Research ReportMotor coordination deficits in mice lacking RGS9
Introduction
The regulators of G protein signaling (RGS) family of proteins negatively modulate heterotrimeric G protein signaling by stimulating the GTPase activity of G protein α subunits (Berman and Gilman, 1998) and can function as effector molecules in certain signaling networks (De Vries et al., 2000). RGS proteins also regulate cellular excitability via their indirect modulation of G protein-coupled inwardly rectifying K+ channels (GIRK) and voltage-dependent calcium channels (Berman et al., 1996, Chuang et al., 1998, Doupnik et al., 1997, Hollinger and Hepler, 2002, Sondek and Siderovski, 2001, Zhou et al., 2000).
The greater than 25 mammalian RGS proteins identified to date are defined by their 120 amino acid RGS domain and can be organized into subfamilies based on structural features and relative specificity for different G protein subunits (Traynor and Neubig, 2005). Numerous RGS genes are expressed in brain with highly region-specific expression patterns (Dohlman and Thorner, 1997). The biological role of specific RGS proteins is currently an area of active research.
The RGS9 gene gives rise to two splice forms RGS9-1 and RGS9-2 (Granneman et al., 1998, He et al., 1998, Rahman et al., 1999) that differ only at their C-terminus, where 18 C-terminal amino acid residues of RGS9-1 are replaced by a longer sequence of 209 amino acid residues. Furthermore, the 2 splice forms display highly specific and non-overlapping tissue distributions: RGS9-1 is expressed exclusively in retina, while RGS9-2 is highly enriched in striatal regions of the brain, with very low levels of expression seen throughout the remainder of the brain or in peripheral tissues (Granneman et al., 1998, Rahman et al., 1999, Thomas et al., 1998). The striatum, together with other neural structures of the basal ganglia, acts via multiple intrinsic and extrinsic circuits to control motor and cognitive functions. Moreover, one key feature of striatal neurons is their rich innervation by dopamine and high levels of expression of dopamine receptors (Aizman et al., 2000, Graybiel et al., 2000). Given the high expression of RGS9-2 in the striatum and its localization to medium spiny projection neurons (Kovoor and Lester, 2002, Rahman et al., 2003, Thomas et al., 1998), one would predict RGS9 to play a role in striatal dopamine-mediated behavior. Indeed, RGS9-2 over-expression diminishes sensitivity to the behavioral effects of DA agonists, while loss of RGS9 has the opposite effect (Rahman et al., 2003). In addition, RGS9 has been shown to be a critical negative regulator of opiate action in vivo (Zachariou et al., 2003). For instance, RGS9 KO mice show a 10-fold increase in sensitivity to the rewarding effects of morphine, as well as increased morphine analgesia, delayed development of analgesic tolerance, and severe morphine dependence and withdrawal.
Despite the growing literature on RGS9's role in dopamine signaling as a result of G protein modulation, little has been published on the role of RGS9-2 in dopamine modulated, striatum-dependent behaviors in the absence of prior pharmacologic manipulation. Thus, we have systematically examined the function of RGS9 in striatal-specific and dopamine-mediated behaviors, as well as other additional behavioral domains. Overall, our findings suggest that loss of this regulator of G protein signaling in the striatum leads to focal abnormalities in specific behavioral domains. In particular, RGS9 KO mice display deficits in motor coordination and working memory, but show normal performance in other tasks. Deficits in motor coordination and working memory are consistent with abnormal regulation of dopamine signaling in the striatum or prefrontal cortex, respectively (Fowler et al., 2002, Glickstein et al., 2002, Kellendonk et al., 2006). This is the first demonstration of the role of RGS9 in endogenously mediated complex behavior, as opposed to the effects of exogenously applied drugs of abuse. Our findings suggest that RGS9-2 is a potential therapeutic target for disorders involving motor or cognitive dysfunction.
Section snippets
Results
The creation of RGS9 KO mice is described in detail elsewhere (Chen et al., 2000). For all behavioral tests, 11 male pairs of RGS9 KO and WT littermate offspring of heterozygous matings after 4 backcrosses into the C57BL6 background were used.
Discussion
Our data represent the first demonstration of RGS9 function in endogenously mediated complex behavior. RGS9 KO mice have impaired motor coordination and deficits in working memory, as measured in the delayed-match-to-place version of the water maze. In contrast, RGS9 KO mice exhibit normal locomotor activity, emotional learning, anxiety-like behavior, startle amplitude, and pre-pulse inhibition. Our findings suggest that RGS9-2 may be a potential therapeutic target for disorders involving motor
Conclusions
We have systematically examined the function of RGS9 in complex behavior. Overall, our findings suggest that loss of RGS9-2 leads to focal abnormalities in specific behavioral domains. In particular, RGS9 KO mice display deficits in motor coordination and working memory, but show normal locomotor activity, anxiety-like behavior, startle threshold, and pre-pulse inhibition. Our findings suggest that manipulation of RGS9-2 may be a useful target for disorders with motor or cognitive dysfunction.
Genetic manipulations
To reduce genetic and experimental variability, male RGS9 KO and their male wild-type littermate control mice (Chen et al., 2000) were generated from heterozygous matings following 4 backcrosses into C57BL6 background. For all data presented we used 11 male pairs of RGS9 KO and their wild-type (WT), littermate controls. Mice were housed in a temperature- and humidity-controlled environment with a 12-h light/12-h dark cycle and had free access to food and water.
Behavioral overview
Experimenters were blind to
Acknowledgments
Supported by grants from the National Institute of Mental Health (K08 MH065975-04), NARSAD, and Autism Speaks (all to C.M.P.).
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Current address: Merck Research Laboratories, Rahway, NJ 07065, USA.