Blebs lead the way: how to migrate without lamellipodia

Blebs are spherical membrane protrusions that are produced by contractions of the actomyosin cortex. Blebs are often considered to be a hallmark of apoptosis; however, blebs are also frequently observed during cytokinesis and during migration in three-dimensional cultures and in vivo. For tumour cells and a number of embryonic cells, blebbing migration seems to be a common alternative to the more extensively studied lamellipodium-based motility. We argue that blebs should be promoted to a more prominent place in the world of cellular protrusions.     

Robertsonian translocations: mechanisms of formation,aneuploidy, and uniparental disomy and diagnostic considerations

Robertsonian translocations (ROBs) are rearrangements of the acrocentric chromosomes 13-15 and 21-22. Cytologically, ROBs between homologous chromosomes cannot be distinguished from isochromosomes that originate through duplication of a single homologue. Both types of rearrangements can be involved in aneuploidy. A conceptus with a trisomy or a monosomy can be rescued, and in a proportion of cases, a uniparental disomy (UPD) would result. If there are regions of genome imprinting on a uniparental chromosome pair, phenotypic consequences can result. Chromosomes 14 and 15 are imprinted, and UPD of these are known to result in abnormalities. Thus, prenatal testing should be considered in all pregnancies when one of the parents is a balanced carrier of a ROB because of the risk for aneuploidy, and UPD testing should be considered in fetuses found to carry a balanced ROB or isochromosome that involves chromosomes 14 or 15. Additionally, infants or children with congenital anomalies who carry a ROB should also be considered for UPD testing.     

Pooling and comparing estimates from several experiments of a Michaelis constant for an enzyme

Often the Michaelis constant of an enzyme will be determined several times. This may be done for various reasons such as ensuring reproducibility, comparing different enzyme preparations, or examining the effects of variations in experimental conditions. In these circumstances, two questions arise. First, how can the various estimates of the Michaelis constant be compared to determine whether they are the same within the limits of experimental variation? Secondly, if they are all the same, how can the values be combined to give an overall estimate? These questions are addressed here and a solution proposed in which the sets of data are pooled and analyzed with a separate maximum velocity for each set but a common Michaelis constant. The pooled data are partitioned in suitable ways and reanalyzed to examine, by means of a variance ratio test, whether a single Michaelis constant gives a satisfactory fit to the data.     

A review about nothing: Are apolar cavities in proteins really empty?

Cavities within proteins that are strictly apolar typically appear to be empty. It has been suggested, however, that water molecules may be present within such cavities but are too disordered to be seen in conventional crystallographic analyses. In contrast, it is argued here that solvent mobility will be limited by the size of the cavity and for this reason high‐occupancy solvent in cavities of typical volume should be readily detectable using X‐ray crystallography. Recent experimental studies of cavity hydration are reviewed. Such studies are consistent with theoretical predictions that it is energetically unfavorable to have a single water molecule in an apolar cavity. As apolar cavities become larger, a point is reached where it is favorable to have the cavity occupied by a cluster of mutually H‐bonded water molecules. The exact size of such a cavity in a protein is yet to be verified.     

Assessing the health of sediment ecosystems: use of chemical measurements

1. This paper outlines the use of chemical measurements as surrogate indicators of the health of sediment ecosystems. 2. For chemical measurements to be used for this purpose, links must be able to be made between adverse biological effects and the chemical composition of sediments. 3. Benchmark sediment quality guidelines allow decisions to be made about whether or not a sediment ecosystem is likely to be impacted. These guidelines are established using an effects database and a weight-of-evidence approach that gives ranges of chemical concentrations associated with known adverse biological effects. 4. If guidelines are exceeded the measured values are compared to concentrations of that contaminant in a comparable background or reference sediment. Exceedance of these concentrations leads to site-specific estimates of contaminant bioavailability. If a potential problem is indicated, laboratory sediment bioassays are used to assess the likelihood that the sediment will harm biota. 5. Trace metals are used as an example of a sediment contaminant.     

Abdominal surgical emergencies in the puerperium.

Since surgical emergencies in the puerperium are rare, surgeons and obstetricians amass little experience of them. There may be considerable delay in making a diagnosis, firstly, because the abdominal symptoms are thought to be related to the pregnancy, and, secondly, because the signs are rarely convincing in contrast to the symptoms. Any of the common surgical emergencies may occur in pregnancy and the puerperium and there are some others that appear to be a particullar problem of the puerperium.     

