NMDA Receptor-mediated Synaptic Plasticity in Developing Mammalian Visual Pathways

Precise connections in many mammalian nervous systems require a great deal of remodeling during development. In the visual system, many excess synapses are originally formed in the lateral geniculate nucleus and striate cortex. Only the correct set of axon terminals are retained during normal development, while imprecise ones withdraw. The mechanism by which only correct axons are retained requires neural activity, and may be regulated by specific receptors at synapses. The transmission of neural signals at these synapses is carried out in part by the glutamate-activated NMDA receptor. It is hypothesized that NMDA receptor activation plays a crucial role in enhancing only those connections in the immature system which will form a retinotopically correct map in the LGN and cortex. NMDA receptor activation requires depolarization of the neuron membrane. Possibly, only neurons transmitting information from nearby areas in the retina summate to produce NMDA receptor- mediated currents. The result is an influx of Ca++ ions that has been shown to cause trophic effects within the cell that could enhance the synaptic connection. Thus, NMDA receptors may act to detect coincident neural activity in immature animals, thereby allowing only visuo-topically related axon terminals to undergo enhancement of synaptic transmission and structure. As development proceeds, NMDA receptor function decreases, possibly reducing these intracellular effects. Blocking NMDA receptor activation experimentally does alter the normal set of connections in the visual system. Yet, is there a direct cause- and-effect relation between NMDA receptor activity and anatomical changes? Many cellular events probably result from NMDA-mediated currents. Intracellular changes in phosphorylation states and protein levels could eventually alter a synapse at the anatomical level. Study of the changing NMDA receptor subunit types making up the receptor within visual system structures could reveal, in part, the means by which plasticity is down-regulated. The experimental regulation of these subunits in vivo could reveal important information concerning their specific function if plasticity and development were to be altered as a result. A summary of previous studies, and proposals for further research concerning the role of the NMDA receptor and its various types in developing visual pathways are presented in this manuscript

The Roles of daf-6 and Cell-Cell Interactions in Sensory Organ Morphogenesis

The development of multicellular organs depends on the regulation of cell shape, position, and orientation. The genetic regulation of these morphogenetic processes is poorly understood. As a model for organ morphogenesis, I studied the development of the Caenorhabditis elegans amphid sensory organ. Sensory organs in diverse species are often composed of neuronal sensory endings accommodated in a lumen formed by ensheathing epithelia or glia. The generation of this structure may require cell-autonomous factors that control lumen formation, as well as cell non-autonomous factors that coordinate the morphogenesis of the lumen with the resident neuronal processes. Understanding these processes would provide insight into lumen formation, glia morphogenesis, and cell-cell interactions during development, especially neuronal regulation of glia morphogenesis. In this thesis, I identify and characterize genes required for lumen formation in the amphid sensory organ. First, the gene daf-6 is required cell autonomously during amphid lumen formation. daf-6 encodes a Patched-related protein that is a member of a previously uncharacterized sub-family of sterolsensing domain containing proteins. Interestingly, daf-6 is expressed and required in several tubular structures, such as the excretory system and vulva. Thus, a similar genetic pathway is required for the formation of different lumens. Secondly, I conducted a forward genetic screen and identified and characterized mutations that suppress the lumen formation defects in daf-6 mutants. Finally, by examining mutants defective in sensory neuron process formation, I showed that amphid lumen shape is determined by its resident sensory endings

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Initial Experience with Sildenafil, Bosentan, and Nitric Oxide for Pediatric Cardiomyopathy Patients with Elevated Pulmonary Vascular Resistance before and after Orthotopic Heart Transplantation

Background. Although pulmonary hypertension complicating dilated cardiomyopathy has been shown to be a significant risk factor for graft failure after heart transplantation, the upper limits of pulmonary vascular resistance (PVR) that would contraindicate pediatric heart transplantation are not known. Methods. A retrospective review of all pediatric orthotopic heart transplant (OHT) performed at our institution from 2002 to 2007 was performed. Seven patients with PVR > 6 Wood's units (WU) prior to transplant were compared pre- and postoperatively with 20 matched controls with PVR < 6 WU. All pulmonary vasodilator therapies used are described as well as outcomes during the first year posttransplant. Results. The mean PVR prior to transplantation in the 7 study cases was 11.0 ± 4.6 (range 6–22) WU, compared to mean PVR of 3.07 ± 0.9 WU (0.56–4.5) in the controls (P = .27 × 10−6). All patients with elevated PVR were treated pre-OHT with either Sildenafil or Bosentan. Post-OHT, case patients received a combination of sildenafil, iloprost, and inhaled nitric oxide. All 7 case patients survived one year post-OHT, and there was no statistical difference between cases and controls for hospital stay, rejection/readmissions, or graft right ventricular failure. Mean PVR in the cases at one and three months post-OHT was not significantly different between the two groups. Only one of the cases required prolonged treatment with iloprost after OHT. Conclusions. A PVR above 6 WU should not be an absolute contraindication to heart transplantation in children

Four-dimensional endocardial surface imaging with dynamic virtual reality rendering: a technical note.

