Uncertainty–guided learning with scaled prediction errors in the basal ganglia

To accurately predict rewards associated with states or actions, the variability of observations has to be taken into account. In particular, when the observations are noisy, the individual rewards should have less influence on tracking of average reward, and the estimate of the mean reward should be updated to a smaller extent after each observation. However, it is not known how the magnitude of the observation noise might be tracked and used to control prediction updates in the brain reward system. Here, we introduce a new model that uses simple, tractable learning rules that track the mean and standard deviation of reward, and leverages prediction errors scaled by uncertainty as the central feedback signal. We show that the new model has an advantage over conventional reinforcement learning models in a value tracking task, and approaches a theoretic limit of performance provided by the Kalman filter. Further, we propose a possible biological implementation of the model in the basal ganglia circuit. In the proposed network, dopaminergic neurons encode reward prediction errors scaled by standard deviation of rewards. We show that such scaling may arise if the striatal neurons learn the standard deviation of rewards and modulate the activity of dopaminergic neurons. The model is consistent with experimental findings concerning dopamine prediction error scaling relative to reward magnitude, and with many features of striatal plasticity. Our results span across the levels of implementation, algorithm, and computation, and might have important implications for understanding the dopaminergic prediction error signal and its relation to adaptive and effective learning.     

Prognostic role of c-met expression in breast cancer patients

Background

Hepatocyte growth factor plays an important role in tumor growth, metastasis and angiogenesis. C-met is HGF''s high affinity receptor.

Aim

The aim of the study was to assess the correlations between c-met expression and clinic-pathological factors in breast cancer tissues. Furthermore, the purpose of the study was to evaluate the prognostic value of the hepatocyte growth factor receptor (HGFR, c-met) expressions in homogenous group of breast cancer patients.

Materials and methods

Tumor samples were collected from 302 patients with breast carcinoma treated with primary surgery. We have assessed the percentage of tumor cells with c-met expression, the intensity of reaction and the ratio of these two factors—immunoreactivity according to the Remmele score.

Results

We have observed no correlations between HGFR immunoreactivities and clinical parameters (tumor size, grade, axillary lymph node status, age). In 5-year observation we have found prognostic value of assessing c-met immunoreactivity in primary tumor.

Conclusion

Our study has revealed prognostic value of c-met. Unlike in other authors’ studies, our patients’ group is very homogenous which might contribute to obtained results.     

Formation and function of the polar body contractile ring in Spisula

Initial studies suggested that spatial organization of the putative polar body contractile ring was determined by the peripheral aster in Spisula [Biol. Bull. 205 (2003) 192]. Here we report detailed supporting observations, including testing of aster and ring function with inhibitors. The metaphase peripheral aster was confirmed to spread cortically in an umbrella-like pattern, with microtubule-poor center. The aster disassembled during anaphase, leaving the spindle docked at the F-actin-poor center of a newly generated cortical F-actin ring that closely approximated the aster in location, measured diameter range, and pattern. Cytochalasin D and latrunculin-B permitted all events except ring and polar body formation. Nocodazole disassembly or taxol stabilization of the peripheral aster produced poorly defined rings or bulging anaphase asters within the ring center, respectively, inhibiting polar body formation. Polar body extrusion occurred at the ring center, the diameter of which diminished. Ring contractility-previously assumed-was verified using blebbistatin, a myosin-II ATPase inhibitor that permitted ring assembly but blocked polar body extrusion. The data support the hypothesis that peripheral aster spreading, perhaps dynein-driven, is causally related to polar body contractile ring formation, with anaphase entry and aster disassembly also required for polar body biogenesis. Previously reported astral spreading during embryonic micromere formation suggests that related mechanisms are involved in asymmetric somatic cytokinesis.     

Drosophila p24 homologues eclair and baiser are necessary for the activity of the maternally expressed Tkv receptor during early embryogenesis

p24 proteins are assumed to play an important role in the transport of secreted and transmembrane proteins into membranes. However, only few cargo proteins are known that partially, but in no case completely require p24 proteins for membrane transport. Here, we show that two p24 proteins are essential for dorsoventral patterning of Drosophila melanogaster embryo. Mutations in the genes, eclair (eca) and baiser (bai), encoding two p24 proteins reduce signalling by the TGF-beta homologue, Dpp, in early embryos. This effect is strictly maternal and specific to early embryogenesis, as Dpp signalling in other contexts is not notably affected. We provide genetic evidence that in the absence of eca or bai function in the oocyte, the maternally expressed type I TGF-beta receptor Tkv is not active. We propose that during early embryogenesis eca and bai are specifically required for the activity of the maternal Tkv, while the zygotic Tkv is not affected in the mutant embryos. Mutations in either eca or bai are sufficient for the depletion of Tkv activity and no enhancement of the phenotypes was observed in embryos derived from oocytes mutant for both genes. The dependence of maternal Tkv protein on the products of p24 genes may serve as an in vivo model for studying p24 proteins.     

