Figure 7. Dscam Expression Levels Correlate with Presynaptic Arbor Sizes.

(A) Hiw and FMRP pathways converge at the level of Dscam translational control to regulate presynaptic arbor growth. dFMRP was expressed with ppk, Gal4 either in wild-type (wt) or hiw mutant (hiw^ΔN + OE dFMRP) C4da neurons. C4da presynaptic arbors were visualized with mCD8 ∷ GFP. C4da presynaptic arbors in abdominal segments 4 (A4) through 6 are shown. Scale bar: 5 µm. (B) Dscam expression levels correlate with presynaptic arbor length. The relative presynaptic arbor sizes of single ddaC neurons from different genetic backgrounds were normalized to corresponding wild-type controls and denoted as fold change. Dscam expression levels from Western analyses were normalized to corresponding wild-type controls and presented as fold change. The presynaptic arbor size of Dscam¹⁸ was used for Dscam−/−. Dscam¹⁸is a protein-null allele (Soba et al., 2007). R² value was derived from linear regression. (C) The present study suggests a model that explains how presynaptic arbor patterning and size control may be differentially controlled by a shared molecule, Dscam. The Dscam ectodomain diversity determines the pattern of presynaptic terminals, whereas its expression level instructs presynaptic terminal size. The DLK pathway and FMRP regulate Dscam expression levels to control presynaptic arbor size. Also see Figure S5.