Graph Matching: Relax at Your Own Risk.

Graph matching-aligning a pair of graphs to minimize their edge disagreements-has received wide-spread attention from both theoretical and applied communities over the past several decades, including combinatorics, computer vision, and connectomics. Its attention can be partially attributed to its computational difficulty. Although many heuristics have previously been proposed in the literature to approximately solve graph matching, very few have any theoretical support for their performance.

Fast approximate quadratic programming for graph matching.

Quadratic assignment problems arise in a wide variety of domains, spanning operations research, graph theory, computer vision, and neuroscience, to name a few. The graph matching problem is a special case of the quadratic assignment problem, and graph matching is increasingly important as graph-valued data is becoming more prominent. With the aim of efficiently and accurately matching the large graphs common in big data, we present our graph matching algorithm, the Fast Approximate Quadratic assignment algorithm.

The generalized spherical homeomorphism theorem for digital images.

The spherical homeomorphism conjecture, proposed by Shattuck and Leahy in 2001, serves as the backbone of their algorithm to correct the topology of magnetic resonance images of the human cerebral cortex. Using a canonical image-thickening technique and the authors' previously proven "spherical homeomorphism theorem for surfaces," we formulate and prove a spherical homeomorphism theorem which is valid for all digital images when utilizing the (26,6)-connectivity rule.

Proficiency in interscalene anesthesia-how many blocks are necessary?

Study Objective: To determine the number of interscalene blocks that are necessary for a resident in anesthesiology to complete so as to achieve autonomous success with that specific block.

Design: Survey questionnaire of all CA1 and CA2 residents in the Department of Anesthesiology, Mount Sinai School of Medicine.

Setting: University hospital.

A proof of the spherical homeomorphism conjecture for surfaces.

The human cerebral cortex is topologically equivalent to a sphere when it is viewed as closed at the brain stem. Due to noise and/or resolution issues, magnetic resonance imaging may see "handles" that need to be eliminated to reflect the true spherical topology. Shattuck and Leahy present an algorithm to correct such an image.

Spatial and temporal dynamics of the secretory pathway during differentiation of the Plasmodium yoelii schizont.

A specialized complex of apical organelles facilitates Plasmodium merozoite invasion into the erythrocyte. Even though the apical organelles are crucial to the invasion process, relatively little is known about how they function or their biosynthesis during asexual replication. MAEBL is an erythrocyte binding protein located in the rhoptries and on the surface of mature merozoites and is expressed at the beginning of schizogony before the first nuclear division.

An insertional mutant of Chlamydomonas reinhardtii with defective microtubule positioning.

cmu1-1 is a new mutation of Chlamydomonas reinhardtii that causes a change in cell shape due to an alteration of cytoplasmic microtubule organization. cmu1 mutant cells were first identified based on their altered cell shape. Unlike wild-type cells, which are ellipsoid, cmu1 cells tend to be either round or egg-shaped with the flagella extending from the narrow end of the cell.

Use of digoxin, diuretics, beta blockers, angiotensin-converting enzyme inhibitors, and calcium channel blockers in older patients in an academic hospital-based geriatrics practice.

Objective: To investigate the prevalence of and indications for digoxin use and the prevalence of beta blocker and calcium channel blocker use in older patients with previous myocardial infarction or coronary artery disease (CAD), and the prevalence of use of diuretics, beta blockers, angiotensin-converting enzyme (ACE) inhibitors, and calcium channel blockers in older patients with hypertension in an academic hospital-based geriatrics practice.

Design: A retrospective analysis of charts from 528 unselected older patients, seen from June 1995 through July 1996 at an academic hospital-based geriatrics practice, was performed to investigate the prevalence of digoxin use and indications for digoxin use, the prevalence of beta blocker and calcium channel blocker use in older patients with previous myocardial infarction or coronary artery disease (CAD), and the prevalence of use of diuretics, beta blockers, angiotensin-converting enzyme (ACE) inhibitors, and calcium channel blockers in older patients with hypertension.

Setting: An academic hospital-based, primary care geriatrics practice staffed by fellows in a geriatrics training program and full-time faculty geriatricians.

Function of spindle microtubules in directing cortical movement and actin filament organization in dividing cultured cells.

The mitotic spindle has long been recognized to play an essential role in determining the position of the cleavage furrow during cell division, however little is known about the mechanisms involved in this process. One attractive hypothesis is that signals from the spindle may function to induce reorganization of cortical structures and transport of actin filaments to the equator during cytokinesis. While an important idea, few experiments have directly tested this model.

