Characterization of rat ARPP-21 mRNA: sequence analysis, tissue distribution, and regulation

Regulator of calmodulin signaling knockout mice display anxiety-like behavior and motivational deficits

Regulator of calmodulin (CaM) signaling (RCS), when phosphorylated by protein kinase A (PKA) on Ser55, binds to CaM and inhibits CaM-dependent signaling. RCS expression is high in the dorsal striatum, nucleus accumbens and amygdala, suggesting that the protein is involved in limbic-striatal function. To test this hypothesis, we examined RCS knockout (KO) mice in behavioral models dependent on these brain areas. Mice were tested for food-reinforced instrumental conditioning and responding under a progressive ratio (PR) schedule of reinforcement and in models of anxiety (elevated plus maze and open field). While RCS KO mice showed normal acquisition of a food-motivated instrumental response, they exhibited a lower breakpoint value when tested on responding under a PR schedule of reinforcement. RCS KO mice also displayed decreased exploration in both the open arms of an elevated plus maze and in the center region of an open field, suggesting an enhanced anxiety response. Biochemical studies revealed a reduction in the levels of dopamine and cAMP-regulated phosphoprotein (DARPP-32) in the striatum of RCS KO mice. DARPP-32 is important in reward-mediated behavior, suggestive of a possible role for DARPP-32 in mediating some of the effects of RCS. Together these results implicate a novel PKA-regulated phosphoprotein, RCS, in the etiology of motivational deficits and anxiety.

Quantitative assessment of transcriptome differences between brain territories

Transcriptome analysis of mammalian brain structures is a potentially powerful approach in addressing the diversity of cerebral functions. Here, we used a microassay for serial analysis of gene expression (SAGE) to generate quantitative mRNA expression profiles of normal adult mouse striatum, nucleus accumbens, and somatosensory cortex. Comparison of these profiles revealed 135 transcripts heterogeneously distributed in the brain. Among them, a majority (78), although matching a registered sequence, are novel regional markers. To improve the anatomical resolution of our analysis, we performed in situ hybridization and observed unique expression patterns in discrete brain regions for a number of candidates. We assessed the distribution of the new markers in peripheral tissues using quantitative RT-PCR, Northern hybridization, and published SAGE data. In most cases, expression was higher in the brain than in peripheral tissues. Because the markers were selected according to their expression level, without reference to prior knowledge, our studies provide an unbiased, comprehensive molecular signature for various mammalian brain structures that can be used to investigate their plasticity under a variety of circumstances.

TARPP, a novel protein that accompanies TCR gene rearrangement and thymocyte education

Studies on thymic T cell development have usually concentrated on cell surface molecules. However, intracellular proteins expressed only in thymocytes have never been described. Here we report the discovery of a novel thymocyte-specific protein, named TARPP, which represents a high molecular mass ( approximately 100 kDa) variant of the previously identified protein ARPP-21 ( approximately 21 kDa). TARPP is a cytosolic protein that is expressed at high levels in immature thymocytes. It appears concomitant with the commitment to T cell lineage, and its expression is switched off as a consequence of TCR engagement during positive selection. Such an expression pattern, correlating with the rearrangement of the TCR genes and thymocyte education, suggests a role for TARPP during this important phase of thymocyte development.

Drugs of abuse modulate the phosphorylation of ARPP-21, a cyclic AMP-regulated phosphoprotein enriched in the basal ganglia

ARPP-21 is a cyclic AMP-regulated phosphoprotein of M(r) 21 kDa that is enriched in the cell bodies and terminals of medium-sized spiny neurons in the basal ganglia. Using a new phosphorylation state-specific antibody selective for the detection of ARPP-21 phosphorylated on Ser(55), we have demonstrated that activation of dopamine D1 receptors increased the level of ARPP-21 phosphorylation in mouse striatal slices. Conversely, activation of D2 receptors caused a large decrease in ARPP-21 phosphorylation. Treatment of mice with either methamphetamine or cocaine resulted in increased ARPP-21 phosphorylation in vivo. Studies using specific inhibitors of protein phosphatases and experiments in mice bearing a targeted deletion of the gene for DARPP-32, a dopamine-activated inhibitor of protein phosphatase-1, indicated that protein phosphatase-2A is primarily responsible for dephosphorylation of ARPP-21 in mouse striatum. These results demonstrate that phosphorylation and dephosphorylation of ARPP-21 are tightly regulated in the striatum. We speculate that ARPP-21 might mediate some of the physiologic effects of dopamine and certain drugs of abuse in the basal ganglia.

