Downloaded from genesdev.cshlp.org on May 19, 2020 - Published by Cold Spring Harbor Laboratory Press Temperature regulates splicing efficiency of the cold-inducible RNA-binding protein gene Cirbp Ivana Gotic,1 Saeed Omidi,2 Fabienne Fleury-Olela,1 Nacho Molina,2,3 Felix Naef,2 and Ueli Schibler1 1Department of Molecular Biology, University of Geneva, CH-1211 Geneva 4, Switzerland; 2The Institute of Bioengineering, School of Life Sciences, Ecole Polytechnique Fédérale de Lausanne, Swiss Institute of Bioinformatics, CH-1015 Lausanne, Switzerland In mammals, body temperature fluctuates diurnally around a mean value of 36°C–37°C. Despite the small differences between minimal and maximal values, body temperature rhythms can drive robust cycles in gene expression in cultured cells and, likely, animals. Here we studied the mechanisms responsible for the temperature- dependent expression of cold-inducible RNA-binding protein (CIRBP). In NIH3T3 fibroblasts exposed to simulated mouse body temperature cycles, Cirbp mRNA oscillates about threefold in abundance, as it does in mouse livers. This daily mRNA accumulation cycle is directly controlled by temperature oscillations and does not depend on the cells’ circadian clocks. Here we show that the temperature-dependent accumulation of Cirbp mRNA is controlled primarily by the regulation of splicing efficiency, defined as the fraction of Cirbp pre-mRNA processed into mature mRNA. As revealed by genome-wide “approach to steady-state” kinetics, this post-transcriptional mechanism is widespread in the temperature-dependent control of gene expression. [Keywords: Cirbp; splicing efficiency; temperature; circadian rhythms] Supplemental material is available for this article. Received July 12, 2016; revised version accepted August 19, 2016. Temperature is a fundamental physical parameter that they must be synchronized by the SCN and/or environ- influences metabolism in all organisms by modulating mental Zeitgebers (timing cues), such as light–dark cy- the rate of biochemical reactions. Endothermic organisms cles, in order to maintain phase coherence and rhythmic like mammals have acquired special thermoregula- physiology in the body. Without a functional SCN, labora- tory adaptation mechanisms in order to decrease their tory rodents kept in constant darkness lose virtually all dependence on environmental temperature. These mech- overt rhythms in behavior and physiology, including anisms maintain core body temperature (CBT) within a CBT cycles (Refinetti et al. 1994). favorable range, allowing efficient metabolic activity While the period length (τ) of circadian oscillations is re- throughout diurnal and seasonal cycles (for review, see markably resilient to temperature variations, a phenome- Tattersall 2012). non called temperature compensation, the phase is Although regulated around a species-specific set point, exquisitely sensitive to temperature perturbations, in par- mammalian CBT shows diurnal oscillations of ∼0.4°C– ticular in peripheral cells. In fact, in cultured fibroblasts 6.0°C (for review, see Refinetti 2010). These regular oscil- and tissue explants, the phase of circadian clock gene ex- lations are generated under the control of the circadian pression can be perfectly synchronized by simulated CBT timekeeping system, which is composed of a master pace- cycles (Brown et al. 2002; Buhr et al. 2010; Saini et al. maker in the brain’s suprachiasmatic nucleus (SCN) and 2012). subsidiary peripheral clocks in nearly all other cells of In intact animals, the systemic synchronization cues the body (Dibner et al. 2010). Although peripheral circadi- governed by the SCN and/or environment also comprise an oscillators are self-sustained and cell-autonomous, feeding–fasting behavior and blood-borne factors (for review, see Schibler et al. 2015). Owing to this com- plexity, it is challenging to assess to what extent CBT 3Present address: Institute of Genetics and Molecular and Cellular Biol- rhythms contribute to diurnal gene expression and the ogy, Centre National de la Recherche Scientifique, Institut National de la Santé et de la Recherche Médicale, University of Strasbourg, 67400 Ill- kirch, France Corresponding author: [email protected] © 2016 Gotic et al. This article, published in Genes & Development,is Article is online at http://www.genesdev.org/cgi/doi/10.1101/gad.287094. available under a Creative Commons License (Attribution-NonCommer- 116. Freely available online through the Genes & Development Open Ac- cial 4.0 International), as described at http://creativecommons.org/licens- cess option. es/by-nc/4.0/. GENES & DEVELOPMENT 30:2005–2017 Published by Cold Spring Harbor Laboratory Press; ISSN 0890-9369/16; www.genesdev.org 2005 Downloaded from genesdev.cshlp.org on May 19, 