Trends in Neurosciences
Volume 32, Issue 10, October 2009, Pages 538-547
Journal home page for Trends in Neurosciences

Review
Looking BAC at striatal signaling: cell-specific analysis in new transgenic mice

https://doi.org/10.1016/j.tins.2009.06.005Get rights and content

Understanding how molecular signaling pathways participate in behavioral responses requires determining precisely in which neuronal populations they are activated. The recent development of bacterial artificial chromosome (BAC) transgenic mice expressing a variety of reporters, epitope tagged-proteins or Cre recombinase driven by specific promoters, is a significant step forward in this direction. These mice help overcome the limitations of traditional approaches that examine an average of signaling events occurring in mixed populations of cells. Here, we review how recent studies using such tools have revisited the regulation of striatal signaling pathways, demonstrating the striking segregation between neurons expressing dopamine D1 and D2 receptors and significantly extending our overall knowledge of striatal neurons. Thus, BAC transgenic mice are changing the way to conceive experiments and provide an opportunity to fill the gaps between molecular and systems neurosciences.

Introduction

Since the pioneering work of Santiago Ramón y Cajal, neuroscientists have been fascinated by the beauty and variety of brain neurons. This diversity is daunting because it implies that to fully understand the brain function, it is necessary to decipher the molecular events that take place in each type of neuron. The task is particularly difficult not only because there are hundreds of distinct neuronal populations but also because these populations are not always easy to distinguish. A combination of anatomical, physiological and molecular features is often necessary for classifying neurons, as recently exemplified in the case of cortical interneurons [1]. The pattern of gene expression, arguably the ultimate consequence of cell differentiation, is a great help, when studied by single cell RT-PCR [2]. Its applicability, however, is limited to studies in which one or a few neurons are recorded using whole cell patch-clamp.

Until recently, the expression of reporter genes driven by specific promoters was not sufficiently precise to reliably identify cell populations, because transgenes are subject to positional effects, resulting in variable expression patterns that vary depending on their insertion site. This limitation was overcome to a large extent by the use of transgenic mice carrying bacterila artificial chromosomes (Box 1), pioneered by N. Heintz and his collegues at the Rockefeller university and Gensat. BACs contain several hundreds of thousands of base pairs of regulatory sequences, which recapitulate the regulation of endogenous genes much better than shorter transgenes [3]. Furthermore, they can be easily manipulated by homologous recombination in bacteria [3]. BAC-driven expression of tagged proteins allows an easy and reproducible identification of specific neuronal populations ([4], Figure 1). The usefulness of these approaches is illustrated by recent work in the striatum, a region of the brain that receives abundant dopamine innervation and is involved in several pathological conditions including Parkinson's disease and Huntington's disease, drug addiction, Tourette syndrome and obsessive–compulsive disorder. We review anatomical evidence supporting the validity of BAC transgenic mice to distinguish neurons expressing D1 and D2 dopamine receptors (D1R and D2R) (Figure 2). The main focus of this review is on signaling mechanisms and we show how the distinction of these neurons allowed for untangling the regulation of the extracellular signal-regulated kinase (ERK) pathway, dopamine- and cAMP-regulated phosphoprotein of Mr 32,000 (DARPP-32) and gene expression. We also summarize the main in vivo methods developed so far based on BAC transgenesis and describe the results brought about by some of these approaches concerning the morphology and physiology of principal striatal neurons.

Section snippets

A simple view of the striatum output pathways

The dorsal striatum and its ventral extension, the nucleus accumbens (NAc), constitute the primary input structure of the basal ganglia, an ensemble of interconnected subcortical nuclei involved in the selection and execution of action through interactions with sensorimotor and associative brain areas 5, 6, 7, 8, 9. The striatum is unique in its complete lack of intrinsic glutamatergic neurons. Instead, most of the cells (∼95% of striatal neurons in rodents) are GABAergic medium-sized spiny

Selective activation of the ERK pathway in striatonigral MSNs by psychostimulants and l-DOPA

The striatum is perhaps the most extensively studied region of the brain in terms of pharmacology and signaling pathways, because of its involvement in many diseases and because of its size, which makes it accessible to biochemical studies. However, most studies used methods examining mixed populations of cells, whereas the use of BAC transgenic mice allows the identification of the actual cell populations in which the signaling events take place. This is well illustrated by the case of the ERK