Analytical solutions of a minimal model of species migration in a bounded domain

 A minimal model of species migration is presented which takes the form of a parabolic equation with boundary conditions and initial data. Solutions to the differential problem are obtained that can be used to describe the small- and large-time evolution of a species distribution within a bounded domain. These expressions are compared with the results of numerical simulations and are found to be satisfactory within appropriate temporal regimes. The solutions presented can be used to describe existing observations of nematode distributions, can be used as the basis for further work on nematode migration, and may also be interpreted more generally. Received: 15 August 1999     

Studies on water and ion transport in homopteran insects: ultrastructure and cytochemistry of the cicadoid and cercopoid hindgut

The hindgut of cicadoid and cercopoid insects consists of a very long ileum and a relatively short rectum. The ileum is a single cell epithelium comprising several large primary cells between which are small secondary cells. Primary cells are packed with spherical mitochondria and the apical surface of the cells is extensively infolded to form leaflets, whilst the secondary cells are relatively unspecialized. An ATPase appears to be associated with the apical leaflets and small basal infoldings. These cells are presumed to be engaged in ion reabsorption and the formation of a hypoosmotic urine. It is suggested that apical leaflets may be a common feature of all cells concerned with ion reabsorption in the insect hindgut. The cells of the rectum do not appear to be specialized for either ion or water transport and the function of this organ appears to be urine storage.     

Two-stage design of quantal response studies

In a quantal response study, there may be insufficient knowledge of the response relationship for the stimulus (or dose) levels to be chosen properly. Information from such a study can be scanty or even unreliable. A two-stage design is proposed for such studies, which can determine whether and how a follow-up (i.e., second-stage) study should be conducted to select additional stimulus levels to compensate for the scarcity of information in the initial study. These levels are determined by using optimal design theory and are based on the fitted model from the data in the initial study. Its advantages are demonstrated using a fishery study.     

MacSECPROT: Two programs in basic to evaluate protein secondary structure

Two interactive programs in BASIC are described, which provide useful tools to evaluate protein secondary structure. Output is given in two formats: (1) graphics are displayed on screen, which can be printed immediately, and (2) textfiles are saved to disk as permanent records and can be printed with a word-processing program. The programs are fast and easy to use and could be a valuable teaching aid in biochemical and molecular biology courses. Program lists are written in Microsoft® BASIC for the Apple® Macintosh™, but can be adapted to other machines accepting graphic commands.     

How advantageous is a sensory prey detection mechanism to predatory microflagellates?

The advantage conferred on a microflagellate predator by possessionof a sensory prey detection mechanism has been estimated usinga model. The calculations demonstrate that a sensory mechanismis important and sometimes essential for microflagellate survivalin environments where prey are scarce. Even where prey are relativelyabundant such a mechanism still confers an advantage on a microflagellate.It allows more energy to be diverted to growth and reproduction.It may also play a role in prey discrimination. Due to the advantageconferred, sensory mechanisms are probably widespread amongmicroflagellates. This model can be generally applied to smallaquatic predators to determine whether a sensory mechanism islikely to be present.     

The terminology problem for T cells: a discussion paper

The school of thought that owes allegiance to Ludwig Wittgenstein teaches that language conditions perceptions. When we use the term ''cytotoxic T lymphocyte'' or ''helper T cell'' we tend to orientate our own thinking processes, and those of listeners or readers, down particular paths. Part of the problem is that we are often describing cell populations by functions that may either be a property of only a proportion of those that are being assayed, or are simply inferred from the expression of various cell-surface markers. The consequence can be a measure of confusion that might be avoided if we could communicate with greater clarity. Is it possible to achieve a better terminology that will be accepted generally? The following are some examples of why there may be some value in thinking about this.     

