Theoretical Study of DNA unwinding under the action of formaldehyde.

A simple model is used to investigate the relationship between clone number and patch number for each of two cell types in one and two-dimensional arrays. Considering the two cell types separately, this relationship is shown to vary with the relative proportions of the two cell types. If both cell types are considered, the total number of patches in a one-dimensional array reaches a maximum when the two cell types are present in equal proportions. Over the range considered for a two-dimensional array, the total number of patches is at a minimum when the two cell types are present in equal proportions because aggregation of patches is then maximal. The significance of these results is discussed in the light of previous interpretations of work with mouse aggregation chimaeras.     

Two types of murine helper T cell clone. I. Definition according to profiles of lymphokine activities and secreted proteins

A panel of antigen-specific mouse helper T cell clones was characterized according to patterns of lymphokine activity production, and two types of T cell were distinguished. Type 1 T helper cells (TH1) produced IL 2, interferon-gamma, GM-CSF, and IL 3 in response to antigen + presenting cells or to Con A, whereas type 2 helper T cells (TH2) produced IL 3, BSF1, and two other activities unique to the TH2 subset, a mast cell growth factor distinct from IL 3 and a T cell growth factor distinct from IL 2. Clones representing each type of T cell were characterized, and the pattern of lymphokine activities was consistent within each set. The secreted proteins induced by Con A were analyzed by biosynthetic labeling and SDS gel electrophoresis, and significant differences were seen between the two groups of T cell line. Both types of T cell grew in response to alternating cycles of antigen stimulation, followed by growth in IL 2-containing medium. Examples of both types of T cell were also specific for or restricted by the I region of the MHC, and the surface marker phenotype of the majority of both types was Ly-1+, Lyt-2-, L3T4+, Both types of helper T cell could provide help for B cells, but the nature of the help differed. TH1 cells were found among examples of T cell clones specific for chicken RBC and mouse alloantigens. TH2 cells were found among clones specific for mouse alloantigens, fowl gamma-globulin, and KLH. The relationship between these two types of T cells and previously described subsets of T helper cells is discussed.     

A thermodynamical model of cell distributions in the slug of cellular slime mold

A theoretical model is proposed for the formation of cell distribution patterns in the slug stage of the cellular slime moldDictyostelium discoideum. The equilibrium distribution of two types of cells, prestalk and prespore, is obtained by minimizing the free energy, which is defined in terms of differential chemotaxis, differential cell adhesion and randomness of cell movement. Resulting distributions show various segregation patterns of cell types. The condition for cell sorting is obtained from stability analysis of the set of diffusion equations governing the evolution of cell type distribution and the concentration of chemoattractant. The intensities of differential chemotaxis and random cell movement are quantitatively evaluated from experimental data to show that two cell types can sort themselves completely by these forces.     

Comparison of Ehrlich ascites tumour and mouse liver cells by analytical subcellular fractionation combined with a sensitive computational method for data analysis

A simple method of analytical subcellular fractionation, combined with a sensitive computational method for data analysis and presentation, has been used to reinvestigate the distribution and relative amounts of several enzymes in the cytoplasmic and plasma membranes of two different cell types: one is a neoplastic, transformed cell type (Ehrlich ascites tumour cells), the other an untransformed, highly differentiated cell type (liver hepatocytes plus Kupffer and endothelial cells). In general the distribution of the enzymes in particular membranes is similar in the two cell types, however the relative amounts differ. Ehrlich ascites tumour cells have a higher specific activity of galactosyltransferase and ouabain-sensitive (Na,K)ATPase, while liver cells have higher glucose-6-phosphatase, 5'-nucleotidase and succinate dehydrogenase activity. These differences appear to be correlated with morphological and, in some cases, functional differences between the two cell types.     

Pale and dark bipolar cells in the chicken retina

Ultrastructurally, two different bipolar cell types can be distinguished in the retina of the chick embryo: one pale or electron-lucent and the other dark or electron-dense. The different electron density was seen over the whole cell, from its enclave in the outer limiting membrane to its termination in the inner plexiform layer. These observations prompted us to study the content and cytoplasmic variations of both cell types. The pale bipolar cell has a higher vacuole, vesicle and endoplasmic reticulum content and a lower number of microtubules and glycogen than the dark bipolar cell. The presence of these two cell types is probably due to a characteristic physiologic state, and the difference between the pale and dark bipolar cells can be attributed to the diverse number of gap unions which they establish with A II amacrine cells.     

Fine structure of scolopidia in Johnston's organ of female Aedes aegypti compared with that of the male.

