Fig 5. Schematic depiction of how Sema-1a regulates appropriate PN dendritic patterns in the developing AL.

After the birth of PNs (PN neurogenesis), the repulsive Sema-1a signal plays an essential role in PNs to determine whether PN dendrites reside within the developing AL in the initial PN dendritic targeting step and PN dendrites often mistakenly invade the region ventromedial to the developing AL (and SEZ; arrowheads) in the absence of Sema-1a (from solid-outline wild-type PNs to dash-outline Sema-1a-deficient PNs). Once entering the developing AL, dendrites of different types of PNs (e.g., DA3-, DA4l and DC3-adPNs and DA1 vPN) in wild-type animals normally stay away from each other in order to sort into the destined glomeruli (the round (e.g., DA3), square (e.g., DA4l), trapezoid (e.g., DC3) and hexagonal (e.g., DA1) glomeruli, respectively). The repulsive Sema-1a signal may be differentially transmitted in various types of PNs: high (e.g., DC3 adPN and DA1 vPN; thick solid-outline), moderate (e.g., DA4l adPN; less thick solid-outline) and low (e.g., DA3 adPN; thin solid-outline). In the absence of the Sema-1a repulsion, dendrites of Sema-1a^P1 PNs (e.g., DA4l- and DC3-adPNs and DA1 vPN) invade select AL regions (e.g., the DA3 glomerulus), resulting in the dendritic mis-targeting phenotypes. In contrast, ectopic and excessive expression of the repulsive Sema-1a signal in the Sema-1a^P1 DA3 adPN (very thick solid-outline) drives their dendrites into adjacent glomeruli (e.g., mis-projection of the dendrites of the Sema-1a^P1 DA3 adPN into the square (e.g., DA4l) glomerulus and the triangular (e.g., DL3) glomerulus).