Ultrastructure of cells cultured on polycarbonate membranes

A simple and efficient method for preparation of isolated ovarian follicles for transmission electron microscopy

OBJECTIVE

A simple method for preparation of isolated ovarian follicles for transmission electron microscopy (TEM) using transwell inserts is described.

MATERIALS AND METHODS

Pre-antral follicles were enzymatically isolated from mouse ovaries and cultured overnight on transwell insert polyester membranes. The following day, isolated ovarian follicles were processed for TEM by moving the transwell insert through successive wells containing the fixation and embedding reagents. After polymerization of the resin, the polyester membrane with the follicles embedded in the resin was disengaged from the transwell unit. The resin was sectioned. Semi-thin sections were stained with toluidine blue while ultra-thin sections were stained by uranyl acetate and examined by light microscopy and TEM, respectively.

RESULTS

Isolated ovarian follicles were easily processed in groups for TEM. Follicles were well embedded and there appeared to be no loss of tissue during processing. The ultra-structure of processed isolated ovarian follicles was well preserved with little evidence of processing artifacts.

CONCLUSIONS

In situ processing and preparation of isolated ovarian follicles by first allowing attachment on transwell insert membranes was shown to be a simple, rapid and effective method for TEM.

In situ embedding of cell monolayers cultured on plastic surfaces for electron microscopy

Various procedures suitable for routine in situ embedding of cell monolayers were tested including: (1) the use of different Epon substitutes, (2) the use of different types of plasticware obtained from different sources, and (3) different methods of preparing capsules for sectioning. Different resins reacted differently with different plastics and type of preparation. Merck Epon substitute bound to most of the plastics tested. Ladd Epon substitute released cleanly from all plastics tested when a suitable method of preparation was used. The results show that for routine embedding of cell monolayers it is necessary to select an appropriate Epon substitute and method of preparation of capsules for the type of plasticware used. A routine method is described, with various alternative steps which can be applied when particular difficulties are encountered.

Preparation of cultured mammalian cells for transmission and scanning electron microscopy using Aclar film

Common methods for the preparation of cultured cells for concurrent light microscopy (LM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) are not completely satisfactory. This article describes how we grow mammalian cells on plastic disks made from Aclar film. Aclar is a transparent fluorinated-chlorinated thermoplastic that contains no volatile components and is, for all practical purposes, chemically inert. Cells adhere to it readily and remain attached after fixation, dehydration, and critical-point drying or embedding. The film also accepts heavy metal coating by ionic bombardment and is extremely stable in the vacuum of the SEM. LM observations are unhindered by Aclar, since the film is as transparent as glass. Fluorescence microscopy is possible with this film, since it exhibits no detectable autofluorescence. During SEM observation, the film has great dimensional stability, and the cells and heavy metal coating remain attached to the Aclar even under high-resolution operating conditions. TEM processing of specimens grown on Aclar is simplified by the fact that Aclar does not stick to the epoxy resins used in EM. Furthermore, Aclar is easily sectioned and does not damage knives used in ultramicrotomy. The use of Aclar film considerably simplifies the preparation of cultured cells for all types of microscopy. This method is particularly useful in correlating surface features between SEM and TEM observations.

Versatile method for evaluating a cell culture by various morphological techniques

Cellulose acetate is a versatile material for evaluating cells grown under identical conditions by various morphological techniques. This inexpensive material is transparent, easily cut to size and shape, nontoxic to cell cultures, and resistant to most chemicals used in histochemistry and in scanning and transmission electron microscopy. Samples may be obtained during and after the culture process. Cellulose acetate slides can be mounted directly over glass slides for direct observation and are easily peeled off plastic blocks for electron microscopy, leaving the cells behind. Relative disadvantages include its autofluorescence and a tendency to soften in strong acids or pure solutions of organic solvents such as xylene and propylene oxide.

A convenient culture chamber for observation and embedding of macrophage monolayers for transmission electron microscopy

A chamber adapted from a polypropylene test tube is described for the cultivation and processing of undisturbed monolayers of normal mouse macrophages for transmission electron microscopy (TEM). Peritoneal exudate cells are grown in the chambers on Visking dialysis membranes pretreated with Polybrene (Sigma Chemical Co.) and normal mouse serum. The cells are not further disturbed after adherence since the entire chamber, including dialysis membrane and cells, is processed for electron microscopy using standard material and protocols and the embedded dialysis membrane is readily oriented and thin-sectioned. This method is efficient for studying adherent cells since growth can be nearly confluent and cells remain firmly attached throughout the manipulations. Since a transparent membrane is used, cells can also be observed with the light microscope at all stages prior to sectioning.

A quantitative study on growth and cell population identification in murine salivary gland culture

Differentiation of neonatal salivary gland cell populations was studied in vitro using primary explant cultures. Growth on glass of the submandibular, sublingual and parotid salivary glands was optimal if the initial explant diameter was less than 0.4 mm and culture was in 199 medium plus 20 per cent newborn-calf serum. Growth was measured by planimetry of the area of cellular outgrowth as a monolayer with continuous cell contacts. Duct epithelial cells identified using ultrastructural, histochemical and immunological criteria, produced evidence of altered morphology by in-vitro conditions. Preservation of enzymic and antigenic markers of ductal epithelial cell origin in vitro irrespective of gross cell morphology allowed quantification of these cells in a mixed cell population.

The use of polystyrene microcarriers to prepare cell monolayers for transmission electron microscopy

A simple method is described, using polystyrene microcarrier beads, that allows cell monolayers to be prepared without distortion for transmission electron microscopy. Cells cultured on polystyrene beads (Biosilon R, Nunc, Kamstrup, Denmark) are held in an agar matrix. Before embedding, the beads are dissolved in 1,2-epoxypropane. The technique increased the number of observable cells, when compared to preparations of planar monolayers, and there is good preservation of morphological detail.

Biocompatibility of echinoderm skeleton with mammalian cells in vitro: preliminary evidence

The physical and chemical properties of echinoderm skeleton are reviewed. A method is described for preparing cell-free, sterile echinoderm skeletal plates (ossicles) which were used as porous substrates for cell cultures. Ossicles of the starfish Pisaster ochraceus were evaluated as substrates for the culture of three mammalian cell lines. Each line grew vigorously on ossicles, and fibroblasts quickly infiltrated their porous microstructure. Echinoderm skeletal plates provide a simple, convenient alternative to coverslips and porous membranes for SEM or correlated SEM/TEM studies of cell behavior. More importantly, the preliminary evidence for biocompatibility presented suggests that native echinoderm skeleton has potential use as a biomaterial and, because of its microstructure and relative solubility; deserves evaluation as a kind of biodegradable ceramic.

Separation of epoxy-embedded cell cultures from plastic flasks for electron microscopy

Monolayers of cells grown in ordinary plastic flasks are fixed and embedded "in situ" into Epon. When polymerized at 40 C for 4 days instead of the usual 60 C, the Epon sheet containing the cells is easily detached from the bottom of the plastic container. The Epon sheet is observed by light microscopy as a histological preparation. Ultrathin sectioning of preselected areas can then be carried out in a horizontal plane.

Transmission and scanning electron microscope preparations of the same cell culture

A technique has been developed which allows transmission electron microscopy and scanning electron microscopy to be performed on the same cell culture sample. The technique uses the Costar 3,393 Leighton Tube containing a plastic insert, which does not stick to epoxy, for transmission electron microscopy. A cut piece of the plastic insert can be critical point dried, sputter coated and viewed under high vacuum with the scanning electron microscope.