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PubMed1983

Surface-replica topography of retinal pigment epithelium during phagocytosis.

The initial step in retinal phagocytosis may be mediated by complementary recognition molecules on the pigment epithelial microvilli and outer segment membrane surfaces. These molecules may display a surface morphology which is related topographically to phagocytic events. In order to explore this, we have developed a method for replicating the membrane surfaces of rat pigment epithelial explants during phagocytosis of latex beads. The explants are fixed in a mixed aldehyde and osmium fixative and the basal surface glued to a coverslip. After dehydration and critical point drying, the tissue is replicated with platinum and carbon in a freeze-fracture apparatus using either rotary or unidirectional coating and the replicas are examined by transmission electron microscopy. The membrane surfaces of the pigment epithelial cells and their microvilli are studded with numerous surface particles varying in size from 20 to 50 nm that are closely packed and give a cobblestone appearance to the membrane topography. During the early stages of phagocytosis, microvillous processes appear to spread over the beads and form branched processes as they contact bead surfaces. During bead engulfment the microvilli have shortened into flattened sheets with interdigitating processes overlapping the beads. These uptake sites resemble Venus' fly-traps, which as they close over the beads create craters in the membrane surfaces of the pigment epithelium. The crater-like uptake sites appear to flatten out in the later stages and form flattened membrane domains which are surrounded by crenulated membrane that displays an irregular particulate morphology.

Animals↗
PubMed1997

Branching design of the bronchial tree based on a diameter-flow relationship.

We propose a method for designing the bronchial tree where the branching process is stochastic and the diameter (d) of a branch is determined by its flow rate (Q). We use two principles: the continuum equation for flow division and a power-law relationship between d and Q, given by Q approximately dn, where n is the diameter exponent. The value of n has been suggested to be approximately 3. We assume that flow is divided iteratively with a random variable for the flow-division ratio, defined as the ratio of flow in the branch to that in its parent branch. We show that the cumulative probability distribution function of Q, P(> Q) is proportional to Q-1. We analyzed prior morphometric airway data (O. G. Raabe, H. C. Yeh, H. M. Schum, and R. F. Phalen, Report No. LF-53, 1976) and found that the cumulative probability distribution function of diameters, P(> d), is proportional to d-n, which supports the validity of Q approximately dn since P(> Q) approximately Q-1. This allowed us to assign diameters to the segments of the flow-branching pattern. We modeled the bronchial trees of four mammals and found that their statistical features were in good accordance with the morphometric data. We conclude that our design method is appropriate for robust generation of bronchial tree models.

Animals↗
PubMed2003

Wnt11 and Ret/Gdnf pathways cooperate in regulating ureteric branching during metanephric kidney development.

Reciprocal cell-cell interactions between the ureteric epithelium and the metanephric mesenchyme are needed to drive growth and differentiation of the embryonic kidney to completion. Branching morphogenesis of the Wolffian duct derived ureteric bud is integral in the generation of ureteric tips and the elaboration of the collecting duct system. Wnt11, a member of the Wnt superfamily of secreted glycoproteins, which have important regulatory functions during vertebrate embryonic development, is specifically expressed in the tips of the branching ureteric epithelium. In this work, we explore the role of Wnt11 in ureteric branching and use a targeted mutation of the Wnt11 locus as an entrance point into investigating the genetic control of collecting duct morphogenesis. Mutation of the Wnt11 gene results in ureteric branching morphogenesis defects and consequent kidney hypoplasia in newborn mice. Wnt11 functions, in part, by maintaining normal expression levels of the gene encoding glial cell-derived neurotrophic factor (Gdnf). Gdnf encodes a mesenchymally produced ligand for the Ret tyrosine kinase receptor that is crucial for normal ureteric branching. Conversely, Wnt11 expression is reduced in the absence of Ret/Gdnf signaling. Consistent with the idea that reciprocal interaction between Wnt11 and Ret/Gdnf regulates the branching process, Wnt11 and Ret mutations synergistically interact in ureteric branching morphogenesis. Based on these observations, we conclude that Wnt11 and Ret/Gdnf cooperate in a positive autoregulatory feedback loop to coordinate ureteric branching by maintaining an appropriate balance of Wnt11-expressing ureteric epithelium and Gdnf-expressing mesenchyme to ensure continued metanephric development.