New horizons for cytokinesis.

The mechanism of cytokines is an old problem in cell biology that has received fresh attention recently with a large variety of powerful approaches and experimental systems. Significant advances have been made on the structure of the cortical cytoskeleton, the identification of proteins and genes involved, and the regulatory mechanism. Many surprises have surfaced within the past two years, leading us toward a major revision in our understanding of this important process.

Orientation and three-dimensional organization of actin filaments in dividing cultured cells.

The current hypothesis of cytokinesis suggests that contractile forces in the cleavage furrow are generated by a circumferential band of actin filaments. However, relatively little is known about the global organization of actin filaments in dividing cells. To approach this problem we have used fluorescence-detected linear dichroism (FDLD) microscopy to measure filament orientation, and digital optical sectioning microscopy to perform three-dimensional reconstructions of dividing NRK cells stained with rhodamine-phalloidin.

Localization and dynamics of nonfilamentous actin in cultured cells.

Although the distribution of filamentous actin is well characterized in many cell types, the distribution of nonfilamentous actin remains poorly understood. To determine the relative distribution of filamentous and nonfilamentous actin in cultured NRK cells, we have used a number of labeling agents that differ with respect to their specificities toward the filamentous or nonfilamentous form, including monoclonal and polyclonal anti-actin antibodies, vitamin D-binding protein (DBP), and fluorescent phalloidin. Numerous punctate structures were identified that bind poorly to phalloidin but stain positively with several anti-actin antibodies.

A novel vesicle-associated protein (VAP-1) in sea urchin eggs containing multiple RNA-binding consensus sequences.

We have identified a novel high molecular weight, vesicle-associated protein (VAP-1) in the eggs of the sea urchin Strongylocentrotus purpuratus. Biochemical fractionation and immunofluorescence analysis of unfertilized eggs indicate that VAP-1 is a peripheral membrane protein associated with microsomal membrane fractions. Sequence analysis of partial VAP-1 cDNA clones reveals that the protein contains at least four RNA-binding consensus sequences.

Microinjection of the catalytic fragment of myosin light chain kinase into dividing cells: effects on mitosis and cytokinesis.

Myosin light chain kinase (MLCK) is thought to regulate the contractile activity in smooth and non-muscle cells, and may play an important role in controlling the reorganization of the actin-myosin cytoskeleton during cell division. To test this hypothesis we have microinjected the 61-kD catalytic fragment of MLCK into mitotic cells, and examined the effects of unregulated MLCK activity on cell division. The microinjection of active 61 kD causes both a significant delay in the transit time from nuclear envelope breakdown to anaphase onset, and an increase in motile surface activity during and after metaphase.

Isolation and localization of a spectrin-like protein from echinoderm sperm.

Thyone sperm undergo an explosive acrosome reaction resulting in the extension of a 90 microns long acrosomal process. In unreacted sperm, profilamentous actin is sequestered within the profilactin cup (Tilney: Journal of Cell Biology 69:73-89 1976), which consists of four major polypeptides: actin, profilin, and a 250/235 kDa equimolar doublet (TS 250/235). Dialysis of profilactin preparations into an actin assembly buffer resulted in the formation of acrosomal-like macromolecular aggregates containing actin, TS 250/235, and several other polypeptides as detected by SDS-PAGE.

Sea urchin spectrin in oogenesis and embryogenesis: a multifunctional integrator of membrane-cytoskeletal interactions.

Using indirect immunofluorescence microscopy on semithin cryosections of maturing ovarian tissue, eggs, and developing embryos, we have mapped the cellular distribution and dynamic redistribution of spectrin in oogenesis and early embryogenesis. During oogenesis, spectrin is initially found in the cortex of oogonia and previtellogenic oocytes, and later accumulates in the cytoplasm of vitellogenic oocytes on the surfaces of cortical granules, pigment granules/acidic vesicles, and yolk platelets. Following egg activation, spectrin undergoes a rapid redistribution coincident with three major developmental events including: (1) restructuring of the cell surface, (2) translocation of pigment granules/acidic vesicles to the cortex during the first cell cycle, and (3) amplification of the embryo's surface during the rapid cleavage phase of early embryogenesis.

