Cell Pseudopodia Research Articles

Participation of bone marrow stromal cells in hemopoietic recovery of rats irradiated and then parabiosed with a non-irradiated litter mate. II. Scanning and transmission electron microscopic observations.

A light microscopical study on the recovery process after lethal irradiation and parabiosis has been made. Electron microscopically, in the bone marrow of lethally irradiated rats, hemorrhage occurred due to detachment of sinus endothelial cells. Afterwards, reticulum cells with small intracytoplasmic lipid droplets appeared. On day 3, these cells were rapidly replaced by the reticulum cells with large lipid droplets, and resulted in fatty marrow within 7 days. Spindle-shaped fibroblastoid reticulum cells were also observed. In the bone marrow of lethally irradiated rats parabiosed with non-treated litter mates, hemopoiesis was initiated by adhesion of nucleated blood cells to intricate fine cytoplasmic pseudopods of fat-storage cells. On days 3 to 5, in parallel with progressive hemopoietic recovery, fibroblastoid and reticulum cells with large lipid droplets decreased whereas those with small droplets increased. On day 8, reticulum cells with lipid droplets were seldom seen, and hemopoietic distribution became the same as normal. These results suggested that bone marrow stromal cells, namely reticulum, fat-storage, and fibroblastoid cells share a common cellular origin, and also that they regain their structure and function when fat-storage cells were placed in contact with hemopoietic precursor cells.

Basal lamina breaks in the histogenesis of cholesteatoma.

Aural cholesteatomas may arise in the middle ear by a variety of mechanisms; in some cases it appears that cholesteatomas arise within or behind an intact tympanic membrane. We have observed that microcholesteatomas arise within the tympanic membrane of mongolian gerbils which have keratin accumulations on the lateral surface of the tympanic membrane. An ultrastructural study of the keratinizing epithelium of these animals showed that breaks in the basal lamina allow pseudopods of epithelial cells to extend into the lamina propria and form epithelial cones. The basal lamina later reconstituted itself. Keratinization may occur within these ingrowing cones forming microcholesteatomas. This sequence of events may explain the occurrence of intratympanic cholesteatomas in humans in the absence of invagination or perforation.

A novel cell-to-cell interaction between mast cells and other cell types

Time-lapse cinephotomicrography and transmission electron microscopy (TEM) have been used to study the interactions between rat mast cells and different cell monolayers in culture (fibroblasts, vascular endothelial cells and cardiac muscle cells). This report documents a novel form of behavior between mast cells and certain other cell types. We have tentatively termed this cellular behavior ‘transgranulation’, which involves sequential changes not seen in control cells, including: (1) formation of a granule-containing mast cell pseudopod that becomes closely applied to an adjacent cell; (2) development of specialized plasma membrane interrelationships between apposing cells; (3) alteration of granules and perigranular membranes within the mast cell pseudopod; (4) occasional transfer of exocytosed mast cell granules to the cytoplasm of the adjacent cell; (5) presence of a specialized inclusion body in the mast cell; and finally, (6) either withdrawal of the pseudopod by the mast cell, or casting-off of the pseudopod from the mast cell, leaving it on the surface of the adjacent cell (pseudopod translocation). These mast cell interactions occur specifically with fibroblasts and endothelial cells in vitro and are never observed with cardiac muscle cells or non-cellular substrates. Our investigations of rat mesenteries in situ confirm that these cell-cell interactions also occur in vivo. We suggest it represents a form of cell-to-cell communication involving secretion from a mast cell pseudopod to another cell type. The significance of specialized contacts between mast cells and other cell types in vivo is discussed.

Distribution of receptors and functions on cell surfaces: quantitation of ligand-receptor mobility and a new model for the control of plasma membrane topography.