Expression of the striatal DARPP-32/ARPP-21 phenotype in GABAergic neurons requires neurotrophins in vivo and in vitro

The medium spiny neuron (MSN) is the major output neuron of the caudate nucleus and uses GABA as its primary neurotransmitter. A majority of MSNs coexpress DARPP-32 and ARPP-21, two dopamine and cyclic AMP-regulated phosphoproteins, and most of the matrix neurons express calbindin. DARPP-32 is the most commonly used MSN marker, but previous attempts to express this gene in vitro have failed. In this study we found that DARPP-32 is expressed in <12% of E13- or E17-derived striatal neurons when they are grown in defined media at high or low density in serum, dopamine, or Neurobasal/N2 (Life Technologies), and ARPP-21 is expressed in <1%. The percentage increases to 25% for DARPP-32 and 10% for ARPP-21 when the same cells are grown in Neurobasal/B27 (Life Technologies) for 7 d. After growth in Neurobasal/B27 plus brain-derived neurotrophic factor (BDNF) for 7 d, E13-derived MSNs are 53.7% DARPP-32-positive and 29. 0% ARPP-21-positive; E17-derived MSNs are 66.8% DARPP-32-positive and 51.5% ARPP-21-positive. The percentage of calbindin-positive neurons also is increased under these conditions. Finally, ARPP-21 expression is reduced in mice with a targeted deletion of the BDNF gene. We conclude that BDNF is required for the maturation of a large subset of patch and matrix MSNs in vivo and in vitro. In addition, we introduce a culture system in which highly differentiated MSNs may be generated, maintained, and studied.

Basal ganglia precursors found in aggregates following embryonic transplantation adopt a striatal phenotype in heterotopic locations

Transplantation of immature CNS-derived cells into the developing brain is a powerful approach to investigate the factors that regulate neuronal position and phenotype. CNS progenitor cells dissociated from the embryonic striatum and implanted into the brain of embryos of the same species generate cells that reaggregate to form easily recognizable structures that we previously called clusters and cells that disperse and integrate as single cells into the host brain. We sought to determine if the neurons in the clusters differentiate according to their final location or acquire a striatal phenotype in heterotopic positions. We transplanted dissociated cells from the E14 rat medial and lateral ganglionic eminences, either combined or in isolation, into the E16 embryonic rat brain. At all time points, we found clusters of BrdU- and DiI-labelled donor cells located in the forebrain and hindbrain, without any apparent preference for striatum. Immunocytochemical analyses revealed that cells in the clusters expressed DARPP-32 and ARPP-21, two antigens typically co-expressed in striatal medium-sized spiny neurons. In agreement with observations previously noted by several groups, isolated cells integrated into heterologous host areas do not express basal ganglia phenotypes. These data imply that immature striatal neuronal progenitors exert a community effect on each other that is permissive and/or instructive for development of a striatal phenotype in heterotopic locations.

Hippocampal plasticity involves extensive gene induction and multiple cellular mechanisms

Long-term plasticity of the central nervous system (CNS) involves induction of a set of genes whose identity is incompletely characterized. To identify candidate plasticity-related genes (CPGs), we conducted an exhaustive screen for genes that undergo induction or downregulation in the hippocampus dentate gyrus (DG) following animal treatment with the potent glutamate analog, kainate. The screen yielded 362 upregulated CPGs and 41 downregulated transcripts (dCPGs). Of these, 66 CPGs and 5 dCPGs are known genes that encode for a variety of signal transduction proteins, transcription factors, and structural proteins. Seven novel CPGs predict the following putative functions: cpg2--a dystrophin-like cytoskeletal protein; cpg4--a heat-shock protein: cpg16--a protein kinase; cpg20--a transcription factor; cpg21--a dual-specificity MAP-kinase phosphatase; and cpg30 and cpg38--two new seven-transmembrane domain receptors. Experiments performed in vitro and with cultured hippocampal cells confirmed the ability of the cpg-21 product to inactivate the MAP-kinase. To test relevance to neural plasticity, 66 CPGs were tested for induction by stimuli producing long-term potentiation (LTP). Approximately one-fourth of the genes examined were upregulated by LTP. These results indicate that an extensive genetic response is induced in mammalian brain after glutamate receptor activation, and imply that a significant proportion of this activity is coinduced by LTP. Based on the identified CPGs, it is conceivable that multiple cellular mechanisms underlie long-term plasticity of the nervous system.

