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K Simons

Publications and source records attributed to K Simons.

264 records · Page 15Linked to original sources
PubMedDate not supplied

Two-dimensional gel mapping of small GTPases reveals transformation-specific changes during oncogenesis.

Epithelial cells transformed by oncogenes in vitro change their gene expression program, thereby losing features of cell polarity and cell adhesion. Using ras-transformed mammary epithelial cells, we have investigated the expression of other small GTP-binding proteins by high-resolution two-dimensional gel electrophoresis and direct GTP ligand binding after renaturing transfer onto nitrocellulose. Ras-transformed cells lost the expression of one epithelial-specific GTP-binding protein (21-22 kDa, pI 4.5-4.8) and instead expressed a fibroblast GTP-binding protein (21-22 kDa, pI 4.8-5.0).

Animals↗
PubMedDate not supplied

Visual acuity norms in young children.

There are no universally accepted standards for visual acuity tests or norms in young (3-6-year-old) children, although acuity measurement is important in both clinical and screening settings. This review outlines the requirements for such standards. Although more research is needed, available data suggest that a standard test should meet the following requirements. It should utilize a letter optotype (tumbling E, Landolt C, or HOTV variant of the STYCAR), and single optotype with contour interaction bar surround. It should permit nonverbal pointing responses in younger children and verbal responses in older children. If an orientation-specifying method is followed, as with the E or Landolt C, the test should use a three-alternative choice--up, down, and sideways with a nondifferentiated left-right--rather than the traditional four alternative choice. A C-like O pseudo-optotype should be considered in a paired-comparison test format when the Landolt C is utilized, with a similar format for the tumbling E if a suitable pseudo-optotype can be derived. The optical grating test, which is widely used in infant testing, may underestimate acuity deficits and so is not a test of choice for determination of Snellen-equivalent acuity. A letter-based variant of the grating test may hold promise. Reduction in testing distance from 6 to 3 or 4 meters is recommended.

Age Factors↗
PubMedDate not supplied

Preschool vision screening for amblyopia and strabismus. Programs, methods, guidelines, 1983.

Amblyopia and strabismus, which afflict at least 5% of children, require treatment early in life for best visual results. At present, many such children are treated late or not at all. Mass screening at preschool age, and perhaps ultimately of infants, appears the only viable solution to this problem. To ascertain the present status of preschool screening in the United States, on-site visits, mail questionnaires and telephone interviews were used to study existing preschool vision screening programs at the federal, state and private organization levels. We estimate that, at most, 21% of preschool children receive any form of vision screening. Only two states, Michigan and Minnesota, have legislated requirements for such screening. Several organizations have attempted to establish screening guidelines, with suggestions of specific test and referral criteria. These guidelines are reviewed. The guidelines are of particular interest because screening programs following them typically indicate far lower prevalence rates than most studies indicate actually exist, suggesting that the guidelines result in underreferrals. In order to assess this matter, vision screening methods appropriate for preschoolers or infants, based on current evidence, are reviewed. Stereoscopic testing, utilizing a random dot stereogram format, appears the best instrument available for amblyopia and strabismus screening, but large scale comparative studies of the different test methods are needed to arrive at a final determination. Suggestions are made for the physician interested in initiating preschool vision screening programs.

Amblyopia↗
PubMedDate not supplied

Preschool vision screening: rationale, methodology and outcome.

Although population outcome studies support the utility of preschool screening for reducing the prevalence of amblyopia, fundamental questions remain about how best to do such screening. Infant photoscreening to detect refractive risk factors prior to onset of esotropia and amblyopia seems promising, but our current understanding of the natural history of these conditions is limited, thus limiting the prophylactic potential of early screening. Screening for strabismic, refractive and ocular disease conditions directly associated with amblyopia is more clearly proven, but the diversity of equipment, methods and subject populations studied make it difficult to draw precise summary conclusions at this point about the efficacy of photoscreening. Sensory-based testing of preschool-age children exhibits a similar combination of promise and limitations. The visual acuity tests most widely used for this purpose are prone to problems of testability and false negatives. Moreover, the utility of random-dot stereograms has been confused by misapplication, and new small-target binocularity tests, while attractive, are as yet inadequately field-proven. The evaluation standard for any screening modality is treatment outcome. However, variables in amblyopia classification and quantitative definition differences, timing of presentation, nonequivalent treatment comparisons, and compliance variability have been uncontrolled in virtually all extant studies of amblyopia treatment outcome, making it difficult or impossible to evaluate either the relative efficacy of different treatment regimens for amblyopia or the effects of age on treatment outcome within the preschool age range. The latter issue is a central one, since existence of such an age effect is the primary rationale for screening at younger rather than older preschool ages. The relatively low prevalence of amblyopia makes it difficult to achieve a high screening yield in terms of predictive value, but functionally increasing prevalence by selective screening of high risk populations causes further problems. Unless a "supertest" can be devised, with very high sensitivity and specificity, health policy decisions will be required to determine which of these two characteristics should be emphasized in screening programs. Performance of screening tests can be optimized, however, with adequate training, perhaps via instructional videotapes.

