TatA complexes exhibit a marked change in organisation in response to expression of the TatBC complex.

The twin-arginine translocation (Tat) system is an integral membrane protein complex that accomplishes the remarkable feat of transporting large, fully folded polypeptides across the inner membrane of bacteria, into the periplasm. In Escherichia coli, Tat comprises three membrane proteins: TatA, TatB and TatC. How these proteins arrange themselves in the inner membrane to permit passage of Tat substrates, whilst maintaining membrane integrity, is still poorly understood. TatA is the most abundant component of this complex and facilitates assembly of the transport mechanism. We have utilised immunogold labelling in combination with array tomography to gain insight into the localisation and distribution of the TatA protein in E. coli cells. We show that TatA exhibits a uniform distribution throughout the inner membrane of E. coli and that altering the expression of TatBC shows a previously uncharacterised distribution of TatA in the inner membrane. Array tomography was used to provide our first insight into this altered distribution of TatA in three-dimensional space, revealing that this protein forms linear clusters in the inner membrane of E. coli upon increased expression of TatBC. This is the first indication that TatA organisation in the inner membrane alters in response to changes in Tat subunit stoichiometry.

From colony to rodlet: "A six meter long portrait of the xerophilic fungus Aspergillus restrictus decorates the hall of the Westerdijk institute."

The extreme xerophilic fungus Aspergillus restrictus is used as a model for a large artwork created out of five microscopic pictures in total measuring 80 cm by 624 cm. The artwork is printed on aluminium and located at the entrance of the Westerdijk Institute, Utrecht, The Netherlands. The first picture is made from a colony of the fungus, which has a dimension of 1 cm and the last picture shows details of ornamentation on conidia and phialides of the fungus. The first two pictures of the artwork are made using a unique method of light microscopy in which many hundreds of pictures are made at different focal depths resulting in high detail and resolution of the pictures. For three other pictures, cryo-electron scanning microscopy was used including both a conventional system for lower magnification and a field emission scanning electron microscope for high resolution micrographs. The range of magnification is, at real size, between 78 and 63,000 times. When the observer passes the artwork it acts like a virtual microscope, just by walking past it you zoom-in to the smallest possible details. This coherent increase of magnification of one fungus, with very high quality light- and electron microscopy micrographs, shows different layers of fungal organization and emergent properties. These include the occurrence of secondary outcrops of hyphae and conidiophores in a colony; the formation of a stipe on a thin aerial hyphae; the presence and formation of characteristic structures on stipes, vesicles and phialides and a continuous zone between the forming conidia and phialides.

Tomographic reconstruction reveals the morphology of a unique cellular organelle, the aggregated macrotubules (Macrotubuli aggregati) of human retinal horizontal cells.

Horizontal cells of the human retina contain unique tubular organelles that have a diameter which is about 10 times larger than that of microtubules (~230 nm). These macrotubuli in most cases form regular aggregates. Therefore we propose to introduce them as Macrotubuli aggregati in the Terminologia histologica. Tomographic investigation of the structures revealed that the walls of the tubules most probably consist of intermediate filaments running nearly parallel to each other and show somewhat regularly attached ribosomes on their inner and also outer surface. About 2% of the organelles exhibit double- to multiple layered walls and less than 1% resemble large scrolls. The tubules may extend 10 to over 20 µm in the cytoplasm and are also encountered in soma-near processes extending into the outer plexiform layer. It remains unclear why these structures are only present in humans and few other species and why almost only in horizontal cells. Speculations on possible functions are discussed.

Atmospheric scanning electron microscope for correlative microscopy.

The JEOL ClairScope is the first truly correlative scanning electron and optical microscope. An inverted scanning electron microscope (SEM) column allows electron images of wet samples to be obtained in ambient conditions in a biological culture dish, via a silicon nitride film window in the base. A standard inverted optical microscope positioned above the dish holder can be used to take reflected light and epifluorescence images of the same sample, under atmospheric conditions that permit biochemical modifications. For SEM, the open dish allows successive staining operations to be performed without moving the holder. The standard optical color camera used for fluorescence imaging can be exchanged for a high-sensitivity monochrome camera to detect low-intensity fluorescence signals, and also cathodoluminescence emission from nanophosphor particles. If these particles are applied to the sample at a suitable density, they can greatly assist the task of perfecting the correlation between the optical and electron images.