Expression of the snoRNA Host Gene gas5 in the Hippocampus Is Upregulated by Age and Psychogenic Stress and Correlates with Reduced Novelty-Induced Behavior in C57BL/6 Mice Ingo Meier, 1 Laetitia Fellini, 1 Mira Jakovcevski, 1 Melitta Schachner, 1,2,3 and Fabio Morellini 1,4 * ABSTRACT: The growth arrest specific 5 (gas5) is a noncoding pro- tein gene that hosts small nucleolar RNAs. Based on the observation that gas5 RNA level in the brain is highest in the hippocampus and remarkably enhanced in aged mice, we tested the hypothesis that gas5 is involved in functions controlled by the hippocampus and known to be affected by age, such as spatial learning and novelty-induced behaviors. We show that aged (22-month-old) C57BL/6 male mice have spatial- learning impairments, reduced novelty-induced exploration, and enhanced gas5 RNA levels in the hippocampus compared to young (3- month-old) mice. At both ages, levels of gas5 RNA in the hippocampus negatively correlated with novelty-induced exploration in the open field and elevated-plus maze tests. No correlations were found between gas5 RNA levels in the hippocampus and performance in the water maze test. The expression of gas5 RNA in the rest of the brain did not corre- late with any behavioral parameter analyzed. Because variations in nov- elty-induced behaviors could be caused by stressfull experiences, we an- alyzed whether gas5 RNA levels in the hippocampus are regulated by acute stressors. We found that gas5 RNA levels in the hippocampus were upregulated by 50% 24 h after a psychogenic stressor (60-min olfactory contact with a rat) but were unchanged after exposure to an unfamiliar environment or after acquisition of new spatial information in a one-trial learning task. The present results suggest that strong psychogenic stressors upregulate gas5 RNA in the hippocampus, which in turn affects novelty-induced responses controlled by this region. We hypothesize that long-life exposure to stressors causes an age-dependent increase in hippocampal gas5 RNA levels, which could be responsible for age-related reduced novelty-induced behaviors, thus suggesting a new mechanism by which ageing and stress affect hippocampal function. V V C 2009 Wiley-Liss, Inc. KEY WORDS: ageing; behavior; hippocampus; snoRNA; stress INTRODUCTION Small nucleolar RNAs (snoRNAs) are short (up to 500 nucleotides) nonmessenger RNAs that do not code for proteins, but have several functions among which the best described is the proc- essing of ribosomal and small nuclear RNAs by site specific 2 0 -O-ribose methylation and pseudouridylation (Cavaille ´ et al., 1996; Kiss-Laszlo et al., 1996; Ganot et al., 1997). snoRNAs regulate protein expression and guidance modification and processing by targeting other RNAs such as tRNAs and possibly mRNAs (Bachellerie et al., 2002, Rogelj and Giese, 2004). Some snoRNAs have been linked to behavioral func- tions in mice: expression of the brain-specific snoR- NAs MBII-48 and MBII-52 in the hippocampus is enhanced and decreased, respectively, 90 min after contextual fear conditioning (Rogelj et al., 2003), and the snoRNA Snord116 regulates growth and feeding behavior (Ding et al., 2008). The growth arrest specific 5 (gas5) is a nonprotein coding gene, which hosts snoRNAs and belongs to the 5 0 -terminal oligopyrimidine (5 0 TOP) gene family (Smith and Steitz, 1998). The members of the 5 0 TOP gene family include all ribosomal proteins as well as protein synthesis elongation factors and a number of genes without apparent ribosome-related functions (Amaldi and Pierandrei-Amaldi, 1997). Messenger RNAs belonging to the 5 0 TOP gene fam- ily shift from polysomes into submonosomal (or mes- senger ribonucleoprotein) particles during periods of growth arrest in a process, which is reversed when cell growth resumes (Meyuhas et al., 1996). Growth arrest results in the inhibition of 5 0 TOP mRNA translation. Gas5 was first discovered by a screen for genes that are enriched in cells undergoing growth arrest (Schnei- der et al., 1988). The mouse gas5 pre-mRNA contains 12 exons and 11 introns. From these introns, 9 C/D RNAs are excised that guide methylation at conserved complementary regions in ribosomal RNA (Smith and Steitz, 1998; Lestrade and Weber, 2006). Gas5 overex- pression increases apoptosis and reduces the rate of progression through the cell cycle of human T-cells, whereas opposite effects were observed after downreg- ulation of endogenous gas5 expression (Mourtada- Maarabouni et al., 2008). Gas5 is ubiquitously expressed in the mouse (Coccia et al., 1992). In the brain, it shows a remarkably elevated expression in the hippocampus (Feldker et al., 2003), suggesting that gas5 RNA is involved in some functions typical of this brain region. Interestingly, Verbitsky et al. (2004) reported that gas5 expression is higher in the 1 Universita ¨tsklinikum Hamburg-Eppendorf, Zentrum fu ¨r Molekulare Neurobiologie Hamburg, Germany; 2 Department of Cell Biology and Neuroscience, Keck Center for Collaborative Neuroscience, Rutgers University, Piscataway New Jersey; 3 Shantou University Medical Col- lege, Center for Neuroscience, Shantou, China; 4 Universita ¨tsklinikum Hamburg-Eppendorf, Experimentelle Neuropa ¨diatrie, Hamburg, Germany *Correspondence to: Fabio Morellini, Experimentelle Neuropa ¨diatrie, Universita ¨tsklinikum Hamburg-Eppendorf, Martinistrasse 52, 20246 Hamburg, Germany. E-mail: fmorell@zmnh.uni-hamburg.de Accepted for publication 23 July 2009 DOI 10.1002/hipo.20701 Published online in Wiley InterScience (www.interscience.wiley.com). HIPPOCAMPUS 00:000–000 (2009) V V C 2009 WILEY-LISS, INC.