The long-range movements of membrane ligand-receptor complexes into surface caps and into the pseudopods of cells performing phagocytosis, the uropods of motile cells and the cleavage furrows of dividing cells appear to be analogous processes. A common mechanism to explain these movements must take into account several recent observations. First, laser photobleaching studies have indicated that Concanavalin A-receptor movement occurs unidirectionally; and analyses of Con A redistribution by quantitative video intensification microscopy (QUAVIM) have shown that movement may exceed the maximum rates measured for protein diffusion in membranes. These are the results predicted for a process of directed migration but not for a process of diffusion with entrapment. In addition it has been found that membrane receptors may segregate out of as well as into cap, pseudopod, uropod and cleavage furrow regions and that topographical heterogeneity on asymmetric cells is not restricted to membrane molecular determinants but extends to a range of endocytic functions and to a macromolecular complex, the coated pit. All dynamic surface events are arrested during mitosis. A new model for the regulation of plasma membrane topography has been developed from these diverse quantitative, functional and morphological data. Its essence is the entrainment of selected membrane determinants on membrane waves directed towards regions such as caps, pseudopods, uropods and cleavage furrows. The waves are initiated by tension due to asymmetric microfilament-membrane interaction.

Micro-invasion of epidermis caused by substituted anisoles.

ONE of the earliest morphological lesions to be observed in tumours of the epidermis is the protrusion of pseudopods through defective areas in the basement membrane—a phenomenon termed micro-invasion1. Such lesions have been found in the early stages of experimental tumours induced by the local application of the carcinogen dimethylbenzanthracene to the cheek pouch epithelium of hamsters, whereas non-carcinogenic irritants failed to produce them2. It therefore seems from these findings that micro-invasion may serve as an early sign of a neoplastic change in the epithelial cells and hence might be interpreted as an indication of the carcinogenicity of substances which produce it. Since our initial report of basal cell pseudopods caused by applications of 4-hydroxyanisole and 3-hydroxyanisole to guinea-pig epidermis3, we have investigated a number of related substances (Fig. 1). Some of these, notably 7C-phenyl-4-hydroxy-anisole and butylated hydroxyanisole (BHA), have been shown to cause micro-invasion.

Studies on the cellular basis of morphogenesis in the sea urchin embryo: Directed movements of primary mesenchyme cells in normal and vegetalized larvae

A time-lapse study has been made of the movements of the primary mesenchyme cells in the developing sea urchin larva. It shows that these cells move by pseudopod formation and contraction, and that a transition takes place—within a few hours—from a more or less random cluster, in the early mesenchyme blastula, to a well-organized, coherent pattern on the ectoderm of the gastrula. This organization is achieved by a striking random exploration of the wall of the larva by the pseudopods, followed by their contraction. The final pattern of the mesenchyme reflects those regions of the wall where the contacts between pseudopods and wall are most stable. The mechanism is thus one of selective fixation rather than of selective conduction. The pseudopodal contacts are seen to be continually made and broken, even when the final pattern is formed. The pseudopods of several cells may fuse to form a common pseudopod, these cells then migrating together. This is particularly evident in vegetalized larvae, but is also typical of the ventral side. Despite considerable variations in the way in which the final pattern is achieved, several main phases can be distinguished. The first is a radial displacement of the cells from the vegetal plate onto the presumptive ectoderm, followed by a phase of dispersion. The cells then gradually accumulate at a characteristic level, and form a ring. During this process, and when the ring is formed, the cells tend to accumulate in two clusters along the ring. The pseudopods of the cells in these clusters join into a cable, the end of which is highly branched; it explores the ectoderm, and extends the cell clusters to form branches from the ring. In vegetalized larvae, the pattern of distribution is simplified, but the same principles apply. It is suggested that the variations in the way in which the pattern is achieved are, in all probability, merely a reflexion of the lack of precision in the time sequence of changes in adhesive properties of the primary mesenchyme and blastocoel wall.

Superficial border of pseudopods on mesothelial cells on the surface of the peritoneum of mammals

The surface of the mesothelial peritoneal cells (Rat) show with electron microscope very thin pseudopods, 0.6–0.8 µ by 0.04–0.045 µ, separated by 0.1–0.3 µ spacings, and different from vibratile cilia, but similar to the submicroscopic pseudopods of alveolar or endothelial cells.