Molecular diversity among marine picophytoplankton as revealed by psbA analyses

Photosynthetic microorganisms play a crucial role in the marine environment. In vast areas of the oceans, marine primary productivity is performed by cells smaller than 2-3 micro m (picoplankton). Here, we report on molecular analyses of the conserved photosynthetic psbA gene (coding for protein D1 of photosystem II reaction centre) as a diversity indicator of naturally occurring marine oxygenic picophytoplankton. The psbA genes proved to be good indicators of the presence of a wide variety of photosynthetic marine microbial groups, including new cyanobacterial groups and eukaryotic algae (prasinophytes). Furthermore, using environmental bacterial artificial chromosome (BAC) libraries, we were able to correlate psbA genes with small subunit rRNAs and, therefore, to confirm their phylogenetic affiliation.     

A Synechococcus PglnA::luxAB fusion for estimation of nitrogen bioavailability to freshwater cyanobacteria

In contrast to extensive studies of phosphorus, widely considered the main nutrient limiting phytoplankton biomass in freshwater ecosystems, there have been few studies on the role of nitrogen in controlling phytoplankton populations. This situation may be due partly to the complexity in estimating its utilization and bioavailability. In an attempt to provide a novel tool for this purpose, we fused the promoter of the glutamine synthetase-encoding gene, P glnA, from Synechococcus sp. strain PCC7942 to the luxAB luciferase-encoding genes of the bioluminescent bacterium Vibrio harveyi. The resulting construct was introduced into a neutral site on the Synechococcus chromosome to yield the reporter strain GSL. Light emission by this strain was dependent upon ambient nitrogen concentrations. The linear response range of the emitted luminescence was 1 mM to 1 micro M for the inorganic nitrogen species tested (ammonium, nitrate, and nitrite) and 10- to 50-fold lower for glutamine and urea. When water samples collected from along a depth profile in Lake Kinneret (Israel) were exposed to the reporter strain, the bioluminescence of the reporter strain mirrored the total dissolved nitrogen concentrations determined for the same samples and was shown to be a sensitive indicator of the concentration of bioavailable nitrogen.     

Angiogenic synergism,vascular stability and improvement of hind-limb ischemia by a combination of PDGF-BB and FGF-2

The establishment of functional and stable vascular networks is essential for angiogenic therapy. Here we report that a combination of two angiogenic factors, platelet-derived growth factor (PDGF)-BB and fibroblast growth factor (FGF)-2, synergistically induces vascular networks, which remain stable for more than a year even after depletion of angiogenic factors. In both rat and rabbit ischemic hind limb models, PDGF-BB and FGF-2 together markedly stimulated collateral arteriogenesis after ligation of the femoral artery, with a significant increase in vascularization and improvement in paw blood flow. A possible mechanism of angiogenic synergism between PDGF-BB and FGF-2 involves upregulation of the expression of PDGF receptor (PDGFR)-alpha and PDGFR-beta by FGF-2 in newly formed blood vessels. Our data show that a specific combination of angiogenic factors establishes functional and stable vascular networks, and provides guidance for the ongoing clinical trials of angiogenic factors for the treatment of ischemic diseases.     

Which objectively assessed limitations in health status, activities of daily living, or in psychological and social spheres are decisive for referral to a nursing home or to a home for the aged

Which type of limitation is most decisive for a positive indication for a residential home or a somatic or psycho-geriatric nursing home, and to what extent do data on living situation (independent, adapted or intramural) and the social situation (alone or living together) influence this qualification? To obtain an answer to this question three experiments with an integrated, objective and independent assessment-for-care system were set up in the Netherlands. We studied one of them, in the town of Meppel, started in 1996. The study population consisted of all older people living in and around Meppel who had a positive indication for either a residential home, or a somatic or psycho-geriatric nursing home (N = 206 in 1998). Differences in limitations were computed by means of analysis of variance and the types of limitation and their impact on the type of allocated institutions were computed by logistic regression. The limitations only partially explain the types of indication. Indication for a residential home is based on physical limitations. When these increase they become a contra-indication for a residential home and a somatic nursing home indication is given. Mental limitations primarily yield indications for psycho-geriatric nursing homes. Social limitations have a higher incidence among persons with an indication for a somatic nursing home but cannot fully explain this indication. Persons with a residential home indication were significantly more often from an adapted living situation background. The living situation -alone or together-does not have an impact on the indication. We may not conclude that the assessment took place objectively, for, based on the registration it is impossible to conclude for what criteria a person was indicated for a specific type of institution. The objective of assessment, the allocation and distribution of collectively financed care in residential homes and nursing homes based on verifiable assessment methodology could not be realised.     

