The Drosophila immunoglobulin gene turtle encodes guidance molecules involved in axon pathfinding

Background: Neuronal growth cones follow specific pathways over long distances in order to reach their appropriate targets. Research over the past 15 years has yielded a large body of information concerning the molecules that regulate this process. Some of these molecules, such as the evolutionarily conserved netrin and slit proteins, are expressed in the embryonic midline, an area of extreme importance for early axon pathfinding decisions. A general model has emerged in which netrin attracts commissural axons towards the midline while slit forces them out. However, a large number of commissural axons successfully cross the midline even in the complete absence of netrin signaling, indicating the presence of a yet unidentified midline attractant. Results: The evolutionarily conserved Ig proteins encoded by the turtle/Dasm1 genes are found in Drosophila, Caenorhabditis elegans, and mammals. In Drosophila the turtle gene encodes five proteins, two of which are diffusible, that are expressed in many areas, including the vicinity of the midline. Using both molecular null alleles and transgenic expression of the different isoforms, we show that the turtle encoded proteins function as non-cell autonomous axonal attractants that promote midline crossing via a netrin-independent mechanism. turtle mutants also have either stalled or missing axon projections, while overexpression of the different turtle isoforms produces invasive neurons and branching axons that do not respect the histological divisions of the nervous system. Conclusion: Our findings indicate that the turtle proteins function as axon guidance cues that promote midline attraction, axon branching, and axonal invasiveness. The latter two capabilities are required by migrating axons to explore densely packed targets

Capacity building in economics : education and research in transition economies

The development of the institutional capacity to create and evaluate economic policies remains a critical need-and constraint-in most transition economies if they are to complete the successful passage to fully functioning market economies. To take an active role in the transition process, economic policymakers, business leaders, government officials, and others need a thorough grounding in market-based economics. This requires strengthening economics education and providing support for qualified economists to teach economics at all levels and to carry out high-quality research and policy analysis. Although the education systems in a handful of countries have already risen to the challenge, in many other transition countries, the structure of educational and research institutes remains grounded in the Communist model. This paper presents findings from a comprehensive study assessing the state of economics education and research in 24 countries in East-Central Europe and the former Soviet Union. While 20 countries were initially included because preliminary assessments showed that they lacked the capability to offer high-quality economics education, four additional countries-the Czech Republic, Hungary, Russia, and Ukraine-were included to highlight five centers of excellence that they already host. Based on the experience of these successful centers, the study's findings, and information gathered from a series of donor meetings in Berlin, New York, and Washington, D.C., this paper presents an approach to building new indigenous capacity for teaching and research on market-based economics in regions where the need is particularly critical-the Caucasus, Central Asia, and Southeast Europe.Curriculum&Instruction,Decentralization,Agricultural Knowledge&Information Systems,Teaching and Learning,Public Health Promotion,Tertiary Education,Health Monitoring&Evaluation,Agricultural Knowledge&Information Systems,Teaching and Learning,Curriculum&Instruction

Pitfalls when examining gap junction hemichannels: interference from volume-regulated anion channels

Human HeLa cells transfected with mouse connexin45 were used to explore the experimental conditions suitable to measure currents carried by gap junction hemichannels. Experiments were performed with a voltage-clamp technique and whole-cell recording. Lowering [Ca2+]o from 2mM to 20nM evoked an extra current, I m, putatively carried by Cx45 hemichannels. However, the variability of I m (size, voltage sensitivity, kinetics) suggested the involvement of other channels. The finding that growth medium in the incubator increased the osmolarity with time implied that volume-regulated anion channels (VRAC) may participate. This assumption was reinforced by the following observations. On the one hand, keeping [Ca2+]o normal while the osmolarity of the extracellular solution was reduced from 310 to 290mOsm yielded a current characteristic of VRAC; I VRAC activated/deactivated at negative/positive voltage, giving rise to the conductance functions g VRAC,inst=f(V m) (inst: instantaneous; V m: membrane potential) and g VRAC,ss=f(V m) (ss: steady state). Moreover, it was reversibly inhibited by mibefradil, a Cl-channel blocker (binding constant K d=38μM, Hill coefficient n=12), but not by the gap junction channel blocker 18α-glycyrrhetinic acid. On the other hand, minimizing the osmotic imbalance while [Ca2+]o was reduced led to a current typical for Cx45 hemichannels; I hc activated/deactivated at positive/negative voltage. Furthermore, it was reversibly inhibited by 18α-glycyrrhetinic acid or palmitoleic acid, but not by mibefradil. Computations based on g VRAC,ss=f(V m) and g hc,ss=f(V m) indicated that the concomitant operation of both currents results in a bell-shaped conductance-voltage relationship. The functional implications of the data presented are discussed. Conceivably, VRAC and hemichannels are involved in a common signaling pathwa

