Figure 1: A cis-acting LCR is essential for the efficient activation of Dscam exon 6 in D. melanogaster.

(a) Schematic diagrams of a series of constructs that were designed to mimic the approximation of sequences caused by RNA pairing between the docking site and selector sequence. The dashed circle depicts the ‘hardwired’ site after deleting the loop–stem sequence. (b) Effects of deletions on the selection of alternative exons. (c) LCR elements act in a proximity-dependent mode. (d) Overview of scanning deletions of the ~700-bp intronic sequence upstream of the docking site of Dscam exon cluster 6 in D. melanogaster. (e,f) Effect of deletion on exon 6 inclusion. (g) Overview of locus insertion to test the effects of the LCR on the inclusion of exon 6.47 and exon 6.48 is shown. A red cross in IE denotes the nucleotide mutations, which destroyed the splice sites of alternative exon 6; a green arrow depicts activating the inclusion of the alternative exon. (h) The alternative exon is activated by a locus-inserted LCR. Data are expressed as mean±s.d. from three independent experiments (b,f,h). *P<0.05; ***P<0.001 (Student’s t-test, two-tail). WT, wild-type.