Tidally driven distribution of phytoplankton blooms in a shallow, macrotidal estuary

The influence of the ebb tide on the abundance and distributionof bloom-forming species, as well as the mechanisms for theselection of those species which remain, were investigated inthe shallow, tidal-flushed Urdaibai estuary, north Spain. Phytoplanktonwas collected monthly from May to September 1998 during differenttidal conditions (neap-spring) at five stations along the salinitygradient of the estuary. During the neap tides of May, Leptocylindrusdanicus dominated in the lower estuary, together with Thalassiosiraguillardii and Peridinium foliaceum in the upper segment; T.guillardiiexperienced the broadest displacement along the estuary. Duringthe June and July cruises, coinciding with mid-tidal amplitudesand high temperatures, Peridinium quinquecorne densely aggregatedin the upper estuary at the slack high tide, whereas Chaetocerossalsugineum bloomed at the intermediate stations. Cyclotellaatomus and Protoperidinium achromaticum reached high concentrationsin the upper zone only during the late stages of the ebb. Duringthe spring tides of September, Prorocentrum minimum, Heterocapsapygmaea and Heterocapsa rotundata appeared in the lower marineestuary, being washed out at low tide. By contrast, the diatomsSkeletonema costatum, Thalassiosira guillardii and Cyclotellaatomus were the most abundant species in the upper reaches,peaking during the ebb. Physical trapping and high water residencetimes served to retain blooming species in the upper estuary.The intense growth of the estuarine diatoms may compensate forthe advective seaward losses of cells during the ebb, thus allowingthe development of stable populations in the estuary. Only Peridiniumquinquecorne seems to combine an endogenous tidal rhythm witha photic response to remain in the tidal area of the estuary.     

Observations on Chaetoceros salsugineus (Chaetocerotales,Bacillariophyceae): first record of this bloom-forming diatom in a European estuary

Examination of material obtained from the Urdaibai estuary (North Spain) during a 2 year phytoplankton sampling programme revealed a rare species of the genus Chaetoceros, C. salsugineus Takano. The morphology of this small (4·0×5·5?µm) member of the subgenus Hyalochaetae has been described using both light and electron microscopy. Regarding the original material, two new features have been observed: longer chains up to 24 cells and a new type of aperture, bisected by the fusion of central protuberances of adjacent valves. This bloom-forming diatom reached high densities in the poly-euhaline zone of the estuary closely related with high temperatures, denoting its neritic and summer preferences. Maximal cell densities (10⁶–10⁷ cells l^?1) were reached in August and September when the water column was completely mixed and the salinity and temperature were about 31 psu and 20°C, respectively. This is the first report of C. salsugineus in Europe and contributes to the knowledge of the morphological and ecological features of this species. Relationships with other small species of the subgenus Hyalochaetae are also discussed.     

Tales of biomaterials, molecules, and cells for repairing and treating brain dysfunction

Current therapies have limited or no capacity to restore lost function, slow ongoing neurodegeneration, or promote regeneration following damage to the brain. Biomaterials are playing an increasingly important role in the development of novel, potentially efficacious approaches to brain treatment and repair. Programmable biomaterials enable and augment the targeted delivery of drugs into the brain and allow cell/tissue transplants to be effectively delivered and integrate into the brain, to serve as delivery vehicles for therapeutic proteins, and rebuild damaged circuits. Similarly, biomaterials are being increasingly used to recapitulate specific aspects of brain niches to promote regeneration and/or repair damaged neuronal pathways with stem cell therapies. Many of these approaches are gaining momentum because nanotechnology allows greater control over material-cell interactions that induce specific developmental processes and cellular responses including differentiation, migration, and outgrowth. This review discusses the state of the art and new directions in the convergence of biomaterial science, drug delivery, and stem cell biology in the treatment of degenerative and malignant brain diseases.     

