MicroRNA Mirn140 modulates Pdgf signaling during palatogenesis

Disruption of signaling pathways such as those mediated by sonic hedgehog (Shh) or platelet-derived growth factor (Pdgf) causes craniofacial abnormalities, including cleft palate. The role that microRNAs play in modulating palatogenesis, however, is completely unknown. We show that, in zebrafish, the microRNA Mirn140 negatively regulates Pdgf signaling during palatal development, and we provide a mechanism for how disruption of Pdgf signaling causes palatal clefting. The pdgf receptor alpha (pdgfra) 3' UTR contained a Mirn140 binding site functioning in the negative regulation of Pdgfra protein levels in vivo. pdgfra mutants and Mirn140-injected embryos shared a range of facial defects, including clefting of the crest-derived cartilages that develop in the roof of the larval mouth. Concomitantly, the oral ectoderm beneath where these cartilages develop lost pitx2 and shha expression. Mirn140 modulated Pdgf-mediated attraction of cranial neural crest cells to the oral ectoderm, where crest-derived signals were necessary for oral ectodermal gene expression. Mirn140 loss of function elevated Pdgfra protein levels, altered palatal shape and caused neural crest cells to accumulate around the optic stalk, a source of the ligand Pdgfaa. These results suggest that the conserved regulatory interactions of mirn140 and pdgfra define an ancient mechanism of palatogenesis, and they provide candidate genes for cleft palate.     

Cholera toxin genes: nucleotide sequence, deletion analysis and vaccine development

Nucleotide sequence and deletion analysis have been used to identify the regulatory and coding sequences comprising the cholera toxin operon (ctx). Incorporation of defined in vitro-generated ctx deletion mutations into Vibrio cholerae by in vivo genetic recombination produced strains which have practical value in cholera vaccine development.     

Voltage-sensor activation with a tarantula toxin as cargo

The opening and closing of voltage-activated Na+, Ca2+ and K+ (Kv) channels underlies electrical and chemical signalling throughout biology, yet the structural basis of voltage sensing is unknown. Hanatoxin is a tarantula toxin that inhibits Kv channels by binding to voltage-sensor paddles, crucial helix-turn-helix motifs within the voltage-sensing domains that are composed of S3b and S4 helices. The active surface of the toxin is amphipathic, and related toxins have been shown to partition into membranes, raising the possibility that the toxin is concentrated in the membrane and interacts only weakly and transiently with the voltage sensors. Here we examine the kinetics and state dependence of the toxin-channel interaction and the physical location of the toxin in the membrane. We find that hanatoxin forms a strong and stable complex with the voltage sensors, far outlasting fluctuations of the voltage sensors between resting (closed) conformations at negative voltages and activated (open) conformations at positive voltages. Toxin affinity is reduced by voltage-sensor activation, explaining why the toxin stabilizes the resting conformation. We also find that when hanatoxin partitions into membranes it is localized to an interfacial region, with Trp 30 positioned about 8.5 A from the centre of the bilayer. These results demonstrate that voltage-sensor paddles activate with a toxin as cargo, and suggest that the paddles traverse no more than the outer half of the bilayer during activation.     

蠕变断裂试验及初步研究(英文)

混凝土的蠕变断裂试验是一个相当困难的试验,以前还没有人成功地做过这样的试验。我们利用预裂的办法尽量减少混凝土的离散性进行了蠕变断裂试验,获得了蠕变断裂时间和荷载比关系,充分证实了篇变断裂的存在,以及发现在篇变断裂过程中伴随有微裂纹扩展。目前,我们用粘弹性理论蠕变断裂现象进行了初步分析,计算成果和试验非常好地呈现一致性。     

Wing bone stresses in free flying bats and the evolution of skeletal design for flight.

