cDNA fingerprinting of osteoprogenitor cells to isolate differentiation stage-specific genes

A cDNA fingerprinting strategy was developed to identify genes based on their differential expression pattern during osteoblast development. Preliminary biological and molecular staging of cDNA pools prepared by global amplification PCR allowed discrim-inating choices to be made in selection of expressed sequence tags (ESTs) to be isolated. Sequencing of selected ESTs confirmed that both known and novel genes can be isolated from any developmental stage of interest, e.g. from primitive progenitors, intermediate precursors or mature osteoblasts. EST expression provides insight into possible interrelated physiological functions and putative interacting molecules during differentiation. This method offers a functional genomics approach to isolate differentiation stage-specific genes in samples as small as a single cell.     

Information theoretic analysis of dynamical encoding by filiform mechanoreceptors in the cricket cercal system

1. The stimulus/response properties of 20 mechanosensory receptors in the cricket cercal sensory system were studied using electrophysiological techniques. These receptors innervated filiform hairs of various lengths and directional selectivities. Previous studies have characterized the sensitivity of such cells to the direction of air currents and to the amplitude of sinusoidal stimuli. In the experiments reported here, the quantity and quality of information encoded in the receptors' elicited responses about the dynamics of more complex air current waveforms were characterized. 2. Based on a white analysis of receptor response properties, the median frequency of each receptor's frequency tuning curve was found to be strongly correlated with the length of its associated mechanosensory hair. The receptors connected to hairs > 900 microns encoded frequencies below approximately 150 Hz very accurately and the receptors connected to shorter hairs encoded progressively higher bands of frequencies. These results were interpreted within the constraints imposed by the biomechanics of the air current-to-cercus boundary. 3. The encoding accuracy was expressed in the information theoretic units of bits/second, which characterizes the information transmission rate of a receptor. The information rates of the neuronal spike trains ranged from 75 to 220 bits/s. The information transmission rate was not correlated with the length of the mechanosensory hair. The average amount of information transmitted per action potential was negatively correlated with receptor hair length and ranged between 0.6 and 3.1 bits/spike. Decoding of the receptor responses was restricted to linear transformations of the spike trains. 4. The stimulus/response latencies of the different receptors ranged between 5 and 11 ms, and the integration time of the receptors ranged between 8 and 30 ms. The latency of a receptor was only weakly correlated with the length of its associated hair, and a receptor's integration time was correlated with hair length. 5. The stimulus/response phase difference for receptor cells that innervated hairs longer than approximately 800 microns increased with frequency > 50 Hz. The phase responses for receptor cells connected to hairs < 800 microns did not vary for frequencies > 50 Hz.     

Requirement for the leukocyte-specific adapter protein SLP-76 for normal T cell development

The leukocyte-specific adapter molecule SLP-76 (Src homology 2 domain-containing leukocyte protein of 76 kilodaltons) is rapidly phosphorylated on tyrosine residues after receptor ligation in several hematopoietically derived cell types. Mice made deficient for SLP-76 expression contained no peripheral T cells as a result of an early block in thymopoiesis. Macrophage and natural killer cell compartments were intact in SLP-76-deficient mice, despite SLP-76 expression in these lineages in wild-type mice. Thus, the SLP-76 adapter protein is required for normal thymocyte development and plays a crucial role in translating signals mediated by pre-T cell receptors into distal biochemical events.     

Susceptibility to atrial fibrillation: a study in an ovine model of pacing-induced early heart failure

INTRODUCTION: The development of susceptibility to atrial fibrillation (AF) is a common consequence of many forms of cardiovascular disease, especially heart failure. In this study we used a sheep model of pacing-induced stable early heart failure to describe, quantify, and relate the level of susceptibility to AF to changes in structural and electrophysiologic parameters. METHODS AND RESULTS: Epicardial electrodes were implanted on the atria and right ventricles of nine sheep. The AF threshold, atrial vulnerability period, atrial effective refractory period (ERP), and interatrial conduction time were examined during control and over a 6-week period of ventricular pacing at 190 beats/min. Left atrial (LA) area and left ventricular (LV) fractional shortening were monitored using echocardiography. There were significant increases in LA susceptibility to AF (P < 0.0003), LA area (P < 0.0002), and LA ERP400 (P < 0.0002). Rate of increase in LA area was related positively to AF susceptibility (P = 0.02) and inversely to LA ERP400 (P = 0.002). LV fractional shortening decreased to approximately 50% of control value (P < 0.00001). No changes were observed in right atrial electrophysiology. CONCLUSION: In this study, susceptibility (the ability of an extrastimulus to induce AF) was rigorously measured within a predetermined format. Significant relationships were found to exist between susceptibility, certain of the observed changes in atrial electrophysiology and structure.     

Characteristics of multicellular spheroids formed by primary cultures of human thyroid tumor cells

Features of multicellular tumor spheroids (MCTS) differed depending on their types of cells. MCTS formed by 4000 human thyroid primary culture epithelial tumor cells displayed diameters between 0.31 and 0.33 mm within 2 days regardless of the stage of malignancy of the originating tumors. Their cellular composition reflected that of the originating tumor in regard to DNA content and the expression of cytokeratin, vimentin, as well as thyroglobulin. During the following 3 weeks, their sizes increased up to diameters of 0.42 mm when their cells had been derived from carcinomas, and MCTS originating from adenomas stopped growing within the next 2 days. After 8 days of incubation, proliferating cells were only found in carcinoma MCTS. The cells were randomly distributed over the total volume of the spheroids, which displayed irregular cell arrangements but not concentric cell layers and did not form necrotic centers.     

Asterlingulatosides C and D, cytotoxic triterpenoid saponins from Aster lingulatus

Over the last few decades, European courses in which 'classical' tropical medicine (i.e. parasitology, entomology, and clinical aspects of tropical diseases) is taught have largely become anachronisms. Most countries in the tropics have their own medical schools and few have much need of expatriate doctors. There do, however, appear to be other ways in which Europeans may still help improve health in the tropics. One is to control the quality of the expatriate nurses who are still in demand in the tropics (often as cheaper, generally less demanding substitutes for doctors). This may be achieved by only training the best, insisting they spend some time after graduation gaining maturity before they leave for the tropics, ensuring they realise that their clinical skills will probably be inferior to their local counterparts in the tropics, and encouraging them to continue studying once abroad. The second way Europeans may help is to change the bias of their courses from teaching to training. There seems little doubt that the intellectual personalities of the brightest young men and women in the tropics often develop far better when they spend a period in a foreign environment, especially when they are allowed to function within a team, with trainees and trainers from other countries. Some 'international' courses may offer such benefits, especially if closely tailored to the needs of the trainees and their home countries.