@article {53171, title = {The high efficacy of muscarinic M4 receptor in D1 medium spiny neurons reverses striatal hyperdopaminergia.}, journal = {Neuropharmacology}, volume = {146}, year = {2019}, month = {2019 Mar 01}, pages = {74-83}, abstract = {

The opposing action of dopamine and acetylcholine has long been known to play an important role in basal ganglia physiology. However, the quantitative analysis of dopamine and acetylcholine signal interaction has been difficult to perform in the native context because the striatum comprises mainly two subtypes of medium-sized spiny neurons (MSNs) on which these neuromodulators exert different actions. We used biosensor imaging in live brain slices of dorsomedial striatum to monitor changes in intracellular cAMP at the level of individual MSNs. We observed that the muscarinic agonist oxotremorine decreases cAMP selectively in the MSN subpopulation that also expresses D dopamine receptors, an action mediated by the M muscarinic receptor. This receptor has a high efficacy on cAMP signaling and can shut down the positive cAMP response induced by dopamine, at acetylcholine concentrations which are consistent with physiological levels. This supports our prediction based on theoretical modeling that acetylcholine could exert a tonic inhibition on striatal cAMP signaling, thus supporting the possibility that a pause in acetylcholine release is required for phasic dopamine to transduce a cAMP signal in D1 MSNs. In vivo experiments with acetylcholinesterase inhibitors donepezil and tacrine, as well as with the positive allosteric modulators of M receptor VU0152100 and VU0010010 show that this effect is sufficient to reverse the increased locomotor activity of DAT-knockout mice. This suggests that M receptors could be a novel therapeutic target to treat hyperactivity disorders.

}, issn = {1873-7064}, doi = {10.1016/j.neuropharm.2018.11.029}, author = {Nair, Anu G and Castro, Liliana R V and El Khoury, Marianne and Gorgievski, Victor and Giros, Bruno and Tzavara, Eleni T and Hellgren-Kotaleski, Jeanette and Vincent, Pierre} } @article {38424, title = {Switch-like PKA responses in the nucleus of striatal neurons.}, journal = {J Cell Sci}, year = {2018}, month = {2018 Jul 02}, abstract = {

Although it is known that Protein Kinase A (PKA) in the nucleus regulates gene expression, the specificities of nuclear PKA signaling remain poorly understood. Here, we combined computational modeling and live-cell imaging of PKA-dependent phosphorylation in mouse brain slices to investigate how transient dopamine signals are translated into nuclear PKA activity in cortical pyramidal neurons and striatal medium spiny neurons. We observed that the nuclear PKA signal in striatal neurons featured an ultrasensitive responsiveness, associated with fast, all or none responses, which is not consistent with the commonly accepted theory of a slow and passive diffusion of catalytic PKA in the nucleus. Our numerical model suggests that a positive feed-forward mechanism inhibiting nuclear phosphatase activity - possibly mediated by DARPP-32 - could be responsible for this non-linear pattern of nuclear PKA response, allowing for a better detection of the transient dopamine signals that are often associated with reward-mediated learning.

}, issn = {1477-9137}, doi = {10.1242/jcs.216556}, author = {Yapo, Cedric and Nair, Anu G and Hellgren Kotaleski, Jeanette and Vincent, Pierre and Castro, Liliana R V} } @article {21469, title = {Detection of phasic dopamine by D1 and D2 striatal medium spiny neurons.}, journal = {J Physiol}, year = {2017}, month = {2017 Aug 07}, abstract = {