Subcellular localization of sea urchin egg spectrin: evidence for assembly of the membrane-skeleton on unique classes of vesicles in eggs and embryos.

A recent study from our laboratory on the sea urchin egg suggested that spectrin was not solely restricted to the plasma membrane, but instead had a more widespread distribution on the surface of a variety of membranous inclusions. (E. M.

The cortical actin-membrane cytoskeleton of unfertilized sea urchin eggs: analysis of the spatial organization and relationship of filamentous actin, nonfilamentous actin, and egg spectrin.

Whole mounts, cryosections, and isolated cortices of unfertilized sea urchin eggs were probed with fluorescent phalloidin, anti-actin and anti-egg spectrin antibodies to investigate the organizational state of the cortically associated actin-membrane cytoskeleton. Filamentous actin and egg spectrin were localized to the plasma membrane, within microvillar and nonmicrovillar domains. The nonmicrovillar filamentous actin was located immediately subjacent to the microvilli forming an extensive interconnecting network along the inner surface of the plasma membrane.

A calsequestrin-like protein in the endoplasmic reticulum of the sea urchin: localization and dynamics in the egg and first cell cycle embryo.

Using an antiserum produced against a purified calsequestrin-like (CSL) protein from a microsomal fraction of sea urchin eggs, we performed light and electron microscopic immunocytochemical localizations on sea urchin eggs and embryos in the first cell cycle. The sea urchin CSL protein has been found to bind Ca++ similarly to calsequestrin, the well-characterized Ca++ storage protein in the sarcoplasmic reticulum of muscle cells. In semi-thin frozen sections of unfertilized eggs, immunofluorescent staining revealed a tubuloreticular network throughout the cytoplasm.

Functional diversity among spectrin isoforms.

The purpose of this review on spectrin is to examine the functional properties of this ubiquitous family of membrane skeletal proteins. Major topics include spectrin-membrane linkages, spectrin-filament linkages, the subcellular localization of spectrins in various cell types and a discussion of major functional differences between erythroid and nonerythroid spectrins. This includes a summary of studies from our own laboratories on the functional and structural comparison of avian spectrin isoforms which are comprised of a common alpha subunit and a tissue-specific beta subunit.

Contributions of the beta-subunit to spectrin structure and function.

The three avian spectrins that have been characterized consist of a common alpha-subunit (240 kD) paired with an isoform-specific beta-subunit from either erythrocyte (220 or 230 kD), brain (235 kD), or intestinal brush border (260 kD). Analysis of avian spectrins, with their naturally occurring "subunit replacement" has proved useful in assessing the relative contribution of each subunit to spectrin function. In this study we have completed a survey of avian spectrin binding properties and present morphometric analysis of the relative flexibility and linearity of various avian and human spectrin isoforms.

Transport of membrane-bound macromolecules by M cells in follicle-associated epithelium of rabbit Peyer's patch.

M cells in Peyer's patch epithelium conduct transepithelial transport of luminal antigens to cells of the mucosal immune system. To determine the distribution of specific lectin-binding sites on luminal membranes of living M cells and to follow the transport route of membrane-bound molecules, lectin-ferritin conjugates and cationized ferritin were applied to rabbit Peyer's patch mucosa in vivo and in vitro. The degree to which binding enhances transport was estimated by comparing quantitatively the transport of an adherent probe, wheat germ agglutinin-ferritin, to that of a nonadherent BSA-colloidal gold probe.

Isolation and characterization of sea urchin egg spectrin: calcium modulation of the spectrin-actin interaction.

Sea urchin egg spectrin has been purified from a homogenate of unfertilized Strongylocentrotus purpuratus eggs using standard biochemical procedures. SDS-PAGE analysis of the molecule revealed a closely spaced, high molecular weight doublet at 237/234 kDa (present in an equimolar ratio). Rotary shadowed images of egg spectrin revealed a double-stranded, elongate, flexible rod-shaped contour, measuring 210 nm in length and approximately 4-8 nm in width.

Actin assembly and filament cross-linking in the presence of TW 260/240, the tissue-specific spectrin of the chicken intestinal brush border.

TW 260/240 is a tissue-specific spectrin found in the terminal web region of the chicken intestinal brush border. We have examined the effects of TW 260/240 on assembly rates and critical concentrations (Co's) for monomer addition at the barbed and pointed ends of the actin filament. For these studies, acrosomal processes (AP) from Limulus sperm were used as nuclei for actin assembly.