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PubMed1980

Branching of microvilli in the human conjunctival epithelium.

Biopsy specimens were obtained from the upper tarsal and limbal conjunctivae of ten normal persons and from the upper tarsal conjunctivae of five asymptomatic contact lens wearers and five patients with giant papillary conjunctivitis (GPC) associated with contact lens wear. The microvillar surface of the conjunctival epithelium was studied by transmission and scanning electron microscopy. Branches often stemmed from the side of a straight tubular microvillus and formed an acute angle with the main process. Branches sprouted at various distances from the origin of the microvillus. The most common branching pattern was the bifurcated (bifid) form. Occasionally, both primary and secondary bifurcations were primary and secondary bifurcations were observed on the same microvillus. Some microvilli were branched in the normal conjunctivae, but the conjunctivae of asymptomatic contact lens wearers and patients with GPC had more branched microvilli and greater polymorphism, which correlated with the degree of alteration. This report demonstrates the presence of branched microvilli and describes the types seen in normal conjunctivae and compares the frequency with which branched microvilli are seen in altered conjunctival surfaces.

Cell Membrane↗
PubMed1980

Short-term tissue culture observations of experimental primary and transplanted nervous system tumors.

Tumors of the central and peripheral nervous system were induced in BD-IX rats and transplanted serially. Both primary and transplanted tumors in different generations were cytologically analyzed, using primary explants in vitro. Four hundred and thirty single tumors were examined in vitro over th period 1969 to 1977, using the following methods: conventional aniline staining, special silver impregnation, supravital observation of cells by phase contrast microscopy, locomotion studies with time-lapse cinematography, and ultrastructural analysis from transmission and scanning electron microscopy. Cells grown in vitro were subdivided into the following groups, according to their morphology: (1) Apolar cells: Round cells only observed in rare tumors of the nasal cavity and sporadically in transplanted neurinomas; they are thought to represent cells from the reticular variant of neurinoma in the latter. (2) Bipolar cells occurred in two forms: As bipolar fibroblasts and as slender bipolar cells observed in explants of malignant neurinomas. The latter cells grow in parallel arrangements; their tentative interpretation as Schwann cells is consistent with their description in human neurilemomas. (3) Semipolar cells with one clear-cut edge and a broad ruffled membrane opposite. They are described as fibroblasts in the course of locomotion. (4) Multipolar cells, observed in several forms in primary and transplanted gliomas exclusively. Variants with long processes were seen in the first passages of intracerebrally transplanted tumors only; in later generations, all cells had short branching processes and little cytoplasm. Conclusions concerning the cytologic derivation of experimental tumors are discussed.

Animals↗
PubMed1981

Ontogeny of medullary raphe nuclei in the rabbit brain stem: a Golgi study.

Nuclei raphe obscurus, pallidus, and magnus, found in the midline and paramedian regions of the medulla, were examined in rabbits between day 22 of gestation and adulthood. At day 22 of gestation (total gestation period of 32 days), the neurons were small with sparsely branched processes. Between day 26 of gestation and 6 days of age, the dendrites expanded, increased the number and length of their branches, and developed abundant spines. During this period, the cell bodies grew in size. From postnatal day 6 to adulthood, a mature pattern of dendritic branching was achieved, and the number of spines on the dendrites was reduced. Nuclei raphe obscurus, pallidus and magnus each possessed cells with unique morphological appearances early in ontogeny, but showed a similar pattern of enhanced dendritic branching with numerous spines through early neonatal development, followed by a reduction in the number and size of the spines. Despite the morphological heterogeneity of the medullary raphe nuclei, their general pattern of dendritic development is similar, suggesting that afferent connections to these nuclei may be formed during cellular maturation by a process similar to that described for the reticular formation and other central neurons.

Aging↗
PubMed2003

Induced repatterning of type XVIII collagen associates with ectopic Sonic hedgehog and lung surfactant C gene expression and changes in epithelial epigenesis in the ureteric bud.

How cell and tissue interactions lead to complex organ structures and differentiated cell types during organogenesis is one of the most fundamental questions in developmental biology. The embryonic lung and kidney of the mouse are useful models for studying the molecular mechanisms of morphogenesis, and in both of these organs, the epithelial bud undergoes a characteristic branching process. This review discusses the potential role of an extracellular matrix molecule, type XVIII collagen, in the generation of the branching patterns in the lung and kidney and how its experimental respecification in tissue recombinants between the ureteric bud and lung mesenchyme correlates with changes in expression of signaling molecules such as sonic hedgehog and changes in cell fate as judged by ectopic expression of the lung surfactant C gene.

