4.

Aberrant muscle innervation along the SNb branch in larvae overexpressing Comm(2PY→AY) and Comm(10K→R). Confocal analysis of Cy3 anti-HRP staining of motoneurons innervating muscles 12 and 13 of third-instar larvae grown at room temperature from the following crosses: (A) 24B-GAL4 (+/24B-GAL4); (B) UAS-comm^2PY→AY/24B-GAL4; (C) UAS-comm^10K→R/24B-GAL4; and (D) comm/+. Note the abnormal branching (arrowheads). (E and F) UAS-comm^10K→R expressed in comm heterozygote background (UAS-comm^10K→R/5-GAL4 comm^Δe39/±). (F) Note that only small type II boutons innervate muscle 13 (arrowheads), with a “stalled” axon primarily innervating the neighboring muscle (arrow), leaving the muscle largely devoid of innervation. Where indicated, the second chromosome embryonic muscle driver 5-GAL4 was used for the crosses (55), which allows expression in a comm-reduced background (comm is located on the third chromosome). (B to E) Arrows indicate aberrant innervation of muscle 13 in the comm mutants. Right-hand images in each panel depict the fluorescent (confocal) image overlaid onto a differential interference contrast image of the muscle. Dashed white lines represent the border separating muscles 12 and 13. Het denotes heterozygote.