Dynamics of a Kalahari long-lived mega-lake system: hydromorphological and limnological changes in the Makgadikgadi Basin (Botswana) during the terminal 50 ka

The Kalahari features a long-lived lacustrine system which may exist since the Early Pleistocene. The emergence of an extant cichlid fish radiation from this (palaeo-) lake during the Middle Pleistocene indicates an ancient lake character. The early history of the system remains speculative, but it is established that lake extensions matching modern Lake Victoria in size have occurred during the Late Pleistocene. It has been assumed that the hydrographical dynamics chiefly depended on the inflow from the Okavango River and thus on ITCZ-controlled precipitation. Our studies, which focused the hydromorphological and palaeolimnological development of the Makgadikgadi Basin during the last 50 ka, suggest that from c. 46–16 ka it did not receive water from the Okavango River but from palaeo-rivers located in the northern and south-western catchment. A northward shift of the winter rainfall zone during the Last Glacial Maximum sustained a high lake level for a period of c. 6 ka. During Heinrich Event 1 (17–16 ka) the lake probably desiccated abruptly and completely. Higher lake levels, controlled by water from the Okavango river system, were reached again during the Holocene before the lake dried up in the middle of the last millennium.     

Analyzing female gametophyte development and function: There is more than one way to crack an egg

In flowering plants, gametes are formed in specialized haploid structures, termed gametophytes. The female gametophyte is a few-celled structure that integrates such diverse functions as pollen tube attraction, sperm cell release, gamete fusion and seed initiation. These processes are realized by distinct cell types, which ensure reproductive success in a coordinated manner. In the past decade, much progress has been made concerning the molecular nature of the functions carried out by the different cell types. Here, we review recent work that has shed light on female gametophyte development and function with a particular focus on approaches that have led to the isolation of genes involved in these processes.     

ADAM10 is the physiologically relevant, constitutive ��-secretase of the amyloid precursor protein in primary neurons

The amyloid precursor protein (APP) undergoes constitutive shedding by a protease activity called α‐secretase. This is considered an important mechanism preventing the generation of the Alzheimer's disease amyloid‐β peptide (Aβ). α‐Secretase appears to be a metalloprotease of the ADAM family, but its identity remains to be established. Using a novel α‐secretase‐cleavage site‐specific antibody, we found that RNAi‐mediated knockdown of ADAM10, but surprisingly not of ADAM9 or 17, completely suppressed APP α‐secretase cleavage in different cell lines and in primary murine neurons. Other proteases were not able to compensate for this loss of α‐cleavage. This finding was further confirmed by mass‐spectrometric detection of APP‐cleavage fragments. Surprisingly, in different cell lines, the reduction of α‐secretase cleavage was not paralleled by a corresponding increase in the Aβ‐generating β‐secretase cleavage, revealing that both proteases do not always compete for APP as a substrate. Instead, our data suggest a novel pathway for APP processing, in which ADAM10 can partially compete with γ‐secretase for the cleavage of a C‐terminal APP fragment generated by β‐secretase. We conclude that ADAM10 is the physiologically relevant, constitutive α‐secretase of APP.     

On the use of N‐dicyclopropylmethyl aspartyl‐glycine synthone for backbone amide protection

To prevent aspartimide formation and related side products in Asp‐Xaa, particularly Asp‐Gly‐containing peptides, usually the 2‐hydroxy‐4‐methoxybenzyl (Hmb) backbone amide protection is applied for peptide synthesis according to the Fmoc‐protocols. In the present study, the usefulness of the recently proposed acid‐labile dicyclopropylmethyl (Dcpm) protectant was analyzed. Despite the significant steric hindrance of this bulky group, N‐terminal H‐(Dcpm)Gly‐peptides are quantitatively acylated by potent acylating agents, and alternatively the dipeptide Fmoc‐Asp(OtBu)‐(Dcpm)Gly‐OH derivative can be used as a building block. In contrast to the Hmb group, Dcpm is inert toward acylations, but is readily removed in the acid deprotection and resin‐cleavage step. Copyright © 2009 European Peptide Society and John Wiley & Sons, Ltd.     

The adapter protein Nck: Role of individual SH3 and SH2 binding modules for protein interactions in T lymphocytes

Nck is a ubiquitously expressed, primarily cytosolic adapter protein consisting of one SH2 domain and three SH3 domains. It links receptor and nonreceptor tyrosine kinases to actin cytoskeleton reorganizing proteins. In T lymphocytes, Nck is a crucial component of signaling pathways for T cell activation and effector function. It recruits actin remodeling proteins to T cell receptor (TCR)‐associated activation clusters and thereby initiates changes in cell polarity and morphology. Moreover, Nck is crucial for the TCR‐induced mobilization of secretory vesicles to the cytotoxic immunological synapse. To identify the interactome of Nck in human T cells, we performed a systematic screen for interaction partners in untreated or pervanadate‐treated cells. We used GST fusion proteins containing full length Nck, the combined SH3 domains or the individual SH3 and SH2 domains to precipitate putative Nck interactors from cellular lysates. Protein bands were excised from gels, processed by tryptic in‐gel digestion and analyzed by mass spectrometry. Using this approach, we confirmed previously established interactions (e.g., with Slp76, CD3ε, WASP, and WIPF1) and identified several novel putative Nck‐binding proteins. We subsequently verified the SH2 domain binding to the actin‐binding protein HIP55 and to FYB/ADAP, and the SH3‐mediated binding to the nuclear proteins SFPQ/NONO. Using laser scanning microscopy, we provide new evidence for a nuclear localization of Nck in human T cells. Our data highlight the fundamental role of Nck in the TCR‐to‐cytoskeleton crosstalk and point to yet unknown nuclear functions of Nck also in T lymphocytes.     

