Vulnerability of Mediterranean Ecosystems to Long-Term Changes along the Coast of Israel

Although human activity is considered to be a major driving force affecting the distribution and dynamics of Mediterranean ecosystems, the full consequences of projected climate variability and relative sea-level changes on fragile coastal ecosystems for the next century are still unknown. It is unclear how these waterfront ecosystems can be sustained, as well as the services they provide, when relative sea-level rise and global warming are expected to exert even greater pressures in the near future (drought, habitat degradation and accelerated shoreline retreat). Haifa Bay, northern Israel, has recorded a landward sea invasion, with a maximum sea penetration 4,000 years ago, during an important period of urban development and climate instability. Here, we examine the cumulative pressure of climate shifts and relative sea-level changes in order to investigate the patterns and mechanisms behind forest replacement by an open-steppe. We provide a first comprehensive and integrative study for the southern Levant that shows that (i) human impact, through urbanization, has been the main driver behind ecological erosion in the past 4,000 years; (ii) climate pressures have reinforced this impact; and (iii) local coastal changes have played a decisive role in eroding ecosystem resilience. These three parameters, which have closely interacted during the last 4,000 years in Haifa Bay, clearly indicate that for an efficient management of the coastal habitats, anthropogenic pressures linked to urban development must be reduced in order to mitigate the predicted effects of Global Change.     

Nitrous oxide and methane fluxes of a pristine slope mire in the German National Park Harz Mountains

Pristine peatlands covered by Histosols (bogs and fens) with high water table and a restricted oxygen (O₂) availability are known to have low emissions of nitrous oxide (N₂O) but may be a significant source for atmospheric methane (CH₄) which are both important greenhouse gases. For the first time N₂O and CH₄ fluxes of a pristine slope mire in the German Harz Mountains have been monitored. Previously reported peatlands are characterised by anaerobic conditions due to high water table levels. Slope mires monitored here receive O₂ through slope water inflow. Gas fluxes have been monitored deploying closed chamber method on a central non-forested area and a forested area at the periphery of the slope mire. By means of groundwater piezometers water table levels, ammonium and nitrate contents as well as hydro-chemical variables like oxygen content and redox potential of the mire pore water have been concurrently measured with trace gas fluxes at both monitoring sites of the slope mire. The slope mire took up small amounts of atmospheric methane at a rate of −0.02 ± 0.01 kg C ha⁻¹ year⁻¹ revealing no significant difference between the forested and non-forested site. Higher uptake rates were observed during low water table level. In contrast to pristine peatlands influx of oxygen containing pore water into slope mire does limit reduction processes and resultant CH₄ emission. N₂O fluxes of the forested and non-forested sites of the slope mire did not differ and amounted to 0.25 ± 0.44 kg N ha⁻¹ year⁻¹. Higher emissions were observed at low water table levels and during thawing periods. In spite of favourable conditions N₂O fluxes of the slope mire have been comparable to those of pristine peatlands.     

Fibroblast growth factor receptor 1-IIIb is dispensable for skin morphogenesis and wound healing

Alternative splicing in the extracellular domain is a characteristic feature of members of the fibroblast growth factor receptor (FGFR) family. This splicing event generates receptor variants, which differ in their ligand binding specificities. A poorly characterized splice variant is FGFR1-IIIb, recently found to be a functional FGF receptor predominantly expressed in the skin. Here we show that FGFR1-IIIb is expressed in normal and wounded mouse skin. Reduced expression of this type of receptor was found in wounds of healing-impaired genetically diabetic mice, suggesting that downregulation of FGFR1-IIIb is associated with wound healing defects. To address this possibility, we deleted the IIIb exon of FGFR1 in mice. The lack of FGFR-IIIb did not alter the expression of either FGFR1-IIIc, other FGF receptor genes or of FGFR1-IIIb ligands in normal and wounded skin. Histological analysis of the skin of FGFR1-IIIb knockout animals did not reveal any obvious abnormalities. Furthermore, full-thickness excisional skin wounds in these mice healed normally and no defects could be observed at the macroscopic or histological level. Finally, several genes that encode key players in wound repair were normally expressed in these animals. These data demonstrate that FGFR1-IIIb is dispensable for skin development and wound repair.     