Cochlear detection of double-slip motion in cello bowing

A double-slip motion of a cello sound is investigated experimentally with a bowing machine and analyzed using a Finite-Difference Time Domain (FDTD) cochlear model. A double-slip sound is investigated. Here the sawtooth motion of normal bowing is basically present, but within each period the bow hair tears off the strings once more within the period, resulting in a blurred sound. This additional intermediate slip appears around the middle of each period and drifts temporally around while the sound progresses. When the double-slip is perfectly in the middle of one period the sound is that of a regular sawtooth motion. If not, two periodicities are present around double the fundamental periodicity, making the sound arbitrary. Analyzing the sound with a Wavelet-transform, the expected double-peak of two periodicities around the second partial cannot be found. Analyzing the tone with a cochlear FDTD model including the transfer of mechanical energy into spikes, the doubling and even more complex behaviour is perfectly represented in the Interspike Interval (ISI) of two adjacent spikes. This cochlear spike representation fits perfectly to an amplitude peak detection algorithm, tracking the precise time point of the double-slip within the fundamental period. Therefore the ear is able to detect the double-slip motion right at the transition from the basilar membrane motion into electrical spikes.Comment: 9 pages, 7 figure

Regulation of Cx45 hemichannels mediated by extracellular and intracellular calcium

Connexin45 (Cx45) hemichannels (HCs) open in the absence of Ca2+ and close in its presence. To elucidate the underlying mechanisms, we examined the role of extra- and intracellular Ca2+ on the electrical properties of HCs. Experiments were performed on HeLa cells expressing Cx45 using electrical (voltage clamp) and optical (Ca2+ imaging) methods. HCs exhibit a time- and voltage-dependent current (I hc), activating with depolarization and inactivating with hyperpolarization. Elevation of [Ca2+]o from 20nM to 2μM reversibly decreases I hc, decelerates its rate of activation, and accelerates its deactivation. Our data suggest that [Ca2+]o modifies the channel properties by adhering to anionic sites in the channel lumen and/or its outer vestibule. In this way, it blocks the channel pore and reversibly lowers I hc and modifies its kinetics. Rapid lowering of [Ca2+]o from 2mM to 20nM, achieved early during a depolarizing pulse, led to an outward I hc that developed with virtually no delay and grew exponentially in time paralleled by unaffected [Ca2+]i. A step increase of [Ca2+]i evoked by photorelease of Ca2+ early during a depolarizing pulse led to a transient decrease of I hc superimposed on a growing outward I hc; a step decrease of [Ca2+]i elicited by photoactivation of a Ca2+ scavenger provoked a transient increase in I hc. Hence, it is tempting to assume that Ca2+ exerts a direct effect on Cx45 hemichannel

Monitoring contractile dermal lymphatic activity following uniaxial mechanical loading

It is proposed that direct mechanical loading can impair dermal lymphatic function, contributing to the causal pathway of pressure ulcers. The present study aims to investigate the effects of loading on human dermal lymphatic vessels. Ten participants were recruited with ages ranging from 24-61 years. Participants had intradermal indocyanine green injections administrated between left finger digits. Fluorescence was imaged for 5 minute sequences with an Infra-Red camera prior to lymph vessel loading, immediately after axial loading (60mmHg) and following a recovery period. Image processing was employed to defined transient lymph packets and compare lymph function between each test phase. The results revealed that between 1-8 transient events (median =4) occurred at baseline, with a median velocity of 8.1mm/sec (range 4.1-20.1mm/sec). Immediately post-loading, there was a significant (p&lt;0.05) reduction in velocity (median = 6.4, range 2.2-13.5mm/sec), although the number of transient lymph packages varied between participants. During the recovery period the number (range 1-7) and velocity (recovery median =9.6mm/sec) of transient packets were largely restored to basal values. The present study revealed that some individuals present with impaired dermal lymphatic function immediately after uniaxial mechanical loading. More research is needed to investigate the effects of pressure and shear on lymphatic vessel patency. <br/