Collagen Type XVIII↗
PubMed2002

Cellular architecture of the synovium in the tendon sheath of horses: an immunohistochemical and scanning electron microscopic study.

The intimal lining cells of the synovium in joints have been studied morphologically and histochemically and shown to consist of macrophagic cells (type A) and fibroblast-like cells (type B). It is believed that the structure of the synovium in the tendon sheath is similar to that in the joint, but there have been only a few morphological studies of the tendon sheath. The present study revealed the cellular architecture of synovium in the tendon sheath of horses by histochemistry and scanning electron microscopy (SEM). Like the joint, the inner surface of the tendon sheath was covered with a cell-rich intimal layer. Acid phosphatase-positive A cells accumulated in the mesotendon but few in other regions. B cells were selectively immunolabeled with protein gene product (PGP) 9.5 antiserum and distributed in the entire length of the synovial intima in the tendon sheath. The synovial intima consisted of a surface layer rich in the processes of B cells and a deep layer containing cell bodies of B cells. Using SEM, B cells could be classified into two types according to the morphology of their processes. B cells of dendritic type were located mainly in the joint-side of the tendon sheath and extended branched processes to form a meshwork on the intimal surface. B cells of flat type were located in the skin-side of the tendon sheath and in the mesotendon. Their membranous processes extended in a horizontal direction and covered the intimal surface, resembling epithelium. It appears likely that the morphology and distribution of synovial intimal cells are influenced by various factors, such as the nature of the underlying tissues and the magnitude of mechanical stress.

Animals↗
PubMed1987

Modulation of growth and of morphological characteristics in glioma cells by nerve growth factor and glia maturation factor.

Anaplastic glioma T9 cells were treated with either nerve growth factor (NGF) or glia maturation factor (GMF) or both. It was found that, when T9 cells were treated with these factors in a chemically defined medium, both NGF and GMF induced characteristic changes of cell morphology and growth pattern. Several differences in the effects of NGF and GMF were noted. NGF retarded growth rate, whereas GMF did not. The cells treated with NGF were characterized by a flattened extended cytoplasm with numerous protruding processes. The cell masses were somatically connected by cell bridges. GMF, on the other hand, produced slender cells with long, branching processes forming an interconnecting cell net. Concomitant administration of NGF and GMF retarded cell growth as was demonstrated with NGF alone and induced morphological changes predominantly attributable to GMF. The maximal effect of either NGF or GMF or both was attained after 4 days of treatment. A withdrawal of the factors from the medium following various periods of treatment revealed that the effects of GMF were readily reversible while morphological changes induced by NGF persisted in its absence.

Animals↗
PubMed1980

Spreading of fibroblasts in medium containing cytochalasin B: formation of lamellar cytoplasm as a combination of several functional different processes.

Normal cultured mouse fibroblasts spreading on solid substrate extend and attach numerous pseudopods; lamellar cytoplasm is eventually formed from the attached pseudopods. Fibroblasts spreading in the presence of cytochasin B (CB) from de novo a system of arbor-like branched processes rather than lamellar cytoplasm. The growing and fully formed arbor-like processes, in contrast to normal lamellar cytoplasm, have low contractility and are unable to clear patched concanavalin A receptors from their surfaces; their attachement sites are not associated with microfilament bundles. The cells spreading in medium containing CB and Colcemid do not form well-organized branched structures but extend and attach numerous unstable pseudopods. It is suggested that normal formation of lamellar cytoplasm can be regarded as a combination of several functionally different processes: (a) of rudimentary pseudopodial reactions resistant to CB and Colcemid; (b) of CB-sensitive lamellization; and (c) of Colcemid-sensitive stabilization.

Animals↗
PubMed1999

Modeling insight into spontaneous regression of tumors.