Selective activation of signaling pathways by D2R antagonists in striatopallidal neurons

A striking observation in naive mice treated with psychostimulants or in 6-OHDA-lesioned mice receiving l-DOPA is that the ERK pathway is not activated in D2R-expressing neurons, although the degree of colocalization with D1R (Table 1) suggests that it should be the case in a fraction of these neurons. One possible explanation is that D2Rs exert a strong tonic inhibition on the activation of the ERK pathway. Indeed, the pharmacological blockade of D2R by haloperidol, raclopride or eticlopride

Untangling the complexity of DARPP-32 phosphorylation in vivo

DARPP-32 is a dual-function protein that plays a key role in striatal signaling [42]. When phosphorylated on Thr34 by protein kinase A (PKA), DARPP-32 becomes an inhibitor of serine/threonine protein phosphatase-1 (PP-1), thereby enhancing phosphorylation of proteins targeted by PP-1. In contrast, when DARPP-32 is phosphorylated on Thr75 by cyclin-dependent kinase 5 (Cdk5), it is converted into an inhibitor of PKA. However, although the regulation of the phosphorylation state of these two sites

Differential morphological plasticity of striatonigral and striatopallidal MSNs

The dendritic spines of MSNs integrate information from glutamate afferents from cortical, limbic and thalamic areas and dopamine fibers from the SNc or the VTA [45]. The number of dendritic spines correlates with the number of excitatory synapses, whereas the size of the spine heads reflects synaptic strength 46, 47, 48. Therefore, a change in spine number and spine head diameter is thought to indicate functionally important neuronal plasticity. Long-term exposure to cocaine or amphetamine

Cell population-specific gene profiling in the striatum

Microarray analysis is a powerful method to understand the changes in gene expression underlying normal and dysfunctional biological processes. Many studies have started to characterize the gene expression profiles in various brain regions in response to a variety of therapeutic agents or drugs of abuse. However, the exploitation of these results is limited by the cellular heterogeneity of brain structures. As outlined below, new and exciting strategies taking advantage of BAC transgenic mice

Perspectives

The BAC transgenic mice expressing fluorescent proteins provide an invaluable resource to easily identify specific neuronal types in vivo and in fixed tissues, and thus study specific cellular functions including signaling pathways and electrophysiological properties in identified neuronal populations. These mouse models revealed a profound, functional dichotomy of striatal neurons in physiological and pathological conditions, far beyond expectations. This dichotomy strongly suggests that the

Acknowledgements

This work was supported by Inserm and grants from Fondation pour la Recherche Médicale (FRM) to DH and JAG, from Agence Nationale de la Recherche to JAG (ANR-05-NEUR-020-03, ANR-BLAN08-1_346422), from Neuropôle de Recherche Francilien (NeRF), Région Ile de France, from Swedish Research Grants 20175, 13482 and 14862, the Wenner-Gren Foundations, the Swedish Brain Foundation and the Parkinson Foundation in Sweden (GF).

References (80)

  • J.E. Westin

    Spatiotemporal pattern of striatal ERK1/2 phosphorylation in a rat model of L-DOPA-induced dyskinesia and the role of dopamine D1 receptors

    Biol. Psychiatry

    (2007)
  • S. Schuster

    Antagonizing L-type Ca2+ channel reduces development of abnormal involuntary movement in the rat model of l-3,4-dihydroxyphenylalanine-induced dyskinesia

    Biol. Psychiatry

    (2009)
  • G.S. Robertson

    D1 and D2 dopamine receptors differentially regulate c-fos expression in striatonigral and striatopallidal neurons

    Neuroscience

    (1992)
  • J.M. Tepper

    Basal ganglia macrocircuits

    Prog. Brain Res.

    (2007)
  • M. Park

    Plasticity-induced growth of dendritic spines by exocytic trafficking from recycling endosomes

    Neuron

    (2006)
  • S.D. Norrholm

    Cocaine-induced proliferation of dendritic spines in nucleus accumbens is dependent on the activity of cyclin-dependent kinase-5

    Neuroscience

    (2003)
  • C.A. Ingham

    Spine density on neostriatal neurones changes with 6-hydroxydopamine lesions and with age

    Brain Res.