Functional complementation of human centromere protein A (CENP-A) by Cse4p from Saccharomyces cerevisiae

We have employed a novel in vivo approach to study the structure and function of the eukaryotic kinetochore multiprotein complex. RNA interference (RNAi) was used to block the synthesis of centromere protein A (CENP-A) and Clip-170 in human cells. By coexpression, homologous kinetochore proteins from Saccharomyces cerevisiae were then tested for the ability to complement the RNAi-induced phenotypes. Cse4p, the budding yeast CENP-A homolog, was specifically incorporated into kinetochore nucleosomes and was able to complement RNAi-induced cell cycle arrest in CENP-A-depleted human cells. Thus, Cse4p can structurally and functionally substitute for CENP-A, strongly suggesting that the basic features of centromeric chromatin are conserved between yeast and mammals. Bik1p, the budding yeast homolog of human CLIP-170, also specifically localized to kinetochores during mitosis, but Bik1p did not rescue CLIP-170 depletion-induced cell cycle arrest. Generally, the newly developed in vivo complementation assay provides a powerful new tool for studying the function and evolutionary conservation of multiprotein complexes from yeast to humans.     

Involvement of Mycobacterium smegmatis undecaprenyl phosphokinase in biofilm and smegma formation

We describe a Mycobacterium smegmatis mutant with impaired biofilm and smegma formation. A gene homologous to Escherichia coli bacA, which has been proposed to play a role as undecaprenyl phosphokinase (Upk) was unmarked in-frame deleted from M. smegmatis. Though Upk is involved in cell wall synthesis, the surface of the mutant strain appeared virtually comparable to that of the wild type by electron microscopy. The absence of Upk influenced colony morphology and bacitracin resistance. The M. smegmatis Deltaupk mutant developed a biofilm characterized by scattered islands of bacteria distinct from the completely covered biofilm surface observed for wild-type bacteria. We further demonstrate biological consequences of upk deletion for smegma development in an in vivo model. These results suggest the upk gene to be essential in biofilm and smegma development.     

Follistatin regulates enamel patterning in mouse incisors by asymmetrically inhibiting BMP signaling and ameloblast differentiation

Rodent incisors are covered by enamel only on their labial side. This asymmetric distribution of enamel is instrumental to making the cutting edge sharp. Enamel matrix is secreted by ameloblasts derived from dental epithelium. Here we show that overexpression of follistatin in the dental epithelium inhibits ameloblast differentiation in transgenic mouse incisors, whereas in follistatin knockout mice, ameloblasts differentiate ectopically on the lingual enamel-free surface. Consistent with this, in wild-type mice, follistatin was continuously expressed in the lingual dental epithelium but downregulated in the labial epithelium. Experiments on cultured tooth explants indicated that follistatin inhibits the ameloblast-inducing activity of BMP4 from the underlying mesenchymal odontoblasts and that follistatin expression is induced by activin from the surrounding dental follicle. Hence, ameloblast differentiation is regulated by antagonistic actions of BMP4 and activin A from two mesenchymal cell layers flanking the dental epithelium, and asymmetrically expressed follistatin regulates the labial-lingual patterning of enamel formation.     

Na(+)-D-glucose cotransporter in muscle capillaries increases glucose permeability

By immunohistochemistry, we demonstrated the localization of the Na(+)-D-glucose cotransporter SGLT1 in capillaries of rat heart and skeletal muscle, but not in capillaries of small intestine and submandibular gland. mRNA of SGLT1 was identified in skeletal muscle and primary cultured coronary endothelial cells. The functional relevance of SGLT1 for glucose transport across capillary walls in muscle was tested by measuring the extraction of D-glucose from the perfusate during non-recirculating perfusion of isolated rat hindlimbs. In this model, D-glucose extraction from the perfusate is increased by insulin which accelerates D-glucose uptake into myocytes by increasing the concentration of glucose transporter GLUT4 in the plasma membrane. The insulin-induced increase of D-glucose extraction from the perfusate was abolished after blocking SGLT1 with the specific inhibitor phlorizin. The data show that SGLT1 in capillaries of skeletal muscle is required for the action of insulin on D-glucose supply of myocytes.     

A molecular dissection of the glycoprotein hormone receptors

In glycoprotein hormone receptors, a subfamily of rhodopsin-like G protein-coupled receptors, the recognition and activation steps are carried out by separate domains of the proteins. Specificity of recognition of the hormones thyrotropin (TSH), lutropin (LH), human chorionic gonadotropin (hCG) and follitropin (FSH) involves leucine-rich repeats (LRRs) present in an N-terminal ectodomain, and can be associated with a limited number of residues at key positions of the LRRs. The mechanism by which binding of the hormones results in activation is proposed to involve switching of the ectodomain from a tethered inverse agonist to a full agonist of the serpentine, rhodopsin-like region of the receptor. Unexpectedly, the picture is complicated by the observation that promiscuous activation of one of the receptors (FSHr) by hCG or TSH can result from activating mutations affecting the serpentine region of the receptors.