Can telomerase be put in its place?

The Cajal body is an intriguing nuclear structure present in a great variety of plant, animal, and some fungal cells. Recent work on the ribonucleoprotein enzyme telomerase has indicated an unanticipated degree of intranuclear dynamics of both its RNA and protein subunits. In this issue, Jady et al. place the Cajal body on the intranuclear traffic route of telomerase RNA (Jady et al., 2004).     

Ion channels: does each subunit do something on its own?

The advent of the patch-clamp technique 25 years ago revolutionized the study of ion channels. This method also made it possible to measure the kinetic behavior of single protein molecules. The low-noise recordings of ionic currents through single channels, coupled with other cutting-edge technologies, have revealed a rich complexity of functional states that are not readily explained by simple allosteric protein models such as the popular concerted model and the sequential model. Although these models can each account for elements of ion channel function, we propose that variations or extensions of the lesser-known general allosteric model provide a more promising framework for explaining the intricate behaviors of ion channels.     

Does pediatrics need its own bioethics?

Pediatric bioethics raises unique issues because children are constantly growing, developing, and changing. The ethical issues that arise for newborns are different from those that arise for seven-year-olds or 17-year-olds. Furthermore, children do not develop cognitive capacities or moral reasoning skills at the same rate. Thus, it is difficult to generalize about what is appropriate or inappropriate for children in either the clinical or the research setting. This article responds to some of the issues raised by a new volume of essays about pediatric bioethics. It puts these issues into historical context by examining the implications of Saul Krugman's famous studies on the etiology and prevention of hepatitis at New York's Willowbrook State School.     

Can chaoborid larvae control their zooplanktonic prey populations in a neotropical lake?

Although it is well known that predatory Chaoborus Lichtenstein 1800 larvae have a strong negative impact on zooplankton populations in many Holarctic lakes, this top‐down control is still not entirely clear in the Neotropics. In Lake Carioca, a Brazilian monomictic lake, chaoborids became one of the main zooplankton predators after the depletion of planktivorous fish by non‐native piscivorous fish. The aim of this research was to test the hypothesis that Chaoborus spp. larvae control the density of their prey populations. Enclosures simulated conditions with higher (Pr+) and lower (Pr?) predatory Chaoborus spp. larva densities over 30 days in two periods (stratification and mixing). Our results indicated that the dominant copepod species was affected only in the stratification period when its population was smaller. In this circumstance, predated individuals were probably not replaced in the same proportion by reproductive output of the smaller population. Rotifers were not sensitive to changes in chaoborids densities in both periods. The lack of a strong top‐down effect recorded by our mesocosm experiments emphasises the importance of continuing to investigate the ecological roles played by this invertebrate predator in aquatic food webs and if its ability to regulate the zooplankton in most Holarctic lakes can (or cannot) be widely generalised to Neotropical communities. Such a result also suggests that alternative research approaches, besides in‐situ experiments, may be necessary to better clarify this topic. Specifically for cladocerans, parallel paleolimnological analyses in Lake Carioca have supported the idea of a possible negative impact of Chaoborus larvae on bosminids after the introduction of non‐native piscivorous fishes. Abstract in Portuguese is available with online material.     

The narial musculature of Alligator mississippiensis: Can a muscle be its own antagonist?

The crocodilian naris is regulated by smooth muscle. The morphology of this system was investigated using a combination of gross, light microscopic, and micro-CT analyses, while the mechanics of narial regulation were examined using a combination of Hall Effect sensors, narial manometry, and electromyography. Alligator mississippiensis, like other crocodilians, routinely switches among multiple ventilatory mechanics and does not occlude the nares during any portion of the ventilatory cycle. In a complex that is unique among vertebrates, a single block of smooth muscle functions in dilation when active, and in constriction when passive. The alligator nares may include one of the best examples of a muscle that functions in “pushing” as well as “pulling.” The central muscle for narial regulation, the dilator naris, can legitimately be viewed as its own antagonist.     

Can cell morphology in monolayer reveal its behaviour in aggregates?

The morphology of HeLa cells was altered to stellate shape by 0.2 – 1.0 mM butyric acid. At similar concentrations butyric acid did not alter the ability of HeLa cells to aggregate, but did inhibit the remodelling of the aggregates. Papaverine at 10 μM, on the other hand, had no effect on cells in monolayer, but severely inhibited the ability of cells to aggregate and the remodelling of the aggregates. Our results show that the effect of a drug on the morphology of HeLa cells in monolayer does not predict its effect in aggregates of cells which more faithfully approximate the behaviour of cells in tissue than the monolayer.     

Hormone replacement therapy--is there a place for its use in neurology?

Stroke remains the third leading cause of mortality in developed countries despite declining tendency over the past decades. As the leading cause of disability and second cause of dementia, primary prevention should be the main way to fight the disease, since therapy is not efficient enough. Several observations pointed to estrogen as a protective agent that may reduce stroke risk, however, studies have shown conflicting data. There is no strong evidence that hormone replacement therapy (HRT) increases stroke risk. Several studies have shown that HRT may reduce the risk of fatal stroke. Conflicting results have been found for Alzheimer's disease and HRT as well. An association between higher serum concentration of estradiol and decreased risk of cognitive decline has been found in some studies, supporting the hypothesis that estrogen concentration may play a significant role in brain protection. Having in mind results of recent randomized trials, it is suggested that HRT should not be recommended on general basis for the primary or secondary prevention of cardiovascular/cerebrovascular diseases or for primary prevention of degenerative diseases such as Alzheimer's disease. Osteoporosis, cognitive decline and climacteric symptoms that are likely to impact on quality of life, speak in favor for recommendation of HRT use. On the other side, family history of breast carcinoma, mastopathy, thromboembolism, in certain cases gallbladder disease, will discourage the commencement of HRT. Respecting the patient's preferences and having benefits and risks in mind as well as science advisory statements, individual counseling regarding HRT should be the leading concept in the healthcare of postmenopausal women.     