The Johnston's organ of the female mosquito, Aedes aegypti, has only three types of scolopidia: types A, B, and C. It lacks the type D scolopidium of the male's organ. The basic structure and the location of each type in the female are similar to the counterparts in the male's organ. A single scolopidium is composed of a scolopale cell, an envelope cell, a long cap, and a third sheath, in addition to the two electron-dense scolopales produced inside the cytoplasm of two satellite cells. Each scolopidium has either two (type A) or three (type B) sensory cells. A type C scolopidium, mononematic in contrast to the amphinematic types A and B scolopidia, has two sensory cells, a microtubular cap cell, two microtubular accessory cells, and a scolopale cell with an intracellular scolopale. Even though the female Johnston's organ has all the components of the male's organ except for the single type D scolopidium, the female's organ shows relatively poorer organization and development. The female has a smaller and thinner basal plate, shorter and thicker prongs, fewer type A sensory cells, and a shorter flagellar flange, in addition to the overall smaller size of the pedicel.The probable function of each scolopidial type is discussed, especially in connexion with the probable identification of a single auditory sensillum in the male.     

Calculation of percentage of hormone independent transplantable cells in experimental mammary tumors

Some cancer types (e.g. breast cancers) are known to consist of mixed populations of cells which respond to hormones, and cells that do not. A theoretical model is proposed to investigate the proportion of these different cell types in experimental tumors. The model exploits the fact that when grafts are treated with hormones, both cell types form an outgrowth, whereas in the absence of hormones only the autonomous cell types can grow.Method 1 consists of serially transplanting the tumor to be investigated in castrated mice that are not treated with hormones, and comparing the growth rates of two consecutive transplant generations. Method 2 involves comparing the growth of the tumor in hormone treated and untreated castrated mice. The merits and limitation of each of these two methods are discussed.     

Calculation of percentage of hormone independent transplantable cells in experimental mammary tumors

Some cancer types (e.g. breast cancers) are known to consist of mixed populations of cells which respond to hormones, and cells that do not. A theoretical model is proposed to investigate the proportion of these different cell types in experimental tumors. The model exploits the fact that when grafts are treated with hormones, both cell types form an outgrowth, whereas in the absence of hormones only the autonomous cell types can grow.Method 1 consists of serially transplanting the tumor to be investigated in castrated mice that are not treated with hormones, and comparing the growth rates of two consecutive transplant generations. Method 2 involves comparing the growth of the tumor in hormone treated and untreated castrated mice. The merits and limitation of each of these two methods are discussed.     

The fine structure of the brain of Gastrocotyle trachuri (Monogenea: Platyhebninthes)

Summary The fine structure of the brain of the monogenean Gastrocotyle trachuri (Platyhelminthes) is described. The brain consists of a central neuropile surrounded by a layer of cell bodies. The neuropile is composed of a fine meshwork of naked neurites which contain various types of vesicles and other organelles although microtubules have not been found. Five kinds of vesicles; three clear types and two dense types, were found within the neuropile.Two types of neuronal cell body were identified on the basis of their vesicle contents although it is possible that these two types represent the extremes of a single cell type. A characteristic feature of the neuronal perikarya of Gastrocotyle is the presence of deep infoldings into the cell of the outer membrane. These infoldings often contain fibrous interstitial material and in a number of cases hemidesmosome-like structures have been found in the distended, distal end of the infoldings.     

Multiplicity of protein serine-threonine phosphatases in PC12 pheochromocytoma and FTO-2B hepatoma cells

Protein purification and molecular cloning have defined five classes of protein serine-threonine phosphatase catalytic subunits referred to as types 1, 2A, 2B (calcineurin), 2C, and X. Protein serine-threonine phosphatases 1, 2A, 2B, and X appear to have significant sequence homologies, whereas the 2C enzyme is more divergent. We have used the polymerase chain reaction to define the multiplicity of the closely related types 1, 2A, 2B, and X phosphatase catalytic subunits in two clonal cell lines, rat PC12 pheochromocytoma and rat FTO-2B hepatoma. RNAs for all four related phosphatase types were expressed in both cell lines. In addition to the phosphatase X enzyme, four phosphatase 1, two phosphatase 2A, and three phosphatase 2B isoforms were identified in PC12 and FTO-2B cells. The results indicate a large multiplicity of protein serine-threonine phosphatases within clonal cells of different tissue origin, suggesting that their role in cell regulation will be as divergent as that for the protein serine-threonine kinases.     

Computer-based tracking of living cells

A computer-based tracing technique has been developed to follow the movement of living cells and keep them centered in the field of view of an optical microscope. With the use of an image-processing system, the video image of a cell can be sufficiently processed to allow computer-recognition of the cell boundaries. Determination of the location of the center of the cell enables comparison of successive cell positions and correction for any cell movement. In order to illustrate the versatility of this technique, patterns of movement were obtained of cancerous and non-cancerous cells in an effort to determine the difference in motility between the two cell types. After examination of the data gathered, it was found that there is no difference in the motility between the two cell types over 1-h periods.     

