On the cover
Enhanced confocal micrograph detailing mitochondria in muscle cells of the adult mouse tongue. McWilliams et al. create a transgenic mouse model that allows visualization of mitochondria in vivo, not only in their normal cytosolic environment (green) but also in lysosomes, where the mitochondria are delivered by a recycling process termed mitophagy (red). The tongue provides a unique organization of muscle fibers, and the multiple nuclei (blue) within the myotubes are surrounded by a distinctive mitochondrial architecture.Image © 2016 McWilliams et al.
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People & Ideas
Polarized epithelial cells assemble a primary cilium by an unknown mechanism. After cytokinesis, the central part of the intercellular bridge, which is referred to as the midbody, is inherited as a remnant by one of the daughter cells. Here, Bernabé-Rubio et al. show that the midbody remnant meets the centrosome at the cell apex, enabling primary ciliogenesis.
Vesicular transport from mitochondria to lysosomes is an emerging mitochondrial quality control mechanism. Here, McLelland et al. identify how mitochondrial vesicles are targeted for degradation, showing that syntaxin-17 is recruited to these structures to govern their SNARE-dependent fusion with endolysosomes.
BLOC-1 and BLOC-3 regulate VAMP7 cycling to and from melanosomes via distinct tubular transport carriers
Dennis et al. analyze cycling of the v-SNARE VAMP7 during melanosome biogenesis in melanocytes. VAMP7 is targeted to and retrieved from maturing melanosomes in separate tubular carriers whose formation requires distinct BLOCs, each defective in variants of Hermansky–Pudlak syndrome.
Metazoan dynein moves processively with the aid of dynactin and the endosomal cargo adaptor Hook3. A structure–function study of Hook3 reveals how it assembles dynein with dynactin and suggests that an additional step of allosteric activation is required beyond complex assembly.
Homogenous populations of cells make up individual tissues, yet how organisms achieve such homogeneity is unknown. Le et al. use the C. elegans intestine to reveal that an initiator of RNA silencing is segregated unequally between cells. Suppression of this inequality during early development achieves tissue homogeneity.
Whether mitophagy occurs within specific cellular subtypes in vivo is unclear. McWilliams et al. present “mito-QC,” a transgenic mouse containing a pH-sensitive fluorescent mitochondrial signal, allowing in vivo detection of mitophagy and mitochondrial morphology at single-cell resolution.
Ferguson et al. demonstrate that clathrin coat growth rates can be utilized as quantitative reporters of clathrin-mediated endocytic dynamics in cellular contexts where errors associated with single-particle tracking are significant. They validate the tool within tissues of Drosophila embryos.