Neuron-specific and state-specific differences in calcium homeostasis regulate the generation and degeneration of neuronal architecture

Many stimuli (e.g., neurotransmitters and electrical activity) regulate neuromorphogenesis by changing intracellular calcium. The ionophore A23187 was employed as a receptor-independent method to investigate neuronal calcium homeostasis. Distinctive neuron-specific (B5 versus B19) and state-specific (growing versus non-growing) differences in calcium homeostasis were observed in cultured identified Helisoma neurons. Fura-2 studies revealed that A23187 induced a transient rise in intracellular calcium in growing neurons B5 but a sustained rise in growing neurons B19. In stable-state (non-growing) cells A23187 evoked only a transient calcium rise. Both neuron-specific and state-specific differences in calcium homeostasis were dependent on extracellular sodium. Morphological studies also indicated that such differences in calcium-regulatory capacity can have profound consequences on the generation and degeneration of neuronal architecture.     

Heterogeneity of epithelial cells in the human thymus

Summary To evaluate interrelationships among epithelial cells, and between morphology and function in the microenvironment, we studied the ultrastructural morphology of epithelial cells in sections of human thymus from donors aged 2 months to 31 years. Six types of epithelial cells were observed: subcapsular-perivascular (type 1); pale (type 2); intermediate (type 3); dark (type 4); undifferentiated (type 5); and large-medullary (type 6). Cells of types 2, 3 and 4 were found throughout the organ. The type-2 to -4 epithelial cells may represent various stages in a differentiation process. In this, type-2 cells are very active and type-4 cells are possibly degenerating elements. Type-4 cells can also contribute to Hassall's corpuscles. Type-5 cells were located mainly in the cortico-medullary region and showed the morphological characteristics of undifferentiated elements. Type-6 cells were located exclusively in the medulla and displayed characteristics of cellular activity. Small Hassall's corpuscles consisted of type-6 epithelial cells; in larger corpuscles many nuclei of type-6 cells were found. Cells of types 2 and 6 contained tubular structures (diameter approximately 20 nm).Concerning the function of thymus epithelial cells, the features associated with protein synthesis observed in cellular types 2 and 6 make them likely candidates for humoral factor-producing and/or secreting elements. In addition, type-2 and -3 cells in the cortex appear to contribute to a special pattern of epithelium-lymphocyte interaction (thymic nurse cells), as demonstrated by the intracytoplasmic location of lymphocytes in the epithelial cells. The various steps in intrathymic T-cell maturation occur at locations in a microenvironment composed of morphologically distinct epithelial cells.     

Response of fibrinolytic activity to venous occlusion.

Resting fibrinolytic activity and the response of the fibrinolytic system to venous occlusion were studied in a group of healthy middle-aged men. All subjects showed increased fibrinolytic activity but of varying degrees. There was a linear relationship between resting and occluded levels of fibrinolytic activity but many subjects with lower levels of fibrinolytic activity showed an anomalous response. Responses over the expected level were more common than unexpectedly low levels of response. Fibrinogen and plasminogen concentrations were inversely correlated with fibrinolytic activity.     

Abundance and accessibility of forage for reindeer in forests of Northern Sweden: Impacts of landscape and winter climate regime

The survival of reindeer during winter, their period of greatest food stress, depends largely on the abundance and accessibility of forage in their pastures. In Northern Sweden, realized availability of forage is notably affected by snow conditions and the impacts of forestry. While these factors have been examined in isolation, their combined effect has, to the best of our knowledge to date, not been researched. In this study, vegetation surveys and analysis of snow conditions were undertaken in forest stands at various stages of recovery from clear‐cutting. The variation in abundance and growth of understory species edible by reindeer, such as lichen, was noted as forests matured. The barrier effect of ice lenses in the snow was also measured in these stands. Lichen biomass was significantly affected by a combination of stand maturity, understory vegetation height, and lichen height. Soil disturbance from the processes of felling and competition in the vegetation communities recovering from this disturbance were identified as key drivers of change in lichen biomass. Overall, clear‐cut forests had some of the greatest prevalence of ice lenses in the snow column, and forage availability at these sites was up to 61% less than in mature stands over 58 years in age. It is suggested that alternative silviculture methods are investigated for use in this reindeer herding region, as frequent clear‐cutting and consequent reduction in the average forest stand age and maturity class may be detrimental to reindeer grazing, reducing both abundance of forage, and access to it during winter.     