The phenomenon of spontaneous regression of benign and malignant tumors is well documented in the literature and is commonly attributed to the induction of apoptosis or activation of the immune system. We attempt at evaluating the role of random effects in this phenomenon. To this end, we consider a stochastic model of tumor growth which is descriptive of the fact that tumors are inherently prone to spontaneous regression due to the random nature of their development. The model describes a population of actively proliferating cells which may give rise to differentiated cells. The process of cell differentiation is irreversible and terminates in cell death. We formulate the model in terms of temporally inhomogeneous Markov branching processes with two types of cells so that the expected total number of neoplastic cells is consistent with the observed mean growth kinetics. Within the framework of this model, the extinction probability for proliferating cells tends to one as time tends to infinity. Given the event of nonextinction, the distribution of tumor size is asymptotically exponential. The limiting conditional distribution of tumor size is in good agreement with epidemiologic data on advanced lung cancer.

Humans↗
PubMed1986

Projection of mean and variance functions for population processes with time-homogeneous laws of evolution.

This paper provides algorithms for projection of mean and covariance functions for stochastic population processes governed by time-homogeneous laws of fertility and mortality. The theoretical foundation of the algorithms is general age-dependent branching processes in discrete time. The algorithms are employed in several illustrative projections, based on 1982 Chinese data, of a population experiencing an abrupt transition to below replacement fertility. Methods of constructing confidence limits for total population size are illustrated. Also developed are procedures for projecting mean and variance functions for populations which may be heterogeneous with respect to mortality or fertility. The projections performed yield two observations. First, the coefficient of variation in population size appears to be inversely related to the Malthusian parameter of population growth. Second, the coefficient of variation for population size is negligible for large homogeneous initial populations. But when the initial population is heterogeneous with respect to fertility or mortality, then substantial coefficients of variation, exceeding 0.4, are observed in some of the projections performed.

Analysis of Variance↗
PubMed1996

Confocal imaging of the keratocyte network in porcine cornea using the fixable vital dye 5-chloromethylfluorescein diacetate.

This study reports on the combined use of an aldehyde fixable, cell viability fluoroprobe, 5-chloromethylfluorescein diacetate (CMFDA), confocal laser scanning microscopy and digital image reconstruction, to produce high resolution images of corneal keratocyte preparations in situ. The central region of freshly enucleated porcine corneae were removed and stained overnight at 4 degrees C with CMFDA. The tissue was washed, fixed, and frozen for cryosectioning in either a horizontal or antero-posterior orientation. Sections from anterior, central and posterior stroma were examined with a confocal microscope, and the digital images rendered as three-dimensional stereo reconstructions. Fluorescent CMFDA which completely permeated the cell bodies and extremes of the finest ramifying cell processes of all keratocytes provided exceptional high resolution images of the three morphologically distinct cell subpopulations at different levels of the stroma, and enabled improved characterisation of each cell type. Anteriorly was a thin, dense, non-lamellar network of keratocytes subjacent Bowman's membrane. In the central stroma, keratocytes were arranged in layers, the cell bodies had a flattened pyramidal or stellate shape, and the fine cell processes formed extensive distal ramifications. Immediately anterior to Descemet's membrane a small subpopulation of keratocytes with large cell bodies and short branched processes was identified. Extensive and diverse cell-to-cell contacts were orientated in all stromal planes, including ramping cell bridges between keratocyte lamellae in the central stroma. The use of the cell viability dye CMFDA is feasible and valuable for enhancing the visibility of entire keratocyte population in the intact cornea. Diverse multi-directional cell processes and intercellular contacts throughout the keratocyte network suggest a strong capacity for direct communication and cohesion in the maintenance and repair of the stromal matrix. Keratocytes closely related to the epithelium and endothelium have unique morphologies which may relate to specialised functions of these interface cells.

Animals↗
PubMed1986

Somatostatin immunocytochemistry in the rabbit retina.

In previous work, radioimmunoassay was used to document the presence of somatostatin-like immunoreactive material in the rabbit retina. The present study was undertaken to determine the cellular localization of that material by light microscopic immunocytochemistry. Rabbit retinas were fixed by immersion in paraformaldehyde-lysine-periodate and reacted, either as whole retinas or as 50 microns Vibratome cross-sections, with an antiserum directed against somatostatin-14. Consistent staining of neuronal perikarya was seen only in the retinas of rabbits that had been pretreated with intravitreal injections of colchicine. Specifically stained cell bodies are present in the ganglion cell layer; the cells give rise to fibers in both the innermost and outermost sublaminas of the inner plexiform layer. In retinal whole mounts, the cells possess two or three primary dendrites with sparse branching. The dendritic fields are up to 1 mm in diameter, and adjacent dendritic fields overlap. Many cells have a thin varicose process arising from the soma or a proximal primary dendrite; these processes branch repeatedly within the retina and resemble intraretinal axons. The somatostatin-reactive cells may be associational ganglion cells or displaced amacrine cells; it is less likely that they are ganglion cells with axons projecting to the brain.