Temephos-resistant larvae of Simulium sanctipauli associated with a distinctive new chromosome inversion in untreated rivers of south-western Ghana

Larvae of the Simulium damnosum Theobald complex (Diptera: Simuliidae) were sampled in June 1996 from two sites in south-west Ghana where larviciding has not been applied: Sutri Rapids on the Tano river (05 degrees 23 minutes N 02 degrees 38 minures W) and Sekyere-Heman on the Pra river (05 degrees 11 minutes N 01 degrees 35 minutes W). All specimens were identified as Simulium sanctipauli Vajime & Dunbar sensu stricto (Diptera: Simuliidae). Bioassays with temephos (organophosphorus larvicide employed by the Onchocerciasis Programme for systematic treatment of most rivers across West Africa since the 1970s) showed about five-fold resistance in the Tano population (LC95 2.37-3.14 mg/L) and slight tolerance to temephos in the Pra population (LC95 0.67-0.76 mg/L), vs. the diagnostic concentration of 0.625 mg/L. Larval salivary polytene chromosomes of S. sanctipauli showed fixed inversions 1S-24/24, standard IIL-6 and a new inversion IL/36 polymorphism at Sutri on the Tano. These karyotype characteristics differ from those of temephos-resistant S. sanctipauli in rivers of C te d'Ivoire and other sites on the Tano in Ghana. Thus, temephos resistance in S. sanctipauli at Sutri is associated with distinct chromosomal configurations, showing that immigration was unlikely. This resistance could have been locally selected by exposure of S. sanctipauli larval populations to agrochemicals run-off from cocoa, coffee and oil plantations flanking the rivers.     

Complement C1q is dramatically up-regulated in brain microglia in response to transient global cerebral ischemia

Recent evidence suggests that the pathophysiology of neurodegenerative and inflammatory neurological diseases has a neuroimmunological component involving complement, an innate humoral immune defense system. The present study demonstrates the effects of experimentally induced global ischemia on the biosynthesis of C1q, the recognition subcomponent of the classical complement activation pathway, in the CNS. Using semiquantitative in situ hybridization, immunohistochemistry, and confocal laser scanning microscopy, a dramatic and widespread increase of C1q biosynthesis in rat brain microglia (but not in astrocytes or neurons) within 24 h after the ischemic insult was observed. A marked increase of C1q functional activity in cerebrospinal fluid taken 1, 24, and 72 h after the ischemic insult was determined by C1q-dependent hemolytic assay. In the light of the well-established role of complement and complement activation products in the initiation and maintenance of inflammation, the ischemia-induced increase of cerebral C1q biosynthesis and of C1q functional activity in the cerebrospinal fluid implies that the proinflammatory activities of locally produced complement are likely to contribute to the pathophysiology of cerebral ischemia. Pharmacological modulation of complement activation in the brain may be a therapeutic target in the treatment of stroke.     

Myc is an essential negative regulator of platelet-derived growth factor beta receptor expression

Platelet-derived growth factor BB (PDGF BB) is a potent mitogen for fibroblasts as well as many other cell types. Interaction of PDGF BB with the PDGF beta receptor (PDGF-betaR) activates numerous signaling pathways and leads to a decrease in receptor expression on the cell surface. PDGF-betaR downregulation is effected at two levels, the immediate internalization of ligand-receptor complexes and the reduction in pdgf-betar mRNA expression. Our studies show that pdgf-betar mRNA suppression is regulated by the c-myc proto-oncogene. Both constitutive and inducible ectopic Myc protein can suppress pdgf-betar mRNA and protein. Suppression of pdgf-betar mRNA in response to Myc is specific, since expression of the related receptor pdgf-alphar is not affected. We further show that Myc suppresses pdgf-betar mRNA expression by a mechanism which is distinguishable from Myc autosuppression. Analysis of c-Myc-null fibroblasts demonstrates that Myc is required for the repression of pdgf-betar mRNA expression in quiescent fibroblasts following mitogen stimulation. In addition, it is evident that the Myc-mediated repression of pdgf-betar mRNA levels plays an important role in the regulation of basal pdgf-betar expression in proliferating cells. Thus, our studies suggest an essential role for Myc in a negative-feedback loop regulating the expression of the PDGF-betaR.     