Controversies over stem cell research

Much interest and effort has focused on the therapeutic potential of stem cell technology to treat presently intractable diseases. However, this scientific promise has been accompanied by important issues, including ethical hurdles, political policies and dilemmas concerning cell-source selection (embryonic versus adult stem cells). Although the contribution of stem cells to medical research seems enormous, many countries now face complex ethical and regulatory questions, which could represent a significant limitation to medical progress and could take years to overcome.     

Biocompatibility evaluation of different alginates and alginate-based microcapsules

Biocompatibility of biomaterials and biomaterial-based medical devices is a critical issue for the long-term function on multiple therapeutic systems. In the past few years, there has been an increasing interest in producing more biocompatible biomaterials and in developing novel assays to analyze the quality of the products. In this study, a battery of in vitro techniques to assess the biocompatibility of alginates with different compositions and purities and alginate-based microcapsules is presented. Study of the protein and polyphenol content of the alginates revealed clear differences between the nonpurified and the purified alginates. A similar behavior was observed when the mitogenic activity and the tumor necrosis factor-alphasecretion induced by the alginates were assessed. Interestingly, when the latter two techniques were adapted to evaluate the different alginate microcapsules, a correlation with the results obtained for the alginate samples was observed. These results reinforce the idea of using the full battery of assays here reported to screen alginates and alginate-based microcapsules before implantation.     

The effects of pollen and seed migration on nuclear-dicytoplasmic systems. II. A new method for estimating plant gene flow from joint nuclear-cytoplasmic data

A new maximum-likelihood method is developed for estimating unidirectional pollen and seed flow in mixed-mating plant populations from counts of joint nuclear-cytoplasmic genotypes. Data may include multiple unlinked nuclear markers with a single maternally or paternally inherited cytoplasmic marker, or with two cytoplasmic markers inherited through opposite parents, as in many conifer species. Migration rate estimates are based on fitting the equilibrium genotype frequencies under continent-island models of plant gene flow to the data. Detailed analysis of their equilibrium structures indicates when each of the three nuclear-cytoplasmic systems allows gene flow estimation and shows that, in general, it is easier to estimate seed than pollen migration. Three-locus nuclear-dicytoplasmic data only increase the conditions allowing seed migration estimates; however, the additional dicytonuclear disequilibria allow more accurate estimates of both forms of gene flow. Estimates and their confidence limits for simulated data sets confirm that two-locus data with paternal cytoplasmic inheritance provide better estimates than those with maternal inheritance, while three-locus dicytonuclear data with three modes of inheritance generally provide the most reliable estimates for both types of gene flow. Similar results are obtained for hybrid zones receiving pollen and seed flow from two source populations. An estimation program is available upon request.     

Encapsulated cell technology: from research to market

Encapsulated cell technology has the potential to treat a wide range of diseases by the controlled and continuous delivery of biological products to the host. Many biotechnology companies have focused their interest in this technology taking into account the promising pre-clinical and clinical results and the potential clinical market. However, on the long way from clinic to market several issues will have to be addressed, including suitable scientific development, ethical obstacles, government regulations and market forces.     

Suspended particulate matter dynamics in the shallow mesotidal urdaibai estuary (Bay of Biscay,Spain)

Seston quantity and quality was measured in the Urdaibai Estuary in summer, when river discharge is low and tidal flushing is the main driving force to transport and resuspend particulate matter in the estuary. The highest seston concentrations are found in the upper estuary, where more than 90% of total suspended particulate matter is made up of particles <20 μm. There is a temporal ebb-flood asymmetry and turbulent mixing is stronger at flood tide. During dry calm periods sediment resuspension is observed for a short period of time at floods during spring tides, decreasing drastically before slack waters. In spite of this, particulate organic matter mainly originates from anthropogenic sources (domestic wastewater discharge) and plankton production.     

A glimmer of hope for diabetics?

Diabetes affects 150 million people worldwide and results from abnormal function of pancreatic islets. The scarcity of human tissue donors has focused interest in developing renewable sources of insulin-producing cells appropriate for engraftment. Advances in stem cell technology and transdifferentiation techniques have provided powerful tools to study pancreatic development, function and disease. Recent results from these two approaches could have significant implications for future therapies of diabetes.