Alleles↗
PubMed1988

An immunohistochemical study of cellular and nervous elements in the taste organ of the bullfrog, Rana catesbeiana.

The cellular and nervous elements of the bullfrog taste organ were examined by immunohistochemical methods using various antibodies. The immunoreactivity for spot 35 protein, a soluble protein isolated from bovine cerebellum, was found in numerous taste cells located at the middle or slightly lower levels within the gustatory cell layer. The immunoreactive cells possessed cytoplasmic processes rising upward the free surface and also issued branched processes to the base of the epithelium. The immunoreaction for spot 35 protein was found diffusely throughout the cytoplasm from the apical to the basal parts of the taste cells. NSE-immunoreactive taste cells were located at the upper or middle levels within the gustatory cell layer in the taste organ. The fact that the cells were smaller in number and size than spot 35 protein-reactive cells and further differed in localization distinguished the NSE-taste cells from the spot 35 protein cells. Serotonin-like immunoreactivity was detectable in the basal cells localized at the base of the taste epithelium. The immunoreactive cells were arranged in a circle at the periphery of the taste organ, each extending a slender process toward the center. The terminal portion of this process spread leaf-like; numerous fine projections protruded from its margin. The serotonin-immunoreactive cells appear to coincide with the monoamine-containing basal cells, which have been previously reported. Substance P-, calcitonin gene-related peptide (CGRP)-, vasoactive intestinal polypeptide (VIP)-, peptide HI (PHI)- or gastrin releasing peptide (GRP)-immunoreactive nerve fibers with varicosities were demonstrated within the taste organ. Some substance P-fibers ran along the bottom of the taste organ epithelium. A few thinner substance P-fibers ascended among the epithelial cells of the organ and terminated closely below the free surface. CGRP-fibers were found to correspond to substance P-fibers from their evidencing a double immunostaining. VIP- and PHI-fibers formed a meshwork in the basal area of the taste epithelium. Abundant substance P- and/or CGRP-fibers formed a meshwork among the ciliated cells located at the periphery of the taste organ. However, PHI- and GRP-fibers were detected less than substance P- and/or CGRP-fibers, though VIP-fibers were rarely present in the same region. Neurofilament protein- or tyrosine hydroxylase-like immunoreactivities were found in thick nerve fibers in the taste organ, whereas no immunoreactivities were present in cellular elements within the taste organ. The relationship between cellular and nervous elements in the taste organ was examined by double immunostainings.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1986

Use of a monoclonal antibody to classify neurons isolated from the head region of Hydra.

A mouse monoclonal antibody (JD1) to Hydra attenuata using the peroxidase-antiperoxidase (PAP) method revealed unipolar, bipolar, and multipolar sensory and ganglion cells in the head region of H. littoralis. Neurons isolated from macerated hypostomes and tentacles were classified according to the number of their cytoplasmic processes and the position of the cilium, when present, relative to the perikaryon. PAP-stained sensory cells had an apical ciliary cone, whereas ganglion cells did not. Neurons with cytoplasmic processes longer than 50 microns stained faintly, whereas those with processes shorter than 50 microns in length stained mainly dense brown. Unipolar neurons had an oval, crescent, round, or elliptic perikaryon with a single short axon. The perikaryal shape of bipolar neurons varied from round to tall triangular, short triangular, crescent, oval, or elliptic with two oppositely directed symmetric or asymmetric processes. Asymmetric processes were present in a bipolar sensory cell with a long apical cilium typical of gastrodermal sensory cells. One type of bipolar ganglion cell had a short perikaryal cilium. Another type had neurites longer than 50 microns. We found seven morphological variations of multipolar neurons, including one with an apical knob, two with a short perikaryal cilium, two with cytoplasmic loops near the perikaryon, one with perpendicular processes projecting from the major neurites, and one with a branched process longer than 50 microns opposite a tangled mass of neurites.

Animals↗
PubMed1988

GABA-containing neurons in the pontine nuclei of rat, cat and monkey. An immunocytochemical study.

