Fig. 5. Neuronal DCas overexpression results in axon guidance defects similar to those seen in DCas loss-of-function mutants. Overexpression of ^MycDCas in all neurons in a wild-type background using the ELAV-GAL4 driver results in ISNb (A-C,G) and SNa (D-G) guidance defects characterized by increased fasciculation of axons and decreased target innervation (A-G, large arrows). (A) Overexpression using one copy (+) each of both the ^MycDCas reporter and the ELAV-GAL4 driver in all neurons results in a reduction of ISNb muscle target innervation (arrows). (B,C) Overexpression using two copies (++) of both ^MycDCas and ELAV-GAL4 in all neurons results in ISNb axons remaining fasciculated with the ISN (arrowheads), and sometimes exiting the ISN in abnormal locations and stalling in large clumps of fasciculated axons (C, small arrows). (D) Overexpression of one copy (+) of both ^MycDCas and ELAV-GAL4 in all neurons results in a reduction of SNa axon target innervation; SNa axons often stalled at the choice point in the dorsal branch of the SNa (D, arrow). (E,F) Overexpression using two copies (++) of both ^MycDCas and ELAV-GAL4 in all neurons results in SNa axons remaining abnormally fasciculated with the lateral branch of the SNa (E, arrowhead) at the choice point (E, small arrow) and remaining abnormally fasciculated with the ISN (F, arrowheads). (G) Following temperature (29°C)-induced elevated expression using two copies of both UAS-^MycDCas and ELAV-GAL4 (+++), many motor axons stalled in the motor roots following exit from the CNS (small arrows), and those ISNb and SNa axons that did extend into the muscle fields often remained fasciculated with the ISN (arrowheads), failing to innervate muscle targets (large arrows). Scale bar: 15 µm in A-F; 7 µm in G.