Amblyopia↗
PubMedDate not supplied

The tight junction does not allow lipid molecules to diffuse from one epithelial cell to the next.

The tight junction (zonula occludens) links epithelial cells into a monolayer by forming a continuous belt of sealing contacts around the apex of each cell. They appear in thin sections as if they were 'fusions' between the apposed plasma membranes and in freeze-fracture replicas as patterns of complementary strands and furrows. These images have led to the proposal that the core of the tight junction is formed by a hexagonal cylinder of lipids. In this model, the cytoplasmic leaflet of the apical and basolateral plasma membrane domains would be continuous, whereas the exoplasmic leaflets of the two plasma membrane domains of the same cell would be separated at the tight junction and are instead predicted to be continuous between the plasma membranes of neighbouring cells. We demonstrate here that this prediction does not hold true. An endogenous glycolipid (Forssman antigen), present in the exoplasmic leaflet of the apical membrane of MDCK strain II cells, is unable to pass to MDCK strain I cells (which lack this glycolipid) under conditions where these cells are connected by tight junctions. In addition, fluorescent lipids which have been fused into the plasma membrane of one MDCK cell do not diffuse to neighbouring cells while the tight junctions between the cells are intact.

Animals↗
PubMedDate not supplied

Involvement of microtubule motors in basolateral and apical transport in kidney cells.

The maintenance of a polarized cell surface requires vectorial transport of vesicles to the apical and the basolateral membrane domains. Transport of newly synthesized apical proteins and trans-cytosis from the basolateral to the apical surface have been demonstrated to depend on microtubules. In contrast, movement of membrane proteins to the basolateral surface has been claimed to occur by diffusion and to be microtubule- and actin-independent. We have re-examined the role of microtubules using a recently developed polarized transport assay in permeabilized Madin-Darby canine kidney cells. Here we report that both apical and basolateral transport is inhibited by nocodazole treatment. Transport to the basolateral surface was inhibited by immunodepletion of cytosolic kinesin. In contrast, apical transport involved both dynein and kinesin. Our data demonstrate that in epithelial cells, microtubule motors are involved in the movement of apical and basolateral vesicles. Moreover, we propose that the differential requirement for microtubule-based motors is related to the microtubule organization.

Animals↗
PubMedDate not supplied

Artifacts in fusion and stereopsis testing based on red/green dichoptic image separation.

A red/green anaglyph stereotest (TNO) was administered to a group of patients who had anisometropic amblyopia, and the Worth 4-Dot test for fusion to two groups of strabismus patients. Both tests were administered twice, with the red/green lens position of the glasses reversed between eyes for the second administration. Twelve of 15 patients with anisometropic amblyopia exhibited a stereo acuity difference of 2:1 or more, and 18 of 89 strabismic patients changed Worth 4-Dot fusion or suppression status, between the two positions of the glasses. A group of seven strabismic patients who showed the reversal effect on the Worth 4-Dot test had the results of one glass' position discrepant with those of a geometrically identical achromatic test. It appears that the red/green format can introduce artifacts in binocular vision testing. Testing twice, with the red/green glasses reversed between trials, will prevent misinterpretation of binocular status and may provide diagnostically useful information.

Adolescent↗
PubMedDate not supplied

Small-target random dot stereogram and binocular suppression testing for preschool vision screening.

BACKGROUND: New, small-target (< 1 degree) random dot stereogram (STRDS) and binocular suppression (STBS) tests appropriate for preschool vision screening were developed to correct the shortcomings of previous such tests, particularly missed cases of anisometropic amblyopia such as found with some RDS-based testing. METHODS: In Experiment 1, the tests were administered to 14 patients with current or a recent history of moderate (< or = 20/60) anisometropic amblyopia, or with accommodative esotropia or monofixation syndrome. All subjects had good binocularity (< or = 100" contour stereoacuity). In Experiment 2, the new tests were administered in a screening setting to a group of 112 three- to five-year-olds to determine testability. Visual acuity, cover testing, and photoscreening were administered as control measures. RESULTS: In Experiment 1, eleven of the 14 patients failed both tests. Two anisometropic amblyopes passing one or both tests had an acuity < or = 20/30 in the worse eye and < or = 25" stereoacuity. Three anisometropic amblyopia patients failing the STRDS passed another RDS test with similar disparity but a larger target size, confirming a report34 that anisometropic amblyopes may pass RDS testing with parafoveal stereopsis despite the presence of central suppression. The STRDS and STBS tests indicated 80% and 96% specificity, respectively, with the original methodologies; STRDS specificity increased to 95% with retesting with a different methodology. Administration time was 30 sec to 60 sec per test. CONCLUSION: Small-target RDS or suppression testing may be more effective for strabismus and amblyopia screening of preschoolers than previous RDS test formats.

Adolescent↗