Analysis of humoral immune responses in rhesus macaques vaccinated with attenuated SIVmac239Δnef and challenged with pathogenic SIVmac251

Background To determine the correlation between protection and humoral immune response against simian immunodeficiency virus (SIVmac251), 11 macaques were immunized with live‐attenuated SIVmac239Δnef either intravenously or via the tonsils and exposed to SIVmac251 after either 6 or 15 months along with unvaccinated controls. Results Independent of the route of vaccine application, viremia was significantly reduced in vaccinees compared with controls 2 weeks post‐challenge. Concomitantly, viremia correlated inversely with SIV‐specific IgG, complement‐mediated lysis and neutralizing antibodies and these parameters seemed to contribute to reduced viremia. During chronic infection, six monkeys controlled viremia in the circulation (two or fewer infectious units per 10⁶ PBMCs) and showed no signs of trapping in lymphatic tissues (Appendix S1). Conclusions As no significant differences were observed throughout the study, with respect to the humoral immune response and viremia control, between the two vaccinated cohorts, mucosal immunization strategies are recommended due to more simplified application.     

Estimation by PLFA of Microbial Community Structure Associated with the Rhizosphere of Lygeum spartum and Piptatherum miliaceum Growing in Semiarid Mine Tailings

The objective of this study was to compare the microbial community composition and biomass associated with the rhizosphere of a perennial gramineous species (Lygeum spartum L.) with that of an annual (Piptatherum miliaceum L.), both growing in semiarid mine tailings. We also established their relationship with the contents of potentially toxic metals as well as with indicators of soil quality. The total phospholipid fatty acid (PLFA) amount was significantly higher in the rhizosphere soil of the annual species than in the rhizosphere soil of the perennial species. The fungal/bacterial PLFA ratio was significantly greater in the perennial species compared to the annual species. The fatty acid 16:1ω5c, the fungal/bacterial PLFA ratio and monounsaturated/saturated PLFA ratio were correlated negatively with the soluble contents of toxic metals. The cyc/prec (cy17:0 + cy19:0/16:1ω7 + 18:1ω7) ratio was correlated positively with the soluble contents of Pb, Zn, Al, Ni, Cd, and Cu. The results of the PLFA analysis for profiling microbial communities and their stress status of both the plant species indicate that perennial and annual gramineous species appear equally suitable for use in programmes of revegetation of semiarid mine tailings.     

Alternans Resonance and Propagation Block during Supernormal Conduction in Cardiac Tissue with Decreased [K]o

Cardiac restitution is an important factor in arrhythmogenesis. Steep positive action potential duration and conduction velocity (CV) restitution slopes promote alternans and reentrant arrhythmias. We examined the consequences of supernormal conduction (characterized by a negative CV restitution slope) on patterns of conduction and alternans in strands of Luo-Rudy model cells and in cultured cardiac cell strands. Interbeat intervals (IBIs) were analyzed as a function of distance during S1S2 protocols and during pacing at alternating cycle lengths. Supernormal conduction was induced by decreasing [K⁺]_o. In control [K⁺]_o simulations, S1S2 intervals converged toward basic cycle length with a length constant determined by both CV and the CV restitution slope. During alternant pacing, the amplitude of IBI alternans converged with a shorter length constant, determined also by the action potential duration restitution slope. In contrast, during supernormal conduction, S1S2 intervals and the amplitude of alternans diverged. This amplification (resonance) led to phase-locked or more complex alternans patterns, and then to distal conduction block. The convergence/divergence of IBIs was verified in the cultured strands, in which naturally occurring tissue heterogeneities resulted in prominent discontinuities of the spatial IBI profiles. We conclude that supernormal conduction potentiates alternans and spatial analysis of IBIs represents a powerful method to locate tissue heterogeneities.     

Abscisic add levels of individual leaf cells

Abscisic acid (ABA) concentrations of guard cells, subsidiary cells and epidermis cells of Comrnelina communis L. and Tradescantia virginiana L. were determined in cell sap samples extracted by means of micro glass capillaries. Concentrations up to 6.7 m M were indicated by commercial immunoassay test kits. A gradient of ABA concentration was found between guard cells (2,49 ± 1.81 m M , n = 25), subsidiary cells (1.25 ± 1.46 m M , n = 21) and epidermis cells (0.86 ± 0.76 m M , n = 20; mean values ± SD).     

Electrophysiological identification of the sugar cell in antennal taste sensilla of the predatory ground beetle Pterostichus aethiops

By single sensillum tip recording technique, in addition to the salt and pH cells found in antennal taste sensilla of some ground beetles earlier, the third chemosensory cell of four innervating these large sensilla was electrophysiologically identified as a sugar cell in the ground beetle Pterostichus aethiops. This cell generated action potentials of considerably smaller amplitude than those of the salt and pH cells, and phasic-tonically responded to sucrose and glucose over the range of 1-1000 mM tested. Responses were concentration dependent, with sucrose generating more spikes than glucose. During the first second of the response, maximum rates of firing of the sugar cell reached up to 19 and 37 imp/s when stimulated with 1000 mM glucose and sucrose, respectively. Three to four seconds later, the responses decreased close to zero. Both sugars are important in plant carbohydrate metabolism. These ground dwelling insects may come into contact with live and decayed plant material everywhere in their habitat including their preferred overwintering sites in brown-rot decayed wood. In conclusion, we hypothesize that high content of soluble sugars in their overwintering sites and refugia is unfavourable for these ground beetles, most probably to avoid contact with dangerous fungi.