Putative GABAergic elements in the pontine nuclei have been studied in the rat, cat and two old world monkeys (Macaca mulatta and Papio papio) using an antiserum against GABA-glutaraldehyde-protein conjugates and the peroxidase-antiperoxidase method. In addition, an antiserum against glutamate decarboxylase has been used in the cat. For comparison, Golgi impregnated material from cat and macaque has been studied. In all species there is a moderately dense plexus of fibres with GABA-like immunoreactivity with only minor regional differences between different parts of the pontine nuclei. The number of cell bodies showing GABA-like immunoreactivity is, however, strikingly different. Thus, in the rat there are very few such neurons. In the cat, they make up about 1% of the total cell population, while the corresponding number in the two primate species is about 5%. The number is consistently somewhat higher in rostral than in caudal parts of the pontine nuclei. Numbers in the cat are essentially the same with the glutamate decarboxylase antiserum as with the GABA antiserum. The size of GABA-like immunoreactivity positive somata is very similar in cat, macaque and baboon, averaging about 160 micron2 in cross-sectional area. The average cross-sectional area of the total neuronal population as measured in adjacent thionin-stained sections is about 280 micron2. However, the range of sizes for GABA-like immunoreactivity positive cells is wide, so that size alone is not a good criterion for their identification. Although their dendritic morphology is varied, a significant proportion of GABA-like immunoreactivity positive cells have very long and straight dendrites. A few examples were found in the primate species of GABA-like immunoreactivity positive cells with processes tentatively identified as axons. Such processes could be seen to divide several times. No such branching processes could be identified, however, in Golgi impregnated material from the same species. In order to determine whether GABA-like immunoreactivity positive cells project to the cerebellum, retrograde tracing of horseradish peroxidase-wheat germ agglutinin was combined with immunocytochemistry. No double labelled cells could be found in the pontine nuclei. Comparison of size distribution of retrogradely labelled pontocerebellar and GABA-like immunoreactivity positive cell bodies showed a high degree of overlap, although the average size of projection neurons and GABA-like immunoreactivity positive ones is clearly different.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed2000

Genetic control of branching morphogenesis during Drosophila tracheal development.

Branching morphogenesis is a widely used strategy to increase the surface area of a given organ. A number of tissues undergo branching morphogenesis during development, including the lung, kidney, vascular system and numerous glands. Until recently, very little has been known about the genetic principles underlying the branching process and about the molecules participating in organ specification and branch formation. The tracheal system of insects represents one of the best-characterised branched organs. The tracheal network provides air to most tissues and its development during embryogenesis has been studied intensively at the morphological and genetic level. More than 30 genes have been identified and ordered into sequential steps controlling branching morphogenesis. These studies have revealed a number of important principles that might be conserved in other systems.

Animals↗
PubMed1989

ABH and related histo-blood group antigens; immunochemical differences in carrier isotypes and their distribution.

This review summarizes present knowledge of the chemistry of histo-blood group ABH and related antigens. Recent advances in analytical carbohydrate chemistry (particularly mass spectrometry and NMR spectroscopy) and the introduction of monoclonal antibodies (MoAbs) have made it possible to distinguish structural variants of histo-blood group ABH antigens. Polymorphism of ABH antigens is induced by: (i) variations in peripheral core structure, of which four (type 1, 2, 3 and 4) are known in man; (ii) variation in inner core by branching process (blood group iI), leading to variation of unbranched vs. branched ABH determinants; (iii) biosynthetic interaction with other glycosyltransferases (Lewis, P. T/Tn blood systems) capable of acting on the same substrate as the ABH-defined transferases, and finally (iv) the nature of the glycoconjugate (glycolipid, glycoprotein of N- or O-linked type). ABH variants induced by item (i) above have been clearly distinguished qualitatively by MoAbs; e.g., at least six types of A determinants can be distinguished by qualitatively different classes of antibody. The variants induced by item (ii) create mono- vs. bivalent antigens which may be responsible for observed differences in antibody-binding affinity. Detailed studies of the chemistry of these antigens have increased our insight into blood groups, providing the basis for blood group iI and A subgrouping, as well as a relation between the ABH and Lewis, P, and T/Tn systems. A survey of the literature on distribution patterns of ABH variants is presented. It has been assumed that expression of histo-blood group antigens is developmentally regulated. Relationships between histo-blood group expression, development, differentiation and maturation, as well as malignant transformation, are discussed.