Open heart surgery requires a proper understanding of the endocardial surface of the heart and vascular structures. While modern four-dimensional (4D) imaging enables excellent dynamic visualization of the blood pool, endocardial surface anatomy has not routinely been assessed. 4D image data were post-processed using commercially available virtual reality (VR) software. Using thresholding, the blood pool was segmented dynamically across the imaging volume. The segmented blood pool was further edited for correction of errors due to artifacts or inhomogeneous signal intensity. Then, a surface shell of an even thickness was added to the edited blood pool. When the cardiac valve leaflets and chordae were visualized, they were segmented separately using a different range of signal intensity for thresholding. Using an interactive cutting plane, the endocardial surface anatomy was reviewed from multiple perspectives by interactively applying a cutting plane, rotating and moving the model. In conclusions, dynamic three-dimensional (3D) endocardial surface imaging is feasible and provides realistic simulated views of the intraoperative scenes at open heart surgery. As VR is based on the use of all fingers of both hands, the efficiency and speed of postprocessing are markedly enhanced. Although it is limited, visualization of the cardiac valve leaflets and chordae is also possible

galign: A Tool for Rapid Genome Polymorphism Discovery

BACKGROUND: Highly parallel sequencing technologies have become important tools in the analysis of sequence polymorphisms on a genomic scale. However, the development of customized software to analyze data produced by these methods has lagged behind. METHODS/PRINCIPAL FINDINGS: Here I describe a tool, 'galign', designed to identify polymorphisms between sequence reads obtained using Illumina/Solexa technology and a reference genome. The 'galign' alignment tool does not use Smith-Waterman matrices for sequence comparisons. Instead, a simple algorithm comparing parsed sequence reads to parsed reference genome sequences is used. 'galign' output is geared towards immediate user application, displaying polymorphism locations, nucleotide changes, and relevant predicted amino-acid changes for ease of information processing. To do so, 'galign' requires several accessory files easily derived from an annotated reference genome. Direct sequencing as well as in silico studies demonstrate that 'galign' provides lesion predictions comparable in accuracy to available prediction programs, accompanied by greater processing speed and more user-friendly output. We demonstrate the use of 'galign' to identify mutations leading to phenotypic consequences in C. elegans. CONCLUSION/SIGNIFICANCE: Our studies suggest that 'galign' is a useful tool for polymorphism discovery, and is of immediate utility for sequence mining in C. elegans

The Caenorhabditis elegans vulva: A post-embryonic gene regulatory network controlling organogenesis

The Caenorhabditis elegans vulva is an elegant model for dissecting a gene regulatory network (GRN) that directs postembryonic organogenesis. The mature vulva comprises seven cell types (vulA, vulB1, vulB2, vulC, vulD, vulE, and vulF), each with its own unique pattern of spatial and temporal gene expression. The mechanisms that specify these cell types in a precise spatial pattern are not well understood. Using reverse genetic screens, we identified novel components of the vulval GRN, including nhr-113 in vulA. Several transcription factors (lin-11, lin-29, cog-1, egl-38, and nhr-67) interact with each other and act in concert to regulate target gene expression in the diverse vulval cell types. For example, egl-38 (Pax2/5/8) stabilizes the vulF fate by positively regulating vulF characteristics and by inhibiting characteristics associated with the neighboring vulE cells. nhr-67 and egl-38 regulate cog-1, helping restrict its expression to vulE. Computational approaches have been successfully used to identify functional cis-regulatory motifs in the zmp-1 (zinc metalloproteinase) promoter. These results provide an overview of the regulatory network architecture for each vulval cell type

Challenges of open innovation: the paradox of firm investment in open-source software

Open innovation is a powerful framework encompassing the generation, capture, and employment of intellectual property at the firm level. We identify three fundamental challenges for firms in applying the concept of open innovation: finding creative ways to exploit internal innovation, incorporating external innovation into internal development, and motivating outsiders to supply an ongoing stream of external innovations. This latter challenge involves a paradox, why would firms spend money on R&D efforts if the results of these efforts are available to rival firms? To explore these challenges, we examine the activity of firms in opensource software to support their innovation strategies. Firms involved in open-source software often make investments that will be shared with real and potential rivals. We identify four strategies firms employ – pooled R&D/product development, spinouts, selling complements and attracting donated complements – and discuss how they address the three key challenges of open innovation. We conclude with suggestions for how similar strategies may apply in other industries and offer some possible avenues for future research on open innovation

IGDB-2, an Ig/FNIII protein, binds the ion channel LGC-34 and controls sensory compartment morphogenesis in C. elegans

Sensory organ glia surround neuronal receptive endings (NREs), forming a specialized compartment important for neuronal activity, and reminiscent of glia-ensheathed synapses in the central nervous system. We previously showed that DAF-6, a Patched-related protein, is required in glia of the C. elegans amphid sensory organ to restrict sensory compartment size. LIT-1, a Nemo-like kinase, and SNX-1, a retromer component, antagonize DAF-6 and promote compartment expansion. To further explore the machinery underlying compartment size control, we sought genes whose inactivation restores normal compartment size to daf-6 mutants. We found that mutations in igdb-2, encoding a single-pass transmembrane protein containing Ig-like and fibronectin type III domains, suppress daf-6 mutant defects. IGDB-2 acts in glia, where it localizes to glial membranes surrounding NREs, and, together with LIT-1 and SNX-1, regulates compartment morphogenesis. Immunoprecipitation followed by mass spectrometry demonstrates that IGDB-2 binds to LGC-34, a predicted ligand-gated ion channel, and lgc-34 mutations inhibit igdb-2 suppression of daf-6. Our findings reveal a novel membrane protein complex and suggest possible mechanisms for how sensory compartment size is controlled