Loss of <i>stai</i> Function Reduces Futsch (MAP1B) Protein Levels in Axons and Alters the Integrity of Axonal Microtubules.

<p>(<b>A</b>–<b>F</b>) Confocal micrographs of segmental nerve axons from third instar larvae immunostained with antibody against the MAP Futsch (mAb 22c10). (<b>A</b>) Wild type larvae have well defined Futsch staining in individual axons within segmental nerve bundles. (<b>B</b>) In contrast, loss of <i>stai</i> function results in an inconsistent distribution of Futsch protein along the length of individual axons within segmental nerve bundles. In some regions of an axon, there is prominent Futsch staining (arrows) whereas Futsch staining is noticeably reduced in other areas of the same axon (small arrowheads). In addition, loss of <i>stai</i> function causes gross perturbations in axon morphology (large arrowheads). (<b>C</b>) The perturbations in axon morphology are more profound in segmental nerve axons from <i>stai</i>^<i>B200</i><i>/Df</i>(<i>2L</i>) <i>Exel6015</i> larvae. (<b>D</b>) Precise excision of the <i>piggyBac</i> element <i>PBac</i>{<i>5HPw⁺</i>}^<i>B200</i> reverts the observed phenotypes to wildtype. The reduction in Futsch staining intensity and perturbations in axon morphology observed in <i>stai</i> deficient segmental nerve axons can be ameliorated with the ubiquitous ectopic expression of <i>Drosophila staiB2</i> (<b>E</b>) or human STMN1 (<b>F</b>). (<b>G</b>) Quantification of average pixel intensity of Futsch immunostained axons of third instar larval segmental nerves. Results are presented in arbitrary units (a.u.) of fluorescence intensity (mean ± S.D.). In panels A-F the scale bar = 10 µm.