Fate and regulation of anterior-like cells in Dictyostelium slugs

A pattern of two tissue types exists in the Dictyostelium slug. Contained within the posterior tissue are anterior-like cells which comprise about 10% of the developing cell mass. For more than 72 hr of slug migration the proportion of these cells is closely regulated. They are randomly distributed along the anterior-posterior axis but about twice as many are localized in the ventral portion of the slug posterior than in the dorsal portion. As the slug begins to form a fruiting body, the anterior-like cells sort out into two groups. One group moves toward the anterior region and one toward the prebasal disc region. In the mature fruiting body the anterior-like cells remain as undifferentiated amoebae at the apex and base of the sorus. Removal of anterior tissue from a slug initiates two events. (1) Some of the anterior-like cells, probably guided by chemotaxis to cyclic AMP, sort out from the posterior tissue. (2) Some prespore cells redifferentiate into anterior-like cells. These events result in the regeneration of a new anterior-posterior pattern after 2 hr and the reestablishment of the original proportions of each cell type by about 8 hr. Furthermore, while the anterior-like cells which lie in slug posteriors remain as amoebae in fruiting bodies, the anterior-like cells which form the anteriors of regenerated slugs subsequently become stalk cells. Thus, it appears that for a cell to differentiate as a stalk cell, it must first be exposed to some form of signal which is present in both the anterior and prebasal disc regions

Cell Sorting daring Pattern Formation in Dictyostelium

Formation of the prestalk-prespore pattern in Dictyostelium was investigated in slugs and submerged clumps of cells. Prestalk and prespore cells were identified by staining with vital dyes, which are shown to be stable cell markers. Dissociated slug cells reaggregate and form slugs that contain a prestalk-prespore pattern indistinguishable from the original pattern. The pattern forms by sorting out of stained prestalk cells from unstained prespore cells. Sorting also occurs in clumps of dissociated slug cells submerged in liquid or agar. A pattern arises in 2 h in which a central core of stained cells is surrounded by a periphery of unstained cells. Sorting appears to be due to differential chemotaxis of stained and unstained cells to cAMP since exogenous cAMP (>10−7 M) reverses the normal direction of sorting-out such that stained cells sort to the periphery of the clumps. Isolated portions of slugs regenerate a new prestalk-prespore pattern. Posterior isolates regenerate a pattern within 2 h due to sorting of a population of vitally stained ‘anterior-like’ cells present in posteriors. Anterior-like cells do not sort in intact slugs due to the influence of a diffusible inhibitor secreted by the anterior region. During posterior regeneration this signal is absent and anterior-like cells rapidly acquire the ability to sort. Anterior isolates regenerate a staining pattern more slowly than posterior isolates by a process that requires conversion of stained prestalk cells to unstained prespore cells. The results suggest that pattern formation in Dictyostelium consists of two processes: establishment of appropriate proportions of two cell types and establishment of the pattern itself by a mechanism of sorting-out

OXYGEN GRADIENTS CAUSE PATTERN ORIENTATION IN DICTYOSTELIUM CELL CLUMPS

We have investigated the formation of the prestalk-prespore pattern in Dictyottelium discoideum. Pattern formation occurs in clumps of Dictyostelium cells embedded in agar under a 100% oxygen atmosphere. Agar embedding allows us to control spatially the environment surrounding the cell clumps. Our results suggest that the ambient oxygen concentration plays a role in controlling the size of the multicellular mass. Further, oxygen gradients established across clumps embedded in agar or held in holes in a plastic barrier cause orientation of the prestalk-prespore pattern such that the anterior prestalk region forms at the highest end of the gradient. The results also indicate that developing cells have the ability to migrate up a gradient of oxygen

Active Inductor and Capacitor for DCS receiver band (1.71GHz – 1.785GHz) using multi-MESFET Negative Resistance Circuit