Asymmetry and directionality in production of new cell types during clonal growth: the switching pattern of homothallic yeast.

Homothallic Saccharomyces yeasts efficiently interconvert between two cell types, the mating types a and alpha. These interconversions have been proposed to occur by genetic rearrangement ("cassette" insertion) at the locus controlling cell type (the mating type locus). The pattern of switching from one cell type to the other during growth of a clone of homothallic cells has been followed by direct microscopic observation, and the results have been summarized as "rules" of switching. First, when a cell divides, it produces either two cells with the same mating type as the original cell or two cells that have switched to the other mating type. This observation suggests that the mating type locus is changed early in the cell cycle, in late Gl or during S. Second, the ability to produce cells that have switched mating type is restricted to cells that have previously divided ("experienced cells"). Spores and buds ("inexperienced cells") rarely if ever give rise to cells with changed mating type. A homothallic yeast cell thus exhibits asymmetric segregation of the potential for mating type interconversion--at each cell division, the mother, but not the daughter, is capable of switching cell types in its next division. Homothallic cells also exhibit directionality in switching: experienced cells switch to the opposite cell type in more than 50% of cell divisions. These results show that the process of mating type interconversion is itself controlled during growth of a clone of homothallic cells. By analogy and extension of these results, we propose that multiple cell types can be produced in a specific pattern during development of a higher eucaryote in a model involving sequential cassette insertion.     

A model for estimating the extent of variegation in mosaic tissues

A method is described which allows the size of patches of like cells in mosaic tissues to be estimated from the frequency with which small samples taken from the tissue contain both of the mosaic cell types. The mosaic patches are represented as close-packed geometric figures arranged in twoor three-dimensional tissues. Small samples drawn at random from these tissues will include portions of one or more patches; only those samples which include portions of two or more dissimilar patches (mixed samples) will contain both cell types. The expected frequency of mixed samples is calculated as a function of the shape of the mosaic patches, the frequency of the two mosaic cell types and the sample to patch size ratio. This expected frequency is not strongly dependent on patch shape for triangular, square and hexagonal patches in two dimensions or for cubic and orthotetrakaidekahedral patches in three dimensions. Elongation of square patches along one axis or of cubic patches along one or two axes results in slight increases in the expected frequency of mixed samples for given sample to patch size ratio.     

Analysis of X-Ray-Induced Cell-Cycle Perturbations In Mouse Osteosarcoma Cells: A Two-Signal Cell-Cycle Model

ABSTRACT The effects of X-irradiation on mouse osteosarcoma cells have been studied by time-lapse cinematography and the resulting pedigrees have been analysed statistically. It is shown that the irradiation treatment causes three types of cell kinetic lesions: cell death (disintegration), cell sterilization (failure to divide) and proliferation delay. the first two lesions are the most important with regard to survival of the irradiated cell in a clonal assay. of these two lesions, sterilization appears to be highly correlated for sister cells, while this is not true for cell disintegration. This indicates that cell survival in a clonal assay may be a function of the ratio of the incidences of these two types of lesions. the X-ray-induced proliferation delay was studied in terms of intermitotic time distributions, mother-daughter correlation and sibling correlation in relation to the current cell-cycle phase at the time of treatment. This analysis shows that the effects of irradiation on these cell-cycle characteristics is highly cellcycle-dependent. A qualitative model to account for the observations is presented.     

Use of lectins for detection of electrophoretically separated glycoproteins transferred onto nitrocellulose sheets

A method of rapidly identifying lectin-binding glycoproteins separated by polyacrylamide gel electrophoresis is described. The method is particularly useful for comparing the glycoprotein content of different cell types and fractions. Normal rat liver, Novikoff hepatoma, and rat mammary tumor cell line 13762 MAT-B were fractionated to give purified nuclei and other fractions defined by their sedimentation properties in low ionic strength buffer. The subcellular fractions were separated by polyacrylamide gel electrophoresis in sodium dodecyl sulfate, transferred to nitrocellulose sheets, and localized by an immunochemical method to identify lectin-binding activities. The localization pattern of concanavalin A and wheat germ agglutinin-binding activities in the fractions from the three cell types showed the greatest similarities between the glycoprotein contents of normal liver and Novikoff hepatoma fractions. On a per-cell basis the purified nuclei from each of the cell types contained less activity overall than did other particulate cell fractions. Washing the nuclei from normal liver and Novikoff hepatoma, but not MAT-B cells, in nonionic detergent removed or depressed most of the lectin-binding activities. However, two major bands were unaffected by the detergent. One of these localized with wheat germ agglutinin at an apparent molecular weight of 62,000 in the nuclei of all three cell types. The other localized with concanavalin A at an apparent molecular weight of 200,000 in normal liver and Novikoff hepatoma nuclei.     

