Animals from flies to humans are able to distinguish subtle gradations in temperature and show strong temperature preferences. Animals move to environments of optimal temperature and some manipulate the temperature of their surroundings, as humans do using clothing and shelter. Despite the ubiquitous influence of environmental temperature on animal behaviour, the neural circuits and strategies through which animals select a preferred temperature remain largely unknown. Here we identify a small set of warmth-activated anterior cell (AC) neurons located in the Drosophila brain, the function of which is critical for preferred temperature selection. AC neuron activation occurs just above the fly's preferred temperature and depends on dTrpA1, an ion channel that functions as a molecular sensor of warmth. Flies that selectively express dTrpA1 in the AC neurons select normal temperatures, whereas flies in which dTrpA1 function is reduced or eliminated choose warmer temperatures. This internal warmth-sensing pathway promotes avoidance of slightly elevated temperatures and acts together with a distinct pathway for cold avoidance to set the fly's preferred temperature. Thus, flies select a preferred temperature by using a thermal sensing pathway tuned to trigger avoidance of temperatures that deviate even slightly from the preferred temperature. This provides a potentially general strategy for robustly selecting a narrow temperature range optimal for survival.

A long-standing model postulates that X-chromosome dosage compensation in Drosophila occurs by twofold up-regulation of the single male X, but previous data cannot exclude an alternative model, in which male autosomes are down-regulated to balance gene expression. To distinguish between the two models, we used RNA interference to deplete Male-Specific Lethal (MSL) complexes from male-like tissue culture cells. We found that expression of many genes from the X chromosome decreased, while expression from the autosomes was largely unchanged. We conclude that the primary role of the MSL complex is to up-regulate the male X chromosome.Supplemental material is available at http://www.genesdev.org.

A daily body temperature rhythm (BTR) is critical for the maintenance of homeostasis in mammals. While mammals use internal energy to regulate body temperature, ectotherms typically regulate body temperature behaviorally [1]. Some ectotherms maintain homeostasis via a daily temperature preference rhythm (TPR) [2], but the underlying mechanisms are largely unknown. Here, we show that Drosophila exhibit a daily circadian clock dependent TPR that resembles mammalian BTR. Pacemaker neurons critical for locomotor activity are not necessary for TPR; instead, the dorsal neuron 2s (DN2s), whose function was previously unknown, is sufficient. This indicates that TPR, like BTR, is controlled independently from locomotor activity. Therefore, the mechanisms controlling temperature fluctuations in fly TPR and mammalian BTR may share parallel features. Taken together, our results reveal the existence of a novel DN2- based circadian neural circuit that specifically regulates TPR; thus, understanding the mechanisms of TPR will shed new light on the function and neural control of circadian rhythms.

Body temperature exhibits rhythmic fluctuations over a 24 h period (Refinetti and Menaker, 1992) and decreases during the night, which is associated with sleep initiation (Gilbert et al., 2004; Kräuchi, 2007a,b). However, the underlying mechanism of this temperature decrease is largely unknown. We have previously shown that Drosophila exhibit a daily temperature preference rhythm (TPR), in which their preferred temperatures increase during the daytime and then decrease at the transition from day to night (night-onset) (Kaneko et al., 2012). Because Drosophila are small ectotherms, their body temperature is very close to that of the ambient temperature (Stevenson, 1985), suggesting that their TPR generates their body temperature rhythm. Here, we demonstrate that the neuropeptide diuretic hormone 31 (DH31) and pigmentdispersing factor receptor (PDFR) contribute to regulate the preferred temperature decrease at night-onset. We show that PDFR and tethered-DH31 expression in dorsal neurons 2 (DN2s) restore the preferred temperature decrease at night-onset, suggesting that DH31 acts on PDFR in DN2s. Notably, we previously showed that the molecular clock in DN2s is important for TPR. Although PDF (another ligand of PDFR) is a critical factor for locomotor activity rhythms, Pdf mutants exhibit normal preferred temperature decreases at night-onset. This suggests that DH31-PDFR signaling specifically regulates a preferred temperature decrease at night-onset. Thus, we propose that night-onset TPR and locomotor activity rhythms are differentially controlled not only by clock neurons but also by neuropeptide signaling in the brain.Key words: circadian rhythm; DH31; Drosophila; PDFR; temperature preference behavior; thermoregulation IntroductionBody temperature rhythm (BTR) is fundamental for maintaining homeostasis, such as in generating metabolic energy and sleep (Aschoff, 1983;Refinetti and Menaker, 1992; Kräuchi, 2002 Kräuchi, , 2007aGilbert et al., 2004;Weinert, 2010;Gerhart-Hines et al., 2013). BTR is one of the most robust circadian outputs and can affect the peripheral clocks of mammals (Brown et al., 2002;Buhr et al., 2010). The rhythmic patterns of BTR and locomotor activity rhythms are analogous. For instance, in diurnal mammals, both body temperature and locomotor activity increase during the daytime and decrease at night (Satlin et al., 1995; Weinert and Received March 23, 2016; revised Aug. 24, 2016; accepted Sept. 22, 2016. Author , and UAS-Pdfr flies, Dr. Michael Nitabach for UAS-t-Pdf, UAS-t-Dh31, UAS-t-PDF-SCR flies and the anti-DH31 antibody, and the Bloomington Drosophila Stock Center for the fly lines. We thank Drs. Christian I. Hong, Emi Nagoshi, and Haruna Kaneko, and the Hamada laboratory members for their comments and advice on this manuscript, as well as Dr. Kazuhiko Kume for advice on sleep data analysis.The authors declare no competing financial interests. Significance StatementBody temperature rhythm (BTR) is fundamental for the maintenance of functions essential for homeostasis, such as ge...