The phasic release of dopamine in the striatum determines various aspects of reward and action selection, but the dynamics of dopamine effect on intracellular signalling remains poorly understood. We used genetically-encoded FRET biosensors in striatal brain slices to quantify the effect of transient dopamine on cAMP or PKA-dependent phosphorylation level, and computational modelling to further explore the dynamics of this signalling pathway. Medium-sized spiny neurons (MSNs), which express either D1 or D2 dopamine receptors, responded to dopamine by an increase or a decrease in cAMP, respectively. Transient dopamine showed similar sub-micromolar efficacies on cAMP in both D1 and D2 MSNs, thus challenging the commonly accepted notion that dopamine efficacy is much higher on D2 than on D1 receptors. However, in D2 MSNs, the large decrease in cAMP level triggered by transient dopamine did not translate in a decrease in PKA-dependent phosphorylation level, owing to the efficient inhibition of Protein Phosphatase 1 by DARPP-32. Simulations further suggested that D2 MSNs can also operate in a "tone-sensing" mode, allowing them to detect transient dips in basal dopamine. Overall, our results show that D2 MSNs may sense much more complex patterns of dopamine than previously thought. This article is protected by copyright. All rights reserved.

}, issn = {1469-7793}, doi = {10.1113/JP274475}, author = {Yapo, Cedric and Nair, Anu G and Clement, Lorna and Castro, Liliana R and Hellgren Kotaleski, Jeanette and Vincent, Pierre} } @article {807, title = {Rapid and enhanced remote homology detection by cascading hidden Markov model searches in sequence space.}, journal = {Bioinformatics}, volume = {32}, year = {2016}, month = {2015 Oct 10}, pages = {338-44}, chapter = {338}, abstract = {

MOTIVATION: In the post-genomic era, automatic annotation of protein sequences using computational homology-based methods is highly desirable. However, often protein sequences diverge to an extent where detection of homology and automatic annotation transfer is not straightforward. Sophisticated approaches to detect such distant relationships are needed. We propose a new approach to identify deep evolutionary relationships of proteins to overcome shortcomings of the available methods.

RESULTS: We have developed a method to identify remote homologues more effectively from any protein sequence database by using several cascading events with Hidden Markov Models (C-HMM). We have implemented clustering of hits and profile generation of hit clusters to effectively reduce the computational timings of the cascaded sequence searches. Our C-HMM approach could cover 94, 83 and 40\% coverage at family, superfamily and fold levels, respectively, when applied on diverse protein folds. We have compared C-HMM with various remote homology detection methods and discuss the trade-offs between coverage and false positives.

AVAILABILITY AND IMPLEMENTATION: A standalone package implemented in Java along with a detailed documentation can be downloaded from https://github.com/RSLabNCBS/C-HMMSupplementary information: Supplementary data are available at Bioinformatics online.

CONTACT: mini@ncbs.res.in.

}, issn = {1367-4811}, doi = {10.1093/bioinformatics/btv538}, author = {Kaushik, Swati and Nair, Anu G and Mutt, Eshita and Subramanian, Hari Prasanna and Sowdhamini, Ramanathan} } @article {7592, title = {Role of DARPP-32 and ARPP-21 in the Emergence of Temporal Constraints on Striatal Calcium and Dopamine Integration.}, journal = {PLoS Comput Biol}, volume = {12}, year = {2016}, month = {2016 Sep}, pages = {e1005080}, abstract = {

In reward learning, the integration of NMDA-dependent calcium and dopamine by striatal projection neurons leads to potentiation of corticostriatal synapses through CaMKII/PP1 signaling. In order to elicit the CaMKII/PP1-dependent response, the calcium and dopamine inputs should arrive in temporal proximity and must follow a specific (dopamine after calcium) order. However, little is known about the cellular mechanism which enforces these temporal constraints on the signal integration. In this computational study, we propose that these temporal requirements emerge as a result of the coordinated signaling via two striatal phosphoproteins, DARPP-32 and ARPP-21. Specifically, DARPP-32-mediated signaling could implement an input-interval dependent gating function, via transient PP1 inhibition, thus enforcing the requirement for temporal proximity. Furthermore, ARPP-21 signaling could impose the additional input-order requirement of calcium and dopamine, due to its Ca2+/calmodulin sequestering property when dopamine arrives first. This highlights the possible role of phosphoproteins in the temporal aspects of striatal signal transduction.

}, issn = {1553-7358}, doi = {10.1371/journal.pcbi.1005080}, author = {Nair, Anu G and Bhalla, Upinder S and Hellgren Kotaleski, Jeanette} }