Trio regulates higher order dendritic branching and field coverage in class IV da neurons.

<p>(<b>A,B</b>) Confocal live images of the dorsal cluster class IV ddaC neuron labeled by the class IV specific reporter <i>GAL4⁴⁷⁷,UAS-GFP</i> at the the third instar larval stage of development. (<b>A</b>) Wild-type class IV ddaC neuron characterized by full coverage of dendritic field and highly complex dendrite branching pattern particularly at dendritic termini. (<b>B</b>) Class IV ddaC neuron expressing a <i>UAS-trio-RNAi</i> transgene. The loss-of-function <i>trio</i> phenotype is characterized by a dramatic reduction in dendrite branching complexity at both proximal primary branches and distal dendritic terminal branches. (<b>C–G</b>) Quantitative analyses of dendritic branching, length, and field coverage in <i>trio^RNAi</i> relative to controls. <i>trio</i> knockdown results in a significant reduction in the number of dendritic terminals reflecting a decrease in overall branching (<b>C</b>) and a reduction in total dendritic length (<b>D</b>). (<b>E</b>) Disruption of <i>trio</i> function also leads to a reduction in the average dendritic length per branch. (<b>F</b>) The percentage of dendritic field coverage is significantly reduced with <i>trio</i> knockdown (71%) as compared to controls (95%) reflecting defects in branching and growth. (<b>G</b>) Analyses of dendritic branch order reveal defects in the specification of higher order branching resulting in a proximal shift in branch order distribution in <i>trio</i> knockdown (<i>n</i> = 7) relative to controls (<i>n</i> = 6). Images were taken at 20× magnification and size bar represents 50 microns. The total <i>n</i> value for each neuron and genotype quantified is reported on the bar graph. Statistically significant <i>p</i> values are reported on the graph as follows (** = <i>p</i><0.01; *** = <i>p</i><0.001). Genotypes: <b>WT</b>: <i>GAL4⁴⁷⁷,UAS-mCD8::GFP/+</i>. <b><i>trio^RNAi</i></b>: <i>GAL4⁴⁷⁷,UAS-mCD8::GFP/+;UAS-trio^RNAi/+</i>.