Carmichael, Stephen W.

Abstract Would it be useful if you could examine a wet, perhaps even a living, specimen in the scanning electron microscope? Of course we think that this would be impossible, given the vacuum the specimen would be subjected to in the microscope. However, in the realm of materials research, the Environmental Scanning Electron Microscope (ESEM) is being developed. Apparently this instrument has not been fully appreciated and utilized by biologists. As reviewed by Athene Donald, a pioneer in developing the ESEM, this instrument has been commercially available for a decade. It is still evolving as a useful tool in looking at materials such as cement, natural fibers, and aqueous dispersions. Applications of the ESEM. to biological Studies are extremely limited. However, studies on biological samples, even living cells, are possible (although not without problems and limitations).

Abstract It is well known that birds frequently attract mates by a ritual display of feathers or other ornaments. The colors for these displays are either derived from pigments, such as carotenoids, or photonic crystalline arrangements near the surface of the skin, feathers, or other ornaments. Add to this the fact that many birds can perceive light in the near-ultraviolet end of the visible spectrum and the range for these visual displays is extended. In a spectrophotometric and microscopic study by Birgitta Dresp and Keith Langley, it was demonstrated that a unique arrangement of crystal-like structures near the surface of the beak horn of the King penguin (Aptenodytes patagonicus) most likely accounts for a photonic effect that probably plays a role in their mating rituals.

Abstract It's always refreshing to read about two old techniques being combined in a novel way to yield new information. Osamu Ohtani and Yuko Ohtani recently accomplished this. Louis Ranvier probably introduced the use of silver nitrate as a histology stain over a century ago. Whereas Ranvier is best known for describing nodes along the nerve fiber, he also demonstrated that silver nitrate stained endothelial cells, allowing their borders to be clearly visualized. In the 1970's, Takuro Murakami first used the scanning electron microscope (SEM) to examine corrosion casts of the vasculature. Much of what we currently know about the microarchitecture of blood vessels has been discovered using this technique.

Abstract The use of fluorescent probes is becoming more and more common in cell biology. It would be useful if we were able to correlate a fluorescent structure with an electron microscopic image. The ability to definitively identify a fluorescent organelle would be very valuable. Recently, Ying Ren, Michael Kruhlak, and David Bazett-Jones devised a clever technique to correlate a structure visualized in the light microscope, even a fluorescing cell, with transmission electron microscopy (TEM). Two keys to the technique of Ren et al are the use of grids (as used in the TEM) with widely spaced grid bars and the use of Quetol as the embedding resin. The grids allow for cells to be identified between the grid bars, and in turn the bars are used to keep the cell of interest in register throughout the processing for TEM. Quetol resin was used for embedding because of its low auto fluorescence and sectioning properties. The resin also becomes soft and can be cut and easily peeled from glass coverslips when heated to 70°C.

Abstract We're all interested in food. Food is the sustenance of life. And you're interested in microscopy, or else you would not be reading this column. So here's a web site that will appeal to both of your interests. Miloš Kaláb is the author of the web site, and he's enlisted a host of food scientists to assist him. There's no lack of expertise here! The home page can send you to many locations, but let's begin with the site that deals with microscopy. It is said that the earliest microscopists trained their simple instruments on food, mainly to look for contaminants. We are then treated to a primer on microscopy, beginning with light microscopy, then advancing to electron microscopy.

Abstract Whereas too much of a good thing can be bad, too little of a good tiling can be good. In this case, the accidental dilution of X-rhodamine tubulin injected into living cells resulted in a heterogeneous labeling of micro tubules, rather than visualization of continuous structures. This heterogeneous labeling rendered a speckled image, hence the term fluorescent speckle microscopy (FSM) was introduced. It turns out that FSM yields particularly useful information on dynamic events within living cells, for example the assembly and disassembly of microtubules. There are two recent reviews of FSM by Clare Waterman-Storer and Gaudenz Danuser, one emphasizing the biologic applications of the technique, the other emphasizing the quantitative aspects. For their purposes, they defined a “speckle” as a diffraction-limited region of the image that is significantly brighter than its immediate environment. It can be calculated from the point-spread function (which is determined by the numerical aperture of the lens) that optimally a diffraction-limited region of about 250 nm can be imaged.

Abstract Since the discovery of nerve growth factor, it has been thought that neurotrophic factors are released or secreted from target cells. However, more recently it has been suggested that a specific neurotrophic factor known as brain-derived neurotrophic factor (BDNF) may reach target cells directly from presynaptic axons. It has not been known how these molecules get from the neuron in which they are produced to the target cells. Keigo Kohara, Akihiko Kitamura, Mieko Morishima, and Tadaharu Tsumoto have demonstrated that BDNF is transported anterogradely from presynaptic neurons to target neurons.

Abstract We are all familiar with the concept of correlating an image acquired by light microscopy (LM) with one obtained by transmission electron microscopy (TEM). This allows us to take advantage of the “wide angle” view of LM and the high resolution of TEM. Correlative microscopy has been taken to a new level by Alvin Lin and Cynthia Goh who have designed a clever device. This device allows repetitive correlative microscopy between TEM and atomic force microscopy (AFM).

Abstract We have all seen beautiful three-dimensional (3D) renderings of molecular models, complete with helices and pleated sheets. And for more than half a century we have also seen electron micrographs of cellular structures, although usually in two dimensions. There has been a gap between these two sets of images. By developing a technique that promises 3D images at resolutions approaching the molecular level, Ohad Medalia, Igor Weber, Achilleas Frangakis, Daniela Nicastro Günther Gerisch, and Wolfgang Baumeister have bridged that gap.

Abstract In the mammalian embryo, the first axis to appear is at the time of the fifth cell division when the inner cell mass (ICM) becomes visible. The localization of the ICM on one side of a cavity formed within the cluster of dividing cells marks the embryonic-abembryonic (E-Ab) axis. This name derives from the fact the most of the embryo will develop from the ICM, whereas other tissues (the placenta, etc.) will develop from the other cells. There has been a long-standing controversy as to what determines the mammalian E-Ab axis; is the information inherently in the zygote, or is it determined after several cell divisions? In an elegant series of studies whereby dividing cells were labeled using new molecular genetic tools and then carefully followed during development, Yoko Kurotaki, Kohei Hatta, Kazuki Nakao, Yo-ichi Nabeshima, and Toshihiko Fujimori have provided an answer in a mouse model.