ABO Blood-Group System↗
PubMed1991

Embryology and secretory activity of labial salivary glands.

This study was carried out on the heads of 20 foetuses aged between 11 and 26 weeks. Four stages were distinguished in the development of labial salivary glands, each stage corresponding to gestational age. Stage I is characterized by a localized, rounded thickening of the stomodial epiblast into the mesenchyma of the mucosal side of the lower lip. This occurs at the 9th-10th week of gestation. Stage II is reached when the epiblastic thickening assumes the form of a single cord. It is oval when sectioned transversally and is the result of the proliferation of epiblastic cells into the underlying mesenchyma during the 11th-12th week. Stage III corresponds to a branching process which takes place at the 13th week. The single cord branches to form the future secretory lobes, which rapidly assume a grape-like appearance. The number of rudimentary glands increases during the first three stages of development, i.e. as long as the first formed glands have not developed ducts. Stage IV corresponds to the process of duct formation at the 18th week. Simultaneous differentiation of acinal and duct cells is observed and this procedes the onset of secretory activity.

Basement Membrane↗
PubMed2003

Relationships among shoot sinks for resources exported from nodal roots regulate branch development of distal non-rooted portions of Trifolium repens L.

Two manipulative experiments tested hypotheses pertaining to the correlative control exerted by nodal roots on branch development of the distal non-rooted portion of Trifolium repens growing clonally under near-optimal conditions. The two experiments, differing in their pattern of excision to manipulate the number of branches formed at the first 9-10 phytomers distal to the youngest nodal root, each found that after 20 phytomers of growth the total number of lateral branches formed on the primary stolon remained between five and seven regardless of where the branches formed along the stolon. Additional treatments established that nodal roots influenced branch development via relationships among shoot sinks for the root-supplied resources rather than through variation in the supply of such resources induced by fluctuations in photosynthate supply to roots from branches. Regression analysis of data pooled from treatments of both experiments confirmed that shoot-sink relationships for root- supplied resources controlled the branching processes on the non-rooted portion of plants. A disbudding treatment, which removed all the apical and axillary buds present on basal branches, but left other branch tissues intact, increased branch development of the apical region in the same way as did complete excision of the basal lateral branches. The apical buds and the elongation processes occurring immediately proximal to the buds were thus identified as strong sinks for the root-supplied resources. Such results suggest that branch development on the non-rooted shoot portion distal to the youngest nodal root is regulated by competition among sinks for root-derived resources, of limited availability, necessary for the processes of elongation of axillary buds and the primary stolon apical bud.

Homeostasis↗
PubMed1993

Immunocytochemical visualization of kappa-opioid receptors on chick embryonic neurons differentiating in vitro.

The present paper is the first immunocytochemical demonstration of kappa-opioid receptors in neurons isolated from seven-day-old chick embryonic forebrains and cultivated for one to seven days. The monoclonal antibody KA8 (IgG1-k) [Maderspach et al. (1991) J. Neurochem. 56, 1897-1904] was raised against the frog brain kappa-opioid receptor as an antigen and recognizes an epitope in or near the ligand binding site. The KA8 immunostaining of the neurons displayed individual variations and changed with the in vitro differentiation. Receptors often appeared at the pole of the primary outgrowing process, later on in the whole soma and finally on the branched processes. Specific radioligand binding and KA8 immunocytochemistry both presented an increase in the receptor concentration with development. The equilibrium binding values that were measured at 1 nM [3H]naloxone concentration were 2.9 and 6.1 fmol/10(6) cells on the first and sixth cultivation days, respectively. Neurons were treated with 10(-7) M bremazocine or dynorphine (agonists with relative specificity to kappa-opioid receptors) on the second and third cultivation days. The agonist promoted the morphological differentiation which was already visible within 24 h. It also promoted the expression of the 200,000 mol. wt neurofilament protein, this became pronounced after two to three days. The changes provoked by the agonist were reduced by the opioid antagonist norbinaltorphimine (10(-7) M) or naloxone (10(-5) M) indicating that the effect was receptor-mediated. The hypothesis that kappa-opioid agonists through their receptors may function as regulatory signals in the early neuronal differentiation is discussed.

