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Satir P.,Yeshiva University | Heuser T.,Electronic Microscopy Facility | Sale W.S.,Emory University
BioScience | Year: 2014

The motile cilium is a mechanical wonder, a cellular nanomachine that produces a high-speed beat based on a cycle of bends that move along an axoneme made of 9+2 microtubules. The molecular motors, dyneins, power the ciliary beat. The dyneins are compacted into inner and outer dynein arms, whose activity is highly regulated to produce microtubule sliding and axonemal bending. The switch point hypothesis was developed long ago to account for how sliding in the presence of axonemal radial spoke-central pair interactions causes the ciliary beat. Since then, a new genetic, biochemical, and structural complexity has been discovered, in part, with Chlamydomonas mutants, with high-speed, high-resolution analysis of movement and with cryoelectron tomography. We stand poised on the brink of new discoveries relating to the molecular control of motility that extend and refine our understanding of the basic events underlying the switching of arm activity and of bend formation and propagation. © 2014 The Author(s).

Bierwagen J.,Max Planck Institute for Biophysical Chemistry | Testa I.,Max Planck Institute for Biophysical Chemistry | Folling J.,Max Planck Institute for Biophysical Chemistry | Wenzel D.,Electronic Microscopy Facility | And 3 more authors.
Nano Letters | Year: 2010

We demonstrate far-field optical imaging at the nanoscale with unlabeled samples. Subdiffraction resolution images of autofluorescent samples are obtained by depleting the ground state of natural fluorophores by transferring them to a metastable dark state and simultaneously localizing those fluorophores that are transiently returning. Our approach is based on the insight that nanoscopy methods relying on stochastic single-molecule switching require only a single fluorescence on-off cycle to yield an image, a condition fulfilled by various biomolecules. The method is exemplified by recording label-free nanoscopy images of thylakoid membranes of spinach chloroplasts. © 2010 American Chemical Society.

Fuest M.,University Hospital Freiburg | Willim K.,University Hospital Freiburg | Macnelly S.,University Hospital Freiburg | Fellner N.,Electronic Microscopy Facility | And 3 more authors.
Hepatology | Year: 2012

Endoplasmic reticulum (ER) stress due to accumulation of hepatoviral or misfolded proteins is increasingly recognized as an important step in the pathogenesis of inflammatory, toxic, and metabolic liver diseases. ER stress results in the activation of several intracellular signaling pathways including Jun N-terminal kinase (JNK). The AP-1 (activating protein 1) transcription factor c-Jun is a prototypic JNK target and important regulator of hepatocyte survival, proliferation, and liver tumorigenesis. Because the functions of c-Jun during the ER stress response are poorly understood, we addressed this issue in primary hepatocytes and livers of hepatocyte-specific c-Jun knockout mice. ER stress was induced pharmacologically in vitro and in vivo and resulted in a rapid and robust induction of c-Jun protein expression. Interestingly, ER-stressed hepatocytes lacking c-Jun displayed massive cytoplasmic vacuolization due to ER distension. This phenotype correlated with exacerbated and sustained activation of canonical ER stress signaling pathways. Moreover, sustained ER stress in hepatocytes lacking c-Jun resulted in increased cell damage and apoptosis. ER stress is also a strong inducer of macroautophagy, a cell-protective mechanism of self-degradation of cytoplasmic components and organelles. Interestingly, autophagosome numbers in response to ER stress were reduced in hepatocytes lacking c-Jun. To further validate these findings, macroautophagy was inhibited chemically in ER-stressed wildtype hepatocytes, which resulted in cytoplasmic vacuolization and increased cell damage closely resembling the phenotypes observed in c-Jun-deficient cells. Conclusion: Our findings indicate that c-Jun protects hepatocytes against excessive activation of the ER stress response and subsequent cell death and provide evidence that c-Jun functionally links ER stress responses and macroautophagy. © 2011 American Association for the Study of Liver Diseases.

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