Epstein-Barr virus (EBV) infection in B-cell non-Hodgkin's lymphomas in children: virus latency and its correlation with CD21 and CD23 molecules

Epstein Barr virus (EBV) infection of human B lymphocytes in vitro results in immortalisation of the cells and augmented membranous expression of numerous B-cell activation molecules, including CD23. Other studies demonstrated that only those B lymphocytes which carry the surface CD21 (EBV receptor) become transformation-competent. Inspired by the relatively unclear relations between expression of EBV and those of CD21 and CD23 in in vivo conditions we have decided to define correlations between tissue markers of EBV and of CD21 and CD23 molecules in B-cell non-Hodgkin's lymphomas (NHLs) in children. The studies were performed on an archival tissue material originating from children with B-cell NHLs (n=26) using immunocytochemical techniques, in situ hybridisation, and PCR. Our studies confirmed the latent phase of EBV infection in all of the EBV-positive patients. Viral proteins as well as viral RNAs (EBERs) was found both in the cytoplasm, in cell nuclei and in cell membranes of mainly the transformed lymphocytes B. Expression of the latent proteins (EBNA2 and LMP1) and that of EBERs in B-cell NHLs was significantly higher as compared to children with nonneoplastic lesions. The studies demonstrated reciprocally positive correlations between expressions of CD21 and CD23 in our children, but no correlation could be demonstrated between expression of EBV tissue markers and that of CD21 and/or CD23. Positive correlation was confirmed between expression of EBNA2 and LMP1 as well as between expression of the two proteins and EBERs in B-cell NHLs. Our studies have shown mainly latency III pattern of EBV. We have also demonstrated a novel form of EBV latency with no EBERs expression. The high detectability of EBV-positive cases both in the group of B-cell NHLs (77%), and in the group with non-neoplastic lesions (64%) suggested that only more pronounced tissue expression of EBV markers in B-cell NHLs as compared to the non-neoplastic material may point to a potential role of EBV in pathogenesis of lymphoma in this group of population in our country.     

Monitoring of Ubiquitin-proteasome Activity in Living Cells Using a Degron (dgn)-destabilized Green Fluorescent Protein (GFP)-based Reporter Protein

Proteasome is the main intracellular organelle involved in the proteolytic degradation of abnormal, misfolded, damaged or oxidized proteins ^{1, 2}. Maintenance of proteasome activity was implicated in many key cellular processes, like cell''s stress response ³, cell cycle regulation and cellular differentiation ⁴ or in immune system response ⁵. The dysfunction of the ubiquitin-proteasome system has been related to the development of tumors and neurodegenerative diseases ^{4, 6}. Additionally, a decrease in proteasome activity was found as a feature of cellular senescence and organismal aging ^{7, 8, 9, 10}. Here, we present a method to measure ubiquitin-proteasome activity in living cells using a GFP-dgn fusion protein. To be able to monitor ubiquitin-proteasome activity in living primary cells, complementary DNA constructs coding for a green fluorescent protein (GFP)–dgn fusion protein (GFP–dgn, unstable) and a variant carrying a frameshift mutation (GFP–dgnFS, stable ¹¹) are inserted in lentiviral expression vectors. We prefer this technique over traditional transfection techniques because it guarantees a very high transfection efficiency independent of the cell type or the age of the donor. The difference between fluorescence displayed by the GFP–dgnFS (stable) protein and the destabilized protein (GFP-dgn) in the absence or presence of proteasome inhibitor can be used to estimate ubiquitin-proteasome activity in each particular cell strain. These differences can be monitored by epifluorescence microscopy or can be measured by flow cytometry.     

Insight into the mechanism of dopamine D1-like receptor activation. Evidence for a molecular interplay between the third extracellular loop and the cytoplasmic tail

A chimeric D1A dopaminergic receptor harboring the cytoplasmic tail (CT) of the D1B subtype (D1A-CTB) has been used previously to show that CT imparts high dopamine (DA) affinity and constitutive activity to the D1B receptors. However, the D1A-CTB chimera, unlike the D1B subtype, exhibits a significantly lower DA potency for stimulating adenylyl cyclase and a drastically lower maximal binding capacity (Bmax). Here, using a functional complementation of chimeric D1-like receptors, we have identified the human D1B receptor regions regulating the intramolecular relationships that lead to an increased DA potency and contribute to Bmax. We demonstrate that the addition of variant residues of the third extracellular loop (EL3) of the human D1B receptor into D1A-CTB chimera leads to a constitutively active mutant receptor displaying an increased DA affinity, potency, and Bmax. These results strongly suggest that constitutively active D1-like receptors can adopt multiple active conformations, notably one that confers increased DA affinity with decreased DA potency and Bmax and another that imparts increased DA affinity with a strikingly increased DA potency and Bmax. Overall, we show that a novel molecular interplay between EL3 and CT regulates multiple active conformations of D1-like receptors and may have potential implications for other G protein-coupled receptor classes.     

Occurrence of 16s rRNA methylase ArmA producing Enterobacteriaceae in a general hospital in Warsaw, Poland

Resistance to gentamicin, amikacin and kanamycin was screened in 270 clinical isolates of Enterobacteriaceae originated from April 19 to May 19, 2010 in a regular hospital in Warsaw, Poland. Most of the isolated bacteria were considered pathogenic. Nineteen isolates (7%) were simultaneously resistant to two or three of the tested aminoglycosides. MICs of the three aminoglycosides ranged form 128 to 1024 mcg/ml for six isolates. These isolates were suspected to produce 16S rRNA methylase. Genes encoding for three methylases reported in Europe: ArmA, RmtB and RmtC were searched by PCR. The armA gene was detected in all of the six isolates. This group encompassed Enterobacter cloacae (n=4), Klebsiella pneumoniae (n=1) and Proteus mirabilis (n=1). Five isolates of this group carried the bla(CAX-M) gene for CTX-M type ESBL. The remaining isolate E. cloacae DM0340 was ESBL negative and lacked bla(CRX-M) that may suggest an altered genetic environment of the armA gene in this isolate. Our results showed that 2.2% of the tested isolates produced 16S rRNA methylase ArmA. This finding may argue for a high incidence of ArmA producing Enterobacteriaceae in Poland when compared to reports from other European countries.