2020 - Published by Cold Spring Harbor Laboratory Press Gotic et al. synchronization of peripheral clocks in vivo. Nonethe- is widespread in the control of temperature-dependent less, experiments with mice harboring inactive hepato- gene expression. cyte clocks revealed robust diurnal accumulation cycles for a number of heat- and cold-inducible transcripts. The peak expression of these transcripts at times when CBT Results was maximal and minimal, respectively, suggests that Mild cold exposure increases the expression of a single they are likely driven directly by body temperature oscil- Cirbp mRNA isoform without affecting its pre-mRNA lations (Kornmann et al. 2007). levels The up-regulation of many heat-inducible genes is me- diated by transcriptional mechanisms depending on heat- In various mouse tissues, Cirbp mRNA levels follow a di- shock transcription factors, mostly HSF1, whose mono- urnal pattern, reaching zenith and nadir values when body mers are sequestered into inert cytosolic protein complex- temperature is minimal and maximal, respectively (Sup- es with HSP90 and other proteins at a lower CBT. Upon plemental Fig. S1A,B). Since local circadian oscillators temperature elevation, HSF1 monomers get released, tri- are not required for these oscillations in animals (Korn- merize, translocate into the nucleus, and bind to heat- mann et al. 2007) and since Cirbp mRNA accumulation shock response elements (HSEs) within promoter and en- is known to be temperature-dependent, we considered hancer sequences of their target genes. The circadian core rhythmic Cirbp expression to be likely driven directly clock gene Per2 is among these targets, possibly explain- by CBT cycles. Indeed, simulated CBT rhythms are suffi- ing the contribution of HSF1 to the synchronization of cient to elicit cyclic Cirbp mRNA and protein expression circadian gene expression by simulated CBT rhythms in cultured NIH3T3 fibroblasts (Morf et al. 2012), and we (Reinke et al. 2008; Buhr et al. 2010; Tamaru et al. 2011; therefore used these cells to study the underpinning Saini et al. 2012). mechanisms. In contrast to mouse livers, this model sys- In contrast to the mechanisms governing heat-induced tem allowed us to identify the impact of temperature in gene expression, those involved in cold-induced gene ex- the absence of potential confounding effects caused by cir- pression are still largely elusive. Cirbp, encoding the culating hormones and metabolites. cold-inducible RNA-binding protein CIRBP (also abbrevi- Previous studies have shown that mild cold exposure ated as CIRP), is among the proteins whose accumulation (32°C) increases the concentration of Cirbp mRNA in cul- displays diurnal oscillations that are likely driven by CBT tured cells (Nishiyama et al. 1997). To examine whether rhythms (Nishiyama et al. 1997, 1998; Kornmann et al. the level of Cirbp pre-mRNA transcripts was also changed 2007; Morf et al. 2012). CIRBP was originally described during cold exposure, we performed RNase protection as- as a human UV stress-induced factor, then named A18 says (RPAs). By using an RNA probe that protects the in- hnRNP, involved in the cellular genotoxic stress response tron 6–exon 7 boundary region of Cirbp transcripts from (Fornace et al. 1988; Yang and Carrier 2001). Its tempera- RNase A/T1 digestion, we were able to simultaneously ture-dependent expression became apparent during a quantify the levels of Cirbp pre-mRNA and mRNA spe- PCR-based search for RNA-binding domain-containing cies within a particular sample (Fig. 1A). As shown in Fig- proteins (RBPs) present in mouse testes (Nishiyama ure 1, B and C, cold exposure caused an increase in Cirbp et al. 1997, 1998). CIRBP appears to be an important mod- mRNA but did not affect the level of its precursors. A sim- ulator of proliferation in cellular stress conditions, includ- ilar conclusion was reached for diurnal Cirbp mRNA and ing cancer, where it is thought to exert an activating or pre-mRNA accumulation in mouse livers when we ana- inhibitory role depending on the cell type and the transfor- lyzed published RNA sequencing (RNA-seq) data (Atger mation state of the tumor (Hamid et al. 2003; Masuda et al. 2015). While Cirbp mRNA oscillated in abundance et al. 2012; Ren et al. 2014; Sakurai et al. 2015; Wang with the expected phase, Cirbp pre-mRNA levels re- et al. 2015). mained nearly constant throughout the day (Supplemen- CIRBP is thought to protect bound target RNAs from tal Fig. S1C). degradation, enhance their export and translation in the Next, we asked whether different temperatures induced cytoplasm (Yang and Carrier 2001; Morf et al. 2012), and the expression of specific Cirbp mRNA isoforms by either regulate the choice of alternative polyadenylation sites the use of different