Do tadpoles affect leaf decomposition in neotropical streams?

1. Of the relatively few studies that have examined consequences of amphibian declines on stream ecosystems, virtually all have focused on changes in algae (or algal‐based food webs) and little is known about the potential effects of tadpoles on leaf decomposition. We compared leaf litter decomposition dynamics in two neotropical streams: one with an intact community of tadpoles (with frogs) and one where tadpoles were absent (frogless) as a result of a fungal pathogen that had driven amphibians locally extinct. The stream with tadpoles contained a diverse assemblage (23 species) of larval anurans, and we identified five species of glass frog (Centrolenidae) tadpoles that were patchily distributed but commonly associated with leaf detritus and organic sediments in pools. The latter reached total densities of 0–318 tadpoles m^?2. 2. We experimentally excluded tadpoles from single‐species leaf packs incubated over a 40‐day period in streams with and without frogs. We predicted that decomposition rates would be higher in control (allowing access of tadpoles) treatments in the study stream with frogs than in the frogless stream and, in the stream with frogs, in the control than in the tadpole exclusion treatment. 3. In the stream with frogs, Centrolene prosoblepon and Cochranella albomaculata tadpoles were patchily distributed in leaf packs (0.0–33.3 m^?2). In contrast to our predictions, leaf mass loss and temperature‐corrected leaf decomposition rates in control treatments were almost identical in our stream with frogs (41.01% AFDM lost, k_{degree day} = ?0.028 day^?1) and in the frogless stream (41.81% AFDM lost, k_{degree day} = ?0.027 day^?1) and between control and tadpole exclusion treatments within each stream. Similarly, there were no significant differences in leaf pack bacterial biomass, microbial respiration rates or macroinvertebrate abundance between treatments or streams. Invertebrate assemblages on leaf packs were similar between treatments (SIMI = 0.97) and streams (SIMI = 0.95) and were dominated by larval Chironomidae, Simuliidae (Diptera) and larval Anchytarsus spp. (Coleoptera). 4. In contrast to dramatic effects of grazing tadpoles on algal communities observed previously, tadpoles had no major effects on decomposition. While centrolenid tadpoles were common in the stream with frogs, their patchy distribution in both experimental and natural leaf packs suggests that their effects on detrital dynamics and microbes are probably more localised than those of grazing tadpoles on algae.     

Can molecular cell biology explain chromosome motions?

Background

Mitotic chromosome motions have recently been correlated with electrostatic forces, but a lingering "molecular cell biology" paradigm persists, proposing binding and release proteins or molecular geometries for force generation.

Results

Pole-facing kinetochore plates manifest positive charges and interact with negatively charged microtubule ends providing the motive force for poleward chromosome motions by classical electrostatics. This conceptual scheme explains dynamic tracking/coupling of kinetochores to microtubules and the simultaneous depolymerization of kinetochore microtubules as poleward force is generated.

Conclusion

We question here why cells would prefer complex molecular mechanisms to move chromosomes when direct electrostatic interactions between known bound charge distributions can accomplish the same task much more simply.     

α-Thalassaemia in Tunisia: some epidemiological and molecular data

Unlike the other haemoglobinopathies, few researches have been published concerning α-thalassaemia in Tunisia. The aim of the present work is to acquire further data concerning α-thalassaemia prevalence and molecular defects spectrum in Tunisia, by collecting and studying several kinds of samples carrying α-thalassaemia. The first survey conducted on 529 cord blood samples using cellulose acetate electrophoresis, have displayed the prevalence of 7.38% Hb Bart’s carriers at birth. Molecular analyses were conducted by PCR and DNA sequencing on 20 families’ cases from the above survey carrying the Hb Bart’s at birth and on 10 Hb H diseased patients. The results showed six α-globin gene molecular defects and were responsible for α-thalassaemia: -α^3.7, - -^MedI, α^TSaudi, α₂^{cd23GAG→Stop}, Hb Greone Hart: α₁^119CCT→TCT corresponding to 11 genotypes out of which two are responsible for Hb H disease (- -^Med/-α^3.7) and (α^TSaudiα/α^TSaudiα) and a newly described polymorphism: α^+6C→G. The geographical repartition of α-thal carriers showed that the -α^3.7 deletion is distributed all over the country, respectively the α^HphI and α^TSaudi seem to be more frequent in the central region of the northeast region. The haematological and clinical data showed a moderate phenotype with a late age of diagnosis for Hb H disease. This work had permitted, in addition to an overview on α-thalassaemia in the country, the optimization of protocols for α-thalassaemia detection in our lab, allowing further investigations concerning phenotype-genotype correlation in sickle cell disease or β-thalassaemia.