Animals↗
PubMed1976

Fine structure of the epidermis of the optic tentacle in a slug, Limax flavus L.

The epidermis at the tip of the optic tentacle in Limax flavus is constructed of columnar epithelial cells, distal processes of nerve cells, and scattered processes of the collar cells. The epithelial cells extend stout microvilli called plasmatic processes by Wright perpendicularly from the free surface. Each plasmic process branches into a few terminal twigs embedded in a fuzzy filamentous substance. Most nerve cells have their nuclei under the basal lamina. The distal processes of these nerve cells reach the free surface and send long microvilli to form the spongy layer under a filamentous covering. At the side surface of the tentacle the epithelial cells are cuboidal or squamous and the neural elements are fewer. Here, no spongy layer is formed; and the collar cell processes are replaced by the lateral cell processes. Peculiar secretion granules are contained in the lateral and collar cell processes as well as in their cell bodies situated beneath the basal lamina.

Animals↗
PubMed1991

Light and electron microscopic analyses of intraspinal axon collaterals of sympathetic preganglionic neurons.

Experiments were performed in pigeons (Columba livia). Sympathetic preganglionic neurons (SPNs) in the first thoracic spinal cord segment (T1) were identified electrophysiologically using antidromic activation and collision techniques and then intracellularly labeled with horseradish peroxidase (HRP). In 6 of 10 HRP-labeled SPNs, the site of axon origin and intraspinal axonal trajectory could be specified. In 2 of the 6 HRP-labeled axons, the peripherally projecting process branched intraspinally. The presence or absence of SPN intraspinal axonal collateralization did not correlate with parent perikaryal subnuclear location or dendritic alignment. None of the collaterals were recurrent onto the SPN of origin. Light microscopically, the collateral branches appeared to end with punctate, bulbous swellings. The spinal regions of the terminal end swellings for the two axons did not overlap one another. In one instance the entire terminal field was confined within the principal preganglionic cell column (column of Terni). The other axon had collateral branches which terminated in the lateral white matter and in a ventrolateral region of lamina VII. A serial section, electron microscopic reconstructive analysis of the entire intraspinal collateral terminal field within the column of Terni revealed that: (a) the primary collateral process was unmyelinated and arose at a node of Ranvier; (b) after issuance of the collateral branch, the myelinated parent axon continued to increase its myelin wrapping throughout the spinal gray; (c) the bulbous swellings observed light microscopically corresponded to axon terminal boutons and regions of synaptic contact; (d) the axon collateral terminals were exclusively presynaptic to small caliber dendrites and formed only asymmetric specializations; and (e) the collateral terminals contained numerous mitochondria, and densely packed, electron-lucent, spherical vesicles.

Animals↗
PubMed1982

Autoradiography of (3H)-5-hydroxytryptamine uptake in the retina of some mammals.

The uptake of indoleamines into the retina of rats, rabbits, cows, pigs, baboons. Cynomolgus monkeys, and man was studied by fluorescence microscopy and autoradiography. Indoleamines were either injected intravitreally or the retinas were incubated with them. Fluorescence microscopy failed to show any indoleamine accumulating neurons in all species investigated except rabbit, confirming previous observations. However, autoradiography showed uptake in a distinct class of neurons in cows and pigs. These neurons had their cell bodies among the amacrine cells and most of their processes branched in the middle of the inner plexiform layer. This is in contradistinction to the dopaminergic neurons, which in cows and pigs have all their processes in the outermost sublamina of the inner plexiform layer. The fluorescence microscopy is quite sensitive to small variations in the indoleamine molecule. The discrepancy between the results with fluorescence microscopy and autoradiography therefore suggest that there is an active uptake mechanism for indoleamines in cows and pigs but that the substances are rapidly transformed to compounds not possible to detect in the fluorescence microscope. No specific indoleamine accumulating mechanism was detected in the retina of rats, baboons, cynomolgus monkeys, or man.

Animals↗
PubMed2004

Fixation of beneficial mutations in the presence of epistatic interactions.

