Peculiar artefacts after fixation with glutaraldehyde and osmium tetroxide

Ultrastructural analysis of different human mesenchymal stem cells after in vitro expansion: a technical review

Transmission electron microscopy reveals ultrastructural details of cells, and it is a valuable method for studying cell organelles. That is why we used this method for detailed morphological description of different adult tissuederived stem cells, focusing on the morphological signs of their functions (proteosynthetic activity, exchange with external environment, etc.) and their comparison. Preparing a specimen from the cell culture suitable for transmission electron microscopy is, however, much more challenging than routine tissue processing for normal histological examination. There are several issues that need to be solved while working with cell pellets instead of solid tissue. Here we describe a simple protocol for the isolation and culture of mesenchymal stem cells from different adult tissues, with applications to stem cell biology and regenerative medicine. Since we are working with population of cells that was obtained after many days of passaging, very efficient and gentle procedures are highly necessary. We demonstrated that our semi-conservative approach regarding to histological techniques and processing of cells for transmission electron microscopy is a well reproducible procedure which results in quality pictures and images of cell populations with minimum distortions and artifacts. We also commented about riskiest steps and histochemical issues (e.g., precise pH, temperature) while preparing the specimen. We bring full and detailed procedures of fixation, post-fixation, infiltration, embedding, polymerization and contrasting of cell obtained from in vitro cell and tissue cultures, with modifications according to our experience. All this steps are essential for us to know more about adult stem cells derived from different sources or about other random cell populations. The knowledge about detailed ultra-structure of adult stem cells cultured in vitro are also essential for their using in regenerative medicine and tissue engineering.

Electron dense artefactual deposits in tissue sections: the role of ethanol, uranyl acetate and phosphate buffer

The occurrence of electron dense deposits in sections of aldehyde-fixed tissue prepared for transmission electron microscopy has been attributed to a number of conflicting factors. In an attempt to clarify this, the precipitating effect of different combinations of phosphate or cacodylate buffer, glutaraldehyde, ethanol and uranyl acetate was investigated in test tubes. As a preliminary investigation the combination of phosphate buffer, ethanol and uranyl acetate was investigated in heart and kidney tissue fixed in glutaraldehyde with or without postosmication. The essential factors in the formation of electron dense deposits in these tissues appear to be phosphate buffer, ethanol, and uranyl acetate, although glutaraldehyde may contribute in some way. The nature and intensity of the deposits seem to vary with the sequence of combination of these factors. Osmium did not appear to be an essential factor in the reaction since deposits were observed in both osmicated and unosmicated tissue. To avoid such deposits, a postosmication distilled water wash for 20 to 30 min followed by en bloc staining with aqueous uranyl acetate is advised if phosphate buffer is used as a fixative vehicle or buffer wash after the primary fixative.

Electron dense granules and the role of buffers: artefacts from fixation with glutaraldehyde and osmium tetroxide

Electron dense granules may appear in tissues after glutaraldehyde prefixation and osmium tetroxide postfixation. In order to determine the conditions under which the granules are formed various vehicles in pre- and post-fixatives were tested on lymph node, thymus and heart. If granules appeared they were found in all cell types investigated, particularly in the nuclei. There was no difference in the distribution of the granules in the different compartments of these organs. The granules probably consist of complexes of glutaraldehyde, osmium and phosphate. The ultimate phosphate concentration in the tissues during the postfixation was shown to determine whether or not the artefacts appeared. Local conditions in the tissues also contributed to the appearance of the granules. It is concluded that phosphate buffers can be used in the double fixation procedure, but to avoid the granules in lymph node, thymus and heart, a concentration of 0.1 mol/l or less phosphate should be used. For brain and kidney other conditions apply.