The Abl/enabled signaling pathway regulates Golgi architecture in Drosophila photoreceptor neurons.
Bottom Line: The Abl effector, Enabled (Ena), selectively labels the cis-Golgi in developing PRs.Finally, we demonstrate that the effects of Abl signaling on Golgi are mediated via regulation of the actin cytoskeleton.Moreover, they raise the possibility that some of the effects of Abl signaling may arise, in part, from alterations of protein trafficking and secretion.
Affiliation: Axon Guidance and Neural Connectivity Unit, Basic Neuroscience Program, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD 20892.Show MeSH
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Mentions: Time-resolved pharmacological experiments further confirmed that Abl controls Golgi distribution through actin regulation (Figure 7, A– H). Third-instar larval eye disks were cultured for 1 h in media containing low concentrations of the actin depolymerizing agent cytochalasin B (CytoB; Figures 7, A– C) or latrunculin D (LatD; Figure 7, F– H) to select a concentration that reduced phalloidin staining but did not alter the overall morphology of PR. In WT, CytoB treatment fragments the cis-Golgi compartment without altering its apical-basal distribution (Figure 7A). These effects resemble Golgi phenotypes observed in Ena loss of function (Figure 2C). We then tested whether pharmacological disruption of actin structure modified the basal redistribution of cis-Golgi in dabmz (Figure 7B) and Abl mutants (Figure 7C). In mock-treated control cultures, we observed a high percentage of basally distributed cis-Golgi structures in dabmz (90.4% ± 6.1) and in Abl mutants (77.3% ± 5.7) compared with WT (60% ± 4.8; Figure 7D). Acute treatment with CytoB (20 μM) significantly restored the WT apical-basal distribution of cis-Golgi structures in dabmz (64% ± 6.4) and in Abl mutant (61.3% ± 4.9), respectively (Figure 7D). These data imply, first, that formation and maintenance of the basal redistribution of Golgi in Abl pathway mutants is an active process unleashed by derepression of Ena, and, second, that actin structure is functionally downstream of Abl/Ena activity for Golgi distribution. We also observed a synergistic increase in the mean number of cis-Golgi fragments in drug-treated dabmz (14.7 ± 1.8) and Abl mutant (18.9 ± 1.8) tissues compared with their respective mutant mock control alone (dabmz, 9.9 ± 1.4; Abl, 13.1 ± 1.3; Figure 7E). Comparable results were obtained with LatD-treated (10 mM) eye disk cultures (Figure 7, F– J). Taken together, these results suggest that the effects of the Abl/Ena pathway on Golgi localization, and probably on Golgi fragmentation, are mediated through regulation of actin dynamics. Consistent with this, in WT eye disks, we often detected enriched F-actin foci adjacent to cis-Golgi structures (Figure 6D).
Affiliation: Axon Guidance and Neural Connectivity Unit, Basic Neuroscience Program, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD 20892.