Animals↗
PubMed2006

Ectopic expression of C/EBPalpha in the lung epithelium disrupts late lung development.

The lung develops from the endoderm through a process of branching morphogenesis. This process is highly active during the pseudoglandular stage of lung development and continues into the canalicular stage, resulting in the formation of terminal sacs. CCAAT/enhancer binding proteins (C/EBPs) are transcription factors regulating central aspects of differentiation and proliferation. We report here the developmental expression of C/EBPalpha, -beta, and -delta in the lung. C/EBPalpha exhibits a dynamic expression pattern and is first detected during the late pseudoglandular stage. At this stage, expression is observed in a subset of epithelial cells in the distal parts of the branching tubules. The expression of C/EBPalpha is confined to nonproliferating cells. To examine the role of C/EBPalpha in lung development, we generated transgenic mice ectopically expressing C/EBPalpha in the lung epithelium using the human surfactant protein C promoter. Lungs from these mice were of normal size but exhibited a phenotype characterized by fewer and larger developing epithelial tubules, indicating that the branching process was affected. No effects on overall proliferation or cellular differentiation were observed. When this phenotype was compared with that of mice carrying a targeted mutation of the Cebpa gene, the Cebpa-/- mice exhibited a similar developmental phenotype. In conclusion, our results show a role for C/EBPalpha in lung development and suggest a function in the later stages of lung branching morphogenesis.

Animals↗
PubMed1989

Neuritic outgrowth in primary cell culture of neurons from the squid, Loligo pealei.

Giant fiber lobe (GFL) cells obtained from healthy squid reliably produced neuritic processes in culture. The processes were of two types, a sheet-like veil or thin branching neurites. The latter type was often associated with bulbous expansions (presumptive growth cones), at the termini, at branch points, or at sites of apparent contact among branches from two different cells. On poly-L-lysine substrate, veiling usually occurred by the fourth or fifth day in culture, while the branching processes appeared by one week to ten days. The elaboration of the outgrowths by the GFL neurons was influenced by the culture substrate and incubation temperature. The development of a preparation in which isolated GFL somata extend neurites in an easily controlled environment will permit the detailed study of axon fusion, channel expression and turnover, and synapse formation in the neurons.

Animals↗
PubMed2003

The mutation process of microsatellites during the polymerase chain reaction.

We build a mathematical model for the mutation process of microsatellites during polymerase chain reaction (PCR) using the theory of branching processes. Based on the model, we develop a method to estimate the mutation rate of microsatellites per PCR cycle and the probability of expansion by maximizing a quasi-likelihood of the observed data. We show by simulations that the proposed estimation method can accurately recover the relationship between the mutation rate and number of repeat units. The theoretical basis for the proposed method is also given. We apply the method to experimental data on poly-A and poly-CA repeats.

Animals↗
PubMed1990

Glial process elongation and branching in the developing murine neocortex: a qualitative and quantitative immunohistochemical analysis.

Cells of astroglial lineage in the murine cerebrum undergo a succession of transformations during prenatal and early postnatal development. The bipolar radial cell, the earliest astroglial form to appear, provides a radially aligned, parallel array of fibers that serves as a guide to neuronal migration. The multipolar astrocyte is the representative of this lineage that persists in the adult cerebrum. The processes of the multipolar astrocytes form a complex reticulum, which is considered critical to the development, function, and maintenance of neural circuits. A monopolar radial cell appears to be transitional between the two. The shift from the radial glial fiber system to a diffuse glial network is achieved largely in the E17-P2 interval in the mouse. This phenomenon has been studied qualitatively and quantitatively by staining cerebral tissue with monoclonal antibody RC2, a specific and sensitive ligand for cells of astroglial lineage in the mouse. Elongation and branching of glial processes contribute to the glial transformation. Elongation of radial fibers occurs under the guidance of other radial glial fibers (fasciculated elongation) or independently of other fibers (nonfasciculated elongation). Fasciculated elongation results in an increase in the density of radial glial fibers that span the cortical layers. Nonfasciculated elongation appears to be associated with process branching. This is the initial event in transformation of the bipolar radial cells to monopolar radial or multipolar cells. Only nonfasciculated elongation is characteristic of processes of the monopolar radial cells and multipolar astrocytes. Branching of the processes of all three cell forms appears to occur both by bifurcation at the elongating tip and by sprouting from the fiber shaft. Elongating fibers are tipped by growth cones that are relatively simple in shape as compared to those observed at the tips of elongating axons. Growth cones at the tips of nonfasciculated fibers are more complex in form than those at the tips of radial fibers elongating in contact with other radial fibers.