Relative phase dynamics in perturbed interlimb coordination: the effects of frequency and amplitude

Sch?ner [Sch?ner G (1995) Ecol Psychol 7: 291-314] argued that the relative phase dynamics of rhythmic interlimb coordination may be attributed to the timing level in that the stability properties of the relative phase are largely independent of dynamical principles operating at the goal level, such as those related to the maintenance of a particular amplitude or target position. Yet, according to the coupling functions in the coupled oscillator model proposed by Haken et al. [Haken H, Kelso JAS, Bunz H (1985) Biol Cybern 51: 347-356], the effect of frequency on the stability properties of relative phase is either wholly or partially mediated by frequency-induced changes in amplitude, implying that the relative phase dynamics strongly depends on spatial factors. In order to distinguish between these contrasting interpretations of the organizational principles underwriting the phase dynamics of interlimb coordination, an experiment was conducted in which the effects of frequency and amplitude on the stability of relative phase were separated. Six subjects performed both in-phase and antiphase coordination patterns at seven different frequencies and three different amplitudes. Two measures of pattern stability were used, the standard deviation of relative phase and the exponent of the relaxation process following phasic perturbations of relative phase. According to both measures, pattern stability decreased with increasing frequency, whereas the amplitude manipulation only had a significant effect on the standard deviation of relative phase. This result was interpreted to imply that the organizational principles at the (relative) timing level are affected only moderately by task constraints pertaining to the goal level, and that models of interlimb coordination in which amplitude coupling plays a partial or subordinate role should be preferred above models relying solely on amplitude coupling.     

Macrophage colony-stimulating factor rapidly enhances beta-migrating very low density lipoprotein metabolism in macrophages through activation of a Gi/o protein signaling pathway

Previous studies have examined lipoprotein metabolism by macrophages following prolonged exposure (>24 h) to macrophage colony-stimulating factor (M-CSF). Because M-CSF activates several signaling pathways that could rapidly affect lipoprotein metabolism, we examined whether acute exposure of macrophages to M-CSF alters the metabolism of either native or modified lipoproteins. Acute incubation of cultured J774 macrophages and resident mouse peritoneal macrophages with M-CSF markedly enhanced low density lipoproteins (LDL) and beta-migrating very low density lipoproteins (beta-VLDL) stimulated cholesteryl [(3)H]oleate deposition. In parallel, M-CSF treatment increased the association and degradation of (125)I-labeled LDL or beta-VLDL without altering the amount of lipoprotein bound to the cell surface. The increase in LDL and beta-VLDL metabolism did not reflect a generalized effect on lipoprotein endocytosis and metabolism because M-CSF did not alter cholesterol deposition during incubation with acetylated LDL. Moreover, M-CSF did not augment beta-VLDL cholesterol deposition in macrophages from LDL receptor (-/-) mice, indicating that the effect of M-CSF was mediated by the LDL receptor. Incubation of macrophages with pertussis toxin, a specific inhibitor of G(i/o) protein signaling, had no effect on cholesterol deposition during incubation with beta-VLDL alone, but completely blocked the augmented response promoted by M-CSF. In addition, incubation of macrophages with the direct G(i/o) protein activator, mastoparan, mimicked the effect of M-CSF by enhancing cholesterol deposition in cells incubated with beta-VLDL, but not acetylated LDL. In summary, M-CSF rapidly enhances LDL receptor-mediated metabolism of native lipoproteins by macrophages through activation of a G(i/o) protein signaling pathway. Together, these findings describe a novel pathway for regulating lipoprotein metabolism.