Biomedical subjects

Alexander Egner

Publications and source records attributed to Alexander Egner.

5 recordsLinked to original sources

PubMed2005

Hair cell synaptic ribbons are essential for synchronous auditory signalling.

Hearing relies on faithful synaptic transmission at the ribbon synapse of cochlear inner hair cells (IHCs). At present, the function of presynaptic ribbons at these synapses is still largely unknown. Here we show that anchoring of IHC ribbons is impaired in mouse mutants for the presynaptic scaffolding protein Bassoon. The lack of active-zone-anchored synaptic ribbons reduced the presynaptic readily releasable vesicle pool, and impaired synchronous auditory signalling as revealed by recordings of exocytic IHC capacitance changes and sound-evoked activation of spiral ganglion neurons. Both exocytosis of the hair cell releasable vesicle pool and the number of synchronously activated spiral ganglion neurons co-varied with the number of anchored ribbons during development. Interestingly, ribbon-deficient IHCs were still capable of sustained exocytosis with normal Ca2+-dependence. Endocytic membrane retrieval was intact, but an accumulation of tubular and cisternal membrane profiles was observed in ribbon-deficient IHCs. We conclude that ribbon-dependent synchronous release of multiple vesicles at the hair cell afferent synapse is essential for normal hearing.

Action Potentials↗

PubMed2005

Fluorescence microscopy with super-resolved optical sections.

The fluorescence microscope, especially its confocal variant, has become a standard tool in cell biology research for delivering 3D-images of intact cells. However, the resolution of any standard optical microscope is at least 3 times poorer along the axis of the lens that in its focal plane. Here, we review principles and applications of an emerging family of fluorescence microscopes, such as 4Pi microscopes, which improve axial resolution by a factor of seven by employing two opposing lenses. Noninvasive axial sections of 80-160 nm thickness deliver more faithful 3D-images of subcellular features, providing a new opportunity to significantly enhance our understanding of cellular structure and function.

Cellular Structures↗

PubMed2004

4Pi-microscopy of the Golgi apparatus in live mammalian cells.

We report the applicability of 4Pi-microscopy to live mammalian cells. Controlled interference of the counterpropagating wavefronts is possible despite the slight variations in cellular refractive index. Superresolved 3D-fluorescence imaging is exemplified with the first representation of the Golgi apparatus in a live cell at approximately 100 nm resolution.

Animals↗

PubMed2003

Spatial and temporal dynamics of budding yeast mitochondria lacking the division component Fis1p.

The mitochondrial compartment of budding yeast (Saccharomyces cerevisiae) is a highly dynamic net-like structure of tubules that constantly undergo fusion and fission. The outer membrane protein Fis1p plays a crucial role in mitochondrial fission. Here we report on the temporal and spatial dynamics of this organelle in wild-type cells and in fis1Delta mutants. Mitochondria of fis1Delta mutants adapt their mitochondrial network to a change in carbon source. We find that the frequencies of apparent matrix separation and fusion events decrease in both wild-type cells and in mutants lacking Fis1p upon glucose repression. Matrix separation could be caused by matrix constriction and does not necessarily require fission of the inner or outer membrane. Double-labelling experiments demonstrated that some of these matrix separations in fis1 mutants are due to genuine tubule fissions, whereas others do not involve fission of the outer membrane. The rates of matrix separation in fis1Delta mutants almost approach those of the wildtype, demonstrating that, although apparently involved in outer membrane fission, Fis1p is not crucial for the separation of the mitochondrial matrix. In mutants lacking the GTPase Dnm1p no complete tubule fissions were recorded, although dnm1Delta mutants display matrix separations as well. The data suggest that different molecular machineries are responsible for the separation of the matrix and the fission of the outer membrane in budding yeast.

Carbon↗

PubMed2002

Fast 100-nm resolution three-dimensional microscope reveals structural plasticity of mitochondria in live yeast.

By introducing beam-scanning multifocal multiphoton 4Pi-confocal microscopy, we have attained fast fluorescence imaging of live cells with axial super resolution. Rapid scanning of up to 64 pairs of interfering high-angle fields and subsequent confocal detection enabled us to perform three to five times finer optical sectioning than confocal microscopy. In conjunction with nonlinear image restoration, we demonstrate, to our knowledge for the first time, three-dimensional imaging of live eukaryotic cells at an equilateral resolution of approximately 100 nm. This imaging mode allowed us to reveal the morphology and size of the green fluorescent protein-labeled mitochondrial compartment of live Saccharomyces cerevisiae (bakers' yeast) growing on different carbon sources. Our studies show that mitochondria of cells grown on medium containing glycerol as the only carbon source, as opposed to glucose-grown cells, exhibit a strongly branched tubular reticulum. We determine the average tubular diameter and find that it increases from 339 +/- 5 nm to 360 +/- 4 nm when changing from glucose to glycerol, that is, from a fermentable to a nonfermentable carbon source. Moreover, this change is associated with a 2.8-fold increase of the surface of the reticulum, resulting in an average increase in volume of the mitochondrial compartment by a factor of 3.0 +/- 0.2.

Fluorescence↗