The primary mechanical functions of limb bones are to resist deformation, and hence provide stiff levers against which muscles can act, and to be sufficiently strong to prevent breaking under static or dynamic loads which arise from normal and accidental activities. If bones perform these functions with a minimum amount of material, the energetic costs associated with building, maintaining and transporting the skeleton will be minimized. Appropriate skeletal architecture for minimizing mass while maximizing strength depends on forces imposed on structural elements. In the evolutionary acquisition of flight in the bat lineage, the forelimb skeleton must have come to experience locomotor-forces that differed from those engendered by the terrestrial locomotion of non-flying bat relatives. Here we successfully measure in vivo strain on the wing bones of flying mammals. Our data demonstrate that torsion and shear are unique and crucial features of skeletal biomechanics during flight, and suggest that the evolution of skeletal design in bats and other flying vertebrates may be driven by the need to resist these loads.     

Effect of different methods of exposure to cyproterone acetate on mortality in chick embryos

Summary 33-h chick embryos exposed to 0.25 mg or 0.50 mg cyproterone acetate injected into the yolk sac showed a significantly lower mortality rate than embryos receiving the same dosage applied directly onto the developing blastodisc.This work was supported by a Government Research Support Grant awarded to Louisiana State University School of Medicine. Cyproterone acetate supplied through courtesy of Schering AG, Berlin, West Germany.     

Has the Earth's sixth mass extinction already arrived?

Palaeontologists characterize mass extinctions as times when the Earth loses more than three-quarters of its species in a geologically short interval, as has happened only five times in the past 540?million years or so. Biologists now suggest that a sixth mass extinction may be under way, given the known species losses over the past few centuries and millennia. Here we review how differences between fossil and modern data and the addition of recently available palaeontological information influence our understanding of the current extinction crisis. Our results confirm that current extinction rates are higher than would be expected from the fossil record, highlighting the need for effective conservation measures.     

Portability of paddle motif function and pharmacology in voltage sensors

Voltage-sensing domains enable membrane proteins to sense and react to changes in membrane voltage. Although identifiable S1-S4 voltage-sensing domains are found in an array of conventional ion channels and in other membrane proteins that lack pore domains, the extent to which their voltage-sensing mechanisms are conserved is unknown. Here we show that the voltage-sensor paddle, a motif composed of S3b and S4 helices, can drive channel opening with membrane depolarization when transplanted from an archaebacterial voltage-activated potassium channel (KvAP) or voltage-sensing domain proteins (Hv1 and Ci-VSP) into eukaryotic voltage-activated potassium channels. Tarantula toxins that partition into membranes can interact with these paddle motifs at the protein-lipid interface and similarly perturb voltage-sensor activation in both ion channels and proteins with a voltage-sensing domain. Our results show that paddle motifs are modular, that their functions are conserved in voltage sensors, and that they move in the relatively unconstrained environment of the lipid membrane. The widespread targeting of voltage-sensor paddles by toxins demonstrates that this modular structural motif is an important pharmacological target.     

FKF1 is essential for photoperiodic-specific light signalling in Arabidopsis

Adaptation to seasonal change is a crucial component of an organism's survival strategy. To monitor seasonal variation, organisms have developed the capacity to measure day length (photoperiodism). Day-length assessment involves the photoperiodic control of flowering in Arabidopsis thaliana, whereby the coincidence of light and high expression of CONSTANS (CO) induces the expression of FLOWERING LOCUS T (FT), leading to flowering in long-day conditions. Although controlling CO expression is clearly a key step in day-length discrimination, the mechanism that generates day-length-dependent CO expression remains unknown. Here we show that the clock-controlled FLAVIN-BINDING, KELCH REPEAT, F-BOX (FKF1) protein has an essential role in generating the diurnal CO peak and that this function is dependent on light. We show that a recombinant FKF1 LIGHT, OXYGEN OR VOLTAGE (LOV) domain binds the chromophore flavin mononucleotide and undergoes light-induced photochemistry, indicating that FKF1 may function as a photoperiodic blue-light receptor. It is likely that the circadian control of FKF1 expression and the light regulation of FKF1 function coincide to control the daytime CO waveform precisely, which in turn is crucial for day-length discrimination by Arabidopsis.