.2.