Negative dielectrophoretic patterning with different cell types

In this paper, a novel method for patterning different cell types based on negative dielectrophoresis (n-DEP), without any special pretreatment of a culture slide, has been described. An interdigitated array (IDA) electrode with four independent microelectrode subunits was fabricated with indium-tin-oxide (ITO) and used as a template to form cellular micropatterns. A suspension of C2C12 cells was introduced into the patterning device between the upper slide and the bottom IDA. In the present system, the n-DEP force is induced by applying an ac voltage (typically 12V(pp), 1MHz) to direct cells toward a weaker region of electric field strength. The cells aligned above one of the bands of IDA within 1min since the aligned areas on the slide were regions with the lower electric field. The application of an ac voltage for 5min allows the cells to adsorb onto the cell culture slide. After removing excess cells, the second cell type was patterned in lines using the same method as with the first set of cells. Periodic and alternate cell lines incorporating two cell types were also fabricated by changing the ac voltage mode. A second cell type was introduced into the device and guided to other areas to form a different pattern. The described system enables two cell types to be patterned in 15min. The patterning method provides a novel tool for use in fundamentals studies of cell biology based on cell-cell interactions between different cell types.     

Nest architecture inParischnogaster alternata Sakagami (Vespidae,Stenogastrinae), intra-specific variability in building strategies

Summary P. alternata is a cave-dwelling stenogastrine wasp of the South Asian rain forests; it builds two distinct types of nest which differ in substrate and other characteristics. Both types of nest were examined and compared for overall dimensions, cell size and building material. The inhabitants taken from both types of nests, were also measured. Significant differences between the two types of nests were found in cell size and percentages of inorganic and organic material. A significant difference was also found in the wing size of the inhabitants. Both nest styles are described in detail, and the evolutionary implications are discussed in terms of behavioural plasticity and the possibility of sympatric speciation.     

A deterministic model of the cell cycle

The variability of the duration of the cell cycle is explained by the phenomenon of sensitive dependence upon initial conditions; as may occur in deterministic non-linear systems. Chaotic dynamics of a system is the result of this sensitive dependence. First a deterministic system is formulated that is equivalent to the Smith-Martin transition probability model of the cell cycle. Next the model is extended to a dynamic process that ranges over the cell generations. A deterministic non-linear relationship between the cycle time of the mother and daughter cell is established. It clarifies the variability of mother-daughter correlation for the different cell types. The model is fitted to two different cell cultures; it shows that the graph of the non-linear relation has the same shape for different cell types.     

The morphology and ultrastructure of “amphipod silk” glands in <Emphasis Type="Italic">Ampithoe rubricata</Emphasis> (Crustacea,Amphipoda, Ampithoidae)

The anatomy and ultrastructure of “amphipod silk” glands in Ampithoe rubricata Montagu 1818 (Ampithoidae) have been studied. The morphology and ultrastructure of the glands in pereopods 3 and 4 have been examined in semithin and ultrathin sections using light and transmission electron microscopy. The glands of two types producing secretions different in their chemical compositions are observed in these pereopods. The ducts of the glands of both types lead to a common reservoir in the dactylus. Each gland comprises several secretory cells and one duct cell. The structure earlier regarded as the chitin wall of the duct is the cytoplasm of the duct cell; the presence of this cell in the studied glands is demonstrated for the first time. The secretory cells contain one or two nuclei and form rows along each duct cell. A new, previously unknown type of crustacean glands is described.     

Nonparametric One‐way Analysis of Variance of Replicated Bivariate Spatial Point Patterns

A common problem in neuropathological studies is to assess the spatial patterning of cells on tissue sections and to compare spatial patterning between disorder groups. For a single cell type, the cell positions constitute a univariate point process and interest focuses on the degree of spatial aggregation. For two different cell types, the cell positions constitute a bivariate point process and the degree of spatial interaction between the cell types is of interest. We discuss the problem of analysing univariate and bivariate spatial point patterns in the one‐way design where cell patterns have been obtained for groups of subjects. A bootstrapping procedure to perform a nonparametric one‐way analysis of variance of the spatial aggregation of a univariate point process has been suggested by Diggle, Lange and Bene? (1991). We extend their replication‐based approach to allow the comparison of the spatial interaction of two cell types between groups, to include planned comparisons (contrasts) and to assess whole groups against complete spatial randomness and spatial independence. We also accommodate several replicate tissue sections per subject. An advantage of our approach is that it can be applied when processes are not stationary, a common problem in brain tissue sections since neurons are arranged in cortical layers. We illustrate our methods by applying them to a neuropathological study to investigate abnormalities in the functional relationship between neurons and astrocytes in HIV associated dementia. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)