Midline Signalling Systems Direct the Formation of a Neural Map by Dendritic Targeting in the Drosophila Motor System
Figure 3
Medio-lateral dendritic targeting in the absence of cholinergic synaptic transmission.
Single DiI/DiD-labelled dendritic trees of four representative motorneurons (as described in Figure 2) are shown at 18.5 h AEL in wild-type and cha mutant embryos. (A, E) By 18.5 h AEL, both in the control and mutant condition, MN-VO4/5 has established its characteristic medial dendritic subtree (straight arrow), respectively (n = 9). (D, H) MN-DO2 (n = 3) and MN-DO1 (n = 10; not shown) dendrites are strictly confined to the lateral neuropile in cha mutant embryos as in the wild-type (note that in [D] the “common exciter” RP2 was also labelled). (B, C) MN-LL1 and MN-DA3 can normally be clearly distinguished: MN-LL1 has manifest branches innervating the intermediate neuropile (curved arrow), which are not formed by MN-DA3 (asterisk). (F, G) In 18.5 h cha mutants, some MN-LL1 and MN-DA3 cells form dendrites that are less distinct than in the wild-type and examples of such cases are shown here: in 3/10 cases MN-LL1 dendrites in the intermediate territory were less extensive than in the wild-type (curved arrow in [F], compare with [B and G]); in 4/11 cases MN-DA3 dendrites extended slightly more medially than in controls (curved arrow in [G], compare with [C and F]). Asterisks in (C, D, and H) indicate intermediate neuropile devoid of dendritic branches. Dotted lines indicate CNS midlines. Scale bar: 20 µm.