    (1989)
  • J.P. Doyle

    Application of a translational profiling approach for the comparative analysis of CNS cell types

    Cell

    (2008)
  • M. Heiman

    A translational profiling approach for the molecular characterization of CNS cell types

    Cell

    (2008)
  • Z. Wang

    Dopaminergic control of corticostriatal long-term synaptic depression in medium spiny neurons is mediated by cholinergic interneurons

    Neuron

    (2006)
  • G.A. Ascoli

    Petilla terminology: nomenclature of features of GABAergic interneurons of the cerebral cortex

    Nat. Rev. Neurosci.

    (2008)
  • X.W. Yang

    Homologous recombination based modification in Escherichia coli and germline transmission in transgenic mice of a bacterial artificial chromosome

    Nat. Biotechnol.

    (1997)
  • S. Gong

    A gene expression atlas of the central nervous system based on bacterial artificial chromosomes

    Nature

    (2003)
  • J.P. Bolam

    Synaptic organisation of the basal ganglia

    J. Anat.

    (2000)
  • A.M. Graybiel

    The basal ganglia and adaptive motor control

    Science

    (1994)
  • G.E. Alexander

    Parallel organization of functionally segregated circuits linking basal ganglia and cortex

    Annu. Rev. Neurosci.

    (1986)
  • O. Aizman

    Anatomical and physiological evidence for D1 and D2 dopamine receptor colocalization in neostriatal neurons

    Nat. Neurosci.

    (2000)
  • C. Le Moine et al.

    D1 and D2 dopamine receptor gene expression in the rat striatum: sensitive cRNA probes demonstrate prominent segregation of D1 and D2 mRNAs in distinct neuronal populations of the dorsal and ventral striatum

    J. Comp. Neurol.

    (1995)
  • D.J. Surmeier

    Coordinated expression of dopamine receptors in neostriatal medium spiny neurons

    J. Neurosci.

    (1996)
  • J. Bertran-Gonzalez

    Opposing patterns of signaling activation in dopamine D1 and D2 receptor-expressing striatal neurons in response to cocaine and haloperidol

    J. Neurosci.

    (2008)
  • M. Matamales

    Striatal medium-sized spiny neurons: identification by nuclear staining and study of neuronal subpopulations in BAC transgenic mice

    PLoS ONE

    (2009)
  • J.A. Shuen

    Drd1a-tdTomato BAC transgenic mice for simultaneous visualization of medium spiny neurons in the direct and indirect pathways of the basal ganglia

    J. Neurosci.

    (2008)
  • T.S. Gertler

    Dichotomous anatomical properties of adult striatal medium spiny neurons

    J. Neurosci.

    (2008)
  • M.K. Lobo

    FACS-array profiling of striatal projection neuron subtypes in juvenile and adult mouse brains

    Nat. Neurosci.

    (2006)
  • P.F. Durieux

    D(2)R striatopallidal neurons inhibit both locomotor and drug reward processes

    Nat. Neurosci.

    (2009)
  • E. Valjent

    Addictive and non-addictive drugs induce distinct and specific patterns of ERK activation in mouse brain

    Eur. J. Neurosci.

    (2004)
  • E. Valjent

    Involvement of the extracellular signal-regulated kinase cascade for cocaine-rewarding properties

    J. Neurosci.

    (2000)
  • L. Zhang

    Cocaine-induced intracellular signaling and gene expression are oppositely regulated by the dopamine D1 and D3 receptors

    J. Neurosci.

    (2004)
  • E. Valjent

    Regulation of a protein phosphatase cascade allows convergent dopamine and glutamate signals to activate ERK in the striatum

    Proc. Natl. Acad. Sci. U. S. A.

    (2005)
  • C.R. Gerfen

    Differences between dorsal and ventral striatum in Drd1a dopamine receptor coupling of dopamine- and cAMP-regulated phosphoprotein-32 to activation of extracellular signal-regulated kinase

    J. Neurosci.

    (2008)
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