We investigate the effect of deleterious mutations on the process of fixation of new advantageous mutants in an asexual population. In particular we wish to study the dependence of the process on the strength of the deleterious mutations. We suppose the existence of epistatic interaction between the genes. We study the model by means of branching process theory and also by numerical simulations. Our results show the occurrence of two distinct regimes of behavior for the probability of fixation of these variants. The occurrence of either regime depends on the ratio between the selective advantage of the beneficial mutation sb and on the selective parameter for deleterious mutations sd. In the former, which takes place for sb/sd< or =1, the probability of fixation increases with the epistasis parameter , whereas for sb/sd>>1 the probability of fixation is a complex function of and the mutation rate U. Surprisingly, we find that for the multiplicative landscape (alpha=1) the probability of fixation Pfix is given by Pfix= pib)e-U/sd where pi(sb) is the probability of fixation for the two-allele model in the absence of mutations as calculated by Haldane (1927, Proc. Camb. Phil. Soc., 26, 220-230) and Kimura (1962, Genetics, 47, 713-719).

Alleles↗
PubMed2003

Solid phase DNA amplification: a simple Monte Carlo Lattice model.

Recently, a new way to amplify DNA, called solid phase amplification (SPA), has been introduced. SPA differs from the traditional polymerase chain reaction (PCR) in the use of surface-bound instead of freely-diffusing primers to amplify DNA. This limits the amplification to two-dimensional surfaces and therefore allows the easy parallelization of DNA amplification in a single system. Furthermore, SPA could provide an alternate route to DNA target implantation on DNA chips for genomic studies. Standard PCR processes are usually characterized (at least initially) by an exponential growth and a broad population distribution, and they are well described by the theory of branching processes, wherein a generating function can be used to obtain the probability distribution function for the population of offspring. This theoretical approach is not appropriate for SPA because it cannot properly take into account the many-body (steric) and geometric effects in a quenched two-dimensional environment. In this article, we propose a simple Lattice Monte Carlo technique to model SPA. We study the growth, stability, and morphology of isolated DNA colonies under various conditions. Our results indicate that, in most cases, SPA is characterized by a geometric growth and a rather sharp size distribution. Various non-ideal effects are studied, and we demonstrate that such effects do not generally change the nature of the process, except in extreme cases.

Computer Simulation↗
PubMed2005

Transport on randomly evolving trees.

The time process of transport on randomly evolving trees is investigated. By introducing the notions of living and dead nodes, a model of random tree evolution is constructed which describes the spreading in time of objects corresponding to nodes. It is assumed that at t=0 the tree consists of a single living node (root), from which the evolution may begin. At a certain time instant tau> or =0, the root produces v> or =0 living nodes connected by lines to the root which becomes dead at the moment of the offspring production. In the evolution process each of the new living nodes evolves further like a root independently of the others. By using the methods of the age-dependent branching processes we derive the joint distribution function of the numbers of living and dead nodes, and determine the correlation between these node numbers as a function of time. It is proved that the correlation function converges to square root of 3/2 independently of the distributions of v and tau when q1-->1 and t-->infinity. Also analyzed are the stochastic properties of the end nodes; and the correlation between the numbers of living and dead end nodes is shown to change its character suddenly at the very beginning of the evolution process. The survival probability of random trees is investigated and expressions are derived for this probability.

Aging↗
PubMedDate not supplied

[Formation of processes during fibroblast spreading in an in vitro medium with cytochalasin B].

The spreading of normal mouse fibroblasts in a solid substrate involves extension and attachment of numerous pseudopodia resulting in the formation of lamellar cytoplasm in the cell periphery which is attached to the substrate. During the spreading of fibroblasts in the presence of cytochalasin B (CB), a system of arbor-like branched processes forms de novo, rather than lamellar cytoplasm. Unlike the normal lamellar cytoplasm, the arbor-like processes are unable to clear their surface from concanavalin A-patched receptors and do not reveal microfilament bundles in their attachment sites. The cells spreading in the presence of both CB and colcemid do not form well-organized branched structures but extend numerous unstable pseudopodia. The formation of lamellar cytoplasm can be regarded as a combination of several functionally different processes: a) rudimentary pseudopodial CB- and colcemid-resistant reactions, b) CB-sensitive lamelliation, and c) colcemid-sensitive stabilization.

Animals↗