Role of the Rap1 GTPase in astrocyte growth regulation

Tuberous sclerosis complex (TSC) is an autosomal dominant syndrome in which affected individuals develop nervous system abnormalities that might reflect astrocyte dysfunction. The TSC2 gene product, tuberin, encodes a GTPase-activating protein (GAP) domain, which regulates the activity of Rap1 in vitro. To determine whether dysregulated Rap1, resulting from TSC2 inactivation, leads to increased astrocyte proliferation in vivo, we generated transgenic mice expressing activated Rap1(G12V) specifically in astrocytes. We observed no statistically significant difference in the number of astrocytes between wild-type and GFAP-Rap1(G12V) littermates in vivo; however, during log-phase growth, we observed a 25% increase in GFAP-Rap1(G12V) astrocyte doubling times compared to wild-type controls. This decreased proliferation was associated with delayed MAP kinase, but not AKT, activation. Lastly, to determine whether constitutive Rap1 activation could reverse the increased astrocyte proliferation observed in transgenic mice expressing oncogenic Ras(G12V), we generated transgenic mice expressing both Ras(G12V) and Rap1(G12V) in astrocytes. These double transgenic mice showed a striking reversion of the Ras(G12V) astrocyte growth phenotype. Collectively, these results argue that the tumor suppressor properties of tuberin are unlikely to be related to Rap1 inactivation and that Rap1 inhibits mitogenic Ras pathway signaling in astrocytes.     

A model for emergent complex order in small neural networks

A new neural network model is introduced in this paper. The aim of the proposed Sierpinski neural networks is to provide a simple and biologically plausible neural network architecture that produces emergent complex spatio-temporal patterns through the activity of the output neurons of the network and is able to perform computational tasks. Such networks may play an important role in the analysis and understanding of complex dynamic activity observed at various levels of biological neural systems. The proposed Sierpinski neural networks are described in detail and their functioning is analyzed. We discuss about emerging neural activity patterns and their interpretations, neuro-computation with such emerging activity patterns, and also possible implications for computational neuroscience.     

A paradox resolved: Sulfide acquisition by roots of seep tubeworms sustains net chemoautotrophy

Vestimentiferan tubeworms, symbiotic with sulfur-oxidizing chemoautotrophic bacteria, dominate many cold-seep sites in the Gulf of Mexico. The most abundant vestimentiferan species at these sites, Lamellibrachia cf. luymesi, grows quite slowly to lengths exceeding 2 meters and lives in excess of 170-250 years. L. cf. luymesi can grow a posterior extension of its tube and tissue, termed a "root," down into sulfidic sediments below its point of original attachment. This extension can be longer than the anterior portion of the animal. Here we show, using methods optimized for detection of hydrogen sulfide down to 0.1 microM in seawater, that hydrogen sulfide was never detected around the plumes of large cold-seep vestimentiferans and rarely detectable only around the bases of mature aggregations. Respiration experiments, which exposed the root portions of L. cf. luymesi to sulfide concentrations between 51-561 microM, demonstrate that L. cf. luymesi use their roots as a respiratory surface to acquire sulfide at an average rate of 4.1 micromol x g(-1) x h(-1). Net dissolved inorganic carbon uptake across the plume of the tubeworms was shown to occur in response to exposure of the posterior (root) portion of the worms to sulfide, demonstrating that sulfide acquisition by roots of the seep vestimentiferan L. cf. luymesi can be sufficient to fuel net autotrophic total dissolved inorganic carbon uptake.     

The benefit of treatment intensification is age and histology-dependent in patients with locally advanced non-small cell lung cancer (NSCLC): a quality-adjusted survival analysis of radiation therapy oncology group (RTOG) chemoradiation studies

Purpose: Currently, chemoradiation treatment strategies in locally advanced NSCLC are essentially the same irrespective of tumor histology or patient age. The purpose of this study is to analyze the impact of age, histology, Karnofsky performance status (KPS), and specific toxicities on the median survival time (MST) and quality-adjusted survival (QTime) for each treatment strategy.

Methods and Materials: Nine hundred seventy-nine patients with Stage II–IIIB inoperable NSCLC were enrolled on 6 prospective Phase II and III studies from 1983 to 1995. Treatment regimens ranged from standard RT (SRT) to 60 Gy, hyperfractionated RT (HRT) to 69.6 Gy, induction chemotherapy (ICT) of cisplatin (CIS) and vinblastine (VBL) followed by SRT, ICT + concurrent CT (CCT) + SRT, and CCT + HRT; CCT consisted of etoposide or VBL + CIS. Toxicities assessed were skin, mucous membrane, lung, esophagus, neurologic, hematologic, and upper GI. QTime was calculated by weighting the time spent with a specific toxicity, as well as local or distant tumor progression. Each toxicity was weighted with increasing severity as the toxicity increased in grade.

Results: As expected, patients with the worst KPS (50–70) had the lowest MST (7.8 months) and QTime (6.7 months). Patients < 70 years had improved survival with more aggressive therapy (i.e., ICT + SRT or CCT + HRT), while patients > 70 years achieved the best QTime with standard RT (SRT) alone. In patients with squamous cell carcinoma, those treated with ICT + CCT + SRT had dramatically improved MST (25.7 months) and QTime (21.8 months) compared to the other treatment regimens (11.7–12.8 and 10.7–12 months, respectively). Patients with adenocarcinoma, however, generally manifested incrementally better MST and QTime as the therapies intensified. Within the concurrent chemoradiation arms, the upper GI and lung toxicities had the greatest impact on QTime.

Conclusion: This quality-adjusted survival analysis suggests that there is a critical relationship between the type of histology and its optimal treatment, age and the ability to tolerate intensive therapy, and the need to reduce lung and upper GI toxicities.     

Immune phenotype in children with therapy-nave remitted and relapsed Crohn’s disease

AIM: To characterize the prevalence of subpopulations of CD4+ cells along with that of major inhibitor or stimulator cell types in therapy-nave childhood Crohn's disease (CD) and to test whether abnormalities of immune phenotype are normalized with the improvement of clinical signs and symptoms of disease. METHODS: We enrolled 26 pediatric patients with CD. 14 therapy-nave CD children; of those, 10 children remitted on conventional therapy and formed the remission group. We also tested another group of 12...