Paradigm lost: reconsidering functional form and group hypotheses in marine ecology

Although functional form and functional group models for marine algae have been used extensively, there is little general literature support for these models, and many studies have shown that associated hypotheses are often incorrect. In functional form/group models, a wide range of ecological and physiological functions are assumed to be correlated with general algal form or morphology. In contrast, functional group approaches have been used most successfully in terrestrial and aquatic systems when groupings are based on a particular function rather than overall plant morphology, and when addressing ecosystem-level questions. In this type of functional group approach, a given set of species would likely be grouped differently depending on the function under consideration. Functional groupings are appropriate for many situations and questions, but not all. Certainly, grouping taxa by a particular function can be very useful and often necessary for many ecosystem-level questions and modeling, especially where qualitative results are more important than quantitative predictions, and when there are too many species in a system to consider them all individually. However, when one considers species–species interactions or questions about population biology, the specific responses of individual species must be considered. To make functional group models more useful, we recommend that groupings be based on specific functions (e.g. nutrient uptake rates, photosynthesis rates, herbivore resistance, disturbance resistance, etc.) rather than gross morphology. Explicit testing of performance of a particular function should be made before generalizations can be assumed, and groupings should be used for questions/approaches where they are most appropriate. If models fail when tested, they should be modified using the additional information to generate new hypotheses and models, and then retested.     

The Preoperative Assessment of Multiple Valve Disease

Representative case histories are used to discuss the difficulties in preoperative assessment of patients with multiple valve disease and the dangers of correcting one lesion when two or more valves are seriously damaged. Errors fall into three broad categories: existing second valve disease (1) may not be suspected, (2) may be considered insignificant or (3) may be considered a consequence of the first.Recommendations are offered to minimize these errors. The four valves should be studied physiologically, no matter how “normal” the other three may appear to be clinically, whenever open-heart surgery is contemplated. In bivalvular disease angiographic methods are preferable to pressure studies, for data so obtained are not dependent on cardiac output. Mitral and tricuspid regurgitation can never be attributed with certainty to a more distal lesion but require direct examination at time of operation for assessment.     

Lethal photosensitisation of oral bacteria and its potential application in the photodynamic therapy of oral infections.

Chemical antibacterial agents are increasingly being used in prophylactic and therapeutic regimes for dental plaque-related diseases, which are among the most common human infections. As these agents are difficult to maintain at a therapeutic concentration in the oral cavity and can be rendered ineffective by resistance development in the target organisms, there is a need to develop alternative antimicrobial approaches. Bacteria and other microbes can be sensitised to light through prior treatment with a chemical photosensitising agent. Lethal photosensitisation of a wide range of bacteria responsible for caries, periodontal diseases and root canal infections has been demonstrated using red light in conjunction with a number of photosensitisers, including Toluidine Blue, phthalocyanines and chlorins. The advantages of this approach are that bacteria can be eradicated in very short periods of time (seconds or minutes), resistance development in the target bacteria is unlikely and damage to adjacent host tissues and disruption of the normal microflora can be avoided. This approach may be a useful alternative to antibiotics and antiseptics in eliminating cariogenic and periodontopathogenic bacteria from disease lesions and for the disinfection of root canals. Not only would this be of benefit for the treatment of these diseases but, by replacing the antimicrobial agents that are currently used for such purposes, it would help to conserve our dwindling supply of antimicrobial agents that are effective in the treatment of serious systemic infections.     

An Improved Technic for the Examination of Chromosomes in Root Tip Smears

Young, vigorous root tips are fixed in aceto-alcohol (1 part glacial acetic acid, 2 parts absolute alcohol) and are left in the fixative from 24 to 48 hours. If it is desired to store the material, the root tips can be transferred to 80% alcohol and be kept indefinitely. In preparing the smears, the root tips are placed on a slide and are sliced as thinly as possible with a sharp razor blade. Then the slices are smeared on the slide and immediately flooded with aceto-carmin, followed by a cover glass. Using absorbent paper and exerting considerable pressure, the excess aceto-carmin can be removed and the material flattened at the same time. Finally the slide is warmed gently to a point slightly below boiling. By sealing with gum mastic and paraffin, such preparations can be kept from 5 to 10 days.     

Die Speicheldrüsenchromosomen der StechmückeCulex pipiens

The salivary gland chromosomes of an autogenous strain ofCulex p. pipiens are described and mapped. The regions of the centromeres are the only large morphological landmarks and can be used for a quick and exact identification of the chromosomes. Asynaptic parts cannot be constantly observed. Balbianirings are not seen. The puffs being small and only visible for a short time, cannot be used as landmarks. Therefore the single arms of the chromosomes can only be recognized by their very clear and distinct pattern.