The fine structure of akinete formation and germination in Cylindrospermum

Summary Akinete formation and germination were studied in a species of Cylindrospermum using the electron microscope. The differentiation of a vegetative cell into an akinete is characterized by cell enlargement, sheath condensation, deposition of several spore envelope layers, including a dense fibrillar layer and deposition of large cyanophycin granules. The mature akinete in addition to the multilayered envelope retains internally a large number of cyanophycin granules, a photosynthetic thylakoid system, polyhedral bodies, lipid deposits and nucleoplasmic regions. Germination of the akinete can take place in several modes differing in detail. Most frequently the spore envelope remains intact and the germling which may or may not have divided emerges through a pore at one end of the envelope. The photosynthetic thylakoid system appears to increase by the fusion of small vesicles found in the cytoplasm. Alpha-granules are numerous and cyanophycin is nearly absent in the germling.     

An ecoclimatic framework for evaluating the resilience of vegetation to water deficit

The surge in global efforts to understand the causes and consequences of drought on forest ecosystems has tended to focus on specific impacts such as mortality. We propose an ecoclimatic framework that takes a broader view of the ecological relevance of water deficits, linking elements of exposure and resilience to cumulative impacts on a range of ecosystem processes. This ecoclimatic framework is underpinned by two hypotheses: (i) exposure to water deficit can be represented probabilistically and used to estimate exposure thresholds across different vegetation types or ecosystems; and (ii) the cumulative impact of a series of water deficit events is defined by attributes governing the resistance and recovery of the affected processes. We present case studies comprising Pinus edulis and Eucalyptus globulus, tree species with contrasting ecological strategies, which demonstrate how links between exposure and resilience can be examined within our proposed framework. These examples reveal how climatic thresholds can be defined along a continuum of vegetation functional responses to water deficit regimes. The strength of this framework lies in identifying climatic thresholds on vegetation function in the absence of more complete mechanistic understanding, thereby guiding the formulation, application and benchmarking of more detailed modelling.     

Southern right whale (Eubalaena australis) calf mortality at Península Valdés,Argentina: Are harmful algal blooms to blame?

Península Valdés (PV) in Argentina is an important calving ground for southern right whales (SRWs, Eubalaena australis). Since 2005, right whale mortality has increased at PV, with most of the deaths (~90%) being calves <3 mo old. We investigated the potential involvement of harmful algal blooms (HABs) in these deaths by examining data that include: timing of the SRW deaths, biotoxins in samples from dead SRWs, abundances of the diatom, Pseudo‐nitzschia spp., and the dinoflagellate, Alexandrium tamarense, shellfish harvesting closure dates, seasonal availability of whale prey at PV and satellite chlorophyll data. Evidence of the whales' exposure to HAB toxins includes trace levels of paralytic shellfish toxins (PSTs) and domoic acid (DA) in tissues of some dead whales, and fragments of Pseudo‐nitzschia spp. frustules in whale feces. Additionally, whales are present at PV during both closures of the shellfish industry (due to high levels of PSTs) and periods with high levels of Pseudo‐nitzschia spp. and A. tamarense. There is a positive statistical relationship between monthly Pseudo‐nitzschia densities (but not A. tamarense) and calf deaths in both gulfs of PV.     

Vasopressin V1a receptor signaling in a rat choroid plexus cell line

A new cell line was derived from primary culture of rat choroid plexus (RCP) by immortalization with the TSOri minus adenovirus. The selected clone expressed vasopressin V1a receptors at a density of 64,000 sites per cell, and a K(d) of 7.2 nM. Addition of vasopressin to the RCP cells induced a transient calcium peak comparable to V1a receptor signalling in different expression systems. This [Ca(2+)](i) increase was dose-dependent with an EC(50) of 22 nM vasopressin. Similar [Ca(2+)](i) increase was elicited by addition of serotonin, angiotensin II, endothelin-1, and bradykinin. Heterologous desensitization of V1a receptor was observed in RCP cells exposed to the phorbol ester PMA or following stimulation of other receptors coupled to the phosphoinositide pathway. Positive immunolabelling with Factor VIII, Flt1 and CD 34 antibodies suggests that this new RCP cell line originated from endothelial cells of rat choroid plexus.     

Polylekithum percai n. sp. (Trematoda: Allocreadiidae) from Percichthys trucha (Perciformes: Percichthydae) in Patagonia,Argentina, and a redescription of Homalometron papilliferum (Szidat, 1956) n. comb.

Two species of Digenea are recorded from the intestine of Percichthys trucha (Percichthydae) from Patagonian water bodies. Polylekithum percai n. sp. (Allocreadiidae) is distinguished by its body size, the relative size of the suckers, the anterior extension of the vitelline fields, the number of eggs in the uterus and the different species of fish host from the two previously described species of Polylekithum. Homalometron (= Austrocreadium) papilliferum (Szidat, 1956) n. comb. is redescribed. Due to its spined tegument and the absence of a cirrus-sac, this species is considered a member of the family Apocreadiidae.     

Toward A Model of Social Course in Chronic Illness: The Example of Chronic Fatigue Syndrome

Retrospective, narrative accounts of illness experience in chronic fatigue syndrome provide the empirical basis for a preliminary conceptual model of social course in chronic illness. Qualities of distress interact with culturally specific expectations for social life and personal conduct to trigger microsocial processes of marginalization: role constriction, delegitimation, impoverishment, and social isolation. Marginalizing processes are opposed by acts of resistance initiated by ill individuals and directed toward integration in social worlds. Social distance from the perceived centers of CFS sufferers' interpersonal worlds expands and contracts with the changing predominance of marginalizing and resisting influences over time. Social course thus consists of successive, bi-directional movements along a continuum of marginality by persons living lives with chronic illness.     

Haploinsufficiency of c-Met in cd44-/- mice identifies a collaboration of CD44 and c-Met in vivo

Recent evidence has shown that the activation of receptor tyrosine kinases is not only dependent on binding of their ligands but in addition requires adhesion molecules as coreceptors. We have identified CD44v6 as a coreceptor for c-Met in several tumor and primary cells. The CD44v6 ectodomain is required for c-Met activation, whereas the cytoplasmic tail recruits ERM proteins and the cytoskeleton into a signalosome complex. Here we demonstrate that c-Met (and hepatocyte growth factor and Gab1) is haploinsufficient in a cd44^−/− background, as the cd44^−/−; met^+/− (and cd44^−/−; hgf^+/− and cd44^−/−; gab1^+/−) mice die at birth. They have impaired synaptic transmission in the respiratory rhythm-generating network and alterations in the phrenic nerve. These results are the first genetic data showing that CD44 and c-Met collaborate in vivo and that they are involved in synaptogenesis and axon myelination in the central and peripheral nervous systems.