Animals↗
PubMed1980

Peripheral fields and branching patterns of buccal mechanosensory neurons in the opisthobranch mollusc, Navanax inermis.

A population of about 75 primary sensory cells were identified on the dorsal surface of each buccal ganglion of Navanax. Each sensory cell possesses at least one mechanosensitive field in the pharyngeal wall or lips that correlates somatotopically with its position in the buccal ganglia. Many cells had additional fields that could be widely separated, requiring that their afferent processes branch. Cells were found with processes in more than one buccal nerve and with multiple processes in the same nerve. Hyperpolarization of the soma or repetitive electrical or physiological stimulation could cause failure of centripetal propagation of impulses. Impulses initiated in different branches could fail at different distances from the soma. Axon spikes that fail to invade the soma may or may not invade other branches. Axon spikes in separate branches that fail to invade the soma can summate to initiate an invading impulse. These findings suggest that integration of information from different branches may occur in a single sensory neuron.

Animals↗
PubMed2002

Regional variations in the cellular matrix of the annulus fibrosus of the intervertebral disc.

The three-dimensional architecture of cells in the annulus fibrosus was studied by a systematic, histological examination using antibodies to cytoskeletal components, in conjunction with confocal microscopy. Variations in cell shape, arrangement of cellular processes and cytoskeletal architecture were found both within and between the defined zones of the outer and inner annulus. The morphology of three, novel annulus fibrosus cells is described: extended cordlike cells that form an interconnected network at the periphery of the disc; cells with extensive, sinuous processes in the inner region of the annulus fibrosus; and cells with broad, branching processes specific to the interlamellar septae of the outer annulus. The complex, yet seemingly deliberate arrangement of various cell shapes and their processes suggests multiple functional roles. Regional variations in the organization of the actin and vimentin cytoskeletal networks is reported across all regions of the annulus. Most notable is the continuous, strand arrangement of the actin label at the disc's periphery in contrast to its punctate appearance in all other regions. The gap junction protein connexin 43 was found within cells from all regions of the annulus, including those which did not form physical connections with surrounding cells. These observations of the cellular matrix in the healthy intervertebral disc should contribute to a better understanding of site-specific changes in tissue architecture, biochemistry and mechanical properties during degeneration, injury and healing.

Actins↗
PubMed2001

A test of whether rates of speciation were unusually high during the Cambrian radiation.

The Cambrian radiation represents an interval when nearly 20 animal phyla appear in the fossil record in a short geological time span; however, whether this radiation also represents a period of extremely rapid speciation remains unclear. Here, a stochastic framework is used to test the null hypothesis that diversity changes in one of the dominant Early Cambrian groups, the olenelloid trilobites, could be produced by tempos of speciation known to have operated during later time periods. Two continuous-time models, the Yule model and the birth and death process model, and one discrete-time model, the Bienaymé-Galton-Watson branching process model, were used. No statistical evidence for uniquely high rates of speciation during the radiation in these trilobites was found when the continuous-time models were used with low or moderate extinction rates, the rates typically associated with the Cambrian radiation, although the p values are fairly low or, in one case, significant when high extinction rates were used. However, rates of speciation were higher than the average Phanerozoic rates of speciation. The discrete-time model produced equivocal results: either rates were unusually high or the model is inapplicable during the Cambrian radiation. This suggests that there was nothing unique about evolutionary processes relating to the tempo of speciation during the Cambrian radiation.

Animals↗