Carmichael, Stephen W.

Abstract It has generally been considered that cereals (such as wheat, rice, and maize) were the first crops to be cultivated by human beings. But a new study that included scanning electron microscopy, by Mordechai Kislev, Anat Hartmann, and Ofer Bar-Yosef (micrographs by Yakov Langsam) provides strong evidence that figs were the first agricultural crop in human history. Kislev et al. recovered nine fig fruits (plus many nutlets called drupelets) from the ruins of a burned building near Jericho. The fire had carbonized the fruit which helped preserve the morphology of the specimens. The site was radiocarbon dated to 11,400 to 11,200 years ago. Microscopic analysis demonstrated that these specimens were of an edible fig that produces drupelets without embryos; that is, these fruits are sterile. Wild fertile figs have a symbiotic relationship with a wasp that plays an essential role in pollinating the fruit, but this fruit is inedible. In this study, no evidence of wasps or where a wasp could exit the fruit were found and these are features found in wild fruit. In other words, wild figs that can be pollinated and reproduce without human intervention are inedible, but edible figs require human intervention. The specimens examined in this study were of the latter variety.

Abstract How do lumens form? Two mechanisms that come readily to mind are a wrapping model, similar to the wrapping of the myelin sheath around a neuronal process, and a solid core of cells followed by apoptosis of the central cells. Another obvious mechanism that was suggested over 100 years ago is the fusion of intracellular vacuoles. Whereas several recent studies have supported this latter mechanism, it has not yet been proven. Now, the appropriate animal model (zebrafish), the modern techniques (transgenic chimeras), dyes (green fluorescent protein and monomeric red fluorescent protein) that can be linked to proteins to label vacuoles, and two-photon imaging in real time finally have provided the strongest support yet. In an article by Makoto Kamei, Brian Saunders, Kayla Bayless, Louis Dye, George Davis, and Brant Weinstein the assembly of endothelial tubes from intracellular vacuoles was observed in vitro and in vivo.

Abstract Proteins in biologic membranes perform a large variety of essential functions. The fact that about one third of all genes code for membrane proteins, and that the majority of drugs target these proteins, attest to that fact. However, until now, proteins have been studied under artificial conditions, such as after being crystallized, frozen, or adsorbed to a substrate. Rui Pedro Gonçalves, Guillaume Agnus, Pierre Sens, Christine Houssin, Bernard Bartenlian, and Simon Scheuring have devised a novel setup with the atomic force microscope (AFM) to allow proteins to be probed while they are in unsupported membranes. Their method is similar in principle to methods where a small area of a membrane is sampled, such as when a piece of membrane is examined by patch clamping. The difference is that instead of attaching a membrane to the end of a pipette, it is spread across a piece of perforated Si(001).

Abstract Many intracellular proteins are catalysts that regulate cellular functions. These catalysts can be assayed to determine their functional state, but untii now it was not possible to simultaneously obtain a functional analysis and spatial data. Tony Ng, Anthony Squire, and others, working in the laboratories of Phillippe Bastiaens and Peter Parker, have combined Fluorescence Lifetime Imaging Microscopy (FLIM) with Fluorescence Resonance Energy Transfer (FRET) to spatially resolve the activation of a protein catalyst within living cells. Their technique was also applied to fixed cells.

Abstract The ability to attach fluorescent molecules onto proteins has allowed specific localization of these proteins within living cells. The traditional approach has been to purify the protein of interest then attach a fluorescent (or another useful tag) molecule in vitro, then somehow introduce the labeled protein into the cell. Whereas this and related techniques have been very useful, there are limitations because each of these three steps is often difficult. Wouldn't it be great if we had a “lock and key” system whereby a protein of interest could be modified to be a specific “lock” and a small tsggable molecule (the “key“) could diffuse into the cell and plug specifically into the lock? Albert Griffin, Stephen Adams, and Roger Tsien have developed such a system

Abstract Ever since the first embryo was put under a microscope, scientists have been trying to determine which embryonic cells form which structures in the mature organism. Classic methods were to kill (ablate) certain cells and see what structures were malformed or missing when the animal developed. More recently, cells have been labeled with visible tags and the tagged cells traced through development. One problem is that the tag gets diluted by half each time a labeled cell divides. A new labeling method that shows a lot of promise has been demonstrated by David Piston, Robert Summers, Susan Knobel, and John Morrill.

Abstract There are many techniques available that enable us to know what is happening at the surface of a living cell. These techniques have allowed us to characterize many aspects of the process of exocytosis, the fnal cellular event in secretion. Patch clamping has given us quantitative measurements of the capacitance changes as the membrane of the secretory vesicle is added to the surface of the cell during exocytosis, and the change in the opposite direction as membrane is retrieved back into the cell during endocytosis. Tiny probes have measured electrochemical changes just outside the surface of the cell as reactive molecules are released into their surroundings. Differential interference contrast microscopy has given us high resolution pictures of the cell surface during exocytosis; real-time images are suggestive of bubbles breaking the surface of a boiling pot of water. However, exocytosis is known to be proceeded by an ordered series of events that occur below the surface of the cell.

Abstract There are scores of microscopes that detect different properties of a specimen. Typically we image ‘visible” properties, but, for example, even the commonly-used atomic force microscope detects physical interactions rather than “visible” characteristics, Mostafa Fatemi and James Greenleaf have introduced the principle of imaging the elastic features of a specimen. This is done with sound waves, but we are not talking about just another acoustic microscope. The method demonstrated by Fatemi and Greenleaf uses radiation force to image the acoustic response of a specimen to mechanical excitation. The mechanical excitation results from focusing two coaxial and confocal ultrasound beams of slightly different frequencies onto a selected region of the specimen.

Abstract As reviewed in this column on previous occasions, the atomic force microscope (AFM) is steadily making headway as an instrument that can make important contributions to biologic observations. Although the AFM is capable of operating in an aqueous environment, relatively little use has been made of this property to examine cellular structures under conditions that resemble those in vivo. A breakthrough in this regard was recently made by Stefan Schneider, Kumudesh Sritharan, John Geibel, Hans Oberleithner, and Bhanu Jena. of Yale University and the University of Würzburg.

Abstract Atomic force microscopy (AFM) has proven to be very useful to material scientists and physicists. Biologists are only beginning to utilize the potential of this methodology. In a recent article, Tatsuo Ushiki, Jiro Hitomi, Shigeaki Ogura, Takeshi Umemoto, and Masatsugu Shigeno reviewed the applications of AFM to biologic studies. They began by reviewing the basic principles of AFM, emphasizing the value of the non-contact mode for visualizing the relatively “soft” surface of biologic specimens. They presented some examples of biologic images: DNA, chromosomes, and collagen fibrils. The specimens examined with the AFM did not need to be coated, theoretically offering a view with a smaller potential for artifacts. AFM images have the advantage of containing quantitative information about the sample height.