Unilateral 6-hydroxydopamine lesions of meso-striatal dopamine neurons and their physiological sequelae

One of the primary approaches in experimental brain research is to investigate the effects of specific destruction of its parts. Here, several neurotoxins are available which can be used to eliminate neurons of a certain neurochemical type or family. With respect to the study of dopamine neurons in the brain, especially within the basal ganglia, the neurotoxin 6-hydroxydopamine (6-OHDA) provides an important tool. The most common version of lesion induced with this toxin is the unilateral lesion placed in the area of mesencephalic dopamine somata or their ascending fibers, which leads to a lateralized loss of striatal dopamine. This approach has contributed to neuroscientific knowledge at the basic and clinical levels, since it has been used to clarify the neuroanatomy, neurochemistry, and electrophysiology of mesencephalic dopamine neurons and their relationships with the basal ganglia. Furthermore, unilateral 6-OHDA lesions have been used to investigate the role of these dopamine neurons with respect to behavior, and to examine the brain's capacity to recover from or compensate for specific neurochemical depletions. Finally, in clinically-oriented research, the lesion has been used to model aspects of Parkinson's disease, a human neurodegenerative disease which is neuronally characterized by a severe loss of the meso-striatal dopamine neurons. In the present review, which is the first of two, the lesion's effects on physiological parameters are being dealt with, including histological manifestations, effects on dopaminergic measures, other neurotransmitters (e.g. GABA, acetylcholine, glutamate), neuromodulators (e.g. neuropeptides, neurotrophins), electrophysiological activity, and measures of energy consumption. The findings are being discussed especially in relation to time after lesion and in relation to lesion severeness, that is, the differential role of total versus partial depletions of dopamine and the possible mechanisms of compensation. Finally, the advantages and possible drawbacks of such a lateralized lesion model are discussed.

ARPP-21: murine gene structure and promoter identification of a neuronal phosphoprotein enriched in the limbic striatum

ARPP-21 (cAMP-regulated phosphoprotein, Mr = 21,000 on sodium dodecyl sulfate polyacrylamide gel electrophoresis) is a phosphoprotein highly enriched in concentration in the neurons of the limbic striatum. It is likely a third messenger in the intracellular cascade of events following neuronal stimulation by first-messenger activators of the adenylate cyclase system, including dopamine via the D1 receptor. ARPP-21 expression is restricted to telencephalic post-mitotic, post-migrational neurons, and its precise pattern of temporal and spatial expression makes it an attractive candidate for the study of transcriptional regulation of neuronal maturation. To define genomic regions likely to contain functional promoter elements, we isolated the murine ARPP-21 gene. Primer extension and T2 RNase protection analyses identified multiple transcription start sites, but 1.3 kb of 5'-flanking DNA revealed few consensus transcription factor binding sequences. A series of transient transfection assays in clonal cell lines which do not express ARPP-21 identified a basal promoter active in both neuronal and non-neuronal lines. Expression in all lines was decreased by the inclusion of regions further upstream, and extinguished by the inclusion of the first intron. Further analyses are likely to reveal cell specific regulatory sequences.

Dopamine D1 agonist SKF 38393 increases the state of phosphorylation of ARPP-21 in substantia nigra

ARPP-21 is a cyclic AMP-regulated phosphoprotein (M(r) = 21,000) that has a distribution in brain similar to that of DARPP-32 (dopamine- and cyclic AMP-regulated phosphoprotein, M(r) = 32,000). It is enriched in the medium-sized spiny neurons in the striatum and in the striatonigral nerve terminals in the pars reticulata of the substantia nigra. The present study shows that dopamine D1 agonist SKF 38393 increases the state of phosphorylation of ARPP-21 by 26% in nigral slices and that pretreatment of the slices with D1 antagonist SCH 23390 blocks this effect. These results demonstrate that ARPP-21 is a dopamine-regulated phosphoprotein. Because D1 receptors are localized on nerve terminals of striatonigral pathway, the phosphorylation of ARPP-21 is likely to mediate some of the intracellular effects of dopamine on these terminals.

Developmental regulation of phosphoprotein gene expression in the caudate-putamen of rat: an in situ hybridization study

The regional and cellular ontogeny of the mRNA encoding the dopamine- and cAMP-regulated phosphoprotein, DARPP-32, has been studied in rat striatum by quantitative in situ hybridization histochemistry. The mRNA for DARPP-32 exhibited a characteristic developmental profile. The hybridization signal was first visible on the day of birth, at which time DARPP-32 mRNA was concentrated in patches in the caudate-putamen. By the end of the first postnatal week, the majority of neurons in the caudate-putamen expressed the DARPP-32 message. Levels of mRNA per cell increased markedly during the second postnatal week, and peaked around the beginning of the third week. The adult level of DARPP-32 mRNA was lower than that observed at the apex of mRNA expression, on a per cell basis, while the proportion of neurons expressing detectable levels of message remained relatively constant. In the nucleus accumbens and olfactory tubercle, DARPP-32 mRNA development lagged somewhat behind that observed in the caudate-putamen, but was similar in other respects. A non-quantitative study employing an oligonucleotide probe complementary to the mRNA encoding another cAMP-regulated phosphoprotein, ARPP-21, revealed a similar developmental sequence to DARPP-32. The present results suggest that for DARPP-32 mRNA, genetic and, possibly, environmental factors play a role in determining the developmental patterns observed.