Glutamate receptor clustering is inhibited by overexpression of tubulin. Overexpression of alpha tubulin in muscles triggers an increase in microtubules (see text). A: Confocal images showing intersegmental nerve branch b (ISNb) innervating ventral longitudinal muscles in first instar larvae (24–28 h AEL). Neuronal tissue was visualized using anti-HRP antibody (magenta). Glutamate receptors were visualized using an antibody against the receptor subunit GluRIIA (green). In UAS-alpha tubulin/24B gal4 animals, sec8 cDNA is overexpressed in postsynaptic muscle cells. Overexpression of tubulin causes a reduction in glutamate receptor cluster size and number (quantified in B and C). B: Quantification of receptor cluster size, showing a reduction in cluster size after postsynaptic overexpression of tubulin (UAS-alpha tubulin/24B gal4). C: Quantification of cluster number, showing a reduction in cluster number after postsynaptic overexpression of tubulin (UAS-alpha tubulin/24B gal4).