Health care ethics and health law in the Dutch discussion on end-of-life decisions: a historical analysis of the dynamics and development of both disciplines

Over the past three or four decades, the concept of medical ethics has changed from a limited set of standards to a broad field of debate and research. We define medical ethics as an arena of moral issues in medicine, rather than a specific discipline. This paper examines how the disciplines of health care ethics and health care law have developed and operated within this arena. Our framework highlights the aspects of jurisdiction (Abbott) and the assignment of responsibilities (Gusfield). This theoretical framework prompted us to study definitions and changing responsibilities in order to describe the development and interaction of health care ethics and health law. We have opted for the context of the Dutch debate about end-of-life decisions as a relevant case study. We argue that the specific Dutch definition of euthanasia as 'intentionally taking the life of another person by a physician, upon that person's request' can be seen as the result of the complex jurisdictional process. This illustrates the more general conclusion that the Dutch debate on end-of-life decisions and the development of the two disciplines must be understood in terms of mutual interaction.     

MADS-box protein complexes control carpel and ovule development in Arabidopsis

The AGAMOUS (AG) gene is necessary for stamen and carpel development and is part of a monophyletic clade of MADS-box genes that also includes SHATTERPROOF1 (SHP1), SHP2, and SEEDSTICK (STK). Here, we show that ectopic expression of either the STK or SHP gene is sufficient to induce the transformation of sepals into carpeloid organs bearing ovules. Moreover, the fact that these organ transformations occur when the STK gene is expressed ectopically in ag mutants shows that STK can promote carpel development in the absence of AG activity. We also show that STK, AG, SHP1, and SHP2 can form multimeric complexes and that these interactions require the SEPALLATA (SEP) MADS-box proteins. We provide genetic evidence for this role of the SEP proteins by showing that a reduction in SEP activity leads to the loss of normal ovule development, similar to what occurs in stk shp1 shp2 triple mutants. Together, these results indicate that the SEP proteins, which are known to form multimeric complexes in the control of flower organ identity, also form complexes to control normal ovule development.     

The use of floral homeotic mutants as a novel way to obtain durable resistance to insect pests

We have developed a novel strategy for the introduction of durable insect resistance in crops. This strategy was based on intervention in the natural relationship between plants and insects. For many insects, including pests such as thrips (Frankliniella occidentalis), the flower is an important factor in their life cycle, serving either as a food source or as a place for mating. The insects are attracted to the flower by scent, which is mainly produced by the petals, and by the bright colour of these floral organs. We therefore anticipated that removal or changing the identity of the petals would significantly reduce the attractiveness of the flower to thrips. To test this hypothesis, we used cucumber as a model species because most modern varieties are parthenocarpic, in which the fruit develops without fertilization. The cucumber mutant green petals, in which the petals are homeotically transformed into green sepals, was particularly useful for this study. The susceptibility of the cucumber plants to damage by thrips was determined by recording thrip numbers and by measuring leaf damage. Large differences were observed when greenhouse compartments with either wild-type or green petal mutant plants were compared. The rate of population growth of the insects on the mutant plants was significantly reduced and the leaves were almost undamaged. These results demonstrate that alterations in the structure of flowers may interfere with the life cycle of insects, providing the means for a novel and natural strategy for obtaining insect resistance.     

Multiple AGAMOUS homologs from cucumber and petunia differ in their ability to induce reproductive organ fate.

The C function in Arabidopsis, which specifies stamen and carpel identity, is represented by a single gene called AGAMOUS (AG). From both petunia and cucumber, two MADS box genes have been isolated. Both share a high degree of amino acid sequence identity with the Arabidopsis AG protein. Their roles in specifying stamen and carpel identity have been studied by ectopic expression in petunia, resulting in plants with different floral phenotypes. Cucumber MADS box gene 1 (CUM1) induced severe homeotic transformations of sepals into carpelloid structures and petals into stamens, which is similar to ectopic AG expression in Arabidopsis plants. Overexpression of the other cucumber AG homolog, CUM10, resulted in plants with partial transformations of the petals into antheroid structures, indicating that CUM10 is also able to promote floral organ identity. From the two petunia AG homologs pMADS3 and Floral Binding Protein gene 6 (FBP6), only pMADS3 was able to induce homeotic transformations of sepals and petals. Ectopic expression of both pMADS3 and FBP6, as occurrs in the petunia homeotic mutant blind, phenocopies the pMADS3 single overexpresser plants, indicating that there is no additive effect of concerted expression. This study demonstrates that in petunia and cucumber, multiple AG homologs exist, although they differ in their ability to induce reproductive organ fate.