Traditional spiral inductors are usually large, bulky, and difficult to model, hence active inductors look very attractive particularly because of their tuning capability. The basic idea of this design is to realize an active inductor and capacitor that could be used to substitute the spiral inductors and lumped capacitors in Monolithic Microwave Integrated Circuit (MMIC) active filters. The resulting negative resistance serves to compensate the pass-band insertion loss. The benefits of reduced cost, small size and weight justify the effort to develop fully integrated Radio Frequency (RF) and Microwave systems using MMIC technology. In line with this interest, this work will lay a key foundation on which the step toward full integration can be made. For proof of concept, a 5GHz active capacitor using single MESFET negative resistance was designed, simulated and fabricated by GEC F20 Foundry. The test and measurement was done using HP8510 Network Analyzer. The simulated and measured results compared well. Following on this concept, an active inductor for dcs receiver band (1.71GHz – 1.785GHz) using multi-MESFET negative resistance circuit was designed and simulated. The results obtained show constant inductor and negative resistance values within the desired frequency ban

Modeling of Orthogonal Frequency Division Multiplexing (OFDM) for Transmission in Broadband Wireless Communications

Orthogonal Frequency Division Multiplexing (OFDM) is a multi carrier modulation technique that provides high bandwidth efficiency because the carriers are orthogonal to each other and multiple carriers share the data among themselves. The main advantage of this transmission technique is its robustness to channel fading in wireless communication environment. This paper investigates the effectiveness of OFDM and assesses its suitability as a modulation technique in wireless communications. Several of the main factors affecting the performance of a typical OFDM system are considered and they include multipath delay spread, channel noise, distortion (clipping), and timing requirements. The core processing block and performance analysis of the system is modeled usingMatlab

Financial Appraisal of the Banks for Cooperatives

This study examines the financial situation of the Farm Credit System Banks for Cooperatives using comparative analysis for the period 1978 through 1991. Profitability and leverage measures of the Banks for Cooperatives are compared with similar measures of large commercial banks. The Banks for Cooperatives were found to have performed as well as large commercial banks. Some differences can be explained as compatible with differences in the goals and objectives of a cooperative versus an investor-owned firm. Most differences can be attributed to the financial strength of the Banks for Cooperatives relative to the commercial banking industry.Agribusiness, Agricultural Finance,

Applications and Benefits of Nonlinearities in Optical Fibres in Wavelength Division Multiplexed Systems

Optical nonlinearities play a major role in optical fibre with respect to transmission capacity and performance of the system. This degrades the system performance, especially in wavelength division multiplexing (WDM) systems, where several channels co-exist in the same fibre and propagating simultaneously, resulting in high optical intensities. They can result in pulse distortion referred to as self phase modulation (SPM), cross phase modulation (XPM), crosstalk between channels, and four wave mixing (FWM). However, these non-linearities also have many useful applications, especially for the implementation of all-optical functionalities in optical networks. In this paper, we briefly review the different kinds of optical nonlinearities encountered in fibres, identify the essential materials and fibre parameters that determine them. The paper simulates two channel WDM optical communication systems in single mode fibre over long haul of 100 km to investigate the effect of SPM, XPM and FWM. Their thresholds, managements and applications are also discussed; and comparative study of these effects is presented

Design and Implementation of a Microprocessor Based Temperature Controller With Real Time Display

The objective of the project was to automate and control temperature for a server room. The system is allowed entry of a desired room temperature within a prescribed range and to exhibit overshoot and steady-state temperature error of less than 1 degree displaying the value in real time. The details of the design developed, based on a PIC18F452 microcontroller are described. Time, cost and energy are saved by delivering power efficiently using this system. It can be applied in industries, auditoriums, green house buildings, server rooms and nuclear facilities. It is shown that the solution requires broad knowledge drawn from several engineering disciplines including electrical, mechanical, and control systems engineering. Keywords: Temperature, Sensor, Display, Control, Microcontroller, Real Time